Hi Tsalo, thanks for the quick response. It turns out that the value for Echo_Time from the PAR header file for the second image was actually zero (which I guess would make sense if it’s a phasediff and not a magnitude image). So that doesn’t help.
EDIT: I should emphasize here that I do not know for sure that the second image is a phasediff. As I mention at the end of the other topic, the image_type_mr field in the PAR file indicates a numeric value which seems to be linked to a “B0” label. If someone with knowledge of PAR/REC files could chime in, that would be one less source uncertainty.
I also noted the delta TE value (from the scanner settings) but couln’t find any info on it, and wasn’t sure how to interpret it, but your interpretation seems plausible.
Do you think a good strategy would be testing it with those values to see if fMRIprep seems to perform a distortion correction correctly? Would this be evident in a visual inspection comparing the images?
And indeed, Chris had some excellent pointers.