Hi Jorge, I'll take a stab at this since it sounds like many of the FS developers are out of town currently, but I'm just an FS user, so hopefully an FS developer can confirm whether my response is accurate.
Each vertex on the pial surface has a one-to-one correspondence with another vertex on the white surface, since the white surface is expanded outwards to yield the pial surface. I believe that the vertex correspondence is maintained as part of this process. I would therefore interpret "thickness at that location" as synonymous with "thickness for that vertex id".
Assume the distance between vertex id 1000 on the PIAL surface to the closest vertex on the white surface is 3.0 mm. Also assume that close to vertex id 1000 on the pial surface, the pial surface curves sharply toward the white surface, such that the shortest distance between vertex id 1000 om the WHITE surface to the pial surface is 2.8 mm. Then, the cortical thickness assigned to vertex id 1000 would be 0.5*(3.0 + 2.8) = 2.9 mm.
cheers, Mike H.
On Fri, 2007-09-07 at 16:33 +0200, jorge luis wrote:
Hello all
In Neuroimage Han. et all ( 2006) it is said about Freesurfer automatic thickness computation :
For each point on the gray/white surface, the shortest distance to the pial surface is first computed. Next, for each point on the pial surface, the shortest distance to the gray/white surface is found, and the cortical thickness at that location is set to the average of these two values.
What the authors mean by "that location"? It is relative to the gray/white surface or to the pial surface? I would like to get a slightly more insight about
In advance thank you
Jorge
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