EPI, susceptibility related artifacts and BOLD contrast

Question 1

What are some possible susceptibility artifacts in EPI?

Answer 1

BOLD signal, signal loss, image distortion(all related to T2* effects due to unanticipated susceptibility gradients) (alien head/hair band person)

Question 2

What regions are most susceptible to susceptibility artifacts in EPI?

Answer 2

Tissue/air interfaces (sinuses and such) Usually you get some signal loss surrounded by image distortion.

Question 3

What are some problem areas for susceptibility artifacts at 1.5T in EPI?

Answer 3

Sinuses, ventral frontal lobe, ears, air/tissue boundaries.

Question 4

What Susceptibility artifacts do you see at 4T as compared to 1.5T in EPI?

Answer 4

Much lower SNR in ventral slices near air/tissue boundaries, more ghost artifact(extra signal outside brain area)

Question 5

What advantage would you have artifact-wise with a 4T

Answer 5

Much higher SNR in superior (dorsal) slices

Question 6

What is the advantage of using a 3T scanner in EPI imaging?

Answer 6

good coverage in most areas

Question 7

What sort of artifacts do you see in a 3T EPI scan?

Answer 7

Some ghosting (not as bad as 4T) higher SNR close to the surface and distortion and signal loss in frontal cortex.

Question 8

How do you deal with susceptibility artifacts if that is what you are measuring in BOLD contrast? and reducing artifacts by adjusting sequence parameters (TE, spatial resolution) will usually decrease BOLD contrast?

Answer 8

If you are imaging a tough-to-scan spot (OFC, lateral/anterior temporal lobes), do a good shim, use subjects with minimal dental work, experiment with different slice orientations and also try for getting more images (shorter TR)

Question 9

T/F: Slice orientation can have a dramatic effect on susceptibility artifacts?

Answer 9

True