Thanks for the reply. Maybe I'm not thinking deeply enough about this, but since there is a 1-to-1 mapping from white to pial vertices, is there a possibility of self-intersection in the average?
-Keith
On Sat, Apr 6, 2013 at 7:59 PM, Bruce Fischl fischl@nmr.mgh.harvard.eduwrote:
Hi Keith
the average white/pial surface doesn't have any topological or smoothness constraints, which is why we don't really use it. Yes, mris_expand is slow, but that's precisely because it prohibits self-intersection. The good nes is that compared to the rest of the recon stream it doesn't add that much time :)
Bruce
On Sat, 6 Apr 2013, Keith Jamison wrote:
I have seen that the official recommendation for making a mid-gray surface
is to use mris_expand. This seems to be a very slow procedure on my machine. I have also tried just loading the ?h.white and ?h.pial surfaces into matlab, averaging their vertices, and exporting the result. This seems to result in a nearly identical surface as mris_expand. On a test subject, only 48 out of 127,998 (0.0375%) vertices differed by more than 0.1mm, and these were almost entirely around the edges of the corpus callosum.
Is there a reason this alternative is a bad idea? I imagine mris_expand does additional topology checks along the way, but if the vertices vary so little, can that be a major problem?
I'm inclined to go with the faster solution, but since I'm relatively new to this procedure, I wanted to see what the community's experience might be.
Thanks! Keith
______________________________**_ Keith Jamison Graduate Research Assistant
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