Modeling the volume conductor-double Fourier series approximation versus spherical harmonic expansion

A method for parametric description of boundary surfaces based on combined second order surface and double Fourier series approximation is presented. Gauss transformation is used to determine the best fitting parameters. The method is applied to approximate the conductivity interfaces of volume conductor models needed for solving the bioelectromagnetic forward and inverse problem. The attained quality of fit was compared to that obtained applying the surface harmonic expansion for modeling the volume conductor shape. In that case, the coefficients of expansion are found by nonlinear least-squares fit.