Artifacts| Brief Overview

SIEMENS Healthineers Artifacts Brief Overview Template Effective Date: 27 MAY 2019 | HOOD05162003010284 Job Aid Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Artifacts – Brief Overview SIEMENS Healthineers Table of Contents HPL Sonata Brief Digression on Requirements for Image Quality 3 MR 2004A HE'S 07/11/2005 14:09:33 Motion Artifacts 6 6 IMA 12/1 Flow Artifacts 9 Susceptibility and Metal Implant Artifacts 14 Aliasing Artifacts 17 RP Truncation Artifacts 19 Field Inhomogeneity Artifacts MF 1.00 21 10cm TI 2500.0 TR 8800.0 TE 117 0 Hardware Artifacts TA 01:45*2 23 BWV 110.0 MIND FoV 230 230 ALAR 256-320 HE SP1 Cor>Seg(-2.3)>Tra(1.6) Electromagnetic Interference Artifacts 26 tir 2d1_21 /180 668 286 2 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Brief Digression: Requirements for Image Quality SIEMENS Healthineers Overview of Characteristics In general, the image quality (IQ) depends on the image characteristics listed below. During Quality Assurance (QA), the user evaluates if the image matches the quality requirements regarding these characteristics. Characteristics Short Description Contrast Differentiation between tissues with different compositions Resolution Image resolution is defined by the voxel size Signal-to-Noise Ratio between the signal of the area of interest and the Ratio (SNR) background noise Artifact Signal variations that can influence image appearance and interpretation 3 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Brief Digression: Requirements for Image Quality SIEMENS Healthineers Some Important Terms (1/2) • Contrast can be influenced by different examination parameters such as TR, TE, TI, flip angle, bandwidth, etc. • Repetition Time (TR) • Time of Echo (TE) • Inversion Time (TI) • Resolution can be of two types: • Spatial Resolution: Ability to differentiate neighboring tissue structures. It is defined by the voxel size • Temporal Resolution: Time gap between two consecutive measurements of the same region • Voxel: Volume element of the sample to be examined which is assigned to a pixel in the image matrix • Voxel Volume = Field of View (FOV) / Matrix x Slice Thickness 4 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Brief Digression: Requirements for Image Quality SIEMENS Healthineers Some Important Terms (2/2) • Signal-to-Noise Ratio (SNR) describes the relationship between the intensity of the signal from a region of interest and its background noise. 6/19/06 5:29:20 PM 2 IMA 2/1 • The signal depends on the field strength, voxel size and examination parameters (e.g., TR, TE, TI, flip angle, etc.). • The noise depends on the receiver coil, number of averages, phase encoding direction, etc. A • Artifacts are changes of the signal intensity in an MR image that do not correspond to the real tissue signal. They result mainly from physiological as 10cm MF 1.00 well as system-related effects. There are several types of artifacts, e.g., motion TI 120.0 TR 2500.0 TE 73.0 TA 01:37*2 BW 130.0 SPR9.2 artifacts, which can affect the image for different reasons. MIND FoV 300*300 256*512s AMIR/SAT1 SP3 4 5 Sag #tir2d1_11 /180 642 251 5 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Motion Artifacts SIEMENS Healthineers Artifacts due to Movement • Motion artifacts can appear in all body regions as a consequence of voluntary (e.g., controllable movements of head, arms, legs, swallowing, etc.) or involuntary movements (e.g., physiological, intestinal, cardiac or respiratory movements, or movements of fluids in the body, e.g., blood or cerebrospinal fluid) during the examination. • They appear as repetitive signal variations in the Phase Encoding Direction that can affect image reading and diagnosis. These artifacts are also called ghosting artifacts. Cardiac HAL mrm MR 20028 15:22:11 STUDY 1 30/01/2004 11:48:25 13.09.2005 20 IMA 1 /1 # 3 RA 10cm MF 1.00 TT 710.0 TR 1801.8 TE 70.0 TA 21.73 TP O BV 240.0 SP A37.1 MIND SL 6.0 FoV 293*360 1027 2004567 246 CT A1/DB 166*256 Cor>Sag(43.1)>Tra(-34.0) L: 25 BO1,2;SP2,3 *tse2d1_15 /180 C 402 176 ommert 6 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Motion Artifacts SIEMENS Healthineers How to manage: Some Hints (1/2) In the event of voluntary movements of the patient, the following scanning Cardiac HAL mrm IR 20028 STUDY 1 hints are applicable for all myExam Companion operation modes: 30/01/2004 11:53:14 23 IMA 1/1 • Advise the patient not to move during the examination. • Increase the patient’s comfort if possible (positioning aids, comfort cushions, etc.). • Especially with flex/contour coils, insufficient fixation of the position RA can lead to motion artifacts. Please ensure the stabilization of the coil and the body region, using straps, sandbags, and positioning aids. 10cm • If the artifact is severe and affects the image reading (e.g. hiding MF 1,00 TT 707.5 anatomy details), it is advisable to repeat the scanning step. TR 1722.7 TE 70.0 E TA 20.90 TP O • If the patient is not moving and the image is still affected by motion BW 240.0 SP A37.1 MIND SL 6.0 CT FoV 293*360 A1/DB 166*256 artifacts, additional investigations may be necessary regarding coil BO1,2;SP2,3 Cor>Sag(43.1)>Tra(-34.0) *tse2d1 15/180 W 402 C 176 positioning or the setup of protocols. Call an expert of your institution for support (e.g., switch to Expert View). 7 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Motion Artifacts SIEMENS Healthineers How to manage: Some Hints (2/2) • If the patient is totally uncollaborative, minimize the Healthineers HD - 12/15/1956 M 134123 02:33 workflow length as far as possible by deleting steps which Anatomic regions were Series AAHead_Scout detected successfully F Scan time 1 . ANHend Scout 0:32 min are not necessary for diagnosis. Discuss the steps which Repeat step can be skipped with the radiologist responsible. 2 . ANHead Scout MER. cky • If the movement is caused by unintentional or physiological movements (e.g., respiration, heartbeats) or 3 - AAHead Scout_MPR cor when the patient is nervous and uncollaborative: • If your workflow has a fast or motion-insensitive mode, Rotate CW Zoom / Pan 658 4 . Al lead_Scout_MPR_tra select this mode to increase the image quality (in Brain Autopilot | Standard | 20:53 Remaining time Autopilot only before starting the scan, in Assist use re- NM O 2:34 4:20 1:56 2:35 4:58 O 6:56 t1_se_sag Stop Stimu N AAHead Scout Check Image 12_tse_darte flund_tra_p2 ep2d_diff_ 4zcan trace .. u_ue_tua 12_hermo Check Image Inject contras run with…) 5:59:59 PM • Using faster or less motion-sensitive sequences can help to at least reduce the artifacts in the image (in Expert View). 8 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Flow Artifacts SIEMENS Healthineers Artifacts due to Flow Flow and pulsation artifacts are specific motion artifacts that derive from periodic repetitive motions. Flow and pulsation artifacts are induced by involuntary movements of fluids in the body and can be found in relation to blood vessels or cerebrospinal fluid (CSF). These artifacts appear in the Phase Encoding direction, and can appear in any body region (e.g. brain, spine, knee, etc.). Head flow AF Symphony 5871 MR 2002B STUDY 1 HFS 05/11/2002 +LPH 10:28:06 4 IMA 1 / 19 In the example images, the flow artifact in the brain examination is caused by vessel flow and fluid movements (a) in L>>R direction RFP RHA (b) in A>>P direction MF 1.00 10cm TR 500.0 TE 7.7 TA 03:11 TP O BW 140.0 SP F33.8 MIND SL 5.0 FoV 230*230 A2 384*512s | HE Tra>Cor(7.0)>Sag(3.0) (a) (b) se2d1 /90 746 372 9 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Flow Artifacts SIEMENS Healthineers Example: Spine The same effects as for the head can be seen in spine examinations due to CSF fluid movement. MR 20 MR 20028 STUDY 274698 19-Aug-04 STUDY 274697 10:04:14 19-Aug-04 2 IMA 3/15 09:31:33 2 IMA 3/15 MF 1.00 MF 1.00 TR 3880.0 TR 3880.0 TE 95.0 E TE 95.0 m TA 02:23 BW 140.0 SP R10.1 TA 04:47 SL 3.0 BW 140.0 SP R10.1 SL 3.0 MIND FOY 300*300 MIND FoV 300*300 A1 314*448s 314*448s SP2,3,4,5 Sag>Tra(-1.0) 42 W 769 SP1,3,4,5 Sag>Tra(-1.0) *tseR2d1nr17/170 tseR2dirr17/170 777 323 328 CSF pulsation - recorded from BWS coil elements 10 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Flow Artifacts SIEMENS Healthineers Example: Knee In joints such as knee, PD and T2 TSE, images can be affected in any orientation due to blood flow. Here is an example of a typical artifact in the sagittal direction. With artifacts Without artifacts (changed PE direction) 11 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Flow Artifacts SIEMENS Healthineers How to manage: Some Hints • This artifact cannot be resolved via the myExam Autopilot view. • Call an expert from your institution for support as you need to switch to the Expert View. Some hints for a solution in the Expert View (myExam Assist or Cockpit): • The most frequent solution is to change the Phase Encoding Direction parallel to the flow direction, in order to minimize the flow effect. Orientation Sagittal Phase Encoding Dir. A>> P Phase Oversampling A>> P P>> A % H>> F F>> H • In some cases, the flow compensation parameter can be activated in the sequences, or flow saturation bands can be used to suppress the signal from the vessel blood. • If applicable, the use of ECG or pulse triggered sequences can minimize the effect. 12 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Susceptibility and Metal Implants Artifacts SIEMENS Healthineers Artifacts due to Magnet Sensitivity Susceptibility artifacts are due to magnetic sensibility relating to something in the body. These artifacts appear as localized image distortions or signal changes due to local magnetic field inhomogeneities caused by different sources. The two most common susceptibility artifacts are: • Generic susceptibility artifact: Caused by air-tissue or air-bone interfaces inside the body. This artifact is quite common in DWI diffusion images. • Metal artifacts: Caused by metal implants and Generic susceptibility artifact prosthesis, as well as dental fixtures. Metal implant artifact In general, artifacts from metal implants appear as an extended area with missing signal and additional susceptibility and distortion artifacts in the image. 13 Effective Date: 19 JUL 2021| HOOD05162003208932 Study ID: 1aaaa3439 Unrestricted © Siemens Healthineers, 2021 Susceptibility and Metal Implants Artifacts SIEMENS Healthineers Artifacts due to Magnet Sensibility Sequences with higher bandwidth as well as lower TE are less affected. FLASH FLASH high BW high BW short TE long TE 17 117 0001, Image: 000029 0001, Image: 000028 Flash Flash BW 150 HZ/Pixel BW 150 HZ/Pixel TE 4.6 ms TE 11 ms 14 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Susceptibility and Metal Implants Artifacts SIEMENS Healthineers How to manage: Some Hints • Check if it is possible to remove the implant. If the implant is mobile and can be removed (e.g., removable dental implants), it is always recommended to remove it for the examination to minimize safety risks for the patient and image artifacts. If this is not possible, warn the patient of possible discomfort during the exam. • In general, lower magnetic fields introduce smaller susceptibility artifacts with metal implants, so, if possible, it is preferrable to scan implanted patients with lower field scanners. Technical sequences have been implemented to help in reducing the metal artifacts. • It is always recommended to set up implant-dedicated workflow strategies/modes based on WARP and SEMAC protocols when examining patients with implants. 15 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Aliasing Artifacts SIEMENS Healthineers Artifact due to Overfolding Overfolding artifacts can happen when the object to be scanned is bigger than the Field of View (FoV) in the Phase Encoding Direction, but is still within the sensitive volume of the coil. Signals from outside the FoV are included as an overlap image on the area of interest, placed on the opposite side from the expected position. A 16 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Aliasing Artifacts SIEMENS Healthineers How to manage: Some Hints • Within myExam Autopilot and myExam Assist: SIEMENS Healthineers Doe, James - 12/15/1956 M 134123 02:36 t1_se_sag Check that the patient and coil are correctly positioned and Scan time 1:15 min re-scan AutoAlign. Repeat stop If you discover that the FoV derived from AutoAlign is producing these artifacts, it is necessary to reset the FoV from the Expert View. 5cm Some hints for the Expert View (myExam Assist and Cockpit): • The artifact is related to coverage, therefore increase the FoV 1271 to include the folded area or use oversampling in Phase Brain Autopilot | Standard 1 8:30 Remaining time SAR NM OOOOOOOO Stimu NM 12 hemo Stop Direction (2D images) or Slice Direction (3D images). 6:16:39 PM • Sometimes these artifacts result from the use of unnecessary coil elements outside the area of interest, which amplifies signals from outside the FoV. In head-foot direction, it is possible to get rid of these artifacts by disabling coil elements which are not needed, and which lie outside the FoV, in order to minimize the signal 17 from those areas. Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Truncation Artifacts SIEMENS Healthineers Artifact due to Abrupt Transition MR images can show periodic oscillations parallel to tissue transitions. The artifacts appear as fine parallel stripes or rings derived by alternating high and low signal intensity adjacent to high contrast interfaces. This effect, also called edge oscillation or Gibbs artifact, must not be confused with motion artifacts. This kind of artifact is quite common in skull-brain and spine areas where the interface is characterized by a sudden change of signal intensity. This artifact is dependent on the data used for image encoding with Fourier transform and is connected with matrix size. If the matrix size is too small, the frequency information contained is not enough to correctly describe the abrupt signal change in the image space, causing this artifact. Reset Rotate CW Zoom / Pan 90º 18 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Truncation Artifacts SIEMENS Healthineers How to manage: Some Hints Some hints for Expert View (myExam Assist and Cockpit): Use a weak raw-data filter (Hamming filter). The strength of the filter determines the extent of loss in sharpness. Increase the size of the measurement matrix. Please note: With the help of raw data filtering we can reduce the edge oscillations. This also decreases the resolution. P88. 3PT : El\nilo S.Save.088 gnudoigude. btwsiil [ Without raw -data filter Raw-data filter (middle) Raw-data filter (strong) 19 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Inhomogeneity Artifacts SIEMENS Healthineers Artifacts due to Spatial Signal Inhomogeneity With gradient-echo techniques, areas of field inhomogeneity may lead to heavy signal losses. The local field inhomogeneity is not compensated for. Reasons for field inhomogeneity artifacts are: • The radio-frequency (RF) field of the transmitting coil is not homogeneous. As a result, the RF pulses are of different strengths and the excitation is different. • The radio-frequency (RF) field of the receiving coil is not homogeneous (different sensitivity). As a result, the signal is lower in less sensitive areas and stronger in areas with higher sensitivity. • Inhomogeneity of the B0 magnetic field, e.g., due to shimming, eddy currents, local B0 inhomogeneities If possible, position the patient in the center of the transmitter coil. If pronounced reproducible inhomogeneities are nevertheless visible, contact the Siemens Healthineers Service. Caution: Inhomogeneities of the transmitting coil and sensitivity fluctuations of the receiving coil may overlap. In this case, it can be difficult to distinguish the causes of image inhomogeneities. 20 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Inhomogeneity Artifacts SIEMENS Healthineers Receiving Coil Sensitivity Hints Only rigid volume coils have uniform sensitivity over larger volumes. Single surface coils always show an intensity transition. • Example of spine coil sensitivity: Signal drops in the posterior-anterior direction. Image as a Single images of the 4 coil combination of the elements. Image calculation of (partial) signals of all the images of the individual coil 4 coil elements elements • As a solution: The combination of additional coil elements (e.g., anterior head coil/surface coils) with suitable scaling factors results in almost homogeneous images. 21 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Hardware Artifacts SIEMENS Healthineers Artifacts due to Coil Positioning, Broken or Wrong Coil First, check that the coil is positioned correctly. Using a wrong coil combination can lead to a loss of signal and noise increase in the image. The use of coils in combination (e.g., spine posteriorly and contour coil anteriorly) is generally possible. Artifacts can occur when a spine coil is combined with a surface coil wrapped around a body region: This can lead to a weaker image quality. The wrong coil position can also lead to inhomogeneity of the signal (e.g., coil not centered on region of interest) A broken coil element can also lead to a signal loss and increase in noise. If a broken coil element is suspected (e.g., repeated signal loss and noise with all patients when using a certain coil correctly positioned), please call the Siemens Healthineers Service and follow their instructions. 22 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Electromagnetic Interference Artifacts SIEMENS Healthineers Artifacts due to Interference Signals Interference signals can be emitted by: • Defective or inadequately shielded electrical equipment, such as injectors or pulse oximeters. • Metal cables fed into the booth from the outside can introduce interfering signals from the outside. They act as (transmitting) antennas in the RF booth. • The door of the room is not closed properly. During the measurement, the RF-sealed door of the examination room should remain closed. UMR IMAC 14 190 Artifacts appear in the images as stripes/dots in the phase encoding direction. The higher the pixel bandwidth, the more sensitive the protocol is to external RF interference. Example of interference signals picked up by the receiving coil due to injector during FL3D CE Angio (a) and defective patient monitoring camera during DWI (b). (a) (b) 2003.02.10 FAR Acq: 1, Image: 21 23 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 Electromagnetic Interference Artifacts SIEMENS Healthineers How to manage: Some Hints • Check if the door is closed properly. • Check if other electrical equipment and shields are defective. • Coil is not correctly plugged in: Noise can appear in the image. Possible solution is unplug and reconnect the coil. • MR conditional objects in the room: Ensure the condition for use in the MR room is satisfied (e.g., distance from magnet, etc.). If conditions are not satisfied, artifacts like interference can occur. • Keep electrical devices that are not strictly needed for the examination outside the magnet room. 24 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021 SIEMENS Healthineers 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. © Siemens Healthcare GmbH 2021 Siemens Healthineers Headquarters Siemens Healthcare GmbH Henkestr. 127 91052 Erlangen, Germany Telephone: +49 9131 84-0 siemens-healthineers.com 25 Effective Date: 19 JUL 2021| HOOD05162003208932 Unrestricted © Siemens Healthineers, 2021