MR Essentials - Artifacts - USA (copy)

Welcome to the MR Essentials - Artifacts Online Training Course. Artifacts are structures in the image that do not correspond to the spatial distribution of tissue in the image place. It is therefore important to understand how to detect and address these artifacts in order to avoid diagnostic misinterpretations.      Upon successful completion of this, you will be able to: Give examples of different methods and techniques to minimize patient motion Explain ways to minimize or correct the artifact Recognize common artifacts and identify their causes Congratulations. You have completed the MR Essentials - Artifacts Online Training course. Listed below are the key points that have been presented. Take time to review the material before you proceed to the final quiz. The following course objectives reviewed in link below: Give examples of different methods and techniques to minimize patient motion Identify properties of common MR artifacts Recognize causes of common artifacts Explain ways to minimize or correct the artifact Select the link to download the MR Essentials - Artifacts Course Review. Potential causes of Artifacts: Limitation/malfunction in the hardware or software of the MRI scanner Environment, such as heat or humidity Specific measurement parameters Physiologic motion by the patient Internal physiological motion (i.e. blood flow)      Shift in pixels = 3.5 x resonance frequency                            bandwidth Example: 1.5 T = 63.8 MHz Receiver Bandwidth = 220 Hz/pixel Shift in Pixels 3.5 x 63.8 = 1.01 pixels      220 Signal 3.5 ppm (chemical shift) The fat molecule: The water molecule: frequency fat water 100 Hz/Pixel 450 Hz/Pixel Motion artifacts always occur in the Phase Encoding direction. They can be divided into two groups: Ghosting Smearing Examples of Patient Motion include: Respiration Heart beat Blood flow Eye movements Swallowing      Patient Motion - Ghosting Learn about motion artifact from ghosting. Ghosting is the result of quasi-periodic motion - for example, respiration. During the periodic movements such as breathing, the thorax is in several, equally-distanced phase-encoding steps during the inspiration phase.  During the steps in between, the thorax is in the expiration phase. This leads to quasi-periodic incorrect encoding. As a result, the thorax appears as locally offset copies in the MR image. Structures rich in signal, for example, subcutaneous fat, further amplify ghosting.   These motion artifacts are seen exclusively in the phase encoding direction.        Patient Motion - Smearing Learn about motion artifact from smearing. Another type of motion artifact is smearing. This results from aperiodic motion acquired using a periodic method of data collection.  Eye movement is random or continuous and adds smearing to the image. These motion artifacts are seen exclusively in the phase encoding direction. To reduce the impact of eye motion artifacts on the image, swap the phase and frequency encoding direction.   Minimizing Motion Artifacts Learn how to minimize motion artifacts. Recommendations for Addressing Motion Artifacts Switching the Phase Encoding & Readout Direction - which relocates the motion artifact to a different area   Recommendations for reducing Ghost Artifacts Choose the appropriate sequence or parameters to adapt to the patient from the following options:   Single-shot sequences BLADE Choice of phase encoding direction PACE Triggering Spatial Presaturation Pulse Flow Comp   Cross talk – interference between adjacent slices of a scan Slice profiles generated by RF pulses are not perfectly rectangular Recommendations: Slice gap is at least 10-20% Excitation order of acquiring interleaved, if applicable   Ideal Slice Profiles Crosstalk Actual Slice Profiles Abrupt signal transitions in tissue may lead to artifacts caused by truncation. Edge oscillations – stripes of rings appear in the image with alternating high and low signal intensity. Caused by a limited number of sampling points during scanning and subsequent Fourier transform Periodic oscillations parallel to tissue interfaces are generated Recommendations for Edge Oscillations: Increase Matrix Size Apply a Raw Data filter or an Elliptical filter MA: 128 x 256                                        MA: 256 x 256                       Without Raw Data Filter   Medium Raw Data Filter Strong Data Filter Patient Motion Flow Aliasing Chemical Shift Truncation Magnetic Field Distortions Field Ambiguity Magnetic Susceptibility Metal RF Interference Herringbone Crosstalk Three main causes of Distortion: Global magnetic field inhomogeneity Local magnetic field inhomogeneity Non-linear gradient fields Recommendations: Only select coils needed for imaging anatomy Location Gradient Mapping Measurement Objects Mapping Distorted Mapping distorted and aliasing Mapping OK Magnetic susceptibility – degree of magnetization of a material in response to a magnetic field Effects of magnetic susceptibility increases linearly with field strength   * Disclaimer: MR imaging of patients with metalic implants brings specific risks. Please contact your local Siemens sales representative for the most current information.   B0 ~ (1 + x) H0 H0 B0 H0 B0 Recommendations: Gradient echo sequences minimize TE and use a smaller voxel size Use spin echo or TSE in critical regions RF Interference – appears as a discrete line on the image at a specific position in frequency Caused by an extraneous RF signal entering the room at a certain frequency Extraneous signal interferes with the inherently weak signal coming from the patient Recommendations: A Faraday cage is an RF-sealed room that protects MR scans from external radio frequency Herringbone or Spike Artifact – a Moire pattern scattered over the whole image in the form of stripes in any direction Seen only on one slice or on multiple slices Occurs in Frequency Encoding or Phase Encoding direction Recommendations For spikes caused by the gradients or equipment in the room, Service Engineer will need to troubleshoot For low humidity, contact Maintenance Personnel Causes Electromagnetic spikes created by the gradients Electronic equipment inside the room Low humidity Recommendations: Increase the FoV Oversampling Sometimes swapping phase and frequency direction Saturation pulses may be applied to structures in the non-imaged portion of the FoV to reduce signal Aliasing – generated when the measurement object is outside the FoV but still within the sensitive volume of the coil Signals from outside the FoV overlap the image   Flow Artifact– ghosting of signal from moving protons in patient's blood or CSF or from a void of signal within the patient's vessels Appear in Phase Encoding Direction Dependent on the nature of the flow and its direction relative to the slice orientation Fast Flow compared to TR will produce an artifact throughout field-of-view Slow Flow compared to TR may generate an artifact like saturation Recommendations for Minimizing Flow Artifact: Swapping the phase encoding direction Triggering Adding saturation bands Flow Comp BLADE Phase cancellation artifact is induced by Chemical Shift Artifact Observed in out-of-phase gradient echo images Water and fat signals either add or subtract from one another depending on the set echo time (TE) Results in a periodic signal increase or signal decrease as a function of TE      Phase Cancellation - Clinical Example Learn about phase cancellation in clinical images. Element HTML Opposed Phase In Phase Sound File Audio ScriptIn the opposed phase image, the fat and water signals have opposite phases.  For voxels with equal amounts of fat and water, such as the interface between the liver, spleen and retroperitoneal fat, complete cancellation of signal occurs producing a dark black outline. Unless an out-of-phase image is needed for a specific reason, an in-phase TE is recommended to minimize the phase cancellation artifact. Metal Artifact - distortions arise from metal implants and appear as a signal void     Standard                                                 VAT                                          SEMAC Recommendations: Use a high bandwidth sequence Metal Reduction Sequences View Angle Tilting (VAT) Slice Encoding for Metal Artifact Correction (SEMAC) 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 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. Please contact your local Siemens sales representative for the most current information. Functionalities described in the material or parts of this functionality may not yet be released for customers and not yet be commercially available in every country. Due to regulatory requirements, the future availability of said functionalities or parts thereof in any specific country is not guaranteed. The Operator Manual shall be used as your main reference, in particular for relevant safety information like warnings and cautions. 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