Hello,
I am attempting to use the B0 unwarping option in FEAT - pre-stats to correct distortion an fMRI (EPI) study in which I am interested in both cortical and particularly brainstem results.
Unfortunately, for a couple of subjects I don't have have B0 fieldmap images. It has been suggested that an average of the other subjects' maps would be much better than not applying B0 unwarping at all (which doesn't give very good results at the individual or group level).
I would like to know if this a reasonable thing to try to do, and if so, how can I proceed?
Here is one idea:
1. For each participant optimize registration parameters between their EPIs (I have three), T1s and standard space using nonlinear registration and BBR.
2. For those participants who have field maps, transform each fmap (radians) and magnitude images to standard space using the transformation matrix from above
3. Average these across all participants
4. For the participants who do not have fieldmaps, transform the averaged maps back into their native space using their inverse transformation matrices
Best regards,
Emily
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