Hi John,
If you would have used the ICV as a covariate in the old VBM, then you can do the same if you're using DARTEL. DARTEL is just a different method of registration. It just depends what you are interested in or what you want to report - absolute volumes or volumes relative to ICV. You can get total GM, WM, and CSF by summing all the values of the modulated segments (get_integrals). The result should be nearly identical to what you got before, but I would re-do it with the DARTEL images to make sure you are covarying the more relevant, exact amount.
-Dana
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of John McLean
Sent: Thursday, June 10, 2010 7:06 AM
To: [log in to unmask]
Subject: [SPM] Do I need an ICV covariate for DARTEL + VBM?
Hi,
Do I need to include ICV as a covariate for DARTEL + VBM? If so, how should I get the GM/WM/CSF estimate from DARTEL? More detial below...
I previously did some VBM analysis using the 'Old' unified segmenation approach during which I used the volumes for GM/WM and CSF to obtain a ICV covariate in the subsequent VBM analysis.
I am now reprocesing the data using DARTEL. I don't observe that there is a GM/WM/CSF volume textual output during this procedure. How do I obtain such an output, can I use the 'old' ICV output, or don't I need to include ICV as a covariate for VBM where the data has been pre-processed with DARTEL?
Any advice about the best approach would be welcome!
Many thanks
John
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