Jeff, Posting this back to the list so that others can see your reply.

cheers, -MH

-------- Forwarded Message -------- From: Jeff Sadino jsadino.queens@gmail.com To: Michael Harms mharms@conte.wustl.edu Subject: Re: [Freesurfer] Surface Area and Cortical Volume Date: Wed, 29 Sep 2010 17:29:45 -1000

Hi Michael,

After reading your answer, I can see it as valid for each individual subject.

If I wanted to picture the average surface area for my controls, I think the approach would break down. I would have to transform all the surface areas onto a common space subject (fsaverage), and then all of the controls would have the exact same surface area, and so would the study group for that matter.

My understanding was that the surface area is a measure of how much each triangle needs to be squished or stretched in order for it to match the triangles in the common space (fsaverage), and so it is a measure of "squishiness", not surface area. I may be getting my understanding of vertex-wise analysis mixed up with something else. Your insight is appreciated!

Mahalo, Jeff Sadino

On Wed, Sep 29, 2010 at 4:35 PM, Michael Harms mharms@conte.wustl.edu wrote:

Hi Jeff, Where do you get the idea that the area measures are not a "real surface area"? Once the surface is parcellated, the area of each surface parcellation as provided in the aparc files is simply the area represented by the triangles in the mesh of the white matter surface. If you want the area of the pial surface instead, you can generate those using the appropriate flag in mris_anatomical_stats. But they are "real" areas, at least at the parcellation level. (It is questionable, as I understand it, whether VERTEX-WISE analyses across groups of the area and volume files are meaningful or informative, but that is a different beast).

Yes, for cortical quantification, you want to use the stuff in the aparc files, since it is based on the surface analysis stream.

cheers, -MH

...

Hello,

As I understand it, the surface area measure is not a real surface area measure. It is more a measure of how much the brain has to be stretched in order to get into a common space. My question is that if the cortical volume is calculated by multiplying the thickness and the surface area (right?), then is it a real volume that can be compared between subjects?

Also, is it is more accurate to use the cortical volume measures from the aparc files rather than the aseg files, since the aseg files overestimate the white matter due to the manual tracing it is based on?

Thank you, Jeff _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer

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