Rotating bvecs - tannerjared/MRI_Guide GitHub Wiki
FSL's newer tool EDDY will rotate the bvecs but after using the old FSL tool eddy_correct, you should rotate your bvecs. One option is using the script fdt_rotate_bvecs.
After downloading, make it executable: chmod +x fdt_rotate_bvecs
./fdt_rotate_bvecs dwi.bvec dwi_ec_rot.bvec dwi_ec.ecclog