Dear John,
Thank you for your useful suggestions.
I would like to ask a related question.
>I suspect that what you really want is some kind of SPM that localises
>significant shape differences (as done by Gaser et al).
I once tried a Gaser's-like method as follows:
Creating a symmetric T1 template by averaging L-R flipped and unflipped
T1 template images.
Creating a symmetric brainmask using the same way.
Smoothing original T1 images with 8mm FWHM (24 subjects).
Normalizing the smoothed images to the symmetric template using
affine transformation only, with the symmetric brain mask.
Normalizing the affine-normalized images with 11*13*10 nonlinear
basis functions using the same template and brainmask.
Creating deformation field images (*_y1-3.img) from the *_sn3d.mat
files produced by the second normalization, using spm_write_defs.m.
Then, I created L-R flipped images of these deformation fields, and
intended to perform 3-variate T-square test or MANOVA on the flipped
and unflipped images. However, I encountered a confusing situation.
All the deformation field images have a linear-like slope in the
corresponding direction. For example, the values in the *_y1.img were
low in the left hemisphere and high in the right hemisphere. They seemed
to increase linearly (not exactly, just approximately) from left to right.
Since this tendency was observed in all subjects, any statistical test on
the hemispheric differences (flipped vs. unflipped) produced awfully
low P values over the whole brain.
Do you have any idea what caused this?
I am afraid I am missing something very important.
>The simplest
>way to do this would be to do tests of local volume differences, which
>can be derived from the Jacobian determinants of the deformation fields.
>Somewhere in the attached file is a routine that will write images of
>Jacobian determinants.
Thanks a lot. I will try that.
Kota KATANODA
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