External Email - Use Caution Now I see. Thank you very much and have a good night!
Best, Qi On Mon, Aug 31, 2020 at 11:12 PM Yendiki, Anastasia < ayend...@mgh.harvard.edu> wrote: > Let me put it this way. It's possible that your amygdala is bigger than > mine without your brain overall being bigger than mine. But if your corpus > callosum has higher average FA than mine, then your brain overall will have > higher average FA than mine (assuming we don't have a reverse difference > somewhere else). Higher average whole-brain FA doesn’t mean that the FA is > higher *everywhere* in the brain, so it's not a global effect in the way > that a bigger brain would be a global effect. I hope this makes sense! > ------------------------------ > *From:* Zeng, Qi <qi.z...@icahn.mssm.edu> > *Sent:* Monday, August 31, 2020 10:57 PM > *To:* Yendiki, Anastasia <ayend...@mgh.harvard.edu> > *Cc:* Freesurfer support list <freesurfer@nmr.mgh.harvard.edu> > *Subject:* Re: [Freesurfer] group level analysis > > > 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 > > -- Ph.D. candidate Icahn School of Medicine at Mount Sinai
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