> we are intending to explore the influence of genetical polymorphims onto
> regional brain volume, esp. a disease-gene-interaction in a large sample of
> patients and controls.
>
> Here we thought to initially use a GLM in a VBM approach with standard
> covariates to remove large influences on brain volumes and to continue with
> the residuals into the genetical analysis.
>
> There are two questions I have,
>
> (1) Is the an easy way to calculate a map of residuals for each subject
> from the output of the estimation (e. g. ANCOVA model or multiple
> regression model)?
The ResSS image is a map of the residuals, although I'm not sure how it is
scaled etc. One of the other experts should be able to tell you this.
>
> (2) Rather independently of this, I would like to understand if Jacobian
> modulation is sensitive for only the non-linear warps or also affine
> transformation? Given a generally smaller brain due to brain size, which
> should come near to an average size after normalization, would the
> potentially massive increase of whole brain volume be reflected in the
> modulated maps?
Jacobian modulation also encodes the relative volumes from the affine
component of the nonlinear transformations. Therefore, the intensities of
smaller brains will be lower in the modulated spatially normalised data.
Best regards,
-John
|