SOMATOM On.site CT Basics Online Training

Continue Continue Continue Continue Continue Continue Continue Continue Continue SOMATOM On.site CT Basics Online Training Master Template HILS2218 | Effective Date: 25 Mar 2022 ? SOMATOM On.site CT Basics Online Training This online training will introduce you to the main features and functionalities of CT scanners and scanning. Identify the system components of a CT scanner Memorize the radiation dose parameters and definitions Describe the image reconstruction parameters Explain the functionality of a CT scanner 1 4 3 2 Welcome [somatom_on-site_ct-basics-olt_01_welcome.wav] Welcome to the SOMATOM On.site CT Basics Online Training.   This online training will introduce you to the main features and functionalities of CT scanners and scanning. By the end of this training, you will be able to achieve the four learning objectives listed. ? Navigation hints Before you start, we would like to give you a few tips on how to navigate: Table with 2 columns and 4 rows Not all pages contain audio. Some pages invite you to read for yourself. All pages show a ? button in the lower-right corner. Select the ? button to get a quick guide through the navigation elements. Select the button on the left upper corner to display or hide the menu. Enjoy the course! ? Navigation hints ? System components of a CT scanner System components of a CT scanner ? This chapter will introduce you to the system components of a CT scanner with a special focus on: X-ray tube Detector Two scanning advancements made possible by modern detector design will be described: Multislice scanning Acquisition modes Introduction system components Introduction system components [somatom_on-site_ct-basics-olt_04_introduction-system-components.wav] This chapter will introduce you to the system components of a CT scanner with a special focus on the X-ray tube and the detector.   Two scanning advancements made possible by modern detector design will be described: Multislice scanning and Acquisition modes ? Overview of system components Laser light marker For patient positioning Gantry operator panel For controlling gantry functions Motorized trolley Contains battery, electronics for gantry, and cooling Telescopic gantry Contains X-ray tube, detector, several filters and fans, and electronic components Two independent gantry compartments: Rear compartment houses X-ray tube and detector; moves during scan acquisition Front part stays in place during scan acquisition Laser light marker Gantry operator panel Mountable fixed stand Telescopic gantry Overview of system components [somatom_on-site_ct-basics-olt_05_overview-system-components.wav] The computer tomograph consists of a stationary and a rotating part.   The stationary part contains the battery, the electronics for the gantry, and the cooling. The rotating part contains the X-ray tube, the detector, several filters and fans, and electronic components (for example those associated with the data transfer).   SOMATOM On.site features a specially designed telescopic gantry with two independent gantry compartments. The rear compartment houses the X-ray tube and the detector and moves during scan acquisition. The front part stays in place during scan acquisition. Due to the telescopic gantry, a movable patient table is not required for the scan. ? X-ray tube The following parameters are generated and controlled by the X-ray tube: Tube voltage Tube current Focal spot The tube voltage determines the X-ray spectrum and the maximum energy of the photons. The tube current in combination with the exposure time influences the amount of the photons (mAs product). The focal spot affects the spatial resolution and, in a way, the lifetime of the anode material. (1) X-ray tube (2) X-ray generator 1 2 X-ray tube [somatom_on-site_ct-basics-olt_06_x-ray-tube.wav] By the x-ray tube the following parameters are generated and controlled: > Tube voltage > Tube current > Focal spot - The tube voltage determines the x-ray spectrum and the maximum energy of the photons - The tube current in combination with the exposure time influences the amount of the photons (mAs product) - The focal spot affects the spatial resolution and in a way the lifetime of the anode material ? Detector Collimator made of tungsten shielding: Suppression of scattered radiation Ultra-Fast Ceramic Detector (UFC): Conversion of X-rays into visible light Photodiode: Conversion of visible light into electrical current A/D (analog/digital) converter: Conversion of electrical signals into digital data Detector [somatom_on-site_ct-basics-olt_07_detector.wav] The detector is located on the opposite side of the X-ray tube. It is the other main part of the computer tomograph that is incorporated into the rotating gantry.   The detector converts the X-ray photons into digital data in several steps: - First, the collimator made of tungsten shielding suppresses scattered radiation. - Second, the Ultra-Fast Ceramic Detector (UFC) converts X-rays into visible light. - Third, the photodiode converts visible light into electrical current. and - Fourth, the analog-to-digital converter transforms electrical signals into digital data. ? Advantage of multislice CT scanner The first scanners were equipped with a single-row detector. That means one image is acquired in each rotation. Nowadays, all CT scanners have multi-row detectors. That means multiple images are acquired during a single rotation. This may lead to a reduced scan time. Another advantage is the reduction of motion artifacts. einzeiler spiral mehrzeilerspiral Scan with a single-row detector in spiral mode Scan with a multi-row detector in spiral mode Advantage of multislice CT scanner [somatom_on-site_ct-basics-olt_08_advantage-multislice-ct-scanner.wav] The first scanners were equipped with a single-row detector. That means one image is acquired in each rotation.   Nowadays, all CT scanners have multi-row detectors. That means multiple images are acquired during a single rotation. This may lead to a reduced scan time. Another advantage is the reduction of motion artifacts. ? Detector design and acquisition modes With the smallest element size (0.75 mm), the minimum reconstruction slice thickness is 0.8 mm. Spiral scan mode is available with SOMATOM On.site. Element design of SOMATOM On.site 32x0.75mm Detector design and acquisition modes [somatom_on-site_ct-basics-olt_09_detector-design.wav] With the smallest element size of 0.75 millimeters, the minimum reconstruction slice thickness is 0.8 mm. Spiral scan mode is available with SOMATOM On.site. ? Functionality of a CT scanner Functionality of a CT scanner ? Introduction scanner functionality This chapter will address the functionality of a CT scanner by covering the topics: Basic image generation process Spiral scanning Automatic scanning parameter adjustments with SureView Introduction scanner functionality [somatom_on-site_ct-basics-olt_11_scanner-functionality.wav] This chapter will address the functionality of a CT scanner. After covering the basics of the image generation process, it will discuss spiral scanning and the automatic adjustment of the scan parameters using the SureView concept. ? Image generation process The X-ray tube generates the radiation. The rays penetrate the body and are attenuated by the tissue. The attenuated X-ray beams are processed by the detector. The detector converts the radiation into electrical signals. The computer converts this digital data into high-resolution images. Detector X-ray tube Image generation process [somatom_on-site_ct-basics-olt_12_image-generation-process.wav] During the CT examination, the X-ray tube and the detector rotate around the patient in the gantry.   Rotation by rotation, axial slices of the body are captured, one at a time. The sequence of the image generation steps is as follows: - The X-ray tube generates the radiation. - The rays penetrate the body and are attenuated by the tissue. - The attenuated X-ray beams are processed by the detector. - The detector converts the radiation into electrical signals. and - The computer converts this digital data into high-resolution images. ? Image elements Voxel Pixel The image generated by the CT scanner is a digital image and consists of a square matrix of elements (pixels), each of which represents a voxel (3D volume element) of the patient’s tissue. Image elements [somatom_on-site_ct-basics-olt_13_image-elements.wav] The image generated by the CT scanner is a digital image and consists of a square matrix of elements (called pixels), each of which represents a voxel (that is, a 3D volume element) of the patient’s tissue. ? Spiral scanning This is a continuous volume imaging mode. Data acquisition and gantry movement are performed simultaneously for the entire scan duration. Each acquisition provides a complete volume data set, from which images with overlapping slices can be reconstructed at any slice position. Only spiral scanning is available with SOMATOM On.site. Conventional CT Spiral CT Spiral scanning [somatom_on-site_ct-basics-olt_14_spiral-scanning.wav] Spiral scanning is a continuous volume imaging mode. Data acquisition and gantry movement are performed simultaneously for the entire scan duration. Each acquisition provides a complete volume data set, from which images with overlapping slices can be reconstructed at any slice position. Only spiral scanning is available with SOMATOM On.site. ? Advantage of spiral scanning Compared to sequential scans, spiral scans offer the following advantages: Examination within one breath hold. Shorter scan times facilitate motion artifact reduction and lower the need for contrast medium. Better differentiation of contrast-enhanced phases, for example, arterial and venous phases. Better method for 3D reconstructions when scanning restless patients. split_second_thorax Advantage of spiral scanning [somatom_on-site_ct-basics-olt_15_advantage-spiral-scanning.wav] Compared to sequential scans, spiral scans offer the following advantages: - The examination can be completed within one breath hold. - Shorter scan times facilitate the reduction of motion artifacts and lower the need for contrast medium. - There is a better differentiation of contrast-enhanced phases, for instance of arterial and venous phases. - It is a better method for 3D reconstructions when scanning restless patients. ? Pitch The pitch (P) is a spiral scan parameter that determines the speed of the gantry movement and the speed of the acquisition. The higher the pitch, the faster the gantry feed and the shorter the scan time. Generally, the pitch for single-source scanners is between 0.35 and 1.5 and can be selected in increments of 0.05. Pitch values (approx.): P 0.5 for high detail detectability P 1 for standard examinations P 1.5 for high scan speed (reduction of breathing or motion artifacts) Pitch 0.5 Pitch 1.0 Pitch 1.5 Gantry feed per rotation (360°) [mm] Collimation [mm] P = Pitch [somatom_on-site_ct-basics-olt_16_pitch.wav] The pitch is a spiral scan parameter that determines the speed of the gantry movement and the speed of the acquisition. The higher the pitch, the faster the gantry feed and the shorter the scan time.   Generally, the pitch for single-source scanners is between 0.35 and 1.5 and can be selected in increments of 0.05. ? Pitch and SureView concept When increasing the pitch, the tube current (mA) must also be increased to obtain the same image noise or dose. This is done automatically with the so-called SureView concept. Due to the effective mAs*, the pitch factor no longer has any influence on the image noise because mA is automatically adjusted according to the pitch. The tube current is adjusted to the gantry feed: Gantry feed high  higher tube current Gantry feed low  lower tube current * Effective mAs = mA x Rotation Time Pitch Pitch 1 = no overlap Pitch 0.5 = 50% overlap Z-axis ___________________________ Pitch and SureView concept [somatom_on-site_ct-basics-olt_17_pitch-sureview.wav] When increasing the pitch, the tube current (that is, the mA value) must also be increased to obtain the same image noise or dose. This is done automatically with the so-called SureView concept.   Due to the effective mAs, the pitch factor no longer has any influence on the image noise because mA is automatically adjusted according to the pitch.   The tube current is adjusted to the gantry feed in the following way: When the gantry feed is high, higher tube current is applied. When the gantry feed is low, lower tube current is applied. ? Image reconstruction parameters Image reconstruction parameters ? Introduction image reconstruction parameters This chapter focuses on a set of essential parameters that are involved in the reconstruction of high-resolution images from the detector-generated digital data: Field of View (FoV) (Convolution) kernel Slice thickness Increment CT number CT window Introduction image reconstruction parameters [somatom_on-site_ct-basics-olt_19_image-reconstruction-params.wav] This chapter focuses on a set of essential parameters that are involved in the reconstruction of high-resolution images from the detector-generated digital data:   - Field of View - Convolution kernel (or short: “kernel”) - Slice thickness - Increment - CT number and - CT window ? Field of View (FoV) The anatomical area displayed within the CT image is called Field of View (FoV). The dimension of such a CT image is determined by the matrix size. The spatial resolution can be generally improved by using a smaller FoV because it reduces the pixel size. However, images should always be reconstructed with an appropriate FoV that is adjusted to the anatomical structure of interest. Thus, the visual impression can be improved without over-magnification. Large FoV Small FoV Field of View (FoV) [somatom_on-site_ct-basics-olt_20_fov.wav] The anatomical area displayed within the CT image is called Field of View. The dimension of such a CT image is determined by the matrix size. The spatial resolution can be generally improved by using a smaller Field of View because it reduces the pixel size. However, images should always be reconstructed with an appropriate Field of View that is adjusted to the anatomical structure of interest. Thus, the visual impression can be improved without over-magnification.   The Field of View is limited by the maximum size of the scan measurement fields. Generally, you can reconstruct a maximum Field of View of 26 centimeters for the head.   To improve the spatial resolution, the Field of View should always be tailored to the object of interest. That means it should be as small as possible. But take care when defining the Field of View because significant findings may be excluded from the images and missed during data interpretation. Usually the first reconstruction is done with a large Field of View as an overview and additional reconstructions are done with a smaller Field of View according to the organs of interest. ? Kernel The (convolution) kernel is a reconstruction parameter affecting image sharpness and noise. The kernel applies a specific mathematical algorithm that digitally filters the raw data during image reconstruction. The image sharpness is defined by the numeric values: The higher the kernel number, the sharper the image but the greater the image noise. Raw data Image data Kernel (e.g. Hr40) Table with 3 columns and 5 rows Image Appearance Typical Kernel Numbers Visualization/ Purpose Smooth 10 - 20 3D post-processing, noise reduction with thin slices Medium 30 - 50 General soft tissue display Sharp 60 - 70 Bone visualization with edge enhancement High Resolution 80 - 90 High spatial resolution assessment of minute structure, for example, inner ear Kernel [somatom_on-site_ct-basics-olt_21_kernel.wav] The convolution kernel (or short: “kernel”) is a reconstruction parameter affecting image sharpness and noise. The kernel applies a specific mathematical algorithm that digitally filters the raw data during image reconstruction. The image sharpness is defined by the numeric values in the kernel name: the higher the kernel number, the sharper the image but the greater the image noise. ? Kernel concept The first upper-case letter stands for the kernel family, the second lower-case letter stands for the kernel group. The resolution, which refers to the image sharpness, is defined by the subsequent number. The higher the number, the sharper the image impression. The first upper-case letter stands for the kernel family, the second lower-case letter stands for the kernel group. The resolution, which refers to the image sharpness, is defined by the subsequent number. The higher the number, the sharper the image impression. Position 1: Kernel Family Pos 1 H Pos 2 r Pos 3 32 S = Special Kernel H = Head Q = Quantitative Sh = Special Head 48 Hc = Head Crisp 40 - 44 Hr = Head Regular 32 - 68 Hv = Head Vascular 36 - 56 Qr = Quantitative Regular 32 - 64 Position 2: Kernel Group, Position 3: Resolution Kernel concept [somatom_on-site_ct-basics-olt_22_kernel-concept.wav] The first upper-case letter stands for the kernel family, the second lower-case letter stands for the kernel group. The resolution, which refers to the image sharpness, is defined by the subsequent number. The higher the number, the sharper the image impression. ? Slice thickness (width) This parameter describes the thickness of the reconstructed images. Slice width should not be confused with collimation. However, for single-slice CT imaging these terms are regarded as synonyms because in this case only images with a width equal to scan collimation can be reconstructed. With MSCT imaging, the possible slice widths depend on the chosen collimation and scan mode. Several slice widths can be selected post-acquisition by combining data from the various detector rows to reconstruct the axial images. Generated (1) 0.6 mm slice, excellent image details (2) 3.0 mm slice, poor image details Slice thickness (width) [somatom_on-site_ct-basics-olt_23_slice-thickness.wav] The parameter slice thickness (also known as slice width) describes the thickness of the reconstructed images.   Slice width should not be confused with collimation. However, for single-slice CT imaging these terms are regarded as synonyms because in this case only images with a width equal to scan collimation can be reconstructed.   With multi-slice CT imaging, the possible slice widths depend on the chosen collimation and scan mode. Several slice widths can be selected post-acquisition by combining data from the various detector rows to reconstruct the axial images. A narrower reconstructed slice width results in improved axial resolution but also increased noise. You can see the effects in the images on the right side. ? Increment Increment is the distance (in mm) between the reconstructed images in z-direction. It can be freely adapted from 0.1 mm upwards for spiral or 3D sequential scanning. If the increment is smaller than the slice width, the images are created with overlap. This provides better detail of the anatomy as well as high quality 2D and 3D post-processing. For routine 2D viewing, image series with contiguous increment are typically reconstructed. This reduces the total number of images for documentation and archiving. Two adjacent slices: CT value underrated Object overlooked Smaller objects are overlayed Three slices with 50% overlap: Full density at least in one slice  correct CT value Real size of the object More details are visible Example of the reconstruction increment effect in lung images Increment [somatom_on-site_ct-basics-olt_24_increment.wav] Increment is the distance (in millimeters) between the reconstructed images in z-direction. It can be freely adapted from 0.1 millimeters upwards for spiral or 3D sequential scanning.   If the increment is smaller than the slice width, the images are created with overlap. This provides better detail of the anatomy as well as high quality 2D and 3D post-processing.   For routine 2D viewing, image series with contiguous increment are typically reconstructed. This reduces the total number of images for documentation and archiving. ? CT number (Hounsfield units) The CT value is used to represent the mean X-ray attenuation value of the corresponding voxel within the slice. CT numbers are normally expressed in terms of Hounsfield units (HU). The CT number scale is defined so that water has a value of 0 HU; denser substances are given positive values and less dense materials negative numbers. Normally, CT values are measured in the range from -1024 to +3071, with values around -1000 HU representing air, and the highest numbers corresponding to very dense materials such as bones. Air 1000 Water Fat HU -1000 -500 Bone 0 500 Soft tissue CT number (Hounsfield units) [somatom_on-site_ct-basics-olt_25_hounsfield-units.wav] The CT value is used to represent the mean X-ray attenuation value of the corresponding volume element (or: voxel) within the slice. CT numbers are normally expressed in terms of Hounsfield units. The CT number scale is defined so that water has a value of 0 Hounsfield units; denser substances are given positive values and less dense materials negative numbers. Normally, CT values are measured in the range from minus 1024 to plus 3071, with values around minus 1000 Hounsfield units representing air, and the highest numbers corresponding to very dense materials such as bones. ? CT window Since the human eye is only able to distinguish approximately twenty gray tones, it is not practical to always represent all possible HU in a single comprehensive grayscale. Therefore, CT window limits the image display to tissue of interest. This results in a better differentiation of tissue with similar densities. All pixels with values above this range are represented in white, and those below this range in black. The window center (also called window level) and the window width define this range of CT numbers displayed in grayscale. Typical window settings for visualization of the brain tissue and bone: (1) Brain tissue window (W = 80, C = 35) reveals brain tissue, but the details of the bone structure cannot be seen so clearly. (2) Bone window (W = 3000, C = 1000) depicts details of the bone structure, but poor visualization of the brain tissue. (1) (2) CT window [somatom_on-site_ct-basics-olt_26_ct-window.wav] Since the human eye is only able to distinguish approximately twenty gray tones, it is not practical to always represent all possible Hounsfield units in a single comprehensive grayscale. Therefore, the parameter CT window limits the image display to tissue of interest. This results in a better differentiation of tissue with similar densities.   All pixels with values above this range are represented in white, and those below this range in black.   The window center (also called “window level”) and the window width define this range of CT numbers displayed in grayscale. ? Radiation dose parameters and definitions Radiation dose parameters and definitions ? Introduction radiation dose The last chapter of this training is dedicated to the important subject of radiation dose and covers the topics: Background radiation Radiation dose in CT Patient dose parameters Radiation dose definitions (absorbed, equivalent, effective dose) Introduction radiation dose [somatom_on-site_ct-basics-olt_28_introduction-rad-dose.wav] The last chapter of this training is dedicated to the important subject of radiation dose.   It gives you an overview of the exposure to background radiation and the dose considerations applying to CT procedures. Furthermore, it explains patient dose parameters and provides dose definitions for the absorbed, equivalent, and effective dose. ? Background radiation Humans are constantly exposed to natural radiation (cosmic and terrestrial). This dose varies, depending on the location, between 1 mSv and 6 mSv per year (average 2.4 mSv per year). If the artificial radiation by medical imaging procedures and human nuclear activities is added, the average radiation dose received is about 4 mSv per year for German and 6.2 mSv per year for US citizens. Effective dose in mSv Average annual natural background radiation 2.4 0.13 X-Ray Chest Stan-dard CT Chest 0.13 CT Chest Low Dose CT Head Background radiation [somatom_on-site_ct-basics-olt_29_background-radiation.wav] Humans are constantly exposed to natural radiation (cosmic and terrestrial). This dose varies, depending on the location, between 1 and 6 milli sieverts per year (with an average of 2.4 milli sieverts per year).   If the artificial radiation by medical imaging procedures and human nuclear activities is added, the average radiation dose received is about 4 milli sieverts per year for German and about 6.2 milli sieverts per year for US citizens. ? Radiation dose in CT Computed Tomography is a very valuable diagnostic tool, and it provides much more information than a conventional radiograph. However, the dose in CT can be much higher compared to conventional examinations. Therefore, it is important to limit the patient dose by using dose reduction techniques and applications. Patients should not be exposed to excessive irradiation, and the clinical indications must be verified before performing a CT exam. The common practice is to apply the ALARA principle. ALARA = As Low As Reasonably Achievable Radiation dose in CT [somatom_on-site_ct-basics-olt_30_radiation-dose-ct.wav] Computed Tomography is a very valuable diagnostic tool and it provides much more information than a conventional radiograph. However, the dose in CT can be much higher compared to conventional examinations.   Therefore, it is important to limit the patient dose by using dose reduction techniques and applications (for example CARE Dose4D). Patients should not be exposed to excessive irradiation, and the clinical indications must be verified before performing a CT exam.   The common practice is to apply the ALARA principle (where ALARA stands for: “As Low As Reasonably Achievable”). The aim of ALARA is to minimize the risk of radioactive exposure to a level that is necessary to obtain the desired diagnostic information. ? Dose overview and absorbed dose We all have an intuitive understanding of what dose is, but a radiation dose that reflects the potential damage to organic tissue cannot be defined simply as a certain amount of radiation energy per kg or sq. cm of body surface. That is why three different definitions are used: Absorbed, equivalent, and effective dose. The energy dose or absorbed dose (D) characterizes the amount of energy deposited in matter after being exposed to a certain amount of radiation. What is Dose? Equivalent Dose H Absorbed Dose D Effective Dose E Definition D = Absorbed Radiation Energy/kg of matter; measured in 1 Gy = 1 J/kg Physical Definition: When we irradiate 1 kg of water with 1 Gy, the water stores 1 J and its temperature increases by only 0.00024°C. Dose overview and absorbed dose [somatom_on-site_ct-basics-olt_31_dose-overview.wav] We all have an intuitive understanding of what dose is, but a radiation dose that reflects the potential damage to organic tissue cannot be defined simply as a certain amount of radiation energy per kilogram or square centimeter of body surface. That is why three different definitions are used: absorbed, equivalent, and effective dose.   The energy dose or absorbed dose (D) characterizes the amount of energy deposited in matter after being exposed to a certain amount of radiation.   However, this physical definition is not suited for living organisms since it does not reflect the biological effects. The type of radiation and the damage it might cause in different tissues have to be taken into account. ? Equivalent dose The biological damages caused by different types of radiation are not the same. Therefore, even if an absorbed dose of X-rays or α-rays is similar, the damage can be dramatically different. The equivalent dose (H) for any type of radiation is defined as the absorbed dose (D) multiplied by a factor (wr) that weights the damage caused to biological tissue by a particular type of radiation. In the case of X-rays used in CT, the weighting factor is 1. Therefore, the equivalent dose is the same as the absorbed dose. What is Dose? Equivalent Dose H Absorbed Dose D Effective Dose E The equivalent dose H is: H = D x wr where wr is an estimate of the amount of biological damage caused by 1 Gy of the corresponding type of radiation (for X-rays: wr = 1; for α-rays: wr = 20). The unit used to measure the equivalent dose is the sievert (Sv). Equivalent dose [somatom_on-site_ct-basics-olt_32_equivalent-dose.wav] The biological damages caused by different types of radiation are not the same. Therefore, even if an absorbed dose of X-rays or α-rays  is similar, the damage can be dramatically different. The equivalent dose (H) for any type of radiation is defined as the absorbed dose (D) multiplied by a factor (wr) that weights the damage caused to biological tissue by a particular type of radiation. In the case of X-rays used in CT, the weighting factor is 1. Therefore, the equivalent dose is the same as the absorbed dose. In the case of α–rays (that occur naturally and are emitted, for example, by some types of uranium isotopes) the absorbed dose has to be multiplied by a factor of 20. This indicates that α-rays cause much more damage to biological tissue. Table with 4 columns and 4 rows Quantity Description Meaning Unit CTDIvol Average dose over the total volume scanned for the selected CT conditions of operation Basic dose parameter in CT mGy DLP Product of the CTDIvol and the scan range Main descriptor of the total energy deposited in the body mGy*cm Effective Dose Average dose to the whole body, which is the weighted average of all affected organs Describes the radiation risk mSv ? Patient dose parameters Three main quantities that describe the patient dose in CT: • CTDIvol (Volume CT Dose Index) • DLP (Dose-Length Product) • Effective Dose (E) The CTDIvol describes a local dose, or "dose density": Energy accumulated per mass. Contrary to common thinking, the CTDIvol does not change when the scan length (coverage) is increased. However, the DLP and the effective dose values take the scan length into consideration. They are more consistent with the general understanding of the patient dose. Patient dose parameters [somatom_on-site_ct-basics-olt_33_patient-dose-parameters.wav] In radiology, the term "dose" or "patient dose" is always related to the absorbed dose: a measure of the energy deposited in a patient‘s body by ionizing radiation. There are three main quantities that describe the patient dose in CT: • CTDIvol  (the Volume CT Dose Index) • DLP (the Dose-Length Product) and • Effective Dose (E) The CTDIvol describes a local dose, or "dose density": energy accumulated per mass. Contrary to common thinking, the CTDIvol does not change when the scan length (the coverage) is increased. However, the DLP and the effective dose values actually do take the scan length into consideration. They are more consistent with the general understanding of the patient dose. ? Volume CT Dose Index (CTDIvol) This is a measure of the dose absorbed during a CT examination. It is a local quantity describing the energy deposited in a unit of mass. The CTDIvol is calculated from the integral of the dose profile produced in a single axial scan corrected for the weight of the patient and the pitch factor. The CTDIvol gives a good estimation of the average dose applied in the scanned volume, as long as the patient size (cross section) is similar to the size (diameter) of the respective dose phantoms. Since the body size can be smaller or larger than the 32-cm plexiglass phantom, the CTDIvol value displayed can deviate from the dose in the scanned volume. Scanlength z [cm] Slice Relative dose [%] Volume CT Dose Index (CTDIvol) [somatom_on-site_ct-basics-olt_34_ctdi-vol.wav] The CTDIvol is a measure of the dose absorbed during a CT examination. It is a local quantity describing the energy deposited in a unit of mass. The CTDIvol is calculated from the integral of the dose profile produced in a single axial scan corrected for the weight of the patient and the pitch factor. The CTDIvol gives a good estimation of the average dose applied in the scanned volume, as long as the patient size (that is: the cross section) is similar to the size (that is: the diameter) of the respective dose phantoms. Since the body size can be smaller or larger than the 32-centimeter plexiglass phantom, the CTDIvol value displayed can deviate from the dose in the scanned volume. ? Dose-Length Product (DLP) Generated DLP = CTDIvol x L X-ray tube Detector * * L = Length of scan range in cm The X-ray tube and the detector scan the patient along L (examination range) on the z-axis. The product of CTDIvol and the length L (cm) of the scan range is called Dose-Length Product (DLP). In order to calculate the total absorbed dose for a complete CT examination, the scan range that is being examined must be taken into account. Because DLP takes into consideration the geometrical extent of irradiation, it is considered to be a better indicator of the patient dose than CTDIvol. It describes the total energy deposited in the body. Therefore, it is often kept with the patient record. With the use of specific organ-related factors, DLP can be used to calculate the effective dose. Dose-Length Product (DLP) [somatom_on-site_ct-basics-olt_35_dlp.wav] The product of CTDIvol and the length L (in centimeters) of the scan range is called Dose-Length Product (DLP).   In order to calculate the total absorbed dose for a complete CT examination, the scan range that is being examined must be taken into account. The Dose-Length Product is measured in milli gray centimeters. Because DLP takes into consideration the geometrical extent of irradiation, it is considered to be a better indicator of the patient dose than CTDIvol.   It describes the total energy deposited in the body. Therefore, it is often kept with the patient record. When multiple series are performed, the DLP value for all series should be added to obtain the total DLP, which reflects the total dose for the entire examination. With the use of specific organ-related factors, DLP can be used to calculate the effective dose. ? Effective dose The weighted average of Organ Dose values for the irradiated organs is defined as the effective dose (E) expressed in mSv. It describes the stochastic radiation risk. The Organ Dose is the product of the average absorbed dose in an organ, multiplied with a weighting factor. This factor indicates the effects of the different types of radiation, such as X-rays or ionizing neutrons. The effective dose can also be estimated by multiplying the DLP with a conversion factor determined from measurements or computer simulations. The conversion factors (f) are reported by the European Commission. E = DLP x f Region of body Head Head & Neck Neck Chest Abdomen & Pelvis Trunk Conversion factor, f (mSv/(mGy cm) 0.0021 0.0031 0.0059 0.014 0.015 0.015 Region of body Head Neck Thorax Abdomen Pelvis Cardio Calculated effective organ dose (mSv) Dual Source CT 0.1 - 1.8 1.2 0.7 - 4.0 3.8 - 4.5 2.6 - 5.3 1.0 - 9.2 Single Source CT 0.2 - 1.7 1.9 - 2.7 0.4 - 3.5 3.8 - 4.8 1.5 - 4.6 0.9 - 4.2 Effective dose [somatom_on-site_ct-basics-olt_36_effective-dose.wav] The weighted average of Organ Dose values for the irradiated organs is defined as the effective dose (E) expressed in milli sieverts. It describes the stochastic radiation risk. The Organ Dose is the product of the average absorbed dose in an organ, multiplied with a weighting factor. This factor indicates the effects of the different types of radiation, such as X-rays or ionizing neutrons. The effective dose can also be estimated by multiplying the DLP with a conversion factor determined from measurements or computer simulations. The conversion factors (f) are reported by the European Commission. The calculation of E using Siemens default protocols depends on the CT source. ? Course review Congratulations. You have completed the SOMATOM On.site CT Basics Online Training. Select the objectives listed below to review the material before proceeding to the final assessment. Memorize the radiation dose parameters and definitions Describe the image reconstruction parameters Explain the functionality of a CT scanner Identify the system components of a CT scanner 1 1 2 2 2 3 3 3 4 4 4 Course review 1 1 2 2 Select the X button to return to the overview page. 3 3 3 Patient dose parameters: Three main quantities that describe the patient dose in CT CTDIvol (Volume CT Dose Index in mGy): Average dose over the total volume scanned for the selected CT conditions of operation, basic dose parameter in CT DLP (Dose-Length Product in mGy*cm): Product of CTDIvol and scan range, main descriptor of total energy deposited in body Effective Dose (E in mSv): See step 2 Memorize the radiation dose parameters and definitions 1 1 2 2 2 3 3 Radiation dose in CT: Important to limit the patient dose by using dose reduction techniques and applications. Patients should not be exposed to excessive irradiation. Common practice: ALARA principle (As Low As Reasonably Achievable = Minimize risk of radioactive exposure to a level that is necessary to obtain the desired diagnostic information). Absorbed dose (D, energy dose): Amount of energy deposited in matter after being exposed to a certain amount of radiation. Equivalent dose (H): Defined as the absorbed dose (D) multiplied by a factor (wr) that weights the damage caused to biological tissue by a particular type of radiation. For X-rays used in CT, the weighting factor is 1  Equivalent dose = Absorbed dose Effective dose (E in mSv): Defines the weighted average of Organ Dose values for the irradiated organs. Describes the stochastic radiation risk. Select step 3 to continue. Memorize the radiation dose parameters and definitions Memorize the radiation dose parameters and definitions 1 1 2 2 3 3 1 Select step 2 to continue. Exposure to background radiation Table with 1 columns and 2 rows Natural radiation (cosmic and terrestrial) Between 1 mSv and 6 mSv per year depending on location (average 2.4 mSv per year) Table with 1 columns and 2 rows Artificial radiation by medical imaging procedures and human nuclear activities Average radiation dose received is about 4 mSv per year for German and 6.2 mSv per year for US citizens 1 1 2 2 2 Select the X button to return to the overview page. Increment: Distance (in mm) between the reconstructed images in z-direction, freely adaptable from 0.1 mm upwards for spiral or 3D sequential scanning. If the increment is smaller than the slice width, the images are created with overlap. They provide better detail of the anatomy as well as high quality 2D and 3D post-processing. CT number (Hounsfield Unit, HU): Used to represent the mean X-ray attenuation value of the corresponding voxel within the slice. CT number scale: Water has a value of 0 HU; denser substances are given positive values and less dense materials negative numbers (for example, around -1,000 HU for air). CT window: Limits the image display - the range of CT numbers (HUs) displayed in grayscale - to tissue of interest. This results in a better differentiation of tissue with similar densities. Describe the image reconstruction parameters 1 1 2 2 1 Select step 2 to continue. Field of View (FoV): Anatomical area displayed within the CT image Please note: Always reconstruct with an appropriate FoV that is adjusted to the anatomical structure of interest. (Convolution) Kernel and updated kernel concept: Reconstruction parameter affecting image sharpness and noise (indicated by kernel number). The kernel applies a specific mathematical algorithm that digitally filters the raw data during image reconstruction. Slice thickness (width): Describes the thickness of the reconstructed images. Unlike for single-slice CT imaging, for MSCT imaging the possible slice widths depend on the chosen collimation and scan mode. Describe the image reconstruction parameters Explain the functionality of a CT scanner Basic image generation process: X-ray tube generates radiation → X-rays penetrate body → tissue attenuates X-rays → detector processes attenuated X-ray beams → detector converts radiation into electrical signals → computer converts these digital data into high-resolution images (square matrix of pixels, each of which represents a voxel - a 3D volume element - of the patient’s tissue) Pitch (P): Spiral scan parameter that determines the speed of the gantry movement and the speed of the acquisition SureView concept: Automatic adjustment of spiral scanning parameters pitch (P) and tube current (mA) → increasing the pitch → tube current must also be increased to obtain the same image noise or dose Table with 1 columns and 3 rows Spiral Scanning Continuous volume imaging mode with data acquisition and table movement performed simultaneously for the entire scan duration Advantages: Examination within one breath hold, shorter scan times → facilitate motion artifacts reduction and lower need for contrast medium, better differentiation of contrast-enhanced phases, e.g. arterial and venous phases, better method for 3D reconstructions when scanning restless patients Identify the system components of a CT scanner X-ray tube: At constant tube current (mA), an increased voltage (kV) leads to increased penetration capacity of the X-ray photons, increased dose, reduced image noise, and reduced low-resolution contrast (for example, in soft tissue). Detector components: Collimator suppressing scattered radiation Ultra-Fast Ceramic Detector (UFC) converting X-rays into visible light Photodiode converting visible light into electrical current A/D (analog/digital) converter converting electrical signals into digital data Multislice scanning possible due to multi-row detectors. Advantages: Shorter scan time, fewer motion artifacts. Acquisition modes: Depending on detector design, smaller detector element sizes enable thinner image reconstructions. Disclaimer Please note that the learning material is for training purposes only. For the proper use of the software or hardware, please always use the Operator Manual or Instructions for Use (hereinafter collectively “Operator Manual”) issued by Siemens Healthineers. This material is to be used as training material only and shall by no means substitute the Operator Manual. Any material used in this training will not be updated on a regular basis and does not necessarily reflect the latest version of the software and hardware available at the time of the training. The Operator Manual shall be used as your main reference, in particular for relevant safety information like warnings and cautions. Please note: Some functions shown in this material are optional and might not be part of your system. Certain products, product related claims or functionalities (hereinafter collectively “Functionality”) may not (yet) be commercially available in your country. Due to regulatory requirements, the future availability of said Functionalities in any specific country is not guaranteed. Please contact your local Siemens Healthineers sales representative for the most current information. The reproduction, transmission or distribution of this training or its contents is not permitted without express written authority. Offenders will be liable for damages. All names and data of patients, parameters and configuration dependent designations are fictional and examples only. All rights, including rights created by patent grant or registration of a utility model or design, are reserved. Unrestricted | Published by Siemens Healthineers AG | © Siemens Healthineers AG, 2024 Siemens Healthineers HQ | Siemens Healthineers AG Siemensstr. 3 91301 Forchheim Germany Phone: +49 9191 18-0 siemens-healthineers.com ? Disclaimer ? Assessment This assessment will test your retention of the presented content. A passing score of 80% or higher is required to complete the course and earn your certificate. You may repeat the assessment as many times as needed. Start Assessment … reduces the dose for the patient. … reduces the image noise. … increases the soft tissue contrast. … increases the scan time. ? Increasing the kV value … Question 1 of 5 Select the correct answer. Multiple Choice Question Incorrect This answer is incorrect. Incorrect This answer is incorrect. Correct This answer is incorrect. Spiral scans require a longer scan time. Spiral scans are not suitable for 2D or 3D reconstructions. Spiral scans require a shorter scan time. In spiral scans, only a dedicated spiral kernel can be used. ? Which statement is correct? Question 2 of 5 Select the correct answer. Multiple Choice Question This answer is incorrect. Correct This answer is incorrect. This answer is incorrect. … should be as low as possible to reduce scan time. … is another term for the CTDIvol. … determines the increment of the acquired data. … doesn‘t influence the total scan time. ? The pitch …? Question 3 of 5 Select the correct answer. Multiple Choice Question This answer is incorrect. Correct Incorrect This answer is incorrect. Incorrect This answer is incorrect. … applies a specific mathematical algorithm that digitally filters the raw data during image reconstruction. … is just important for bony scans. … is a reconstruction parameter to determine the image brightness. … subsequent number shows: The lower the number, the sharper the image impression. ? The kernel … ? Question 4 of 5 Select the correct answer. Multiple Choice Question This answer is incorrect. Correct This answer is incorrect. This answer is incorrect. It is the lead glass window to observe the patient during the scan. It is the gantry bore hole through which the patient moves during the scan. It is a range that limits the image display to the tissue of interest. It is a display method that can‘t be adjusted. ? What is the CT window? Question 5 of 5 Select the correct answer. Multiple Choice Question Incorrect This answer is incorrect. Correct This answer is incorrect. Incorrect This answer is incorrect. ? Review Review Retry Assessment results %Results.ScorePercent%% %Results.PassPercent%% Continue YOUR SCORE: PASSING SCORE: Assessment Results You did not pass the course. Take time to review the assessment then select Retry to continue. Congratulations. You passed the course. Exit To access your Certificate of Completion, select the Certificates tab from the learning activity overview page. You can also access the certificate from your PEPconnect transcript. ? You have completed the SOMATOM On.site CT Basics Online Training. Completion Navigation Help Select the icon above to open the table of contents. Click Next to continue. Next Welcome Slide The timeline displays the slide progression. Slide the orange bar backwards to rewind the timeline. Click Next to continue. Next Tmeline Select the X to close the pop-up. Click Next to continue. Next Layer Slide Some images may have a magnifier icon. Select the image to see an enlarged view. Select it again to return to the normal view. Click Next to continue. Next Zoom Slide Some images have a magnifier icon in the bottom-left corner. Select these image to see an enlarged view of the image. Select the image again to return to the normal view. Select Submit to record your response. Click the X in the upper right corner to exit the navigation help. Assessment Slide Question Bank 1 QR700012804 | Effective Date: 28 Nov 2024 1.1 Welcome 1.2 Navigation hints 1.3 System components of a CT scanner 1.4 Introduction system components 1.5 Overview of system components 1.6 X-ray tube 1.7 Detector 1.8 Advantage of multislice CT scanner 1.9 Detector design and acquisition modes 1.10 Functionality of a CT scanner 1.11 Introduction scanner functionality 1.12 Image generation process 1.13 Image elements 1.14 Spiral scanning 1.15 Advantage of spiral scanning 1.16 Pitch 1.17 Pitch and SureView concept 1.18 Image reconstruction parameters 1.19 Introduction image reconstruction parameters 1.20 Field of View (FoV) 1.21 Kernel 1.22 Kernel concept 1.23 Slice thickness (width) 1.24 Increment 1.25 CT number (Hounsfield units) 1.26 CT window 1.27 Radiation dose parameters and definitions 1.28 Introduction radiation dose 1.29 Background radiation 1.30 Radiation dose in CT 1.31 Dose overview and absorbed dose 1.32 Equivalent dose 1.33 Patient dose parameters 1.34 Volume CT Dose Index (CTDIvol) 1.35 Dose-Length Product (DLP) 1.36 Effective dose 1.37 Course review 1.38 Disclaimer 1.39 Assessment