xSPECT: A clinical overview

White Paper xSPECT: a clinical overview Partha Ghosh, MD Siemens Healthineers Molecular Imaging Business Line SIEMENS siemens.com/xspect Healthineers White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Table of contents Advanced Modeled Iterative Reconstruction Clinical possibilities with xSPECT Bone™ 4 Hybrid imaging in skeletal scintigraphy 4 by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, Clinical case examples of xSPECT Bone 5 and Rainer Raupach, PhD Clinical possibilities with xSPECT Quant™ 21 Skeletal applications 21 Potential for extraskeletal applications 26 Introduction: Evolution of Siemens CT image reconstruction technologies Conclusion 29 Image reconstruction is an essential technology that every computed tomography (CT) References 30 scanner requires for operation. The function of CT image reconstruction is to translate Additional reading all of the acquired X-ray data (raw data) into a meaningful three-dimensional 32 representation of the patient. The most well-known method of image reconstruction is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To address this, Siemens Healthineers CT scanners offer an improved three-dimensional FBP, called weighted filtered back projection (WFBP).2 A common characteristic of both FBP and WFBP is that they do not consider statistical properties of measured X-ray projections. What this means is that all CT projections collected in the detectors are weighted the same, regardless of their quality. With the increased focus in dose reduction, the lack of inclusion of statistical properties of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art CT scanners have been developed with more advanced technology, known as iterative reconstruction (IR). Not surprisingly, among the key advantages of IR is that the statistical properties of measured CT projection data can be readily incorporated into the CT image reconstruction process. This would allow, for example, low-quality (noisy) projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. 2 3 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Clinical possibilities Advanced Modeled Iterative with xSPECT Bone Reconstruction Hybrid imaging in skeletal scintigraphy The integration of diagnostic multi-slice CT with SPECT has been one of the key by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, drivers in nuclear medicine. The ease of CT-based attenuation correction, lesion and Rainer Raupach, PhD localization founded on accurate fusion of diagnostic CT and SPECT datasets, as well as characterization of lesions using CT information in combination with SPECT-based functional assessment, has ushered in a new level of accuracy and scope of SPECT imaging. xSPECT™ technology aims to further enhance the clinical impact of this integration by incorporating CT-based tissue segmentation into SPECT reconstruction to Introduction: Evolution of Siemens CT image reconstruction technologies create a new degree of image quality in skeletal imaging. Development of IR methods Image reconstruction is an essential technology that every computed tomography (CT) Skeletal scintigraphy has been a mainstay of nuclear medicine for decades. It is the It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate key modality for the detection and characterization of skeletal metastases as well in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional as the characterization of numerous non-malignant lesions of the bone, including The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction fractures, infections, avascular necrosis, degenerative, and osteoarthritic bone and Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray joint lesions. xSPECT Bone significantly improves the image quality of SPECT/CT image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely for bone, which may profoundly impact skeletal scintigraphy and empower physicians that is effective in reducing image noise in a variety of clinical applications.4, 5 i.e., not that not all measured data can be used for image reconstruction with FBP,1 to “see the unseen.” However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional Using CT-based segmentation in the reconstruction, xSPECT Bone achieves a sharper with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 definition of bony margins and lesion boundaries. The resulting reconstructed SPECT technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative images (xSPECT Bone) appear to truly reflect the distribution of metabolically active A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ bone within the skeletal system with sharper differentiation between cortical and properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. spongy bone in the vertebrae, as well as in flat bones like the pelvis, scapula, and collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward skull. This also provides fine detail, which helps differentiate between the cortex and the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is marrow cavity in long bones and improved separation of bone from joint spaces— of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image both for large joints such as the knee and shoulder and for small structures, such as radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively carpals and tarsal bones. CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the The following pages review clinical examples to illustrate the image quality the capabilities of SAFIRE to reduce dose while maintaining high image quality in levels in bone scintigraphy made possible by xSPECT Bone to support physicians’ statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) ability to characterize disease and minimize the need for costly follow-up exams and pediatrics.7-10 (eg, MR, biopsies). projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 3 4 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Clinical case examples of xSPECT Bone Advanced Modeled Iterative Figures 1-4 show xSPECT Bone images of a patient with metastatic prostate cancer. A Reconstruction comparison of lumbar vertebral lesions in this patient between standard SPECT and xSPECT Bone (Figure 2 and 3) shows increased lesional uptake at the same background level with xSPECT Bone as well as improved definition of vertebral and disc margins and spinal canal and spinous process definitions. The uptake in the spongy bone within the vertebral body and the vertebral end plates reflects a more accurate visualization of skeletal metabolism and the degree of hypermetabolism of the metastatic lesion compared to the surrounding bone. by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD Figure 4 shows side-by-side visualization of CT and fused images: CT shows focal scle- rotic areas within vertebral bodies and in the Ileum involving the right sacro-iliac joint. Fused images show the focal hot areas exactly corresponding to the zone of sclerosis without any spillage of activity beyond the bone margins. In the coronal image (top row), the intensity of the uptake in the medial cortex of the right ileum with metastatic Introduction: Evolution of Siemens CT image reconstruction technologies involvement is clearly shown as higher, corresponding exactly to the sclerosis with lower uptake levels within the adjacent marrow which appears hypodense on CT. Image reconstruction is an essential technology that every computed tomography (CT) scanner requires for operation. The function of CT image reconstruction is to translate Such distinction between uptake in sclerotic metastatic bone and adjacent marrow all of the acquired X-ray data (raw data) into a meaningful three-dimensional reflecting the true skeletal pathology can be achieved using xSPECT Bone, unlike representation of the patient. The most well-known method of image reconstruction conventional 3D iterative reconstruction. is commonly referred to as filtered back projection (FBP), in which measured X-ray Figures 5 depicts 99mTc-MDP Bone SPECT in a patient with prostate cancer. The 3D projections are directly translated into images. In most modern scanners, it is likely iteration image reflects multiple hypermetabolic vertebral metastases. xSPECT Bone that not all measured data can be used for image reconstruction with FBP,1 i.e., not shows clearer and sharper delineation of the vertebral bodies and defines the extent of all radiation dose applied to the patient is actually used for image reconstruction. To hypermetabolic metastatic foci. Note the sharp definition of intervertebral disc spaces, address this, Siemens Healthineers CT scanners offer an improved three-dimensional as well as vertebral end plates, spinous processes, and vertebral canal. FBP, called weighted filtered back projection (WFBP).2 The perfect correlation of the lesion extent and margins on xSPECT Bone with the zones A common characteristic of both FBP and WFBP is that they do not consider statistical of sclerosis on CT highlights the resolution and true delineation of the tracer uptake properties of measured X-ray projections. What this means is that all CT projections distribution, both within the lesion as well as in the normal bone, made possible by collected in the detectors are weighted the same, regardless of their quality. With xSPECT Bone reconstruction. the increased focus in dose reduction, the lack of inclusion of statistical properties of conventional FBP or WFBP become an important barrier that prevents further Comparison of 3D iterative with the xSPECT Bone study of the lumbar vertebrae in a radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art patient with breast carcinoma (Figure 7) shows improved visualization with xSPECT CT scanners have been developed with more advanced technology, known as iterative Figure 1: Data courtesy of of the lytic regions with increased 99mTc-MDP uptake in the lesion margins and adjacent reconstruction (IR). Not surprisingly, among the key advantages of IR is that the Johns Hopkins University, vertebral body, which confirms the presence of lytic zones in the vertebral body as well Baltimore, Maryland, USA. statistical properties of measured CT projection data can be readily incorporated into as the involvement of the lytic process in the upper vertebral end plate. the CT image reconstruction process. This would allow, for example, low-quality (noisy) projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. Figure 2: Data courtesy of This was in line with the ALARA principle, that is to use a dose that is “As Low As SPECT (AC) XSPECT Bone Johns Hopkins University, Baltimore, Maryland, USA. Reasonably Achievable” to deliver diagnostic image quality. A Figure 3: Data courtesy of XSPECT Bone SPECT (AC) Johns Hopkins University, Baltimore, Maryland, USA. 2 5 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT Bone by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods Image reconstruction is an essential technology that every computed tomography (CT) It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology SPECT (AC) projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 i.e., not that not all measured data can be used for image reconstruction with FBP,1 However, it is expected that IR technologies not only aid in noise reduction but also [A] all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ Figure 5: 99mTc-MDP bone SPECT images comparing xSPECT with properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. 3D iterative reconstruction. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward CT xSPECT/CT the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image Figure 4: Data courtesy of Johns Hopkins University, radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively Baltimore, Maryland, USA. CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. xSPECT Bone There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. SPECT (AC) CT xSPECT/CT * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical Figure 7: xSPECT Bone and SPECT (AC) show the lytic vertebral lesion in location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the Figure 6: CT shows multiple sclerotic metastases in the lumbar and a patient with breast cancer. appropriate dose to obtain diagnostic image quality for the particular clinical task. thoracic vertebrae and fused images showing exact coregistration of the ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical zones of focal hypermetabolism with the sclerotic lesions on CT. Data courtesy of University of Erlangen, Erlangen, Germany. location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 6 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Advanced Modeled Iterative Reconstruction by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD Introduction: Evolution of Siemens CT image reconstruction technologies Figure 8: CT and fused image of xSPECT Bone and CT show Image reconstruction is an essential technology that every computed tomography (CT) lytic vertebral lesion. scanner requires for operation. The function of CT image reconstruction is to translate all of the acquired X-ray data (raw data) into a meaningful three-dimensional Data courtesy of University of Erlangen, Erlangen, Germany. representation of the patient. The most well-known method of image reconstruction CT xSPECT/CT is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 The CT study (Figure 8) shows lytic areas on the left side of the L2 vertebral body with i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To fused images showing areas of increased uptake corresponding to the region adjacent to address this, Siemens Healthineers CT scanners offer an improved three-dimensional the lytic areas. The hypointense regions within the vertebral body correspond exactly to FBP, called weighted filtered back projection (WFBP).2 the lytic regions on CT. The lytic region involves the upper vertebral end plate as shown A common characteristic of both FBP and WFBP is that they do not consider statistical on the sagittal images. Although lytic metastases are common in breast carcinoma, the pattern of the lytic areas suggests the possibility of an aneursymal bone cyst or giant properties of measured X-ray projections. What this means is that all CT projections cell tumor rather than metastases. MRI correlation would be required for proper evalu- collected in the detectors are weighted the same, regardless of their quality. With ation. xSPECT Bone is uniquely suited to sharply define cold areas within areas of high the increased focus in dose reduction, the lack of inclusion of statistical properties or normal bone uptake characteristic of lytic lesions, as in this example. of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art Equivocal bone lesions are a common concern in skeletal scintigraphy and SPECT/CT CT scanners have been developed with more advanced technology, known as iterative has been shown to have significantly improved characterization of such lesions. One reconstruction (IR). Not surprisingly, among the key advantages of IR is that the statistical properties of measured CT projection data can be readily incorporated into study1 determined the added value of multi-slice SPECT/CT in evaluation of equivocal bony lesions in patients with prostate carcinoma. Using SPECT/CT with integrated the CT image reconstruction process. This would allow, for example, low-quality (noisy) 16-slice diagnostic CT, 40 consecutive patients with prostate cancer were studied using projections to carry less weight than high-quality projections. 99mTc-MDP. Of 50 focal lesions with abnormal tracer uptake, 61 percent (30/50) were termed equivocal on planar and SPECT imaging. However, after SPECT/CT evaluation, There has been an expanding utilization of IR in clinical practice in recent years, only 8 percent were still termed equivocal. Thus, the use of SPECT/CT with integrated primarily due to the increased focus on radiation dose optimization. Of note, Siemens diagnostic CT was able to clarify the diagnosis in 84 percent of equivocal lesions. In the Healthineers has been placing emphasis on devising technical solutions that can help majority of cases, SPECT/CT was able to clearly pinpoint benign (24 percent) or malig- to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As nant (68 percent) lesions due to the morphological clarity provided by CT. Six vertebral Reasonably Achievable” to deliver diagnostic image quality. lesions in five patients were reclassified based on CT findings like sclerotic vertebral lesions on CT, suggesting malignancy or compression fracture in the vertebrae indicative of the benign nature of the uptake. Certain SPECT/CT uptake patterns were rated as benign uptake at the edge of vertebral bodies adjacent to the disc space or uptake in the facet joints, but sparing the pedicles. However, uptake within vertebral bodies, including pedicles, was suggestive of metastases. 2 7 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Characterization of solitary skeletal lesions, frequently in patients with known malignancy, often presents diagnostic dilemmas. SPECT has been shown to improve Reconstruction characterization of such lesions as compared to planar. Sudhakar,2 in a study of 20 patients (6 with known malignancy), showed additional detection of 30 percent of solitary vertebral lesions by SPECT compared to planar bone scan. Metastatic lesions were characterized by involvement of posterior vertebral body and pedicles. Lesions localized to anterior vertebral body were commonly characterized as benign osteo- phytes. Other benign solitary lesions included osteoma, facet arthropathy, discitis, by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, spondylolysis, and transverse process fractures. SPECT/CT has also demonstrated significant improvement in characterization of solitary bone lesions. Iqbal,3 in a cohort and Rainer Raupach, PhD of 80 patients with solitary bone lesions (50 with known cancer), demonstrated that SPECT/CT significantly decreased the number of equivocal lesions compared to that with planar imaging (63.8 percent equivocal lesions for planar imaging compared to 13.8 percent with SPECT/CT). In view of the 13.8 percent equivocal rate with SPECT/CT Introduction: Evolution of Siemens CT image reconstruction technologies (performed with non-diagnostic CT), there appears to be a significant scope of improve- Development of IR methods ment in diagnostic confidence with improved SPECT reconstructions and integrated Image reconstruction is an essential technology that every computed tomography (CT) high-quality diagnostic CT. It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional xSPECT Bone images with improved lesion definition as well as absolute quantification The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction of tracer uptake have the potential to further improve the evaluation of such equivocal lesions. Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely Such an equivocal lesion is highlighted in the example in Figure 9. A patient with renal that is effective in reducing image noise in a variety of clinical applications.4, 5 that not all measured data can be used for image reconstruction with FBP,1 i.e., not cell carcinoma underwent 99mTc-MDP bone SPECT/CT. The 3D iterative image shows However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively since its introduction, and a wealth of scientific literature has consistently supported xSPECT Bone CT scanners have been developed with more advanced technology, known as iterative the capabilities of SAFIRE to reduce dose while maintaining high image quality in F LA reconstruction (IR). Not surprisingly, among the key advantages of IR is that the statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. F F SPECT (AC) This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. A CT xSPECT/CT Figure 9: Data courtesy University of Minnesota, Minneapolis, * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical Figure 10: CT shows mild sclerosis in the left lateral part of the vertebral Minnesota, USA. location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the body, which corresponds exactly with the hypermetabolic area defined appropriate dose to obtain diagnostic image quality for the particular clinical task. on xSPECT Bone with sparing of the pedicles, lamina, and transverse ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the processes. This is strongly suggestive of early metastases. appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 8 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT Bone by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD Figure 11: Comparison of 3D iterative Introduction: Evolution of Siemens CT image reconstruction technologies reconstruction and xSPECT Bone in a patient with prostate cancer delineates Image reconstruction is an essential technology that every computed tomography (CT) a small hypermetabolic metastasis in scanner requires for operation. The function of CT image reconstruction is to translate SPECT (AC) the posterior right iliac bone. all of the acquired X-ray data (raw data) into a meaningful three-dimensional representation of the patient. The most well-known method of image reconstruction Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To a solitary focal hypermetabolic lesion in the body of cervical vertebrae. 3D iterative address this, Siemens Healthineers CT scanners offer an improved three-dimensional reconstruction, however, is not able to clearly define the extent of the lesion and FBP, called weighted filtered back projection (WFBP).2 involvement of pedicles. Since this was a solitary lesion, the possibility of a degenera- tive cervical lesion could not be ruled out. xSPECT Bone defines the margins of the A common characteristic of both FBP and WFBP is that they do not consider statistical vertebral body, pedicles, spine, and transverse processes and clearly localizes the properties of measured X-ray projections. What this means is that all CT projections hypermetabolic foci to the left lateral part of the vertebral body without involvement of collected in the detectors are weighted the same, regardless of their quality. With the pedicles, facet joints, or lamina. Since the location of the lesion does not correlate the increased focus in dose reduction, the lack of inclusion of statistical properties with the sites of degenerative changes, metastases become a strong possibility. of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art Another similar equivocal solitary skeletal lesion in a patient with untreated prostate CT scanners have been developed with more advanced technology, known as iterative cancer and progressively increasing PSA is reflected in Figure 11. A comparison of reconstruction (IR). Not surprisingly, among the key advantages of IR is that the standard 3D iterative reconstruction; images of bone SPECT and xSPECT Bone images statistical properties of measured CT projection data can be readily incorporated into at a slice through the sacroiliac joint depicts a small focal hypermetabolic area on the CT image reconstruction process. This would allow, for example, low-quality (noisy) the dorsal aspect of the Ileum adjacent to the right sacroiliac joint. When compared to projections to carry less weight than high-quality projections. SPECT with attenuation correction (AC), the xSPECT Bone images show sharp defini- tion of the hypermetabolic lesion with clear distinction of the lesion location from the There has been an expanding utilization of IR in clinical practice in recent years, adjacent sacroiliac joint margin. With 3D iterative reconstruction, the lesion appears primarily due to the increased focus on radiation dose optimization. Of note, Siemens larger and ill-defined, and no distinction of the lesion location from the sacroiliac joint Healthineers has been placing emphasis on devising technical solutions that can help is possible. to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As CT (Figure 12) demonstrates a small focal area of sclerosis in the ileum adjacent to Reasonably Achievable” to deliver diagnostic image quality. but distinct from the right sacroiliac joint space, which corresponds exactly to the focal hot area seen on the corresponding slices on xSPECT Bone. xSPECT also sharply defines the right sacroiliac joint margin, thereby clearly differentiating the focal hot Iliac bone lesion from the sacroiliac joint. The sharp definition of the focal bone lesion when compared to the minor sclerosis seen in the corresponding CT slices illustrates enhanced lesion margin resolution achieved by xSPECT Bone. 2 9 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT Bone by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD SPECT (AC) Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods Image reconstruction is an essential technology that every computed tomography (CT) It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate Figure 12: CT (top row) fusion of CT and xSPECT Bone (middle row) and in image noise, is the standard tradeoff for achieving a substantial dose reduction. Figure 13: Comparison of 3D iteration and xSPECT Bone in a patient with all of the acquired X-ray data (raw data) into a meaningful three-dimensional xSPECT Bone (bottom row) demonstrates sclerotic focal bone lesion in prostate cancer with solitary vertebral pedicular lesion. The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction the posterior aspect of the right ileum adjacent to the right sacroiliac Data courtesy of Ludwig Maximilians University, Munich, Germany. Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased joint suggestive of a skeletal metastasis. is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. that is effective in reducing image noise in a variety of clinical applications.4, 5 that not all measured data can be used for image reconstruction with FBP,1 i.e., not However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens CT xSPECT/CT Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Figure 14: CT shows well-circumscribed zone of sclerosis in the left Reasonably Achievable” to deliver diagnostic image quality. vertebral pedicle, which corresponds exactly to the zone of increased tracer uptake in the fused images. Clear separation of the hyper- metabolic sclerotic region from the adjacent transverse process and vertebral lamina, as well as the normal vertebral body, is delineated in the fused images. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical Data courtesy of Ludwig Maximilians University, Munich, Germany. location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 10 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: A patient with prostate cancer with borderline increase in PSA and no skeletal Advanced Modeled Iterative symptoms showed focal increase in uptake in the left vertebral pedicle of T10 vertebrae on 99mTc-MDP bone SPECT reconstructed with 3D iteration (Figure 13). xSPECT Bone Reconstruction clearly localizes the lesion in the vertebral pedicle separate from the vertebral body or lamina or transverse process, with sharp delineation of the spinal canal margins as well as proper visualization of adjacent transverse process and lamina. SPECT/CT-based anesthetic injections for treatment of bone pain, especially in thoraco-lumbar spine and sacroiliac joints, have been successfully used. Cui4 used SPECT and CT-guided intra-articular anesthetic injection in sacroiliac joint in 16 by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, patients with ankylosing spondylosis. Sequential 99mTc-MDP SPECT-based follow-up and Rainer Raupach, PhD showed significant decrease in sacroiliac joint uptake within 8 weeks of therapy accompanied by and correlating with a decrease in pain. Accurate delineation of the exact site of articular hypermetabolism, as shown by xSPECT Bone SPECT and CT fusion, can help pinpoint the site of anesthetic injection with the potential for improving outcomes. Introduction: Evolution of Siemens CT image reconstruction technologies Figure 15 shows 99mTc-MDP bone SPECT in a patient with breast cancer with progressive Image reconstruction is an essential technology that every computed tomography (CT) low back pain. xSPECT Bone reconstructions show improved visualization of vertebral scanner requires for operation. The function of CT image reconstruction is to translate bodies as well as pedicular and transverse process uptake and sharp delineation of all of the acquired X-ray data (raw data) into a meaningful three-dimensional uptake in the sacrum and sacroiliac joint. Increased uptake in bilateral lumbar articular representation of the patient. The most well-known method of image reconstruction is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To address this, Siemens Healthineers CT scanners offer an improved three-dimensional FBP, called weighted filtered back projection (WFBP).2 A common characteristic of both FBP and WFBP is that they do not consider statistical properties of measured X-ray projections. What this means is that all CT projections collected in the detectors are weighted the same, regardless of their quality. With xSPECT Bone the increased focus in dose reduction, the lack of inclusion of statistical properties of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art CT scanners have been developed with more advanced technology, known as iterative reconstruction (IR). Not surprisingly, among the key advantages of IR is that the statistical properties of measured CT projection data can be readily incorporated into the CT image reconstruction process. This would allow, for example, low-quality (noisy) projections to carry less weight than high-quality projections. Figure 15: Comparison of SPECT There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens SPECT (AC) and xSPECT Bone in a patient with biltaral facet arthropathy. Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. 2 11 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: processes secondary to bilateral facet arthropathy in L5 vertebrae is clearly delineated Advanced Modeled Iterative along with clear visualization of spinal canal with xSPECT Bone. 3D iterative recon- struction, in comparison, shows comparatively blurred levels of uptake in the facets Reconstruction with inadequate visualization of the spinal canal. Note the clear visualization of the sacral foramina which shows hypodensity, as expected. Sharp margins of the rim of the vertebral body show slightly increased uptake of tracer on xSPECT Bone due to the presence of cortical bone, compared to the central part of the vertebral body showing lower level of uptake due to spongy bone. Thus, xSPECT Bone reflects the true metabo- lism of the vertebral body. The linear area of slightly increased uptake in the left 10th by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, rib posteriorly is more prominently visualized in the xSPECT Bone maximum intensity and Rainer Raupach, PhD projection (MIP) image (left top) and reflects past traumatic fracture. CT (Figure 16) shows sclerosis at bilateral facet joints which corresponds to the areas of increased uptake on xSPECT Bone with clear separation of facet uptake from the pedicle and transverse processes. Clear delineation of hypermetabolic foci within the Introduction: Evolution of Siemens CT image reconstruction technologies facet joints may help SPECT/CT-guided anesthetic therapy. Development of IR methods Image reconstruction is an essential technology that every computed tomography (CT) Figure 17 shows comparison of 3D iterative and xSPECT Bone reconstructions of It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate 99mTc-MDP bone SPECT/CT in a 54-year-old female patient who presented with severe in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional back pain along with fever. X-ray of the spine was inconclusive. SPECT shows increased The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction uptake of tracer in the L3-L4 lumbar vertebral end plates and intervertebral disc. Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray xSPECT Bone shows sharp delineation of the individual vertebrae with clear definition image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely of the focal area of increased uptake within the L3-L4 intervertebral disc and adjacent that is effective in reducing image noise in a variety of clinical applications.4, 5 that not all measured data can be used for image reconstruction with FBP,1 i.e., not vertebral end plates. xSPECT clearly defines the location of the uptake and delineates However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To the sharp vertebral end plate margins, thereby demonstrating the narrowing of the in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional L3-L4 intervertebral disc space as well as the tracer uptake within the disc. Other with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 lumbar vertebrae show normal shape with normal intevertebral disc spaces without technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative abnormal focal uptake. A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults xSPECT Bone the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. SPECT (AC) CT xSPECT/CT * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the Figure 16: CT and fusion of xSPECT Bone and CT delineate the sclerosis Figure 17: Comparison of 3D iteration and xSPECT Bone in a patient appropriate dose to obtain diagnostic image quality for the particular clinical task. and inflammation in bilateral facet joints. with intervertebral disc space infection. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. Data courtesy of University of Erlangen, Erlangen, Germany. appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 3 12 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Advanced Modeled Iterative Reconstruction by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, A A and Rainer Raupach, PhD Introduction: Evolution of Siemens CT image reconstruction technologies Image reconstruction is an essential technology that every computed tomography (CT) Figure 18: CT and fusion of xSPECT scanner requires for operation. The function of CT image reconstruction is to translate Bone and CT shows intervertebral all of the acquired X-ray data (raw data) into a meaningful three-dimensional disc space shortening with end plate representation of the patient. The most well-known method of image reconstruction sclerosis along with skeletal hypermetabolism in the sclerosed is commonly referred to as filtered back projection (FBP), in which measured X-ray end plates and within the projections are directly translated into images. In most modern scanners, it is likely intervertebral disc space. that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To Data courtesy of University of Erlangen, address this, Siemens Healthineers CT scanners offer an improved three-dimensional CT xSPECT Bone/CT Erlangen, Germany. FBP, called weighted filtered back projection (WFBP).2 A common characteristic of both FBP and WFBP is that they do not consider statistical CT (Figure 18) shows narrowing of the L3-L4 intervertebral disc space with severe properties of measured X-ray projections. What this means is that all CT projections erosion of the adjacent vertebral end plates along with mild sclerosis. Fusion of CT collected in the detectors are weighted the same, regardless of their quality. With the increased focus in dose reduction, the lack of inclusion of statistical properties and xSPECT Bone data shows increased uptake within the narrowed intervertebral disc space along with uptake limited to the zone of sclerosis adjacent to the vertebral end of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art plate erosion. The other intervertebral disc spaces appeared normal, without abnor- mally increased uptake or end plate changes on CT. Minor degenerative changes were CT scanners have been developed with more advanced technology, known as iterative visualized in the lateral aspect of L4-L5 vertebral end plates. The clinical presentation reconstruction (IR). Not surprisingly, among the key advantages of IR is that the of the patient along with the SPECT/CT findings of narrowing of disc space, end plate statistical properties of measured CT projection data can be readily incorporated into the CT image reconstruction process. This would allow, for example, low-quality (noisy) erosion, and severely increased bone metabolism within the disc space and in the adjacent vertebral end plates, without major involvement of other intervertebral disc projections to carry less weight than high-quality projections. spaces, were suggestive of an intervertebral disc space infection. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. 2 13 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Reconstruction XSPECT Bone CT xSPECT/CT by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, Figure 20: CT shows sclerosis involving the entire left transverse process and Rainer Raupach, PhD which corresponds exactly to the zone of increased uptake on xSPECT Bone SPECT reconstruction. Note the clear distinction of the increased transverse process uptake from the adjacent rib uptake as well as dis- SPECT (AC) tinction from the normal uptake levels in vertebral pedicle and lamina. The transverse process lesion is clearly defined as a metastatic lesion. Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods Figure 19: 99mTc-MDP bone SPECT in a patient with treated prostate Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. Image reconstruction is an essential technology that every computed tomography (CT) cancer presenting with increased PSA. 3D iteration shows a focal hot It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate area in the T4 vertebrae involving the left side, although the exact region in image noise, is the standard tradeoff for achieving a substantial dose reduction. of involvement was not clear from 3D iteration. 3D iterative images all of the acquired X-ray data (raw data) into a meaningful three-dimensional The first IR technology commercially developed by Siemens Healthineers was Iterative could not differentiate whether the uptake was in the vertebral pedicle representation of the patient. The most well-known method of image reconstruction Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased or left facet joint or left transverse process. xSPECT Bone images, in is commonly referred to as filtered back projection (FBP), in which measured X-ray comparison, show clearly the focal uptake involving the entire left image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely transverse process and are clearly distinct from the vertebral pedicle, that is effective in reducing image noise in a variety of clinical applications.4, 5 i.e., not that not all measured data can be used for image reconstruction with FBP,1 lamina and body. The pattern of involvement of transverse process is However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To strongly suggestive of metastases. in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative CT xSPECT/CT A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. “sinogram”) and added a model of the CT system geometry during the data forward Figure 22: CT shows the small focal sclerotic area in the medial part collected in the detectors are weighted the same, regardless of their quality. With of the left transverse process (arrow), which exactly corresponds to the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is the focal hypermetabolic foci on xSPECT Bone, suggesting a small of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image metastases. The adjacent rib and costo-vertebral junction are delineated radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively on CT with fused images showing mild hypermetabolism in the medial xSPECT Bone CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported end of the rib and the facet, suggesting facet arthropathy coexisting with transverse process metastases. reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, SPECT (AC) primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Figure 21: This shows another patient with prostate carcinoma with Reasonably Achievable” to deliver diagnostic image quality. hypermetabolic foci in the transverse process of mid-thoracic vertebrae. From the 3D iterative image, exact localization and characterization of the lesion is difficult and the lesion would be labeled as equivocal. xSPECT Bone images; however, clearly differentiate focal uptake in the transverse process as well as uptake in the proximal end of the rib and costo-vertebral junction. The space separating the transverse process * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the and the rib is also clearly delineated in xSPECT Bone, which suggests appropriate dose to obtain diagnostic image quality for the particular clinical task. presence of focal metastases in the transverse process along with ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical adjacent costo-vertebral facet arthropathy (arrow). location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 3 14 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Advanced Modeled Iterative Reconstruction Figure 23: 99mTc-MDP bone SPECT in a patient with a history of breast xSPECT Bone carcinoma with osteoporotic collapse of L1 vertebrae and central hypodense zone within the vertebral body, by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, corresponding to zone of osteolysis and impaction with bulging cortical and Rainer Raupach, PhD rim with increased uptake. xSPECT Bone also sharply defines the spinal canal with encroachment of the collapsed vertebral body margin into it, which suggests possibility Introduction: Evolution of Siemens CT image reconstruction technologies of cord compression. SPECT (AC) Image reconstruction is an essential technology that every computed tomography (CT) Data courtesy of University of Erlangen, Erlangen, Germany. scanner requires for operation. The function of CT image reconstruction is to translate all of the acquired X-ray data (raw data) into a meaningful three-dimensional representation of the patient. The most well-known method of image reconstruction ..... is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To address this, Siemens Healthineers CT scanners offer an improved three-dimensional FBP, called weighted filtered back projection (WFBP).2 A common characteristic of both FBP and WFBP is that they do not consider statistical properties of measured X-ray projections. What this means is that all CT projections collected in the detectors are weighted the same, regardless of their quality. With the increased focus in dose reduction, the lack of inclusion of statistical properties of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art CT scanners have been developed with more advanced technology, known as iterative reconstruction (IR). Not surprisingly, among the key advantages of IR is that the statistical properties of measured CT projection data can be readily incorporated into the CT image reconstruction process. This would allow, for example, low-quality (noisy) Figure 24: CT shows collapsed central projections to carry less weight than high-quality projections. part of vertebral body with focal osteolysis with bony hyperdensity in the There has been an expanding utilization of IR in clinical practice in recent years, lateral rim of the vertebral body. Fused primarily due to the increased focus on radiation dose optimization. Of note, Siemens images show absence of tracer uptake Healthineers has been placing emphasis on devising technical solutions that can help in the collapsed portion with increased to consistently achieve the right dose, for the right diagnostic task, for every patient. uptake in the lateral rim. Note the This was in line with the ALARA principle, that is to use a dose that is “As Low As visualization of the encroachment of Reasonably Achievable” to deliver diagnostic image quality. vertebral body into spinal canal both in the CT and fused images, confirming presence of cord compression, as was anticipated from the xSPECT Bone images. Data courtesy of University of Erlangen, CT xSPECT/CT Erlangen, Germany. 2 15 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Figures 23 and 24 reflect a common clinical situation of vertebral collapse, either related to osteoporosis or trauma. Percutaneous vertebroplasty (PV) is an established treatment for vertebral collapse. Bone SPECT/CT is used in patients with vertebral Reconstruction collapse as a pre-vertebroplasty procedure to help in patient selection, treatment planning, and prediction of response to PV. A study was performed with a Symbia T 2 scanner on 33 patients with chronic pain secondary to vertebral compression fractures. Regions of maximum uptake on SPECT were defined for planning of vertebroplasty and bone cement infiltration. A total of 91% of patients with high vertebral uptake on SPECT by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, in the site of cementing showed clinical improvement. SPECT also demonstrated alternative causes of pain in some cases, such as new fractures, persistent bone remod- and Rainer Raupach, PhD eling in previously cemented vertebra, or facet arthropathy. In these cases, SPECT/CT was instrumental in defining proper therapy. Follow-up SPECT/CT demonstrated the decrease in vertebral uptake following cementing correlating with recovery. In clinical situations involving vertebral collapse, xSPECT Bone reconstructions could, possibly, further help define regions of inadequate cementing and improve planning of percuta- Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods neous vertebroplasty. Image reconstruction is an essential technology that every computed tomography (CT) It is well known that the degradation in image quality, most notably an increase The patient delineated in Figure 25 shows a large cold mass in the sacrum, comprising scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. the entire right side and invading into the adjacent right ileum as well as into part of all of the acquired X-ray data (raw data) into a meaningful three-dimensional the left sacrum, with destruction of the bone and intrusion the cauda equine. Compared The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased to 3D iteration, xSPECT Bone shows sharp delineation of the eroded margins of the is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology sacrum and ileum. The thin cortical margins of the eroded sacral anterior and posterior projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 margins are well delineated with xSPECT Bone. i.e., not that not all measured data can be used for image reconstruction with FBP,1 However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To CT images (Figure 26) show large soft tissue mass involving the entire right sacrum in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with bone destruction and extending to adjacent ileum with complete erosion of the left with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 sacro-iliac joint. Part of the tumor extends to the left sacrum as well as slightly towards technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative the left of the midline. There is considerable extension of the soft tissue mass into the A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ pelvis, displacing the iliac vessels. Fused images show exact correlation of the SPECT properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. uptake to the edges of the eroded bone on the CT with increased uptake corresponding collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward in intensity to the mild sclerosis in the eroded sacral margin and sacroiliac joint. The the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is relatively low intensity of uptake at the bony erosion margins reflects the absence of of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image significant osteoblastic reaction to the bone destruction caused by the plasmacytoma. radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens xSPECT Bone Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical SPECT (AC) location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. CT xSPECT/CT ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to Figure 25: xSPECT Bone delineation of sacral erosion in a case of Figure 26: CT and fused images in a case of pelvic plasmacytoma plasmacytoma. determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed eroding the sacrum. with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. Data courtesy of University of Erlangen, Erlangen, Germany. Data courtesy of University of Erlangen, Erlangen, Germany. 2 16 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Advanced Modeled Iterative Reconstruction o CT XSPECT Bone [A] by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD XSPECT/CT SPECT (AC) A Introduction: Evolution of Siemens CT image reconstruction technologies Image reconstruction is an essential technology that every computed tomography (CT) scanner requires for operation. The function of CT image reconstruction is to translate Figure 27: Comparison of 3D iteration and xSPECT Bone shows a lytic Figure 28: CT and fusion of CT and xSPECT Bone shows exact coregistra- lesion in the shaft of left femur. all of the acquired X-ray data (raw data) into a meaningful three-dimensional tion of the hypermetabolic edge of the lytic lesion in the left femoral representation of the patient. The most well-known method of image reconstruction Data courtesy of University of Erlangen, Erlangen, Germany. shaft to the erosion of the inner table of cortex. is commonly referred to as filtered back projection (FBP), in which measured X-ray Data courtesy of University of Erlangen, Erlangen, Germany. projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To Another similar lytic skeletal lesion is depicted in Figure 27, which shows a SPECT/CT address this, Siemens Healthineers CT scanners offer an improved three-dimensional study of a 75-year-old man with a history of multiple myeloma with bilateral thigh FBP, called weighted filtered back projection (WFBP).2 pain. xSPECT Bone demonstrated a large lytic lesion in the upper half of the shaft of A common characteristic of both FBP and WFBP is that they do not consider statistical the left femur with a smaller lesion just below the larger lesion. The central photopenic properties of measured X-ray projections. What this means is that all CT projections area with peripheral hypermetabolism is typical of a lytic lesion with peripheral collected in the detectors are weighted the same, regardless of their quality. With bone erosion. Compared to 3D iterative reconstruction, xSPECT Bone shows sharper the increased focus in dose reduction, the lack of inclusion of statistical properties delineation of the hypermetabolic edges of the lytic bone lesion as well as improved of conventional FBP or WFBP become an important barrier that prevents further delineation of the normal cortical bone of the femoral shaft and of the marrow cavity. radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art Transverse reconstruction of the xSPECT study shows improved delineation of the CT scanners have been developed with more advanced technology, known as iterative hypermetabolic medial margin of the lesion involving the upper part of the shaft reconstruction (IR). Not surprisingly, among the key advantages of IR is that the of the left femur. statistical properties of measured CT projection data can be readily incorporated into CT images (Figure 28) show lesions in the left femoral shaft which reflect erosion of the CT image reconstruction process. This would allow, for example, low-quality (noisy) the inner cortical table with absence of bony expansion and without irregularities of projections to carry less weight than high-quality projections. the outer cortical surface or periosteum. The inner cortical table erosion without any There has been an expanding utilization of IR in clinical practice in recent years, osteoblastic activity, calcification, or sclerosis within the marrow suggests a marrow primarily due to the increased focus on radiation dose optimization. Of note, Siemens lesion with infiltration into and eroding the inner cortical bone. This is typical of multiple myeloma. Fusion of CT and xSPECT Bone images shows exact co-registration Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. of the hypermetabolic peripheral margin of the myeloma lesions arising from the This was in line with the ALARA principle, that is to use a dose that is “As Low As marrow to the erosion of the inner cortical table typical of the myeloma lesions. Reasonably Achievable” to deliver diagnostic image quality. The sharp definition of the hypermetabolic rim of the lesions by xSPECT Bone helps its exact co-registration with the erosion. Focal hyperintensities in regions of the hypermetabolic peripheral rim suggest cortical zones with significantly more active erosion, which may be at risk of fracture. 2 17 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative SPECT/CT has higher accuracy compared to SPECT and planar bone scan for evaluation of skull base osteomyelitis.10 Accuracy for SPECT/CT was 92 percent compared to 85 percent for SPECT only and only 46 present for planar bone scan. Improved resolution Reconstruction of SPECT with better visualization of fine bony structures in the skull base, as visualized on xSPECT Bone, along with enhancement and definition of uptake, could potentially further improve imaging accuracy in such conditions, as evident from the previous case of mastoid osteomyelitis. SPECT/CT has significantly impacted imaging of joints, especially delineation of osteo- by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, arthritis, stress fractures, avascular necrosis, and infections. Sharper delineation of and Rainer Raupach, PhD joint hyper or hypometabolism, as well as joint spaces and articular margins achieved with xSPECT Bone with perfect co-registration with CT, can potentially improve diag- nostic confidence in joint imaging. Figure 31 shows a SPECT/CT bone study in a 28-year-old athletic man who presented with a chronic history of pain in both feet. xSPECT Bone reveals focal increase in uptake Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods within the first metatarsophalangeal joint exactly corresponding to the joint space and Image reconstruction is an essential technology that every computed tomography (CT) adjacent subchondral regions. Increased uptake corresponds to osteophytes on the It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate dorsal subarticular margin of the distal end of the first metatarsal. in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 i.e., not that not all measured data can be used for image reconstruction with FBP,1 However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative xSPECT Bone A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported CT xSPECT/CT SPECT (AC) reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 Figure 29: 99mTc-MDP bone SPECT in a patient with left oto-mastoiditis Figure 30: CT shows a slight loss of trabeculation in the lateral aspect projections to carry less weight than high-quality projections. with suspicion of osteomyelitis. SPECT study shows focal area of of the mastoid process which corresponds to the region of highest tracer There has been an expanding utilization of IR in clinical practice in recent years, increased uptake in the left mastoid. xSPECT Bone shows enhanced uptake on xSPECT Bone SPECT. This strongly suggests osteomyelitis. tracer uptake in the mastoid with improved definition of the extent of The lateral and medial margins are intact. Fusion of thin-slice CT and primarily due to the increased focus on radiation dose optimization. Of note, Siemens uptake and the margins of the involved mastoid, along with improved xSPECT Bone show the exact co-registration of the increased uptake to Healthineers has been placing emphasis on devising technical solutions that can help definition of the uptake in the adjacent skull bones and petrous temporal, the mastoid process, especially localization of the area of maximum to consistently achieve the right dose, for the right diagnostic task, for every patient. as well as improved definition of the maxillary bones and nasal septum. uptake to the zone of loss of mastoid trabeculae. Note the absence of This was in line with the ALARA principle, that is to use a dose that is “As Low As Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. spillage of activity beyond the mastoid bone margins due to the improved Reasonably Achievable” to deliver diagnostic image quality. edge definition of xSPECT Bone compared to 3D iteration. The maxillary bones and nasal septum seen on CT also show exact co-registration with xSPECT Bone reconstructions, which enables visualization of such fine details and reflects true metabolism and tracer uptake levels. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical Data courtesy of University of Minnesota, Minneapolis, Minnesota, USA. location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 18 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: CT (Figure 32) shows subchondral sclerosis and joint space narrowing, which, in Advanced Modeled Iterative addition to the overhanging osteophytes, indicate severe degenerative joint disease. Despite mild sclerosis of the sesamoids, no abnormal tracer uptake is noted within Reconstruction them on either side. xSPECT Bone shows focal increase in uptake of 99mTc-MDP in the right talo-calcaneal joint space (Figure 33) corresponding exactly to a bulky osteophyte within the joint space, which suggests osteoarthritic changes. The sharp definition of the focal uptake limited to and exactly corresponding to the by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, osteophyte within the joint space with clear delineation of the absence of degenerative change in the rest of the joint margins, reflects the high resolution and image quality and Rainer Raupach, PhD achieved with xSPECT Bone. A small focal area of slightly increased uptake of 99mTc-MDP in the anterior and lateral articular facet of the lower right tibia is also demonstrated on xSPECT Bone (Figures 34 and 35). The focal uptake exactly corresponds to a very small osteophyte. CT shows Introduction: Evolution of Siemens CT image reconstruction technologies a sclerotic growth plate scar without cortical disruption, displacement, or joint space Image reconstruction is an essential technology that every computed tomography (CT) alteration. xSPECT Bone shows the articular uptake corresponding exactly to the small scanner requires for operation. The function of CT image reconstruction is to translate osteophyte and clearly separate and distinct from the growth plate sclerosis, while such all of the acquired X-ray data (raw data) into a meaningful three-dimensional separation could not be visualized with standard SPECT reconstruction. representation of the patient. The most well-known method of image reconstruction is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To address this, Siemens Healthineers CT scanners offer an improved three-dimensional GOOD .... FBP, called weighted filtered back projection (WFBP).2 XSPECT Bone A common characteristic of both FBP and WFBP is that they do not consider statistical properties of measured X-ray projections. What this means is that all CT projections collected in the detectors are weighted the same, regardless of their quality. With 0000 the increased focus in dose reduction, the lack of inclusion of statistical properties of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art CT scanners have been developed with more advanced technology, known as iterative reconstruction (IR). Not surprisingly, among the key advantages of IR is that the statistical properties of measured CT projection data can be readily incorporated into SPECT (AC) the CT image reconstruction process. This would allow, for example, low-quality (noisy) projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, Figure 31: Comparison of 3D iteration and xSPECT Bone in a patient with Figure 32: xSPECT Bone (bottom), xSPECT/CT (middle row), and CT (top) ankle joint pain shows sharper definition of 99mTc-MDP uptake in the primarily due to the increased focus on radiation dose optimization. Of note, Siemens images show severe degenerative changes in the first metatarsophalan- articular surface of the distal end of the bilateral first metatarsal, as Healthineers has been placing emphasis on devising technical solutions that can help well as a small focal hot lesion in the left talo-calcaneal joint space. to consistently achieve the right dose, for the right diagnostic task, for every patient. geal joints. Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. 19 2 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Reconstruction Figure 33: xSPECT Bone (left), CT (right), and fused images of CT and xSPECT Bone (middle) show hypermet- abolic osteophyte in the talo-calcaneal by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, joint space suggestive of osteoarthritis. and Rainer Raupach, PhD Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. The above clinical examples help to illustrate the unique image quality improvement Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods that xSPECT Bone brings to skeletal scintigraphy. Sharp definition of lesion margins, Image reconstruction is an essential technology that every computed tomography (CT) clear delineation of hyper and hypometabolic zones, and clear differentiation between It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate cortical and spongy bone obtained by xSPECT Bone, together with the CT information in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional about sclerotic and lytic lesions as well as soft tissue changes, may enhance the diag- The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction nostic confidence and, thereby, revolutionize skeletal scintigraphy. Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 that not all measured data can be used for image reconstruction with FBP,1 i.e., not However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ xSPECT Bone properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. SPECT (AC) There has been an expanding utilization of IR in clinical practice in recent years, Figure 35: xSPECT Bone (left) and CT (right) shows focal increase in primarily due to the increased focus on radiation dose optimization. Of note, Siemens uptake at the anterior edge of the tibial articular surface corresponding Healthineers has been placing emphasis on devising technical solutions that can help to a small osteophyte. The xSPECT Bone and CT fusion image (middle) shows the uptake to correspond exactly to the anterolateral edge of to consistently achieve the right dose, for the right diagnostic task, for every patient. the articular surface without involving the cortical sclerotic growth This was in line with the ALARA principle, that is to use a dose that is “As Low As plate scar. Reasonably Achievable” to deliver diagnostic image quality. Figure 34: A comparison of xSPECT Bone and 3D iteration in the same patient shows sharp delineation of focal uptake at the articular surface Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. of the lower end of the right tibia. Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 3 20 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Clinical possibilities with Advanced Modeled Iterative xSPECT Quant Reconstruction This chapter and associated clinical examples explore and help illustrate the clinical potential of absolute SPECT quantification with xSPECT Quant. Accurate and reproduc- ible quantification supports physicians’ ability to more confidently interpret clinical by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, images, enabling early modification of patient treatment and potentially reducing costs. and Rainer Raupach, PhD Skeletal applications A scientific publication7 highlights the normal regional activity concentration in the spongy bone of the lumbar vertebrae measured using xSPECT Quant in 50 normal Introduction: Evolution of Siemens CT image reconstruction technologies female patients (mean age 69.88 +/- 13.73 years; injected dose 562 +/- 102.33 MBq Image reconstruction is an essential technology that every computed tomography (CT) of 99mTc-DPD; acquisition performed 4 hours post-injection) yielded average bone Figure 36: A 99mTc-MDP planar bone scanner requires for operation. The function of CT image reconstruction is to translate tracer activity concentration of 48.15 +/- 13.66 kBq/ml, which corresponds to average scan in a patient with a history of gas- all of the acquired X-ray data (raw data) into a meaningful three-dimensional Standard Uptake Value (SUV) of 5.91 +/- 1.54. There was close positive correlation of tric carcinoma shows normal distribu- representation of the patient. The most well-known method of image reconstruction SUV to the Hounsfield unit (HU) levels as well as negative correlation between patient tion of tracer throughout the skeletal is commonly referred to as filtered back projection (FBP), in which measured X-ray age and SUV levels. system except for a small focal area of projections are directly translated into images. In most modern scanners, it is likely increased uptake in the 9th rib, which is These average SUV ranges in the spongy bone of normal female lumbar vertebrae that not all measured data can be used for image reconstruction with FBP,1 i.e., not possibly related to past traumatic rib in an elderly population correlate well with similar data obtained using 18F-fluoride PET. all radiation dose applied to the patient is actually used for image reconstruction. To fracture. There is no obvious focal area Frost8 determined average SUV in lumbar vertebrae using 18F-fluoride PET/CT acquired of increased uptake suggestive of address this, Siemens Healthineers CT scanners offer an improved three-dimensional metastases. From the planar image, the 1 hour post-injection to be 5.5, which matches well with that obtained by quantitative FBP, called weighted filtered back projection (WFBP).2 impression of absence of skeletal SPECT/CT. A common characteristic of both FBP and WFBP is that they do not consider statistical metastases can be made with a high The strong correlation of absolute tracer concentration and SUV in the vertebral spongy degree of confidence. However, SPECT properties of measured X-ray projections. What this means is that all CT projections imaging can still improve upon that bone with the HU values is expected. Diphosphonates, which are radiolabeled to obtain collected in the detectors are weighted the same, regardless of their quality. With confidence because small lesions with radiopharmaceuticals for imaging bone metabolism, bind to mineral phase of the bone the increased focus in dose reduction, the lack of inclusion of statistical properties mildly increased skeletal metabolism hydroxyapatite. Hydroxyapatite density reflects bone density as reflected in HU values of conventional FBP or WFBP become an important barrier that prevents further may become more apparent with on CT. Thus, strong correlation between SUV obtained by xSPECT Quant and HU values radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art SPECT, especially with 3D iterative reflects the accuracy of quantification of tracer uptake. CT scanners have been developed with more advanced technology, known as iterative reconstruction (SPECT AC). reconstruction (IR). Not surprisingly, among the key advantages of IR is that the Quantitative measurement of skeletal tracer concentration can potentially be helpful SPECT/CT imaging of the thoracic statistical properties of measured CT projection data can be readily incorporated into in evaluating osteoporosis and metabolic bone disorders. In a 1994 study,9 Israel region was subsequently performed the CT image reconstruction process. This would allow, for example, low-quality (noisy) with a standard acquisition protocol of performed 99mTc-MDP bone SPECT in osteoporotic women and obtained semi-quantita- projections to carry less weight than high-quality projections. 64 frames with 20 seconds per frame. tive indices of bone uptake (expressed as percent injected dose/cc) in the lumbar verte- Diagnostic CT was performed as an brae and femoral head and compared them with age-matched normal female controls. There has been an expanding utilization of IR in clinical practice in recent years, integrated procedure prior to SPECT The tracer concentration decreased with age in trabecular bone of normal women. primarily due to the increased focus on radiation dose optimization. Of note, Siemens acquisition with 140 kV, 50 mAs 3D iter- Tracer concentration was significantly higher both in lumbar vertebrae (10 percent) and Healthineers has been placing emphasis on devising technical solutions that can help ative reconstruction with 20 iterations femoral neck (25 percent) in postmenopausal osteoporotic women, which reflected the to consistently achieve the right dose, for the right diagnostic task, for every patient. and 4 subsets with a Gaussian filter. CT increased bone turnover in osteoporotic women. attenuation correction was performed This was in line with the ALARA principle, that is to use a dose that is “As Low As on the 3D iteration reconstructed data. Reasonably Achievable” to deliver diagnostic image quality. Israel also used similar semi-quantitative measurement of tracer concentration in xSPECT Bone reconstruction was also patients with hyperparathyroidism.10 All patients with primary hyperparathyroidism used with the same dataset using zone showed significantly higher values of skeletal tracer concentration, measured in percent information obtained from the CT data. injected dose/cc in the ilium, sacroiliac region, and the femoral neck and shaft as Data courtesy of University of Erlangen, compared to age- and sex-matched controls. The percentage increase was in the range Erlangen, Germany. of 15–44 percent, the highest increase being in the femoral shaft. 2 21 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Reconstruction SPECT (AC) xSPECT Bone xSPECT Bone Figure 37: Comparison of 99mTc-MDP bone SPECT reconstructed with by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, 3D iterative reconstruction (bottom row) and xSPECT Bone (top row) in and Rainer Raupach, PhD the same patient. There is a visually significant improvement in image SPECT (AC) quality, especially in the delineation of sharp margins of vertebral bodies, end plates, and intervertebral discs as well as vertebral canal, spinous, and transverse processes. The vertebral canal, which is almost smeared over by spilled activity from the vertebral bodies in the 3D Figure 38: An axial comparative section of 99mTc-MDP bone SPECT iterative reconstruction is clearly delineated on xSPECT Bone. This through a thoracic vertebrae in the same patient illustrates, in detail, Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods demonstrates the image impact of CT-based zoning. The diagnostic the improved delineation of the vertebral body, transverse process, and facet joints (arrow) as well as spinal canal (arrow) with xSPECT Bone. Image reconstruction is an essential technology that every computed tomography (CT) implication of such sharpness in reconstruction includes the possibility It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate of improved delineation of vertebral end plate changes and encroach- The vertebral end of the ribs and the transverse processes, as well as the in image noise, is the standard tradeoff for achieving a substantial dose reduction. ments into the spinal canal as in blastic metastases, traumatic facet joint margins, are clearly delineated. In comparison, 3D iterative all of the acquired X-ray data (raw data) into a meaningful three-dimensional axial reconstruction shows complete absence of differentiation of ribs The first IR technology commercially developed by Siemens Healthineers was Iterative vertebral collapse, and spinal tuberculosis. representation of the patient. The most well-known method of image reconstruction from transverse process, poor delineation of spinal canal, and blurry Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray Data courtesy of University of Erlangen, Erlangen, Germany. image noise in reduced dose acquisitions.3 edges of vertebral body and ribs. IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 Data courtesy of University of Erlangen, Erlangen, Germany. i.e., not that not all measured data can be used for image reconstruction with FBP,1 However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ first IR technology that integrated a correction loop in the raw-data domain (a.k.a. 65 kBq/ml 2 PT 30 properties of measured X-ray projections. What this means is that all CT projections “sinogram”) and added a model of the CT system geometry during the data forward SUVmax 4.91 collected in the detectors are weighted the same, regardless of their quality. With SUVaya 4.07 the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is SUVmax 8.67 2 PT 3D 1 PT 3 O of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image SUVavg 7.28 space is applied iteratively to reduce image noise. SAFIRE has been used extensively 1 PT 3D radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art 69 kBq/ml CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults 1 PT 3 the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 373 kBq/ml SUV max 20.34 projections to carry less weight than high-quality projections. SUV ava 13.74 There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help Figure 39: xSPECT Quant measurements in lumbar vertebrae of the to consistently achieve the right dose, for the right diagnostic task, for every patient. patient in Figure 37 with normal tracer distribution in thoracic and Figure 40: xSPECT Quant measurements of absolute tracer concentra- tion and SUV in the patient described in Figure 1 with multiple osteo- This was in line with the ALARA principle, that is to use a dose that is “As Low As lumbar vertebrae show tracer concentration of 69 kBq/ml and average SUV of 7.28 in the center of the T9 vertebral body. Comparison with a blastic skeletal metastases show high SUV in the metastatic foci in L4 Reasonably Achievable” to deliver diagnostic image quality. normal range shows these values to fall around the upper end of the vertebrae, as expected, with SUV average of 4.07 in the body of normal normal range of 7. Injected dose: 574 MBq; patient weight: 141 lb; L3 vertebrae, which is lower than the normal range (7.02 +/-1.67).7 patient height: 5’ 8”. Injected dose: 976 MBq; weight: 117 lb; height: 5’ 4”. Data courtesy of University of Erlangen, Erlangen, Germany. Data courtesy of Johns Hopkins University, Baltimore, Maryland, USA. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 22 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Figure 41 shows a 99mTc-MDP planar bone scan of a patient with operated breast Advanced Modeled Iterative carcinoma who also underwent chemotherapy. The planar study shows focal areas of increased uptake in the cervical, lower thoracic, and lumbar vertebrae, which are Reconstruction suggestive of degenerative changes. Both kidneys are well-visualized. No obvious lytic or blastic bone lesion, suggestive of metastases, is visualized. The patient underwent SPECT/CT of the lumbar spine. 3D iteration and xSPECT Bone reconstructions are shown as comparisons in Figure 40. xSPECT Bone shows higher intensity of uptake secondary to facet arthropathy in the right facet joint in L5 vertebrae compared to 3D iterative reconstruction, as well as clear and sharp delineation of by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, lamina, spinous process, and spinal canal. Sagittal images show sharper definition of and Rainer Raupach, PhD intervertebral disc spaces and vertebral body margins, as well as pedicles and trans- verse processes on xSPECT Bone. Figure 44 shows absolute quantification of tracer concentration in the lumbar vertebrae in the same patient with diffuse lumbar vertebral sclerosis with clinical impression of Introduction: Evolution of Siemens CT image reconstruction technologies post-chemotherapy suppression of 99mTc-MDP uptake in the region of diffuse lumbar vertebral metastases. xSPECT Quant shows 157 kBq/ml of 99mTc-MDP in the center of the Image reconstruction is an essential technology that every computed tomography (CT) body of L3 vertebrae (arrow) with an SUV average of 14.95, which is approximately two scanner requires for operation. The function of CT image reconstruction is to translate times higher than that of normal (SUV average of 7.02) and three times higher than an all of the acquired X-ray data (raw data) into a meaningful three-dimensional representation of the patient. The most well-known method of image reconstruction is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To address this, Siemens Healthineers CT scanners offer an improved three-dimensional XSPECT Bone FBP, called weighted filtered back projection (WFBP).2 A common characteristic of both FBP and WFBP is that they do not consider statistical properties of measured X-ray projections. What this means is that all CT projections collected in the detectors are weighted the same, regardless of their quality. With SPECT (AC) the increased focus in dose reduction, the lack of inclusion of statistical properties of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art CT scanners have been developed with more advanced technology, known as iterative Figure 42: This comparison of 3D iterative and reconstruction (IR). Not surprisingly, among the key advantages of IR is that the xSPECT Bone reconstructions shows increased Figure 41: Planar bone scan in a uptake in vertical facet joint along with sharper statistical properties of measured CT projection data can be readily incorporated into patient with treated breast carcinoma. delineation of vertebral body margins and disc the CT image reconstruction process. This would allow, for example, low-quality (noisy) Data courtesy of Ludwig Maximilians spaces with xSPECT Bone. projections to carry less weight than high-quality projections. CT xSPECT/CT University, Munich, Germany. Data courtesy of Ludwig Maximilians University, There has been an expanding utilization of IR in clinical practice in recent years, Munich, Germany. primarily due to the increased focus on radiation dose optimization. Of note, Siemens Figure 43: CT shows a diffuse increase in sclerosis Healthineers has been placing emphasis on devising technical solutions that can help within the vertebral body interspersed with small to consistently achieve the right dose, for the right diagnostic task, for every patient. hypointense zones of normal spongy bone. The CT This was in line with the ALARA principle, that is to use a dose that is “As Low As pattern is suggestive of diffuse osseous metastases. Reasonably Achievable” to deliver diagnostic image quality. The skeletal metabolism in the vertebral bodies, as seen on xSPECT Bone, appears uniform but is slightly and diffusely increased when compared to the uptake in the pelvis. However, the overall uptake and absence of any focal hot or cold areas suggest that the CT changes in the lumbar spine may be related to post-chemotherapy suppression of skeletal metabolism within the diffuse osseous metastases. Data courtesy of Ludwig Maximilians University, Munich, Germany. 23 2 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: osteoporotic vertebrae demonstrated in Figure 38 with an SUV average of 4.57. This high Advanced Modeled Iterative SUV within the lumbar vertebrae, along with the diffuse sclerosis on CT, is reflective of diffuse osseous metastases. However, the planar bone study did not show diffuse Reconstruction vertebral hypermetabolism and both kidneys were visualized, excluding a “superscan” appearance. This can be explained by the response of the diffuse vertebral metastases to chemotherapy but with persistent higher level of vertebral metabolism, due to the increased bone turnover within the sclerotic component, as evident in the increased tracer concentration and SUV within the vertebrae. by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD PT 3D Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods O Image reconstruction is an essential technology that every computed tomography (CT) It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional The first IR technology commercially developed by Siemens Healthineers was Iterative 1 PT 3D representation of the patient. The most well-known method of image reconstruction Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased SUVmax 17.39 is commonly referred to as filtered back projection (FBP), in which measured X-ray SUVaya 14.95 image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 i.e., not that not all measured data can be used for image reconstruction with FBP,1 However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ 1 PT 3 properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward 157 the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is kBq/cc of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image Figure 44: Data courtesy of space is applied iteratively to reduce image noise. SAFIRE has been used extensively Ludwig Maximilians University, radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art since its introduction, and a wealth of scientific literature has consistently supported Munich, Germany. CT scanners have been developed with more advanced technology, known as iterative reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. Assessment of bone graft function and retention There has been an expanding utilization of IR in clinical practice in recent years, Absolute quantification of skeletal metabolism by measurement of bone concentra- primarily due to the increased focus on radiation dose optimization. Of note, Siemens tion of the tracer in Bq/ml has the potential to be of value in the assessment of bone Healthineers has been placing emphasis on devising technical solutions that can help graft function and retention. Droll11 performed bone SPECT in 104 hips in 93 patients to consistently achieve the right dose, for the right diagnostic task, for every patient. with osteonecrosis of the femoral head treated with vascularized fibular grafting. The This was in line with the ALARA principle, that is to use a dose that is “As Low As signal intensity of the graft was compared with the intensity of the ipsilateral proximal Reasonably Achievable” to deliver diagnostic image quality. femoral diaphysis and assigned a score of 1 if less than diaphysis, 2 if equal to diaph- ysis, and 3 if greater than diaphysis. Graft failure was defined as conversion to total hip arthroplasy. A total of 30 percent of the hips failed treatment with vascular fibular grafting and mean SPECT scores were significantly lower in the failed group compared to the group in which the bone graft was retained. This pattern of scoring of the intensity * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical of SPECT uptake and comparison with adjacent normal bone can potentially be helped location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. by the reproducible absolute quantitative values of tracer uptake within bone that can ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical be obtained by xSPECT Bone. Sequential quantitative imaging of graft uptake of 99mTc- location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the MDP may help compare absolute uptake values between fibular graft and ipsilateral appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to femoral diaphysis. determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 24 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Hip joint replacement follow-up Advanced Modeled Iterative Similar studies using sequential 99mTc-MDP bone SPECT have been successful in following regional periprosthetic bone turnover after total hip arthroplasty. Venesmaa12 Reconstruction performed bone SPECT after 6, 12, and 36 months following hip joint replacement surgery. Regions of interest (ROIs) were drawn in the greater and lesser trochanter and medial femoral cortex and a region above the acetabulum was drawn as a reference. All regional uptake values (counts/voxel) were divided by the reference value to determine regional uptake ratios. The ratios were compared with the contralateral side as well. In uncomplicated total hip arthroplasty cases, the regional uptake values significantly by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, decreased compared to baseline during the follow-up period, although uptake ratios in the medial cortex remained significantly higher compared to the contralateral side even and Rainer Raupach, PhD after three years following surgery. This suggested that bone turnover around femoral prosthesis remains high even after three years in the absence of prosthesis failure. Although this study has used regional uptake ratios with manually drawn symmetric ROIs, absolute quantification of tracer uptake in the bone may potentially be of value Introduction: Evolution of Siemens CT image reconstruction technologies in assessment of the rate of change of bone turnover and serve to provide additional objective information on progression to normalization or failure in sequential studies. Image reconstruction is an essential technology that every computed tomography (CT) Assessment of meniscal pathology scanner requires for operation. The function of CT image reconstruction is to translate all of the acquired X-ray data (raw data) into a meaningful three-dimensional The intensity of lesional uptake visualized in bone SPECT has been used in osteoarthritic knee joints for comparison with arthroscopic findings in order to grade the severity of representation of the patient. The most well-known method of image reconstruction involvement of menisci and femoral condyles. Siegel13 compared SPECT uptake intensity is commonly referred to as filtered back projection (FBP), in which measured X-ray with arthroscopic findings in 41 patients and found significant correlation between projections are directly translated into images. In most modern scanners, it is likely uptake and severity of meniscal pathology. This suggested the possibility that bone that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To SPECT could be used to help surgical decision-making by identifying severe pathology, address this, Siemens Healthineers CT scanners offer an improved three-dimensional which may not be amenable to arthroscopic therapy. Absolute quantification of bone FBP, called weighted filtered back projection (WFBP).2 and meniscal uptake may help such decision-making as well as offer additional objec- tive information about disease severity. A common characteristic of both FBP and WFBP is that they do not consider statistical Another similar study by Hirschman14 evaluated maximum intensity of uptake in properties of measured X-ray projections. What this means is that all CT projections 99mTc-HDP bone SPECT/CT in 85 knees with pain secondary to osteoarthritis. Maximum collected in the detectors are weighted the same, regardless of their quality. With the increased focus in dose reduction, the lack of inclusion of statistical properties intensities in each femoral, tibial, and patellar joint compartment were compared with joint alignment (varus, valgus, or neutral) and osteoarthritis scores assessed on of conventional FBP or WFBP become an important barrier that prevents further standardized radiographs Kelgren-Lawrence osteoarthritis score (KL). The intensity of radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art uptake on SPECT in the medial and lateral knee compartment directly correlated with CT scanners have been developed with more advanced technology, known as iterative reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the degree of varus or valgus alignment of the knee, as well as the degree of osteoar- thritis in the corresponding joint compartments. Intensity of uptake on SPECT was thus statistical properties of measured CT projection data can be readily incorporated into correlated with specific loading pattern on the knee related to the alignment, as well the CT image reconstruction process. This would allow, for example, low-quality (noisy) as degree, of osteoarthritis. In similar evaluations, absolute quantification of knee joint projections to carry less weight than high-quality projections. uptake of 99mTc-MDP may be helpful in objective assessment of patients before and after There has been an expanding utilization of IR in clinical practice in recent years, realignment therapy such as osteotomy, etc. primarily due to the increased focus on radiation dose optimization. Of note, Siemens Grading and follow-up of renal osteodystrophy Healthineers has been placing emphasis on devising technical solutions that can help Semi-quantitative evaluation of radiotracer uptake in bone scintigraphy has been to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As used to estimate bone metabolism in patients with renal osteodystrophy undergoing hemodialysis.15 Using an ROI drawn on the radius and skull, the bone/soft tissue ratio Reasonably Achievable” to deliver diagnostic image quality. (B/ST ratio) was calculated and correlated with parathyroid hormone (PTH) and Alkaline (Alk) phosphatase levels. B/ST ratios for both radius and skull correlated linearly with PTH and Alk phophatase, thereby demonstrating the relevance of semi- quantitative bone scintigraphy in grading and follow-up of renal osteodystrophy. Kurata,16 in a similar study, used B/ST ratios in lumbar spine and femoral neck and found good correlation with PTH. Similar correlations may possibly be achieved using absolute quantification of skeletal tracer concentration in long bones, vertebrae, and skull in metabolic bone disorders such as hyperparathyroidism, renal osteodystrophy, fluorosis, etc. 2 25 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Potential for extraskeletal applications Infection Reconstruction Quantification of tracer concentration using other 99mTc-labeled radiopharmaceuticals opens up further possibilities of adding to the diagnostic information in SPECT imaging. One potential possibility is for characterization of the intensity and severity of infec- tion detected by 99mTc-labeled leucocytes or anti-granulocyte antibodies (approved for use in Europe), as well as sequential evaluation of such infections to detect impact of antibiotic therapy. Diagnosis of infection often involves semi-quantitative comparison by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, of delayed (after 3–4 hours) versus late images (after 20–24 hours). The images are and Rainer Raupach, PhD classified as positive when there is an increase of activity or size between the two acquisitions. Quantification of SUV in the infective foci can potentially add further information to aid evaluation. In cases of infection in prosthetic joints, this can potentially help differentiate normal marrow hyperactivity from sites of infection based on accurate determination of percentage increase in tracer concentration or Introduction: Evolution of Siemens CT image reconstruction technologies SUV, which is expected to be significantly higher in infection.17 Pelosi18 studied 78 Development of IR methods patients with suspected hip or knee prosthetic infection using 99mTc-labeled white blood Image reconstruction is an essential technology that every computed tomography (CT) It is well known that the degradation in image quality, most notably an increase cells (WBC) and showed that the addition of a quantitative evaluation to the qualitative scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. analysis of delayed and late images leads to a significant improvement in both speci- all of the acquired X-ray data (raw data) into a meaningful three-dimensional The first IR technology commercially developed by Siemens Healthineers was Iterative ficity and accuracy of the method. Sequential images were acquired at three different representation of the patient. The most well-known method of image reconstruction Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased time points after the injection of the labeled leukocytes: 50 minutes (early images), is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology 4 hours, and 24 hours (late images). Sensitivity and specificity on semi-quantitative projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 analysis (95.6 percent and 95.8 percent, respectively) were far superior to that obtained that not all measured data can be used for image reconstruction with FBP,1 i.e., not However, it is expected that IR technologies not only aid in noise reduction but also on qualitative analysis (80.4 percent and 65.3 percent). Ballani19 evaluated 24 patients all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions (seven with hip or knee arthroplasty) with semi-quantitative uptake measurements of address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR 99mTc-MDP and 99mTc-HMPAO-labeled WBC, comparing the degree of the radiopharma- FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative ceutical uptake in the area of suspected infection. The semi-quantitative comparison of A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 both scans was most useful in excluding infections. SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections Inflammation first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward 99mTc-HMPAO-labeled WBC have been used in therapy monitoring of chronic inflam- the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is matory conditions such as bronchiectasis and inflammatory bowel disease. Sequential of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image imaging with labeled WBC in 13 patients with active bronchiectasis, before and on radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively the 10th day of therapy, demonstrated significant decrease in uptake ratios in the CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported inflamed lung zones following therapy.20 Similar sequential imaging with labeled reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in leukocytes has been performed in ulcerative colitis to evaluate response to medical statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults therapy.21 Twenty consecutive patients were imaged before and one week after initia- the CT image reconstruction process. This would allow, for example, low-quality (noisy) tion of medical therapy. The ratio of the maximum tracer uptake in the different colon and pediatrics.7-10 projections to carry less weight than high-quality projections. segments compared to that of the lumbar vertebral bone marrow uptake was used There has been an expanding utilization of IR in clinical practice in recent years, as a semi-quantitative indicator of the intensity of colonic inflammation. Favorable primarily due to the increased focus on radiation dose optimization. Of note, Siemens response to therapy was characterized as greater than a 50 percent decrease in the sum Healthineers has been placing emphasis on devising technical solutions that can help of the ratios of individual colonic segment in the post-therapy study compared to the to consistently achieve the right dose, for the right diagnostic task, for every patient. initial study. All patients with clinical and endoscopic proof of response to medical This was in line with the ALARA principle, that is to use a dose that is “As Low As therapy showed positive response on sequential scintigraphy with significant decrease Reasonably Achievable” to deliver diagnostic image quality. in the colonic segmental uptake ratios. The majority of the non-responders showed a >10 percent increase in the sum of segmental ratios. Most of these non-responders required colectomy. Since ratio comparison of the inflamed lesion to normal marrow is the key indicator in such cases, use of SUV, based on quantitative SPECT imaging, may potentially be of value and provide additional information on inflammation severity. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the In addition, percentage and absolute change in SUV could be defined as a criterion for appropriate dose to obtain diagnostic image quality for the particular clinical task. response assessment. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 26 3 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Advanced Modeled Iterative Lung 99mTc-MAA lung perfusion scintigraphy is used for preoperative determination of func- Reconstruction tional lung volume in patients with lung carcinoma. Manual or semi-automatic deter- mination of total perfused lung volume and regional lung function, as well as ratios of upper to lower lung zones, have been correlated with post-operative FEV1 and act as reliable predictors of ventilatory function following lobectomy or pneumonectomy.22 SUVmax-based thresholding for automated or semi-automated generation of volume of interest (VOI) incorporating functioning lung has the potential to improve determination of the extent of functioning lung tissue and also help monitor improvement in func- tional volume. by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, and Rainer Raupach, PhD Renal cortical mass Quantitative evaluation of renal cortical mass has been performed using 99mTc-DMSA in patients with cortical scars as well as post-nephrolithotomy and post-pyeloplasty situations. The quantitative parameters were relative cortical uptake and total cortical volume. Unsal23 performed 99mTc-DMSA SPECT on 50 patients before and after percu- Introduction: Evolution of Siemens CT image reconstruction technologies taneous nephrolithotomy. Total relative uptake and total area of treated kidney, for Image reconstruction is an essential technology that every computed tomography (CT) the entire group, increased from 42.2 percent and 42.3 percent, pre-operatively, to 44.1 scanner requires for operation. The function of CT image reconstruction is to translate percent and 43.9 percent, post-operatively. Split renal function and cortical volume all of the acquired X-ray data (raw data) into a meaningful three-dimensional estimation has been used for pre-transplantation evaluation of renal donors24 using representation of the patient. The most well-known method of image reconstruction cortical uptake from DMSA SPECT and renal volume estimated from CT. Estimation of is commonly referred to as filtered back projection (FBP), in which measured X-ray renal cortical SUV using quantitative SPECT imaging may potentially improve estima- projections are directly translated into images. In most modern scanners, it is likely tion of the volume of functioning cortex using SUVmax-based thresholds for 3D volume that not all measured data can be used for image reconstruction with FBP,1 assessment, as well as compare functioning cortical mass to that of healthy cohorts. i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To Quantitative 99mTc-DMSA SPECT has been used for evaluation of renal allografts. address this, Siemens Healthineers CT scanners offer an improved three-dimensional Evan Shapir25 estimated functioning cortical volume in 19 renal allografts, initially FBP, called weighted filtered back projection (WFBP).2 in the donors and subsequently in the recipients, following transplantation. A total A common characteristic of both FBP and WFBP is that they do not consider statistical of 43 percent of max pixel count was a threshold for defining renal cortical VOI. Renal properties of measured X-ray projections. What this means is that all CT projections cortical tracer concentration was defined as the percentage of injected dose corrected collected in the detectors are weighted the same, regardless of their quality. With for decay per cubic centimeter of kidney tissue. The total kidney uptake was obtained the increased focus in dose reduction, the lack of inclusion of statistical properties by multiplying volume by concentration. Total kidney uptake was increased to an of conventional FBP or WFBP become an important barrier that prevents further average of 190 percent of baseline in healthy renal allografts 6 months following radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art transplantation, while it decreased to an average of 69 percent of baseline in impaired CT scanners have been developed with more advanced technology, known as iterative grafts. Evaluation of graft renal cortical function can potentially be supported by reconstruction (IR). Not surprisingly, among the key advantages of IR is that the quantitative SPECT generating cortical SUV and percentage of SUVmax-based thresholds statistical properties of measured CT projection data can be readily incorporated into for cortical volume estimation and SUV-based comparison among patient the CT image reconstruction process. This would allow, for example, low-quality (noisy) cohorts and healthy controls. projections to carry less weight than high-quality projections. Liver There has been an expanding utilization of IR in clinical practice in recent years, 99mTc-GSA scintigraphy has been used to assess hepatic functional reserve in patients primarily due to the increased focus on radiation dose optimization. Of note, Siemens prior to hepatectomy. Most studies have used dynamic planar imaging with liver to Healthineers has been placing emphasis on devising technical solutions that can help heart ratios as semi-quantitative indicators of hepatic functional reserve.26 Similar to consistently achieve the right dose, for the right diagnostic task, for every patient. studies have been performed in liver transplant recipients as well to assess graft This was in line with the ALARA principle, that is to use a dose that is “As Low As function and predict the recipient’s outcome.27 SPECT-based SUV quantification of Reasonably Achievable” to deliver diagnostic image quality. liver concentration of 99mTc-GSA or 99mTc-Sulfur Colloid may further improve similar evaluation by providing clinical information on hepatic function and may help assessment of hepatic regeneration using sequential SPECT imaging. 2 27 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Advanced Modeled Iterative Another potential application of absolute quantification with SPECT is in assessment of pulmonary shunting of intra-arterial hepatic infusion of 99mTc-MAA, which is performed Reconstruction prior to intra-arterial radionuclide therapy for liver tumors. Current approaches to shunt estimation involve comparison of lung counts to those in the liver and are subjective and often inaccurate. Willowson28 used a quantitative approach similar to xSPECT Quant to quantify the absolute activity in the lungs as a result of arterio-venous shunting and used these results to estimate absorbed dose to lung tissue at the time of treatment. The paper provides support for the potential of quantitative SPECT for by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, estimation of shunts, using more reproducible determination of volume and activity concentration of the shunted tracer. and Rainer Raupach, PhD Autoimmune diseases 99mTc-labeled monoclonal antibodies have been used for imaging of B and T cell lymphocytes as part of research protocols for imaging of inflammatory autoimmune diseases.29 Quantitative SPECT imaging using such radiopharmaceuticals as 99mTc- Introduction: Evolution of Siemens CT image reconstruction technologies Rituximab may support studies involving tracking of lymphocytes. Studies using Development of IR methods Image reconstruction is an essential technology that every computed tomography (CT) 99mTc-anti-TNF-α mAb (infliximab) on rheumatoid arthritis before and after intra- It is well known that the degradation in image quality, most notably an increase articular infliximab therapy29 have demonstrated changes in tracer retention in joint scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional space as a strong therapy response indicator. SUV quantification with SPECT could be The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction ideal for such response evaluation scenarios for objective measurements, as well as Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray response assessment in borderline situations. image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 that not all measured data can be used for image reconstruction with FBP,1 i.e., not However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 3 28 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Conclusion Advanced Modeled Iterative Reconstruction The clinical examples of xSPECT Bone shown in the previous chapters demonstrate the improved image quality of SPECT skeletal scintigraphy using CT segmentation informa- tion inside the SPECT reconstruction enabled by the precise xSPECT alignment of CT and SPECT. The sharper edge delineation achieved improves the definition of lesion margins and enhances the localization of small hyper or hypometabolic lesions. Such visual improvement in bone SPECT imaging has the potential not only for improved lesion detection and characterization but also for improved treatment planning such as intra- by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, articular anesthetic injections for pain management due to the delineation of the exact and Rainer Raupach, PhD location of the active foci. xSPECT Bone thus shows potential to impact a wide range of clinical situations in oncology and orthopedics which require validation with future studies. The potential of quantitative SPECT/CT with xSPECT Quant impacts several clinical situations such as evaluation of therapy response in bone metastases, especially with radionuclide therapy, therapy response in infective processes, and other scenarios Introduction: Evolution of Siemens CT image reconstruction technologies in which 99mTc-labeled isotopes may be used for response assessment. Since SUV for individual SPECT radiopharmaceuticals and their target organ is a novel concept, their Image reconstruction is an essential technology that every computed tomography (CT) routine use would require documentation of normal uptake values and evaluation of scanner requires for operation. The function of CT image reconstruction is to translate the correlation of uptake levels and SUV with other indicators of disease state. The all of the acquired X-ray data (raw data) into a meaningful three-dimensional ability to estimate SUV with SPECT thus opens up a host of research opportunities representation of the patient. The most well-known method of image reconstruction that could potentially impact a wide range of clinical conditions and specialties. is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely that not all measured data can be used for image reconstruction with FBP,1 i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To address this, Siemens Healthineers CT scanners offer an improved three-dimensional FBP, called weighted filtered back projection (WFBP).2 A common characteristic of both FBP and WFBP is that they do not consider statistical properties of measured X-ray projections. What this means is that all CT projections collected in the detectors are weighted the same, regardless of their quality. With the increased focus in dose reduction, the lack of inclusion of statistical properties of conventional FBP or WFBP become an important barrier that prevents further radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art CT scanners have been developed with more advanced technology, known as iterative reconstruction (IR). Not surprisingly, among the key advantages of IR is that the statistical properties of measured CT projection data can be readily incorporated into the CT image reconstruction process. This would allow, for example, low-quality (noisy) projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. 2 29 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: References Advanced Modeled Iterative Reconstruction 1 Helyar, et al. (2010). The added value 11 Droll, et al. (2007). The use of of multi-slice SPECT/CT in patients postoperative bone scintigraphy to with equivocal bony metastasis from predict graft retention. Can J Surg, carcinoma of the prostate. EJNM, August 2007, Vol. 50, No. 4 April 2010, 37(4):706-713 12 Venesmaa, et al. (2012). Periprosthetic 2 Sudhakar, et al. (2010). Efficacy of SPECT bone turnover after primary total hip by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, over planar bone scan in the diagnosis arthroplasty measured by single-photon and Rainer Raupach, PhD of solitary vertebral lesions in patients emission computed tomography. with low back pain. Indian J Nucl Med, Scandinavian Journal of Surgery, April-June 2010, 25(2):44-48 101:241-248 3 Iqbal, et al. (2011). The incremental 13 Siegel, et al. (2006). 99mTc-methylene Introduction: Evolution of Siemens CT image reconstruction technologies value of SPECT/CT in characterizing Development of IR methods diphosphonate single photon emission solitary spine lesions. J Nucl Med Technol, tomography of the knees: intensity Image reconstruction is an essential technology that every computed tomography (CT) 39:201-207 It is well known that the degradation in image quality, most notably an increase of uptake and its correlation with scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. arthroscopic findings. Nucl Med all of the acquired X-ray data (raw data) into a meaningful three-dimensional 4 Cui, et al. (2010). Computed tomography The first IR technology commercially developed by Siemens Healthineers was Iterative Commun, Sep 2006, 27(9):689-693) representation of the patient. The most well-known method of image reconstruction guided intra-articular injection of Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray etanercept in the sacroiliac joint is an image noise in reduced dose acquisitions. 14 Hirschman, et al. (2013). Assessment 3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely effective mode of treatment of ankylosing of loading history of compartments in that is effective in reducing image noise in a variety of clinical applications.4, 5 i.e., not spondylitis. Scand J Rheumatol, May the knee using bone SPECT/CT: a study 1 that not all measured data can be used for image reconstruction with FBP, However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To 2010, 39(3):229-232 combining alignment and 99mTc-HDP in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional tracer uptake/distribution patterns. with reduced dose or fast acquisition techniques. In response to this, the next IR 5 Sola, et al. (2011). Value of bone J Orthop Res, Feb 2013, 31(2):268-274 2 FBP, called weighted filtered back projection (WFBP). technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative SPECT-CT to predict chronic pain relief A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010. after percutaneous vertebroplasty in SAFIRE was Siemens Healthineers’ 15 Nishida, et al. (2005). Usefulness of 6 properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. vertebral fractures. Spine J, Dec. bone uptake ratio of bone scintigraphy collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward 2011,11(12):1102-1107 in hemodialysis patients. Ann Nucl Med, the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is Apr 2005, 19(2):91-94 of conventional FBP or WFBP become an important barrier that prevents further 6 Sharma, et al. (2013). Utility of (99m) particularly helpful for reducing spiral artifacts. A second correction loop in image Tc-MDP hybrid SPECT-CT for diagnosis of 16 Kurata, et al. (2004). A clinical radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative skull base osteomyelitis: comparison with assessment of the relationship since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the planar bone scintigraphy, SPECT, and CT. between bone scintigraphy and serum the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into Jpn J Radiol, Feb 2013, 31(2):81-88 biochemical markers in hemodialysis applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 7 Cachovan, et al. (2013). EJNMMI patients. Ann Nucl Med, Sep 2004,18(6):513-518 projections to carry less weight than high-quality projections. Research, 3:45 There has been an expanding utilization of IR in clinical practice in recent years, 8 Frost, et al. (2008). J Nucl Med 49:700-707 17 Glaudemans, et al. (2013). Leukocyte primarily due to the increased focus on radiation dose optimization. Of note, Siemens and bacteria imaging in prosthetic joint Healthineers has been placing emphasis on devising technical solutions that can help 9 Israel, et al. (1994). Bone turnover in infection. European Cells & Materials, 25:61-77 to consistently achieve the right dose, for the right diagnostic task, for every patient. cortical and trabecular bone in normal This was in line with the ALARA principle, that is to use a dose that is “As Low As women and in women with osteoporosis. 18 Pelosi, et al. 99mTc-HMPAO-leukocyte Reasonably Achievable” to deliver diagnostic image quality. J Nucl Med, 35:1155-1158 scintigraphy in patients with 10 Israel, et al. (1991). In vivo SPECT symptomatic total hip or knee quantitation of bone metabolism in arthroplasty: improved diagnostic hyperparathyroidism and thyrotoxicosis. accuracy by means of semiquantitative * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical J NuclMed, 32:1157-1161 evaluation. J Nucl Med, 45:438-444 location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 3 30 White Paper | White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction xSPECT: a clinical overview ADMIRE: Advanced Modeled Iterative 19 Ballani, et al. The value of quantitative Reconstruction 25 Evan Shapir, et al. (2002). Kidney uptake of (99m)Tc-MDP and (99m) allografts and remaining contralateral Tc-HMPAO white blood cells in detecting donor kidneys before and after osteomyelitis in violated peripheral transplantation: assessment by bones. J Nucl Med Technol, 35:91-95 quantitative (99m)Tc-DMSA SPECT. 20 Altiay, et al. (2012). 99mTc-HMPAO J Nucl Med, 43:584–588 by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, labelled white blood cell scintigraphy in 26 Shimizu, et al. (2010). Natural course the diagnosis and monitoring of response and Rainer Raupach, PhD of the remnant hepatic functional of the therapy in patients with active reserve as estimated by technetium- bronchiectasis. Rev Esp Med Nucl Imagen 99m-galactosyl human serum albumin Mol, Jan/Feb 2012, 31(1):9-14 scintigraphy after a hepatectomy. 21 Bennink, et al. (2004). Evaluation J Gastroenterol, Mar 2010, 45(3):308-316 Introduction: Evolution of Siemens CT image reconstruction technologies of early treatment response and 27 Iida, et al. (2009). Assessment of Image reconstruction is an essential technology that every computed tomography (CT) predicting the need for colectomy in liver graft function and regeneration scanner requires for operation. The function of CT image reconstruction is to translate active ulcerative colitis with 99mTc- by galactosyl-human serum albumin all of the acquired X-ray data (raw data) into a meaningful three-dimensional HMPAO white blood cell scintigraphy. (99mTc-GSA) liver scintigraphy in adult representation of the patient. The most well-known method of image reconstruction J Nucl Med, 45:1698-1704 living-donor liver transplantation. 22 Ohno, et al. (2007). Coregistered Clin Transplant, Mar/Apr 2009, is commonly referred to as filtered back projection (FBP), in which measured X-ray projections are directly translated into images. In most modern scanners, it is likely ventilation and perfusion SPECT using 23(2):271-277 that not all measured data can be used for image reconstruction with FBP,1 krypton-81m and Tc-99m-labeled 28 Willowson, et al. (2011). Quantifying i.e., not all radiation dose applied to the patient is actually used for image reconstruction. To macroaggregated albumin with lung shunting during planning for radio- address this, Siemens Healthineers CT scanners offer an improved three-dimensional multislice CT utility for prediction FBP, called weighted filtered back projection (WFBP).2 embolization. Phys Med Biol, Jul 7, 2011, of postoperative lung function in non- 56(13):N145-152 A common characteristic of both FBP and WFBP is that they do not consider statistical small cell lung cancer patients. Acad 29 Malaviya, et al. (2012). (99m) Tc-labeled properties of measured X-ray projections. What this means is that all CT projections Radiol, Jul 2007, 14(7):830-838 rituximab for imaging B lymphocyte collected in the detectors are weighted the same, regardless of their quality. With 23 Unsal, et al. (2010). Effect of infiltration in inflammatory autoimmune the increased focus in dose reduction, the lack of inclusion of statistical properties percutaneous nephrolithotomy and disease patients. Mol Imaging Biol, Oct of conventional FBP or WFBP become an important barrier that prevents further tract dilatation methods on renal 2012,14(5):637-646 radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art function: assessment by quantitative CT scanners have been developed with more advanced technology, known as iterative single-photon emission computed reconstruction (IR). Not surprisingly, among the key advantages of IR is that the tomography of technetium-99m- statistical properties of measured CT projection data can be readily incorporated into dimercaptosuccinic acid uptake by the CT image reconstruction process. This would allow, for example, low-quality (noisy) the kidneys. J Endourol, Sep 2010, projections to carry less weight than high-quality projections. 24(9):1497-502 There has been an expanding utilization of IR in clinical practice in recent years, 24 Miyazaki, et al. (2010). 99mTc-DTPA primarily due to the increased focus on radiation dose optimization. Of note, Siemens dynamic SPECT and CT volumetry Healthineers has been placing emphasis on devising technical solutions that can help for measuring split renal function in to consistently achieve the right dose, for the right diagnostic task, for every patient. live kidney donors. Ann Nucl Med, This was in line with the ALARA principle, that is to use a dose that is “As Low As Apr 2010, 24(3):189-195 Reasonably Achievable” to deliver diagnostic image quality. 2 31 White Paper | ADMIRE: Advanced Modeled Iterative Reconstruction ADMIRE: Advanced Modeled Iterative Reconstruction | White Paper | xSPECT: a clinical overview White Paper ADMIRE: Additional reading Advanced Modeled Iterative Reconstruction A. H. Vija, “Introduction to xSPECT A. Hans Vija, Jun Ma, Peter Bartenstein, Technology: Evolving Multi-modal Jerry Froelich, Torsten Kuwert, Homer SPECT to Become Context-Based and Macapinlac, Aaron Jessop, Esther Mena, Quantitative.,” Siemens Medical Solutions Harun Ilhan, Shirley Yang, Zsolt Szabo; USA, Inc., Molecular Imaging, White “Reader confidence in lesion detection Paper, 2015. and lesion characterization with xSPECT by Juan C. Ramirez-Giraldo, PhD, Katharine L. Grant, PhD, A. H. Vija, Z. Szabo, T. Kuwert, J. Froelich, Bone”, SNM Annual Meeting Abstracts and Rainer Raupach, PhD P. Bartenstein, C. Daignault, N. Gowda, O. 2014 55:1499 Hadjie, H. Ilhan, and S. Yang, “Evaluation Jun Ma, A. Hans Vija, “Noise and resolution of image quality and clinical acceptance characteristics for xSPECT reconstruction of HD-Bone, a novel multi-modal SPECT/ method”, SNM Annual Meeting Abstracts CT reconstruction method for Tc99m 2014 55:2129 Introduction: Evolution of Siemens CT image reconstruction technologies Development of IR methods diphosphonate imaging,” SNM Annual Image reconstruction is an essential technology that every computed tomography (CT) Meeting Abstracts 2013 54:339 It is well known that the degradation in image quality, most notably an increase scanner requires for operation. The function of CT image reconstruction is to translate in image noise, is the standard tradeoff for achieving a substantial dose reduction. all of the acquired X-ray data (raw data) into a meaningful three-dimensional The first IR technology commercially developed by Siemens Healthineers was Iterative representation of the patient. The most well-known method of image reconstruction Reconstruction in Image Space (IRIS*). IRIS directly addressed the problem of increased is commonly referred to as filtered back projection (FBP), in which measured X-ray image noise in reduced dose acquisitions.3 IRIS is a scientifically validated technology projections are directly translated into images. In most modern scanners, it is likely that is effective in reducing image noise in a variety of clinical applications.4, 5 i.e., not that not all measured data can be used for image reconstruction with FBP,1 However, it is expected that IR technologies not only aid in noise reduction but also all radiation dose applied to the patient is actually used for image reconstruction. To in reducing spiral artifacts, which can be exacerbated when using CT acquisitions address this, Siemens Healthineers CT scanners offer an improved three-dimensional with reduced dose or fast acquisition techniques. In response to this, the next IR FBP, called weighted filtered back projection (WFBP).2 technology developed by Siemens Healthineers was the Sinogram Affirmed Iterative A common characteristic of both FBP and WFBP is that they do not consider statistical Reconstruction (SAFIRE**), launched in 2010.6 SAFIRE was Siemens Healthineers’ properties of measured X-ray projections. What this means is that all CT projections first IR technology that integrated a correction loop in the raw-data domain (a.k.a. collected in the detectors are weighted the same, regardless of their quality. With “sinogram”) and added a model of the CT system geometry during the data forward the increased focus in dose reduction, the lack of inclusion of statistical properties projection. This correction loop that operates through to the raw-data domain is of conventional FBP or WFBP become an important barrier that prevents further particularly helpful for reducing spiral artifacts. A second correction loop in image radiation dose reduction. In an attempt to overcome such limitations, state-of-the-art space is applied iteratively to reduce image noise. SAFIRE has been used extensively CT scanners have been developed with more advanced technology, known as iterative since its introduction, and a wealth of scientific literature has consistently supported reconstruction (IR). Not surprisingly, among the key advantages of IR is that the the capabilities of SAFIRE to reduce dose while maintaining high image quality in statistical properties of measured CT projection data can be readily incorporated into applications ranging from routine to specialized body and neuro CT – in both adults the CT image reconstruction process. This would allow, for example, low-quality (noisy) and pediatrics.7-10 projections to carry less weight than high-quality projections. There has been an expanding utilization of IR in clinical practice in recent years, primarily due to the increased focus on radiation dose optimization. Of note, Siemens Healthineers has been placing emphasis on devising technical solutions that can help to consistently achieve the right dose, for the right diagnostic task, for every patient. This was in line with the ALARA principle, that is to use a dose that is “As Low As Reasonably Achievable” to deliver diagnostic image quality. * In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. ** In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. 2 3 32 Trademarks and service marks used in this material are xSPECT Quant is not commercially available in all countries. property of Siemens Healthcare GmbH. All other company, Due to regulatory reasons, its future availability cannot be brand, product and service names may be trademarks or guaranteed. Please contact your local Siemens organization registered trademarks of their respective holders. for further details. All comparative claims derived from competitive data at the time of printing. Data on file. Siemens reserves the right to modify the design and specifications contained herein without prior notice. As is generally true for technical specifications, the data contained herein varies within defined tolerances. Some configurations are optional. Product performance depends on the choice of system configuration. Please contact your local Siemens sales representative for the most current information or contact one of the addresses listed below. Note: Original images always lose a certain amount of detail when reproduced. “Siemens Healthineers” is considered a brand name. Its use is not intended to represent the legal entity to which this product is registered. Please contact your local Siemens organization for further details. All photographs © 2018 Siemens Healthcare GmbH. All rights reserved. Note: Original images always lose a certain amount of detail when reproduced. Siemens Healthineers Headquarters Published by Global Business Line Siemens Healthcare GmbH Siemens Medical Solutions USA, Inc. Siemens Medical Solutions USA, Inc. Henkestr. 127 40 Liberty Boulevard Molecular Imaging 91052 Erlangen, Germany Malvern, PA 19355-9998 2501 North Barrington Road Phone: +49 9131 84 0 USA Hoffman Estates, IL 60192 siemens.com/healthineers Phone: +1 888 826-9702 USA siemens.com/healthineers Phone: +1 847 304-7700 siemens.com/mi Order No. A91MI-10475-T1-7600 | Printed in USA | All rights reserved | MI-3612.TM.JV.TW.1500 | © Siemens Healthcare GmbH, 01.2018