Hi,
could this be due to not using an absolute threshold when specifying
your model? For VBM studies, it is generally a good idea to exclude
voxels below a certain threshold, say, .1 (with the new segmentations,
likely higher). Otherwise, you may end up comparing noise with other
noise. You could also try an explicit mask. Another alternative would be
one image that did not process correctly, but Christian's tool "check
sample homogeneity" might help you there.
Hope this helps,
Marko
김지현 wrote:
> Dear Gaser and other experts
>
> I've just tried the beta version of vbm8(r335), according to the vbm8
> manual.
> Preprocessing steps worked well with no errors, and the final modulated,
> normalized GM (m0wrp1.nii) images are looked so fine without any
> misalignment.
> However, when comparing GM images between 2 groups (N=19 each, smoothing
> with 10-mm kernel), I found many significant clusters just outside
> skull(pls see the attched figure).
> I cannot figure out why this happens. I'm used at vbm2/5 toolbox and
> have never seen such an error.
> Any hints on my problem would be greatly appreciated.
>
> Thanks you in advance for your kindness.
>
> Kim
--
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Marko Wilke (Dr.med./M.D.)
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Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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