Dear Bruce,
Thank you for the response. So, I more thing if I want to get the mean cortical thickness for whole brain I could simply take the mean between both hemisphere ? If I understood right from the FAQ.
Q. I am trying to measure the global mean cortical thickness (i.e combined across hemispheres), how would I do this?
A: One suggestion is to use the surface area of each hemisphere as the weighting factor. In which case the global mean thickness including both hemispheres would be given by:
bh.thickness = ( (lh.thickness * lh.surfarea) + (rh.thickness * rh.surfarea) ) / (lh.surfarea + rh.surfarea)
If you use the values in the ?h.aparc.stats, it already factors out the 'unknown' region, so you don't have to do it yourself.
Regards,
Nabin
On Sat, Jun 25, 2016 at 3:29 PM, Bruce Fischl fischl@nmr.mgh.harvard.edu wrote:
Hi Nabin
unless the areas are the same size, the mean of the areal means won't equal the overall mean.
cheers Bruce
On Sat, 25 Jun 2016, Nabin Koirala wrote:
Hi freesurfer team,
I extracted the cortical thickness values using aparcstats2table command and I got the cortical thickness values for 34 regions and mean cortical thickness for each hemisphere. But when I averaged the cortical thickness from those 34 regions regions it was different than the mean cortical thickness obtained by aparcstats2table. I would expect it to be the same or very close but I checked it for more than 100 subjects and they are significantly different. Am I missing something silly here ?
Thank you.
Regards, Nabin
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.