It is neither:) See http://surfer.nmr.mgh.harvard.edu/fswiki/eTIV and/or Buckner et al. (2004) NeuroImage 23:724-738.

"Basically, total intracranial volume is found to correlate with the determinant of the transform matrix used to align an image with an atlas. The work demonstrates that a one-parameter scaling factor provides a reasonable TIV estimation. This method uses an atlas based spatial normalization procedure, and requires that the talairach.xfm is correct. "

This performs the talairach registration for a subject. Then, based only on the numbers in the matrix, it estimates the ICV based on subjects that had similar matrices.

doug

On 5/7/13 9:42 PM, Alejandra Infante wrote:

Hi,
I understand that ICV is an estimated measure based on a standard talairach transformation; however, I want to know how freesurfer is defining intracranial volume (i.e., is this a representation of everything within the cranium as the name implies or is it an estimate of total brain volume, which would not include space between skull and dura)?. We are using fs vesion 5.1

--
M. Alejandra Infante
Doctoral Student
SDSU/UCSD Joint Doctoral Program in Clinical Psychology
Phone: (858) 449-2950
E-Mail: infante.alejandra.m@gmail.com
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