Hi Gabriella, sorry for the delay On 05/22/2015 09:15 AM, Hirsch, Gabriella wrote: > > 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? > It may or may not be a problem depending on what you are doing. I prefer to divide the glm input value by the ICV, but some like to use as a regressor. If you want to do it that way, then you'll have to demean, or you might try to just scale all ICVs to bring them into a range similar to that of the input value. > > 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? > Saying that it crashes is not too informative. Can you give more info? Eg, an error message? > > 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. > You can scale the input or scale the ICV as I mention above. You can also run it as a DOSS (different offset, same slope) doug > > I’d really appreciate any help on this. > > Thank you! > > Gabriella > > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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