Hi, there,

From FS Wiki, eTIV - estimated Total Intracranial Volume, aka ICV,

I read

mri_label_volume requires specifying the transform file to use, and the scale factor:

mri_label_volume -eTIV \
 $sdir/transforms/talairach.xfm 1948 \
 $sdir/aseg.mgz 17 53

where $sdir is the path to the subject's mri directory (ie, $SUBJECTS_DIR/<subjid>/mri). The '17' and '53' are label ID's, in this case left and right hippocampus (see the subjects /stats/aseg.stats file for IDs). The output will look like:

using eTIV from atlas transform of 1528 cm^3
processing label 17...
3822 voxels (3822.0 mm^3) in label 17, %0.250119 of eTIV volume (1528075)
processing label 53...
4410 voxels (4410.0 mm^3) in label 53, %0.288598 of eTIV volume (1528075)

From a previous post at FS mailing list, I also read something similar,

Just as an aside, once you have a talairach_with_skull.lta file (whether
from v3 or v4), you can calculate eTIV as scale_factor/determinant(lta),
where the scale_factor employed is 2150.

Just want to know where dose this scale factor number 1948 and 2150 come from?

Thanks a lot!

Guang

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