Hi Jeff,

usually the aseg overestimates the gray matter, I think because the manual segmentations it is based on also overestimate (they label voxels that are mostly CSF as gray), so I don't find the direction of the effect surprising. Both methods use partial volume correction to account for voxels that aren't completely one or the other.

cheers Bruce

On Fri, 12 Feb 2010, Jeff Sadino wrote:

Hello, I want to measure the volume of my groups' cortex, n=139, mostly males. I am using fs 3.0.5.

...

From the aseg.stats file, lh + rh white matter is 548,000 and gray matter is

487,000, for a ratio of 1.1. I know the aseg.stats file is not a good place to go for gray matter volume, as it is usually underestimated.

Looking in the aparc.a2005.stats file, the average white matter is 606,000 and gray matter is 463,000, for a ratio of 1.3.

I was surprised the gray matter actually went down, and the ratio of 1.3 seems a bit high. Is this normal? I see in the aseg.stats file, skin left over after the watershed is counted as cortex and so is a fair amount around the cerebellum. Could partial volumeing also be a possible explanation? I would think that the aparc file would be most accurate, but with these results, I wanted to doublecheck.

Thanks Bruce for answering my earlier question. I am still looking at the pallidum differences and will let you know soon.

Thanks! Jeff Sadino