[Freesurfer] Re: eTIV in SynthSeg

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Thanks. In SynthSeg, if I set a threshold at 0.5 on the segmentation output, should I get exactly the TIV? Label 0 is the background, therefore all the labels above 0 should constitute the TIV. Is this the case?

Best, Marco

From: Iglesias Gonzalez, Juan E. JIGLESIASGONZALEZ@mgh.harvard.edu Date: Tuesday, 1 July 2025 at 05:51 To: Freesurfer support list freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] Re: eTIV in SynthSeg EXTERNAL SENDER The former!

-- Juan Eugenio Iglesias http://secure-web.cisco.com/1UogwMeus6BE-_6ObueYjbFjrZdTcPcVKFrL-tZvlS-tEYy2...

From: Marco Ganzetti marco.ganzetti@biogen.com Date: Monday, June 30, 2025 at 05:57 To: freesurfer@nmr.mgh.harvard.edu freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] eTIV in SynthSeg

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I would like to know how the eTIV is estimated in SynthSeg and SynthSeg+ . Is it a combination of CSF+ventricles+WM+GM masks? Or do you estimate is using the registration to MNI space approach?

Best, Marco