Cristina,
(Your question concerned the correct "model", I presume you did not
mean preprocessing, segmentation, etc.) You have acquired two
images per subject, and so the appropriate estimator of the
population effect from each subject is simply the difference of the
standard space GM images derived respectively from the two acquired
images, say follow-up GM image minus baseline GM image. [As an
aside, the issue of whether you'd modulate with the Jacobian would
depend on whether you want the voxel-wise measures to be of local
GM concentration (no modulation) or local GM volume (modulation) in
standard space.] You could take this difference using imcalc or some
other suitable MATLAB routine. These difference images would then be
entered as the dependent variable in a population level model as you
describe in your step 2.
Eric
Quoting CrisTesta <[log in to unmask]>:
> Dear SPMers,
> I have structural MR images of two AD groups (treated and
> placebo) acquired at baseline, and follow up.
> I processed my longitudinal data following Chetelat's protocol
> (Neuroimage 2005) with SPM2.
> Now I am interested in a second level analysis. I'd like to
> compare GM tissue loss in the placebo group vs GM tissue loss in
> the treated group, including age and gender as nuisances.
> If I correctly understood, I have to:
> 1) determine one con*.img for each subject;
> 2) and then compare con*.img of subjects A with those subj B,
> with a simple t-test ("compare population" model)
>
> Please, could you tell me the correct model I should use for the
> first step (i.e. to determine one con*.img for each subject,
> taking into account that these are longitudinal data)?
> Thank you in advance
>
> Cristina
>
> LENITEM - Laboratory of Epidemiology Neuroimaging & Telemedicine
> IRCCS San Giovanni di Dio FBF - The National Center for Research
> and Care of Alzheimer's Disease
> via Pilastroni 4, 25125 - Brescia, Italy
> Tel: +39 030 3501 361
> www.centroAlzheimer.it
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