[Freesurfer] B0 distortion correction using 2. FSL epidewarp script

Hi,

I am new to fsfast and I trying to create a field map using the AP and PA spin echo maps for B0 distortion correction using the FSL epidewarp script

I have two fieldmaps PA_spinecho.nii and AP_spinecho.nii

1. First I want tow know if my code below is about right epidewarp.fsl --mag $dir/$subj/bold/fieldmap/ PA_spinecho.nii --dph $dir/$subj/bold/fieldmap/ PA_spinecho.nii --epi bold.nii.gz --tediff 2.46 --esp .69 --sigma 2 --vsm shiftmap.nii.gz --epidw bold_dw.nii.gz

1. If it is right, which output goes into my bold folder (“Shiftmap.nii”, I mostly suspect or “bold_dw.nii.gz” ) to be used for later preprocessing in FS-FAST 2. I want to know how to make this efficient for multiple subjects

Reuben A.