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Cherif - the best thing to do is to go and look carefully at the original pathways (fdt_paths). This will give you a good feel for why your numbers are discrepant. It may be casued by several different reasons (e.g. the pathway just misses the mask in some subjects; the pathway is much weaker in some subjects etc. etc. ) Cheers T On 28 Jul 2008, at 07:12, Cherif Sahyoun wrote: > Hi, > > Here's what I'm trying to do: > I resampled fMRI-based ROIs from a group omnibus contrast onto dti > scans to > investigate the tracts underlying my functional networks. The DTI > scans are > 60 directions, b=700. > I ran BEDPOSTX and PROBTRACKX without errors, but it seems that > between > equivalent pairs of ROIs (a seed and a target, registered onto all > individual DTI space), my waytotal varies between 18.00 and 30,000 > depending > on subjects. What could cause such a discrepancy, given that the > seed and > target ROIs seem to have registered fine and are approximately the > same size > in all subjects? > The probtrack command I used for each subject looks like: > probtrackx --mode=seedmask -x $subject/dti/DTI_ROIs/ > lh.TPJ.label.nii -l -c > 0.2 -S 2000 --steplength=0.5 -P 5000 > --stop=$subject/dti/DTI_ROIs/lh_supPrecentralS.label.nii --forcedir > --opd -s > $subject/dti/dti.bedpostX/merged -m > $subject/dti/dti.bedpostX/nodif_brain_mask > --dir=$subject/dti/dti.bedpostX/probtrackx_lhTPJ2lhsupPrecentral > --waypoints=$subject/dti/DTI_ROIs/lh_supPrecentralS.label.nii > > Any help in troubleshooting or ideas welcome! > Thanks, > Cherif >