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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