Florian,
> I am analysing a FDG-PET study (patients before (T1) and after
> treatment (T2) and controls at T1 and T2) with SPM2.
OK. I'll write this
PT1 PT2 CP1 CP2
> I want to address the question which voxels showed a significant
> change with treatment
This would be a contrast of
-1 1 -1 1
> and restrict my search volume for whole brain correction to the
> voxels which showed a significant difference between patients and
> controls at T1 (P<0.01 uncorrected).
and this would be
-1 -1 1 1
or, just using baseline
-1 0 1 0
> Is it legitimate to creat a mask from my baseline contrast (controls
> patients) and use this distributed set of voxels as my search
> volume when hitting the small volume correction button?
Because the contrasts involved are orthogonal
([-1 1 -1 1] and [ -1 -1 1 1], or
([-1 1 -1 1] and [ -1 0 1 0]),
there is then no information in the masking contrast about the
contrast of interest, and hence, yes, it is valid.
-Tom
-- Thomas Nichols -------------------- Department of Biostatistics
http://www.sph.umich.edu/~nichols University of Michigan
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-------------------------------------- Ann Arbor, MI 48109-2029
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