Hi, I was just wandering what determines the area value assigned to a given vertex. Is it the average area of the faces of the triangles to which it is attached? If so, what determines the area of the traingle faces? Do the values in the ?.area file reflect regional variations in surface area? I'm wandering whether using the ?.area file in mris_glm would produce meaningful results (eg., a difference between groups would represent regional differences in surface area), or whether the area is determined by some feature of the surface reconstruction process rather than an intrinsic neuroanatomical variation, and areas for labels would be the only valid way of looking at surface area. Thanks, Alex
Alex Fornito M.Psych/PhD (clin. neuro.) candidate Melbourne Neuropsychiatry Centre and Department of Psychology The University of Melbourne alexander.fornito@wh.org.au
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From: freesurfer-bounces@nmr.mgh.harvard.edu on behalf of Marie Schaer Sent: Thu 3/11/2005 6:01 AM To: Bruce Fischl Cc: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] area file
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&...
I got it, thank you very much!
Marie
Quoting Bruce Fischl fischl@nmr.mgh.harvard.edu:
Hi Marie,
the folding indices are taken from one of the original Van Essen and Drury papers. Sorry I don't have the ref handy.
Bruce
On Wed, 2 Nov 2005, Marie Schaer wrote:
I tried with mris_anatomical_stats from freesurfer-Linux-rh9-v2.1 and I
obtained
exactly the same result for total surface area as in matlab with the sum of
all
the triangles, thanks for the advice!
In the mean time I was just wondering how folding index returned by mris_anatomical_stats is calculated?
Thank you!
Marie Schaer
Quoting Doug Greve greve@nmr.mgh.harvard.edu:
We found a problem with this computation about a year ago (11/12/2004 to be specific). I think I sent an email about it to the list. Any releases prior to that date will have this error in the area computations. Can you try it with a more recent release?
Marie Schaer wrote:
Hello everybody!
I have one question about how surface areas are calculated by
mris_anatomical
stats (release2004). I noticed that the ?h.area file may contain the portion of area
corresponding to
each different vertex. Actually, the sum of all these areas is around
7'500mm^2
for one hemisphere, which is approximately (but not exactely) the result
given
by mris_anatomical_stats. However, when I converted the pial surface in
matlab,
and calculated the sum of the area of each triangle using the following
equation
http://mathworld.wolfram.com/TriangleArea.html, I obtained a very higher
result
(~10'000mm^2). Perhaps because the triangles are too big to calculate an accurate area at this stage?
So my question was, on which basis is calculated the information
contained
in
lh.area? Does the first row of ?h.area correspond to the piece of area attributable to the first vertice, and so on?
Thank you very much for your response!
Marie Schaer
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