Fig 1. Registration of templates and surface points correspondence.

Source template is Civet’s surface while target template is the Freesurfer’ surface template. Starting from two averaged surfaces (previously created from the same set of 10 CTR, 10 sMCI, and 10 AD brains) the hybrid template (characterized by 81924 vertices and 163840 faces) is derived after 15 GFV iterations. In GVF, deformations are achieved by tuning an underlying set of control points (187×187×187) in the source surface. Control point displacements are then interpolated to obtain a continuous transformation through basis spline functions. To keep the contour smooth, a membrane and percentage thin plate energy was used as regularization. The parameters defining the attraction to edges and energy surfaces were empirically determined. Finally, the CPS step defined the mutual correspondence of Civet and Freesurfer thickness values for each vertex. CV: Civet; FS: Freesurfer; X-Y-Z: value of the vertex space coordinates; T: value of the cortical thickness for each vertex; n: number of vertices (min = 0; max = 81924); 3D GVF: 3D gradient vector flow; CPS: Closest point search.