Dear Jesper, Thank you very much, should have realised! I used fslswapdim to flip the RL; I checked it in fslview and all seems ok. fslswapdim real -x y z real_fl fslswapdim imag -x y z imag_fl The correction is now working fine! The only problem I have noticed is that there are black lines in most of the slices in f_mag (mag put back together again). When I compare this to m20_DC - they look exactly the same apart from the streaky lines. Any ideas what this might be? Let me know if sending a screenshot is helpful. Also - was wondering why slice 20 disappears? It is there for mAPPA, slice 20 becomes slice 1 in uPPA, and then slice 20 completely disappears when any of the corrections are performed? Many thanks, Cheers Lucy