HI FS experts, I haven't heard back and am still wrestling with these questions. Any takers?
I'd really appreciate any thoughts at all if possible. Thanks, Gabriella From: Hirsch, Gabriella Sent: Wednesday, May 20, 2015 3:55 PM To: freesurfer@nmr.mgh.harvard.edu Subject: ICV correction for volume analysis Hi FreeSurfer experts, I have a couple quick questions I'm hoping someone can clarify for me; I am conducting a group surface-based morphometry analysis in all three measures in 2 groups (patient and control) and am looking for the best way to correct for brain size variability in the cortical volume analysis. My question is: 1. So far, I've been using Qdec, however qdec seems to crash when I ask it to pose ICV as a nuisance factor. In the archives, we are told to "mean center" the ICV values in order for Qdec to take it, but I was informed that mean centering was not a good idea in morphometry studies. Any thoughts? 2. I've found that in QDEC, if I include ICV AND global mean volume as nuisance factors, the analysis works. If I only include ONE of the two variables, it crashes. This is super frustrating - is there any way around this issue? 3. If I want to keep only the raw ICV values in my analysis (i.e. not demean it), what's the best way to go about this? Do I have to re-run the analysis using mri_glmfit with the ICV values as a covariate in my fsgd file (with a contrast like 1 -1 0 0, with age and ICV as covariates)? I tried doing it this way and got some questionable results. I want to make sure I'm executing this correctly. I'd really appreciate any help on this. Thank you! Gabriella
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