Hi,
On 8 Mar 2009, at 18:02, Stefan Kreisel wrote:
> Hi all.
> Say you are interested in (hypothesis generated a priori of
> course :)) testing
> only one major pathway using TBSS. Is it then legal to limit your
> testing via
> randomize to that one major pathway (i.e. by masking the skeleton
> appropriately) - somewhat like small volume correction in fMRI? The
> quesion
> crops up because of course your volume of interest is in fact larger
> than the
> derived skeleton (whatever this does to the test statistics - what
> volume is
> one actually correcting for? ...).
yes, this is fine because the permutation testing is still valid (and
increased in sensitivity because of this). Just use the intersection
of your ROI and mean_FA_skeleton_mask as the mask to feed into
randomise.
> If legal (but also if not), it would then be nice
> to see which individual voxel actually contributed to the masked
> skeleton,
> somewhat of a back transform of the skeleton's distance map.
You can use tbss_deproject to see where any given final results voxel
on the skeleton came from in each different subject.
Cheers.
> Regards
> Stefan
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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