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Dear all, I am doing a small experiment (comparing different acquisition approaches and averaging of datasets) using the distributions of the angles theta and phi obtained from the BEDPOSTx procedure (using only on fibre). I tried using FSL 3 (using the 'old' BEDPOST) and I observed that the phi angles always range between 0 and 2*pi, and theta between 0 and pi (looking at the histograms in fslview). However, when using FSL4.01 with BEDPOSTx the histograms in the merged_th1_samples and merged_ph1_samples (for a particular volume) suddenly appear a bit strange, the values range from approximately -1e11 and 1e11 with a high peak around zero. Most of the voxels are in the order of a fews radians, what you would expect from the ranges of theta and phi, but some have very strange high values. The merged files I looked at are the ones straight from the BEDPOSTx output (no averaging has been done or other manipulations). I was wondering whether in FSL4.01 the priors on theta and phi used in the Bayesian estimation procedure are bounded to the range of 0 and 2pi resp. 0 and pi or that the angles can 'rotate' infinitely on the unit sphere (hence I should do something like angle mod 2pi). Could you explain why I get these strange histograms? (it happens in all of the 10 subjects). Thank you for your help! Best regards, Jeroen Siero BSc. Applied Physics Master student Biomedical Engineering NeuroImaging Center Grongingen, The Netherlands