Hi Idaumail,
My guess (based on comparison with my data and what I’ve been told at the scanner) is that:
EX_STACKS_0__prep_dir : AP
EX_STACKS_0__fat_shift_dir : A
Means anterior to posterior
EX_STACKS_0__prep_dir : AP
EX_STACKS_0__fat_shift_dir : P
Means posterior to anterior
Also this suggests my guess might be correct: JISCMail - FSL Archives
It’s just a guess in case it helps but the best would likely be to confirm with people who know for sure!
Annick