The area maps do contain the actual surface area of each vertex with units of mm^2. The problem is that the area at a given vertex depends on how many vertices a given patch of cortex was divided into, which is initially uniform but then varies arbitrarily due to topology correction, rendering it useless for making statistical maps.
If you are interested in making statistical maps of between-group differences in surface area, the best way to do that is by calculating the areal expansion measure. This is not a normally used feature of freesurfer, but is possible by using make_average_subject separately for each subject.
If you use the area values in the aparc stats files, those are the sum of area for all vertices in each parcellation, and they have units of surface area (unlike measures of areal expansion).
From: jsadino.queens@gmail.com Date: Wed, 29 Sep 2010 15:57:38 -1000 To: freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] Surface Area and Cortical Volume
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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perhaps an alternative is to use the surface area measure of an ROI, namely the aparc regions, to conduct a group analysis, as the vertex distribution problem is averaged-out over the region.
n.
On Wed, 2010-09-29 at 21:02 -0700, Don Hagler wrote:
The area maps do contain the actual surface area of each vertex with units of mm^2. The problem is that the area at a given vertex depends on how many vertices a given patch of cortex was divided into, which is initially uniform but then varies arbitrarily due to topology correction, rendering it useless for making statistical maps.
If you are interested in making statistical maps of between-group differences in surface area, the best way to do that is by calculating the areal expansion measure. This is not a normally used feature of freesurfer, but is possible by using make_average_subject separately for each subject.
If you use the area values in the aparc stats files, those are the sum of area for all vertices in each parcellation, and they have units of surface area (unlike measures of areal expansion).
From: jsadino.queens@gmail.com Date: Wed, 29 Sep 2010 15:57:38 -1000 To: freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] Surface Area and Cortical Volume
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
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
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Nick Schmansky