Deformable model with surface registration for hippocampal shape deformity analysis in schizophrenia

Changes to the hippocampal structure have been reported as consistent structural abnormalities in schizophrenic patients and have been related to the learning and memory deficits in such patients. Although many magnetic resonance (MR) imaging studies have focused on the hippocampal volume, local structural changes were difficult to discriminate from normal neuroanatomical variations. 3D shape deformation analysis of the brain structure may reflect localized schizophrenic abnormalities. A deformable model, evolved from the ellipsoid to hippocampal surface, with 2562 vertexes, was developed to analyze the left and right hippocampus shapes in 22 schizophrenic patients and 22 healthy age and gender matched controls. One of the most critical issues in the shape analysis is the determination of homologous points between two objects. To determine more accurate corresponding points, an alignment procedure, consisting of coarse and fine steps, following a deformation process, was applied. The performance of the alignment process was tested using artificial data, to get the alignment error to within 3° for each angle. A volume analysis indicated the hippocampal volume to be bilaterally reduced in schizophrenic patients compared to the normal controls, with a shape analysis showing a deformity pattern of the hippocampal surface. Bilateral inward deformities in the anterior and posterior hippocampus and a unilateral outward deformity in the right anterior hippocampus were observed, respectively.