The two methods are totally different. See https://surfer.nmr.mgh.harvard.edu/fswiki/sbTIV
the sb version actually performs a skull segmentation and counts voxels within skull. The eTIV is computed from the talairach registration, which is going to be inherently more variable (eg, more or less neck will affect it).

On 7/20/2021 3:24 PM, AJ wrote:

External Email - Use Caution

Hi,
I am looking at interscanner differences between Philip and GE. I get significantly less variation between the scanners when looking at sbTIV (coefficient of variation < 1.5 %) than eTIV (12%) within subjects. Any thought as to why? Normalizing ROIs with sbTIV improves these differences even more.

Thanks for your help.

AJ
_______________________________________________
Freesurfer mailing list
Freesurfer@nmr.mgh.harvard.edu
https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer