> we are analysing patients with generalized atrophy. If we do a standard VBM
> with a balanced control group, the results show significant differences
> between groups almost in the whole brain, as it should be because the
> modulation of the images, even using very small p values, since the samples
> are very homogeneous.
>
> However, we would like to determine in which areas of the brain the atrophy
> more important, that is, to check the hypothesis if the atrophy on
> hypocampus and thalamus are bigger than that one on the rest of the brain.
>
> The question is if it is correct to remove the effect of the two groups
> having a different brain size by using a intensity normalization on GM
> smoothed modulated images (by Global mean scaling?) in order to determine
> if the atrophy on those two areas are more significant, since the areas to
> check are very small respecting the total brain volume.
>
> If not, are there any other alternative procedure to check the hypothesis
> of one area having bigger atrophy than the others?
The following links may help:
http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0312&L=spm&P=R14322&I=-1
http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0307&L=spm&P=R31341&I=-1
Best regards,
-John
--
Dr John Ashburner.
Functional Imaging Lab., 12 Queen Square, London WC1N 3BG, UK.
tel: +44 (0)20 78337491 or +44 (0)20 78373611 x4381
fax: +44 (0)20 78131420 http://www.fil.ion.ucl.ac.uk/~john
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