I was under the impression that we actually use epi_AP( A>P which is “j-“ ) (field maps) to perform distortion correction of BOLD_AP ( A>P , also "j-“). However, fmripep-pipeline ( https://fmriprep.readthedocs.io/en/0.4.4/sdc/unwarping.html) need opposing direction for this purpose.
If so, in epi.JSON file of fieldmap_AP, at "IntendedFor” I should point the BOLD_image_PA (P>A, bold data collected with opposing phaseEncodingDirection)? please correct me if i am wrong.
Could you please help me understanding this ?