I am trying to correct distortion based on fieldmaps generated by a pair of SE EPI images with same echo spacing and dimensions, as my GRE-EPI fMRI data, which is probably widely done (I was told that due to the signal dropouts in GRE-EPI, correction based on it is not very effective). But I cannot quite figure out how to do it on fmriprep. Maybe it is all in the documentations, which I have thoroughly, but I cant quite get it. Or is it ok to just aquire a GRE-EPI with the opposite polarity and use it for correction? Can someone give me a hand?
Thanks in advance.