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MRI Artifacts
| Question | Answer |
|---|---|
| Aliasing/Wraparound | When the FOV is under sampled, resulting in misrepresentation of location of tissue |
| Parallel Imaging Artifact | occurs when FOV is too small resulting in misrepresentation of tissue primarily in the CENTER of anatomy |
| What is Parallel Imaging? | Also known as GRAPPA/SENSE utilizes RF phased array coil and channels to sample data in parallel - performed by the phase encoding gradient to decrease scan time (lower snr, increase in artifact METAL ART BAD) |
| Chemical Shift Artifact | Bright or dark outlines predominantly around fat/water interfaces (i.e kidneys, optic nerves) |
| Partial Volume Averaging Artifact | occurs when multiple tissue types are contained within a single voxel |
| dielectric Artifacts | caused by local eddy currents due to an increase in conductivity of body tissues resulting in shading /signal loss typically occurs in high mag fields or large FOV |
| Cross Talk Artifacts | occurs when slices overlap or are too close together which creates a band of signal loss |
| Moire Fringes/Zebra Artifact | causes by interference of aliased signals at different phases |
| FID/Fine Line Artifact | look like gibs art, originate from incomplete crushed FID signal after an an RF refocusing pulse. Typically occurs during Fast Spin Echoes |
| Magic Angle | occurs when a tendon or ligament is positioned approx 55 degrees to the direction of the main mag field and when short TE is utilized |
| Annefact | primarily from RF coils out the scanning FOV and typically occurs in spinal imaging. Looks like feathery bright signal |
| How to reduce Annefact | deselecting elements outside FOV |
| How to reduce FID | increase NEX and Flow compensation |
| How to reduce Flow Artifact | using gradient moment nulling (acts as motion artifact suppression by correcting for constant velocity) |
| How to reduce Cross Talk Artifact? | increase slip gap, interleaved slices, and utilizes stacks as packages |
| How to decrease dielectric artifact? | Utilize small FOV or dielectric pads |
| How to reduce partial volume artifact | decrease voxel volume, use thin slices |
| How to reduce Chem shift artifact? | increase parallel imaging |
| How to reduce parallel imaging artifact | increase FOV, decrease parallel imaging |
| How to reduce Aliasing? | increase FOV, increase sampling outside FOV |
| How to reduce METAL Artifact | 1. do not use Gradient (use FSE) 2. do NOT use parallel imaging 3. Utilizing long ETL 4. wide RBW. thin slices (reduces partial volume art) 5. Use STIR instead of fat sat 6. increase NEX |
| Gibbs Truncation Artifact | dark or bright fine lines that appear adjacent to borders (looks like motion or syrinx) caused by using small matrix |
| How to reduce Gibbs Artifact? | increase phase encoding steps (creates more data to define/sharpen boundaries which reduces artifact) |
| What is motion artifact? | smearing across the phase encoding direction |
| How to decrease motion artifact? | decrease in phase encoding steps |
| What axis is the Frequency Encoding Gradient responsible for? | LONG axis (i.e A-P for brains, R to L for abdomens) |
| What does the Phase Encoding Gradient affect? | Short axis, scan time, detail, artifacts. Decrease phase = decrease in scan time. |
Created by:
emjohnson4