Hi, Jesper and other FSL experts   

Since one possible limitation of topup is reducing the angular resolution of diffusion MRI data, It seems that I have two possibilities to acquire diffusion data with the scan time certain:

(1) one repetition of diffusion data with 128 directions and then acquire multiple b0s with opposite phase encoding directions for estimating the warping field
(2) two repetitions of diffusion data with  with 64 diffusion directions and with opposite phase encoding directions,

Is there any major problem associated with Strategy (1)? If not, which strategy is suggested? Also, if (1) works, it seems that we can use it to correct for distortion in fMRI as well, which should work better than field map method, am I right?

Thank you in advance for your help!

Longchuan