[Freesurfer] question abt supratentorial vol and total brain vol.

Hello All,

I am using freesurfer 5.1 for my analysis.

I am interested in calculating the whole brain vol (total Gray vol + total WM vol) excluding the CSF volume and cerebellum.

Total Brain Vol = TotalGrayVol + CorticalWhiteMatterVol

In all of the 79 subjects, when I compare the Total Brain Vol to SupraTentorialVol, I find SupraTentorialVol is smaller than the Total Brain Vol I have calculated.

Here are some measures -

For 79 subjects -

Average Total Brain Vol = 1038395.291

Average SupraTentorialVol = 979996.4684

Is that expected ?

Is it possible that CSF vol is part of Total Brain Vol ?

Any insight will be helpful.

Thanks

Rito