Hi Pame

One relatively easy thing you could try is to adjust the fov to exclude more of the neck so it is similar to your other scans using the "crop volume" tool in freeview, then rerun it.

Cheers Bruce

From: Pame González pamela.gonzalez.m@gmail.com Sent: Saturday, April 11, 2026 7:56 PM To: freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] eTIV underestimation with excessive extracranial tissue

External Email - Use Caution

Dear FreeSurfer experts,

I have a subject with good segmentation (aseg appears accurate, with no FOV truncation), but with substantial extracranial tissue, particularly neck tissue. The eTIV is relatively low (~1070 mL), and the MaskVol/eTIV ratio is high (~1.23). This subject also behaves as an outlier, showing artificially increased cortical volumes after normalization by eTIV.

What would be the recommended approach to obtain a more reliable eTIV in such a case?

[cid:image001.png@01DCCA73.C11179B0]

Many thanks, P.G.