Dear Surferteam,
I have been trying to understand details on how the cortical thickness
is calculated. I read in the article:
"we compute the closest vertex on the pial from each vertex on the
white, and vice-versa, then set the thickness to the average of the
two."
I have tried to carry out this calculation myself, using the generated
surfaces lh.white and lh.pial and compare my results to the thickness
generated by FS (lh.thickness).
There is a one-to-one correspondence between the vertices of the white
and pial meshes, which makes it quite straightforward:
e.g.:
Vertex 100 on white surface has distance from pial surface = 2.5 mm,
vertex 100 on pial surface has distance from white surface = 2.6 mm,
average == thickness at vertex 100 = 2.55 mm.
However, the results that I am getting are different from lh.thickness.
I expected discrepancies on the order of rounding errors, but half of
the thickness values differ more than 0.001, with some differing as much
as 2 mms!
What am I missing?
Could you please elaborate a bit on how you define the cortical
thickness?
Thank you very much,
Miro Drahos