Hi Simon, All,
> The normalisation and segmentation of images in SPM is obviously based on an
> asymmetric template for standard VBM analyses.
Yes (as the average brain is asymetrical, so is the average template :)
> However, how do I specify or
> incorporate symmetric priors for image normalisation in SPM5 for VBM reflection
> asymmetry analysis? Do I need to create one myself?
To specify them is easy (in the segmentation job, click on custom and
specify whatever you like as priors), but creating them will be more
tricky as opposed to the earlier priors, they are not smoothed anymore
(see grey.nii in spm5/tpm, which is the standard GM prior now). By
flipping them to make them symmetrical, you will introduce a smoothness
that was not there before.
You could use the asymmetrical priors to write out native-space images
and then still use a (symetrical-ized and smoothed) GM partition for
normalization, but I am not sure this is the optimal way.
Best,
Marko
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Marko Wilke (Dr.med./M.D.)
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Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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