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Again, thank you for your explanation of how these variables are calculated.
However, the the main question still left is, are these values the most
representative of the whole cerebral surface area and the whole cerebral
thickness for both the left and right hemispheres?
________________________________
From: freesurfer-boun...@nmr.mgh.harvard.edu
<freesurfer-boun...@nmr.mgh.harvard.edu> on behalf of Douglas N. Greve
<dgr...@mgh.harvard.edu>
Sent: Monday, August 24, 2020 10:15:10 AM
To: freesurfer@nmr.mgh.harvard.edu
Subject: Re: [Freesurfer] Global surface area and global thickness values
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The average thickness is the average over all the vertices in the cortex.label
The total surface area is the sum of all the triangles that have all three
corners in the cortex.label
On 8/24/2020 9:35 AM, Palin, Tara wrote:
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I was asking if the Mean Thickness value and the Pial Surface Area values at
the top of the aparc.stats file that is generated when running freesurfer are
the global measures. And if they are, I got very close values on multiple
different apar.stats files by using the Surface Area and AvgThick ROI values
printed at the bottom of the file. Basically, how are those values stated in
the first sentence being calculated.
Thank you.
________________________________
From:
freesurfer-boun...@nmr.mgh.harvard.edu<mailto:freesurfer-boun...@nmr.mgh.harvard.edu>
<freesurfer-boun...@nmr.mgh.harvard.edu><mailto:freesurfer-boun...@nmr.mgh.harvard.edu>
on behalf of Douglas N. Greve
<dgr...@mgh.harvard.edu><mailto:dgr...@mgh.harvard.edu>
Sent: Friday, August 21, 2020 6:42:38 PM
To: freesurfer@nmr.mgh.harvard.edu<mailto:freesurfer@nmr.mgh.harvard.edu>
Subject: Re: [Freesurfer] Global surface area and global thickness values
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I'm not sure what your question is. You can't just average the ROI values to
get the global value unless you weight by the ROI size.
On 8/21/2020 2:55 PM, Palin, Tara wrote:
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Hello freesurfer experts,
I am looking to extract the global surface and global thickness measurements
and am curious if my understanding of the output on the aparc.stats (for lh and
rh) are correct. When looking at these files, at the very top you will find the
Pial Surface Total Area and a Mean Thickness value which I am assuming are the
global measures. Below you have all of the ROIs listed (this was not changed by
us or generated by us this is what comes out of freesurfer to my understanding)
that includes everything EXCEPT the corpus callosum and the unknown. However, I
summed all the surface areas and took and average of all the thickness
measurements and they are very close to the values printed at the top of the
sheet. Another observation I had made was that the total surface area
measurement has a decimal and the surface area for the ROIs appears to be
rounded and if they were not rounded the values would be the same. For the
thickness values, the value I calculated and the one on the sheet are within
the average of the standard deviation each other.
If my understanding is incorrect please let me know and provide insight into
how we may calculate these global measurements correctly.
Thank you in advance for your time,
Tara Palin
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