There are a couple of things that come to mind. - Are you sure you have the same GLM in both analyses? - It might not be the thickness that is changing. Try looking at the jacobian, curvature, and/or gyrfication - Examine the individual VBM results carefully to make sure that they are not being driven by an outlier and that the segmentation looks ok. - Voets, 2008, NI did a comparison where they looked at some of these issues.

doug

Allison Stevens wrote:

Fatima, I can't really say anything on this topic but I did want to point you to some information on FreeSurfer vs. VBM: http://surfer.nmr.mgh.harvard.edu/fswiki/UserContributions/FAQ#Q.Whatarethea...

Allison

On Fri, 8 Jul 2011, Ahmed, F, Me fahmed@sun.ac.za wrote:

...

Hello,

I'm wondering if anyone could help me out with a question I had. For a study I'm working on, I'm comparing the regional brain volumes in adolescents with and without PTSD. I ran VBM analysis and Freesurfer on my subjects and I found some significant results on VBM (however, only using uncorrected p values) and on Freesurfer, I found no group differences in brain regions. Is there an explanation for that?

If anyone has any thoughts I'd really appreciate it. Thank you kindly!

Fatima

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