On Wed, 20 Jul 2005, Anusha Sritharan wrote:
> I have DTI data for two groups; and I wish to compare the FA differences
> in WM between groups.
>
> I am planning to do the following:
>
> 1. After normalising the bo and the DWI images, the FA map will be
> generated for both groups.
> 2. In order to compare FA maps between groups with in WM I ahave copmuted
> a product FA.* WM (WM is segmented from high res anatomical and is in same
> space as the FA maps).
>
> 3. FA.*WM will be smoothed.
>
>
> 4. The smoothed product will then be used to do two sample t-test under
> basic models in SPM2.
Dear Anusha,
your procedure is quite ok. However masking FA with a white matter mask is
not enough to ensure that you are comparing similar structures in both of
your groups. You should convince yourself and your audience that there
are no differences in volume or shape of white matter between your groups
after normalisation. Otherwise you will very likely compare different
parts of white matter in your FA analysis - which is of very little
interest. FA analysis is useful only if each voxel contains information
from the same anatomical region over all of your subjects.
Hope this helps,
--
Volkmar Glauche
-
Department of Neurology [log in to unmask]
Universitaetsklinikum Freiburg Phone 49(0)761-270-5331
Breisacher Str. 64 Fax 49(0)761-270-5416
79106 Freiburg
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