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Dear Martin, > I'm trying to use topup for phase distortion correction of the EPI scans > from the Human Connectome Project. However, for some reason topup gives > a segmentation fault. Here is what I tried: > > 1) Combine LR and RL field map files > > fslmerge -t 100307_3T_SpinEchoFieldMap_LRRL.nii.gz \ > 100307_3T_SpinEchoFieldMap_LR.nii.gz \ > 100307_3T_SpinEchoFieldMap_RL.nii.gz topup takes (differently distorted) EPI images as input. Not field maps. > > this results in 100307_3T_SpinEchoFieldMap_LRRL.nii.gz with a total of 6 > volumes. The first three have L->R phase encoding, the last three R->L. > > 2) Run topup: > > topup --imain=100307_3T_SpinEchoFieldMap_LRRL.nii \ --datain=topup_lrrl.txt You need to use a configuration file for running topup. There should be a file b02b0.cnf with the FSL distribution. Hence, swap your field maps for regular b=0 EPI images, and add --config=b02b0.cnf to the command line. Good luck Jesper