I am writing this post in the hope that you can help me to correct for following artifact I encounter in the data of one of our studies. This artifact is manifesting by differential slice-wise scaling in AP direction (AP direction is phase-encoding direction). The scheme is 2 slices stretched followed by 2 slices squeezed an so on. The artifact manifests itself only in some specific diffusion sensitization directions (in about 10 from 64 directions) and AFAICS it seems that it is present in all of the subjects in the study (consisting of approx 200 subjects). Some of directions are not affected in all subjects, but there are several specific directions which are affected in all subjects.
It is standard Siemens Trio single-band 64 direction sequence, b=1100. Standard interleaved acquisition (that is why it is puzzling me since in the artifact there is interleave in slice scaling in period of 2 slices, not in one slice).
See the screenshot demonstrating the effect:
DWI vol with artifact:
subjequent DWI vol without artifact:
I hoped that the new slice-to-vol registration in
eddy could be able to correct this artifact (Jesper expressed hope that it could be the case in the personal communication) but according to my tests with the new
eddy it is not the case, the artifact is present even in the eddy-corrected data.
It is probably not the movement problem since the slices are not moved to each other, there is systematic scale between them.
Do you have any idea of the source of the artifact and how to correct for that?
I think it could be doable to correct it since the artifact is so systematic.
I was wondering whether I could do following (probably not ideal approach, but it is better than nothing):
- split affected volume into two separate vols with stretched and squeezed slices
- register two vols together by restricting to movement and scale to AP direction (it is possible to do it via
- concatenate mutually correctly scaled volumes again together
Do you have better idea?
Any comments/suggestions will be greatly appreciated.