Hello all
I have made changes in the thickness values in some regions of a left hemisfere of a subject surface after mapped it onto the fsaverage sphere.
The changes were made to have areas close to these in the left colum of the following table:
My area Freesurfer number of vertices
20 mm2 27.88 mm2 (37) 30 mm2 35.09 mm2 (47) 40 mm2 39.17 mm2 (52) 50 mm2 56.89 mm2 (76) 60 mm2 44.05 mm2 (59)
I computed the region areas in the fsaverage surface by adding the areas of the triangular faces inside these regions using the spherical coordinates of the vertices and the Heron formula for the triangle area.
The freesurfer sphere mapping is based in minimal metric distortion, so, why the freesurfer computed areas for these regions are different(the second column in the table)?
In both cases the same surface vertices were found to be inside of the regions (the third column in the table) I would like to have more insight on how freesurfer compute the area of a given ROI in the fsaverage spherical surface.
In advance thank you
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