Hi Paul,

ignore the surface location in non-cortical locations (e.g. hippocampus). We also find the surfaces to be more accurate estimates of cortical gray matter than the voxel-based stuff in the aseg, so we recommend using the surfaces for all cortical measures instead of the aseg.

cheers, Bruce On Fri, 22 Sep 2006 pgreenberg@ucsd.edu wrote:

Hi,

1. I'm interested in the relationship between voxels labeled within the

aseg.mgz file and those bounded by the white matter and pial surfaces. In regions such as the hippocampus, the pial surface (red) may cut through the middle of the gray matter designated as hippocampus in the aseg volume overlay. It therefore looks like some of the hippocampus fits between the white/pial boundary and some lies outside the pial boundary. If I wanted to know hippocampal volume, would the value in the aseg stats file be correct, or would regions of the hippocampus outside the pial boundary not be included? 2) Ignoring the hippocampus and looking at the neocortex only, there again seems to be a difference between the volume of tissue found between the white/pial boundaries and that designated as either R or L hemisphere cerebral cortex in the aseg volume overlay. Specifically, in some of our data sets there is unlabeled gray matter to be found between the white/pial surfaces. If a voxel doesn't have an "aseg" label will it be counted toward the total volume in the aseg stats file? If that same voxel lies within the white/pial surfaces will it be counted as gray matter in a different stats file? Which output will provide the most accurate determination of neocortical gray matter volume?

Thanks very much, Paul _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer