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Hi Graham, interesting. Does sound like it might be a bug. Could you send an example image (tarred and compressed)? Either stick it on a web/ftp site at your end or email it directly to me. Thanks, Steve. On Fri, 23 Apr 2004, Graham Wideman wrote: > Folks: > > On inspection of bias output files, we sometimes see spurious values > cropping up. For example, in a typical bias file, we see a range of numbers > from say 1.75 to 2.25 or so. Then there will be just a few values at 2.5 or > 3.2 or so. > > Per slice, there may be none of these odd values, or maybe 2 or 3 such > pixels, generally located at the border between brain and non-brain (ie: > bordering on the non-brain region that has zeros in the input volume, but > still actually in the non-zero region.). > > Just on the basis of smoothness, it seems to me these values should not be > occurring... any clues as to what's going on? > > When inspecting the actual output seg volume, we see that the input values > have indeed been multiplied by these out-of-whack multipliers. > > We have several MRIs that exhibit this phenomenon. > > Using FSL 3.3 on linux. > > Thanks, > > Graham > Stephen M. Smith DPhil Associate Director, FMRIB and Analysis Research Coordinator Oxford University Centre for Functional MRI of the Brain John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve