External Email - Use Caution
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
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
发件人： "Alex" <free_learner@foxmail.com> 发件时间： 2024年11月13日 00:54 收件人： "freesurfer" <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
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-bounces@nmr.mgh.harvard.edu freesurfer-bounces@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 ________________________________ 发件人： "Alex" <free_learner@foxmail.commailto:free_learner@foxmail.com> 发件时间： 2024年11月13日 00:54 收件人： "freesurfer" <freesurfer@nmr.mgh.harvard.edumailto: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
freesurfer@nmr.mgh.harvard.edu
-
Alex -
Fischl, Bruce R.,PHD