Dear Stefano,
FIRST and VBM measure different things.
FIRST measures the volume of specific structures or local changes in the structure's boundary (shape).
VBM measures differences in local grey matter density without having any knowledge of the
explicit structures. Even if you apply an ROI to VBM it has smoothed the grey matter segmentations
and so you still will be using values from both inside and outside of the ROI. However, if there is
local atrophy then both techniques can be sensitive to this and you can report changes, it is just up
to you to interpret the maps given by VBM as being due to certain structures or not. It is not really
possible to "join" outcomes or put them sensibly into a single analysis, but you can certainly report
both outcomes and then it is up to you to come up with a biologically plausible and consistent
interpretation.
All the best,
Mark
On 4 Apr 2012, at 08:25, Stefano DP wrote:
> Hi Mark,
>
> thank you very much. But, how can I do to put the hypothalamus results in with the changes from FIRST? Is possible to obtain and to include the hypothalamic volumes in the statistic GLM adopted for the other FIRST GM substructures? How can I join VBM outcomes with FIRST volumes?
>
> Stefano
>
>
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