Re: [Freesurfer] how to control for head size differences when measuring global atrophy?
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" <dgr...@mgh.harvard.edu> > *A: *"freesurfer" <freesurfer@nmr.mgh.harvard.edu> > *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 > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > > ___ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > 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 > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer ___ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
Re: [Freesurfer] how to control for head size differences when measuring global atrophy?
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" <dgr...@mgh.harvard.edu> A: "freesurfer" <freesurfer@nmr.mgh.harvard.edu> 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 Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer ___ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu 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 Freesurfer@nmr.mgh.harvard.edu 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.
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 Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer ___ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu 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.
