SPHARM-based shape analysis of hippocampus for lateralization in mesial temporal lobe epilepsy

Spherical harmonics (SPHARM) is a powerful tool for modelling and processing of 3D connected objects of any shape. SPHARM popularity lies in its capability of revealing surfaces global discrepancies in a multi-scale manner. In medical image analysis, this capability is of great importance in diagnosis of diseases that are related to deformations in the brain structures, such as mesial temporal lobe epilepsy that is associated with the hippocampus deformation. In this paper, we present a simple and practical method for SPHARM registration, which is required for conducting shape comparisons. The method utilizes concepts of principal components and solves the challenging problem of SPHARM registration. Our method benefits from characteristics of SPHARM coefficients that have independent [x,y,z] elements; so registration is easily performed in the SPHARM feature space. Then, we propose our feature selection methods that summarize 1536 SPHARM-based features of each subject into three lateralization indices. These three indices measure the distances between left and right hippocampi of healthy and epileptic subjects to detect the epileptogenic hippocampus. This work improves the lateralization accuracy from 78% of conventional volumetric method to 85%, and also in cases where volumetric analysis is uncertain, 16% improvement is achieved. This method could be used as a compliment to other methods to decrease lateralization error.