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We've modified the relevant bit of the FDT manual to clarify the curvature threshold. See: http://www.fmrib.ox.ac.uk/fsl/fdt/ From the drop down menu chose probtrack, then go to the options tab section. Heidi On 11 Oct 2005, at 14:53, Joseph Devlin wrote: > I haven't had any trouble tracking arcuate fibres using the default > curvature threshold (0.2) but if you're worried about it, just set > it to something really small like 0.01. > > In my own experience, arcuate fibres tend to be on the edge of > white matter paths and thus seeds nearest to gray matter are most > likely to reveal these. I tend to anatomically mask a region and > then selectively choose "gray matter" voxels as the seeds by doing > a fast-segmentation, computing the tissue class probabilities, > thresholding the grey matter image at 0.2 and binarising it to > create a grey matter mask. If you then mask the original > anatomical image with the gray mask, you'll get the voxels with at > least 20% chance of being gray matter in your anatomical ROI. The > ones most likely to give good arcuate traces seem to be those > closest to the edge, although this is just anecdotal -- I haven't > systematically looked at this. > > Cheers, > > Joe > > ----------- > Joseph T. Devlin, Ph. D. > FMRIB Centre, University of Oxford > Headley Way, Headington > Oxford, OX3 9DU, UK > Phone: +44-(0)1865-222-494 > Fax: +44-(0)1865-222-494 > Email: [log in to unmask] > Heidi Johansen-Berg FMRIB Centre John Radcliffe Hospital Headington, Oxford OX3 9DU, UK Tel: +44 (0) 1865 222782 Fax: +44 (0) 1865 222717 [log in to unmask] http://www.fmrib.ox.ac.uk/~heidi