Hi Alex
I think the area of a vertex is the average area of the triangles it is
attached to. It isn’t a point measure so it is a bit hard to interpret on an
individual basis, particularly since the individual triangle areas reflect the
white/pial surface deformation dynamics. Probably makes more sense to do it
parcellation-wise or after mapping into fsaverage coords, but perhaps others
have thought about this more?
Cheers
Bruce
From: freesurfer-boun...@nmr.mgh.harvard.edu
<freesurfer-boun...@nmr.mgh.harvard.edu> On Behalf Of Alex
Sent: Tuesday, November 19, 2024 9:55 PM
To: freesurfer <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] 回复：How to interpret the vertex-wise area metric?
External Email - Use Caution
Sorry to bump this post up! I understand that everyone is busy, but I'm really
hoping to get some feedback on my questions. Any thoughts or suggestions would
be greatly appreciated! Thanks in advance!
原始邮件
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发件人： "Alex" <free_lear...@foxmail.com<mailto:free_lear...@foxmail.com>>
发件时间： 2024年11月13日 00:54
收件人： "freesurfer"
<freesurfer@nmr.mgh.harvard.edu<mailto:freesurfer@nmr.mgh.harvard.edu>>
主题： How to interpret the vertex-wise area metric?
Dear FreeSurfer experts,
I have a question about the interpretation of the vertex-wise area metric. For
instance, if Vertex A had a larger area than Vertex B, then what's the
difference between Vertex A and Vertex B biologically?
Based on my simple (probably wrong) understanding of the surface reconstruction
process, the initial surface was created based on the GM-WM boundary voxels, in
which the face of a voxel was divided into two triangles and the area of the
triangles was equal. But after the refinement of the initial surface, the
triangle area was not uniform any more. So what factors may explain the
expansion or contraction of the surface triangles? I believe these factors may
help me understand the vertex-wise area metric. Maybe I should treat the vertex
and the triangles around it as a whole, which is the unit of comparison. For
instance, the Vertex A having a larger area means the area of triangels around
Vertex A is larger. This kind of interpretation would make the comparsion
between Vertex A and B biologically meaningless.
From another perspective, in the voxel-based morphometry (VBM), the voxel size
is fixed and the volume is the proportion or probability of GM (or other tissue
types) in the voxel. In the surface case, if the triangle size is kept fixed,
the area is proportial to the number of triangles, which is conceptually
similar to the VBM approach. Why FreeSurfer did not choose this kind of
approach? Sorry if this question is not reasonable, as I did not have a strong
technical background.
Best,
Yang Hu
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