Dear Hernando,
> In a two-group multi-subject PET study, I would like to be able to examine
> the statistical map (of p-values) at a region with specified x,y,z
> coordinates of every subject. Does SPM create such an image for every
> subject?
SPM99 computes a t-map (on which p-values are estimated), when you enter
a contrast. In your case, you should tell SPM explicitly that you want
to compute subject-specific contrasts. The t-maps are written as
analyze-images. Corrected p-values (e.g. for peak height) are only
computed when you enter the results section. All values needed to
estimate p-values are stored in your matlab workspace.
> If so, can I convert/save that image into a matlab object? Will
> it be saved as an array whose coordinates are the same as the Tailarach's?
The possibly most simple way would be to manually click at each x,y,z,
coordinates and get the p-value interactively for each subject. If you
have too many coordinates to do that, it's possible to use the variables
in workspace and the function spm_P to compute for one subject (after
loading the correct contrast by clicking results) peak height p-values
for all coordinates. Look at struct SPM in workspace, in particular
SPM.Z, SPM.XYZmm. When you call spm_P, you need the df (in struct SPM)
and the resel count (in struct VOL).
Good luck, Stefan
--
Stefan Kiebel
Functional Imaging Laboratory
Wellcome Dept. of Cognitive Neurology
12 Queen Square
WC1N 3BG London, UK
Tel.: +44-(0)20-7833-7478
FAX : -7813-1420
email: [log in to unmask]
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