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.
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*From:* freesurfer-boun...@nmr.mgh.harvard.edu
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<dgr...@mgh.harvard.edu>
*Sent:* Friday, August 21, 2020 6:42:38 PM
*To:* 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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