All,
Upon looking at online forums and the FreeSurfer wiki, I have come to the understanding that "BrainSeg" volume in the aseg.stats file includes all cortical and subcortical gray matter, cerebellar gray matter; cortical, subcortical and cerebellar white matter and white matter hypointensities; and all ventricle volumes, but excludes the brain stem.
When using the aseg.stats file for included subject "bert" to check my understanding of which volumes are used, I cannot seem to produce identical "BrainSegVol-to-TIV" ratios.
I am adding the following volumes, all in mm^3, to obtain the brain volume:
TotalGrayVol: 658087.056198
CorticalWhiteMatterVol: 485627.161537
Left-Lateral-Ventricle: 6562.6
Left-Inf-Lat-Vent: 228.3
Left-Cerebellum-White-Matter: 15708.2
3rd-Ventricle: 997.5
4th Ventricle: 1714.2
Right-Lateral-Ventricle: 6039.9
Right-Inf-Lat-Vent: 160.3
Right-Cerebellum-White-Matter: 15694.5
5th-Ventricle: 14.1
WM-hypointensities: 1002.6
Sum of individual measures: 1191836.418
Output of BrainSegVol: 1193318
And when normalizing the subject's brain volume by the eTIV measure (1594882.911364), I obtain the following:
Individual measures: 0.7473
BrainSegVol-to-eTIV: 0.7482
Is there a reason that these two measurements are slightly off? I'm wondering whether there's certain volumes used for BrainSegVol that I missed, or ones that I included that would not be present in the output. Moreover, I'm wondering whether this could potentially be a result of using surface volumes (BrainSegVol) versus using both surface and voxel-space calculations (my addition method).
Any help is appreciated. Thank you in advance.
Best,
[1455168447449_PastedImage] Bernard L. Cook Biomedical Engineering | Class of 2017 BMES at Ohio State | Professional Development Chair '16-'17 IBRC | Undergraduate Research Assistant
440-623-4710 cook.1327@osu.edumailto:cook.1327@osu.edu
