Hi Ron,

we compute the closest vertex on the pial from each vertex on the white, and visa-versa, then set the thickness to the average of the two. We've played around with other measure, but they don't seem to make much difference.

As for the last question, sure, you can overlay the thickness on any of the surface configurations, and draw ROIs on any of them. You can then compute the average in the ROI by using mris_anatomical_stats -l <label file>

cheers, Bruce

On Fri, 7 Jul 2006, R. Chen wrote:

               Hi,

I want to know the what the thickness map represents. As Bruce said in 'measuring the thickness of human cerebral cortex from magnetic resonance images', page 1, paragraph 6, 'The distance between these two surfaces then gives the thickness of the cortical gray matter at any point.'

What physical variable are measured in thickness map? Is it the distance between a vertex in gray/white surface and the corresponding vertex in pial surface.

Whether each vertex in gray/white surface has a match point in pial surface, and vice verse? If true, this means there is a 1-1 mapping between those two surfaces.

If thickness map represents gray matter. How can we get the average thickness of a ROI. Can we draw a ROI in pial surface, then overlay the thickness map to pial surface, and compute the average.

Thanks, Ron

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