The FS segmentation is a combined segmentation and registration to an
atlas space. This is probabilistic in that the atlas is built from 40
subjects and uses intensity, location, and neighborhood priors. I think
VBM is using unified segementation which performs intensity
normalization, segmentation, and registration simultaneously also using
a probabilistic atlas.  VBM segments GM/WM/CSF whereas FS segments
various GM and ventricular structures as well as WM. VBM is a voxelwise
analysis which is registered to an atlas, modulated, and spatially
smoothed, all of which will have strong effects on the results. Maybe a
VBM expert on the list can chime in with more info.

doug

On 11/05/2013 08:08 PM, jh kim wrote:
> Dear Drs. Bruce and Doug
> Thanks for the valuable comments.
>
> Discrepancy between FS and VBM lies in putamen and hippocampus.
> Would you please briefly comment regarding segmentation method of
> above structures in FS?
> I'm just wondering whether segmentation of grey matter in FS is
> largely different from that of VBM?
> Sorry for bothering you again with my silly question.
>
> Thanks.
> Kim
>
>
> 2013/11/5 Douglas N Greve <greve@nmr.mgh.harvard.edu

> <mailto:greve@nmr.mgh.harvard.edu>>

>
>
>     Hi Kim, the answer is both easy and difficult. The easy answer is that
>     they are completely different methods and will often give inconsistent
>     results. I'm not sure what answer the reviewer will accept, and you
>     might need to post the same question to the VBM and DARTEL crews. In
>     your VBM analysis, I assume that you used modulation (ie, you were
>     looking at volume and not "GM density")? VBM performs a voxel by voxel
>     comparison and you probably smoothed by 10mm or so. Either of those
>     could have washed out the effect. Certainly a reasonable response is
>     that the FS analysis is for the entire ROI and and the VBM is
>     voxelwise.
>     Hope that help.s
>
>     doug
>
>
>
>     On 11/03/2013 11:55 PM, jh kim wrote:
>     > Dear Doug and experts
>     >
>     > I've analyzed structural changes of the subcortical GM by using both
>     > VBM (DARTEL in SPM8) and subcortical volumemetric measurement using
>     > FreeSurfer 5.1. While there is no significant volumetric difference
>     > between the groups in VBM (corrected p<0.05), FS results showed that
>     > some subcortical GM had significant volume reductions in patients
>     > relative to controls (MANCOVA controlling for the effect of ICV,
>     age,
>     > gender, followed by Bonferroni correction).
>     > One of the referees raised the question regarding this discrepancy
>     > between the VBM and FS findings.
>     > How can I cope with it?
>     >
>     > Thank you in advance for your help.
>     >
>     > Kim
>     >
>     >
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>     Douglas N. Greve, Ph.D.
>     MGH-NMR Center

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MGH-NMR Center
greve@nmr.mgh.harvard.edu
Phone Number: 617-724-2358
Fax: 617-726-7422

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