Dear experts,

I would like to correct susceptibility artifacts of the EPI sequence with an inverted phace enconding (PE) EPI sequence that was acquired using the same parameters than the EPI but with inverse phase-encoding directions (P-A and A-P respectively). In order to perform this correction, I want to use 3dQwarp with –plusminus flag and 3dNwarpApply but I have some doubts that I hope you can solve.

What inputs should I give to the 3dQwarp function and what flags should I specify? The EPIs must be aligned and registered to T1 in a previous step, right?
To apply the correction to the sequence with 3dNwarpApply and get the EPI images with corrected distortion, what flags should I use with this function to use the PLUS image/warp and the MINUS image/warp?

Thank you very much in advance!
Best wishes,
Marina