External Email - Use Caution Hi Anastasia,
Thank you for the clarification! As you said, if I regress out the global FA, I could wipe out the regional FA. But what if my question is to find out exactly which regional FA differentiate the two groups rather than if global FA is different between groups. In that case, should I control the global FA when running regional FA between groups? Best, Qi On Mon, Aug 31, 2020 at 10:41 PM Yendiki, Anastasia < ayend...@mgh.harvard.edu> wrote: > Hi Qi - Use eTIV as a covariate for any analyses on volume, thickness, or > surface area measures. > > In a situation where a regional FA difference is high enough to also cause > a whole brain FA difference, regressing out the latter could wipe out the > former. Not sure why you'd want to do that, unless there's a specific > question you want to ask that requires it. > > Anastasia. > ------------------------------ > *From:* freesurfer-boun...@nmr.mgh.harvard.edu < > freesurfer-boun...@nmr.mgh.harvard.edu> on behalf of Zeng, Qi < > qi.z...@icahn.mssm.edu> > *Sent:* Monday, August 31, 2020 10:03 PM > *To:* Freesurfer support list <freesurfer@nmr.mgh.harvard.edu> > *Subject:* Re: [Freesurfer] group level analysis > > > External Email - Use Caution > > Hi Anastasia, > > Thank you for your reply. So for segmentation.stats, should I divide the > regional areas by eTIV or treat it as a covariate for a group comparison? > Is it the same with Total cerebral white matter volume for wmparc.stats. > For Diffusion measurement, for example, FA, if a subject has lower FA in > general in the brain, should I adjust the whole brain FA or average FA for > that matter? > > Best, > Qi > > On Mon, Aug 31, 2020 at 6:53 PM Yendiki, Anastasia < > ayend...@mgh.harvard.edu> wrote: > > Hi Qi - Correcting for overall brain size is important when you are > comparing measures of length/area/volume. As in, you want to know if a > region specifically is bigger in population A vs. B, and not just because > the whole brain is bigger. In that case, use eTIV (estimated total > intracranial volume) from the freesurfer segmentation stats. > > FA is not measuring size of a region, so correcting for brain size is less > of an issue there. It's a possibility perhaps that for someone with a > substantially smaller brain there may be more partial voluming affecting > FA, so it can't hurt to check for an effect before including it in your > analysis. > > Anastasia. > ------------------------------ > *From:* freesurfer-boun...@nmr.mgh.harvard.edu < > freesurfer-boun...@nmr.mgh.harvard.edu> on behalf of Zeng, Qi < > qi.z...@icahn.mssm.edu> > *Sent:* Monday, August 31, 2020 11:44 AM > *To:* Freesurfer support list <freesurfer@nmr.mgh.harvard.edu> > *Subject:* [Freesurfer] group level analysis > > > External Email - Use Caution > > Hi, > > When conducting group-level analysis, for example comparing volumetric > differences or tractography FA across subjects between groups. How we > correct for the size of the brain when comparing volumetric differences or > correct for the whole brain FA? > Thank you so much! > > Best, > Qi > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > > -- > > Ph.D. candidate > Icahn School of Medicine at Mount Sinai > > The information in this e-mail is intended only for the person to whom it > is > addressed. If you believe this e-mail was sent to you in error and the > e-mail > contains patient information, please contact the Partners Compliance > HelpLine at > http://www.partners.org/complianceline . If the e-mail was sent to you in > error > but does not contain patient information, please contact the sender and > properly > dispose of the e-mail. > -- Ph.D. candidate Icahn School of Medicine at Mount Sinai
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