No, the subcortical calculation sums the number of voxels. For voxels on the edge of a structure, there is a partial volume calculation based on the intensity of the voxel and the mean intensities of the adjacent structures. doug

On 01/16/2013 05:52 PM, KimMJ wrote:

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Dear Dr. Greve

Thanks so much for your quick and clear response. One additional question here. Is this volume calculation method you have mentioned also applied to volume measurement of subcortical GM structure (in addition to cortical GM volume)?

Thank you again Kim

Date: Tue, 15 Jan 2013 23:16:04 -0500 From: greve@nmr.mgh.harvard.edu To: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] A question regarding volume calculation

Hi Kim, yes it is surface area times thickness. A volume at each vertex is computed as the average area of the triangles around the vertex times the thickness at that vertex. The volume of a parcellation is then the sum of the volumes of the vertices in that parcellation. doug

On 1/15/13 9:03 PM, KimMJ wrote:

Dear experts


I'm currently preparing a paper using the results of automatic
volumetric segmentation of subcortical and cortical grey matter
structures from aseg.stats and aparc.stats files.
I have cited previous article by Desikan RS, et al (Neuroimage
2006;31:968-980) for the cortical GM volumetric segmentation, and
Fischl B, et al (Neuron 2002;33:341-355) for the subcortical GM
volumetric segmentation.
At this point, my question is how volumes of these structures
calculated. Is this volume of each GM structure based on surface
area multiplied by cortical thickness?

Apology for the newbie's question.
Thank you in advance for your help.

Kim MJ




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