FIGURE 2.

The two primary steps of the ARMM methodological framework: first, establishing an axis‐reference model within a hippocampal atlas; and second, utilizing this model as a template to generate axis‐reference models for any given hippocampi through spatial deformation. Left: The first step including building an axis‐referenced coordinate system of the hippocampus and reshaping the reconstructed surface to obtain laminar distribution along the long axis. To achieve this, a hippocampal boundary surface (a) is extracted from the MR image. (b) The surface is then used to calculate the IMS (pink) by NURBS surface fitting with Voronoi diagram vertexes (yellow) that generate from the hippocampal boundary surface mesh. The blue mesh in (c) is a reparameterized IMS, with the centermost axis (red) manually fitted to be generally agree with the CA‐DG border of the hippocampus. (d) Spokes calculated according to geometric constrains on IMS (yellow) and boundary surface. The superior and inferior spokes, colored in magenta and cyan, respectively, pointing from the IMS to the gray boundary surface. (e) A hippocampal surface with transversal lamellar and longitudinal axes is generated from the IMS and spokes. Note that the boundary surface is composed of the superior and inferior parts colored in magenta and cyan, respectively. Right: The approach to automated generate axis‐reference model of an arbitrary hippocampus, with consideration on longitudinal hippocampi. Ant, anterior; CA, cornu ammonis; DG, dentate gyrus; IMS, inscribed medial surface; Lat, lateral; Med, medial; NURBS, non‐uniform rational B‐splines; Post, posterior; SRLM, stratum radiatum lacunosum moleculare; SUB, subiculum.