3
Artifacts
There will be six questions in the advanced-level examination for MRI on artifacts. These will cover
- Cause and appearance of artifacts
– Aliasing
– Gibbs truncation
– Chemical shift
– Magnetic susceptibility
– Radio frequency
– Motion and flow
– Partial volume averaging
- Compensation for artifacts
Q54 Motion is seen as a smearing in the:
| (a) | Frequency encoding direction |  |
| (b) | Phase encoding direction |  |
| (c) | Slice selection direction |  |
| (d) | Z axis direction |  |
Q55 Aliasing occurs because tissue outside the selected FOV is:
| (a) | Undersampled |  |
| (b) | Oversampled |  |
| (c) | Not sampled |  |
| (d) | Too large |  |
Q56 In order to compensate for aliasing:
| (a) | The scan can be shortened |  |
| (b) | The FOV can be enlarged |  |
| (c) | An oversampling technique can be employed |  |
| (d) | b and c |  |
Q57 Gibbs, or truncation, artifact is seen as:
| (a) | Tissue that looks very similar to aliased tissue |  |
| (b) | A bright pixel in the center of the image |  |
| (c) | Dark lines between fat and water interfaces within the image |  |
| (d) | High and low signal intensity bands |  |
Q58 To correct for Gibbs artifact:
| (a) |
