As far a I know, thickness does not vary with head size, so we don't traditionally make a correction
On 04/10/2018 01:52 PM, Maria Gloria Rossetti wrote: > Thanks for getting back to me. > My hp is the same as for the volumetric analysis. I want to measure > thickness differences between patients and controls while controlling > for major confounders (head size included). However, since > thickness doesn't scale with eTIV as much as volume how can I control > for head size variability? What would you suggest me to do? I am not > that familiar with thickness analysis and I would not add unnecessary > noise. > > Best, > Gloria > > (n.b. in my sample, eTIV is significantly different between > groups) Best, > > > ------------------------------------------------------------------------ > *Da: *"Douglas Greve" <[email protected]> > *A: *"freesurfer" <[email protected]> > *Inviato: *Martedì, 10 aprile 2018 16:24:42 > *Oggetto: *Re: [Freesurfer] how to control for head size differences > when measuring global atrophy? > > I would probably correct total GM, total WM, and total ventricular CSF > by head size. It is not surprising that they covary a lot (as you > point out). But what you want is what is left over after you remove > the effect. You can also divide by the eTIV rather than regressing it > out, but the results will be similar. > > As for thickness, many people regress out the mean thickness, but this > changes the hypothesis that you are testing (and so the interpretation > of the results). As such, this is a question that you will have to > answer yourself. > > > On 4/9/18 10:11 AM, Maria Gloria Rossetti wrote: > > Dear freesurfers > > my study aims to measure volumetric differences between patients X > and controls. As dependent variables, I have (i) a-priori ROIs and > (ii) global brain measures (total gm, total wm and CFS). In the > ROIs analysis, I use eTVI to control for for head size > variability. Now my question is: should I control for head size > when measuring overall brain atrophy? Theoretically speaking I'm > not sure. Practically speaking there is a high positive > correlation (as expected) between global brain measures and > eTVI in my sample so I think it wouldn't be correct to use eTVI. > But still, is global atrophy affected by head size? should I > control for it? > > Second quick question: I'm planning to replicate the analysis > measuring thickness differences. Should I control for tot mean > thickness then? > > Thanks in advance for your help. > > Gloria > > > _______________________________________________ > Freesurfer mailing list > [email protected] > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > > _______________________________________________ > Freesurfer mailing list > [email protected] > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > 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. > > > _______________________________________________ > Freesurfer mailing list > [email protected] > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer _______________________________________________ Freesurfer mailing list [email protected] https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
