Hi Cherry, the total gray matter volume in aseg.stats is a combination of the two approaches. For cortical structures, it computes the volume using surface-based methods. The subcortical structures it uses the volume-based method. To compute total GM, you need both.
doug

On 9/16/13 9:11 PM, Yizhou Ma wrote:

Dear Freesurfer experts,

I'm doing ROI analysis on surface area and gray matter volume using the aparc.2009 parcellation. Now that I wanted to use corresponding whole brain measures as covariates, I could not find whole brain gray matter volume measures in the aparc.a2009s.stats file. However, I find one in the aseg.stats file. Since I believe these two file use different approaches to estimate gray matter volume, I'm stuck with what I choose for the whole brain measure. Do I use the value in aseg.stats or do I add up the volumes of regions in aparc.a2009s.stats? And advice is appreciated.

Thanks,

Cherry 

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