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Actually I was thinking about excluding individual images, not an entire volume/s. I reckon that I have certain images in some volumes that are corrupted, i.e. which does not reflect the DW-coding properly but are just e.g. blank. Would it be possible and advisable to exclude individual images in FSL? Excluding entire volumes seems a bit drastic when just certain images are bad, and as it was pointed out, I would want to keep an isotropic spanning of the directions. / Finn On 4 maj 2007, at 10.54, Saad Jbabdi wrote: > Hi, > Obviously you can discard a volume if you make sure the > corresponding values in the bvecs and bvals files are removed. > > It is however desirable to have an isotropic spanning of the > different gradient orientations to avoid introducing unwanted bias. > I don't have any practical experience on how this will affect the > model fit in fdt, but my feel is that if you have enough diffusion > weighted volumes, removing one or two will not have a huge effect. > You can also test this on some data where all the volumes are not- > corrupted, and compare the results after discarding some of them. > > Saad. > > > On 3 May 2007, at 21:41, Finn Lennartsson wrote: > >> Hi all, >> >> I have a DTI-dataset in which some images are corrupted, e.g. >> signal losses from pseudo-diffusion or blanked out images for some >> reason. Can I exclude these in my analysis in FSL? How is this >> done in practise? I have not found any comments on this anywhere, >> but I guess there are. >> >> Thanks, >> >> Finn Lennartsson >> >> _______________________________ >> Finn Lennartsson, M.Sc. >> MR-Physics group, Dept of Medical Physics >> Karolinska University Hospital, Sweden >> Postal address: MR-Centrum, N8:00 >> 17176 Stockholm,Sweden >> E-mail: [log in to unmask] >> Tel. + 46 8 51776120 >> Cel. + 46 704 838907 >> >> >> > > ---------------------------------------------------------------------- > ----- > Saad Jbabdi, > Postdoctoral Research Assistant, > Oxford University FMRIB Centre > > FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK > +44 (0) 1865 222545 (fax 222717) > [log in to unmask] http://www.fmrib.ox.ac.uk/~saad > ---------------------------------------------------------------------- > ----- > > > >