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Ruth, Assuming that you are giving DTIFit and BEDPOST the same data and bvecs you will get the same result for both programs. You can verify the gradient directions in the BEDPOST by loading the dyadic vectors (or similarly named file) the same way as V1 and mean_fsamples the same as FA. Peace, Matt. -----Original Message----- From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of Ruth Carper Sent: Wednesday, August 01, 2007 7:55 PM To: [log in to unmask] Subject: [FSL] mismatch between DTIFit and BEDPOST results Matt, weeell, It's clear I've got some sort of issue with getting my directions right. I've got the right vectors, but I wasn't sure about the signs. So I tried about every permutation of negating x,y, and/or z in my bvecs file and running it through DTIFit. Looking at the primary eigenvectors resulting from each permutation made it pretty obvious which was the right one.... there was only one result that gave V1 line segments (in FSL_View) that matched the corpus callosum anatomy in all directions. However, when I ran those exact same data and bvecs through BEDPOST, it was as if it was using a bvecs file where x had been negated (x*-1). Even if I do have an error in my bvecs file, shouldn't I get the same erroneous result from both programs? I'll rerun BEDPOST tonite to be sure it replicates, but I already double checked all my command lines. Thanks, Ruth