• sbTIV

sbTIV - segmentation-based (estimated) Total Intracranial Volume

Total intracranial volume (TIV/ICV) is an important covariate for volumetric analyses of the brain and brain regions, where it can provide a proxy of brain volume. It is commonly used to correct for head size variation (ie. 'normalize' hippocampal volume size). The gold-standard method is manual delineation of T2 scans. Freesurfer provides its eTIV measure, described on this page, but the approach suffers from basing the estimate solely on aligned of a T1 scan to an atlas, and not by direct segmentation of skull.

• A unified approach for morphometric and functional data analysis in young, old, and demented adults using automated atlas-based head size normalization: reliability and validation against manual measurement of total intracranial volume Buckner et al. (2004) NeuroImage 23:724-738.

• Accurate automatic estimation of total intracranial volume: A nuisance variable with less nuisance Malone, et al. (2015) NeuroImage 104:366-372.

The segmentation-based estimate of total intracranial volume, sbTIV, attempts to provide the measure making use of the skull segmentation output by the Samseg processing stream. The freesurfer utilities mri_sbTIV and mri_segstats both provide this measure, where a skull segmentation volume is provided as input.

Usage

mri_sbTIV --i <skullsegvol> [--o <file>]

mri_sbTIV accepts a binary volume where 1 indicates skull and 0 is empty. It determines the TIV by insert brief description of algorithm here and outputs to stdout the estimate in mm3 (and optionally to the text file named by <file>). Note that mri_sbTIV development is based on a skull segmented by Samseg, but in principle could accept any skull segmentation volume.

mri_segstats --skullseg <skullsegvol> ...

When a skull segmentation is provided to mri_segstats, the same estimation provided by the algorithm underlying mri_sbTIV is used to insert an additional measure of brain volume to its output summary file:

                5. sbTotalIntracranialVolume (sbTIV) - estimate of the intracranial volume
                based on a skull segmentation. See surfer.nmr.mgh.harvard.edu/fswiki/sbTIV

Validation

The mri_sbTIV measure was validated against these reference sources:

The SASHA and ADNI_T2 datasets support the primary validation efforts, as this data is based on expert manual segmentations. The other datasets compare against the freesurfer eTIV of nearly 2000 subjects.

Project Notes