yes, I think it can happen, although it's probably pretty rare
On Sat, 6 Apr
2013, Keith Jamison wrote:
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 <fis...@nmr.mgh.harvard.edu>
wrote:
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
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