Currently EPI fieldmaps are stored in the fmap directory. The user specifies which scans in func or dwi the fieldmaps are supposed to correct via the IntendedFor field in the corresponding json sidecars.

Sometimes a whole DWI series is acquired with the reverse phase encoding direction of another DWI series and the low b images in each series are meant to correct the opposite PE direction series.

For this use case, would it be best to

1. Manually extract some low b images from each series into a new nifti file in fmaps with IntendedFor specified in its sidecar or
2. Add an IntendedFor field to the sidecars of the images in dwi and func?

Option 1 would go against keeping the images as raw as possible and would make automatic BIDS conversion very tricky. Option 2 might be confusing because images in dwi and func are not really "intended for" distortion correction.

I'd be very interested to hear opinions on this and happy to do a PR