Artifacts

Question 1

1. Motion

Answer 1

• Within-image: phase-encoded motion artifacts appear as stripes oriented in the phase direction, occurring due to motion during the acquisition
• Between-image motion leads to shifts in the fMRI time series

Question 2

2. Aliasing or “wrap-around”

Answer 2

• Common artifact that occurs when the field of view (FOV) is smaller than the body part being imagined

Question 3

3. Zipper Artifacts

Answer 3

• Often due to hardware problems
• Some can be controlled easily because they arise from RF noise entering the scanning room when the door is open during image acquisition

Question 4

4. Gibbs Ringing or truncation artifact

Answer 4

• Occurs at low resolution because the signal is cut off before it reaches baseline
• Size of the ringing depends on the resolution
• Typically occurs in the phase encoding direction because this direction is often acquired at lower resolution

Question 5

5. Susceptibility related distortion – susceptibility artifact

Answer 5

• Air in the ear canal and orbitofrontal sinus locally changes the magnetic field and things are no longer in the location they should be  distortion
• Signal loss due to susceptibility near the ear canal and in the orbito-frontal cortex