Material Coarsening Strategy for Structured Meshless Multigrid Method for Dosimetry in Anisotropic Human Body Models

In this article, a novel multigrid-based method is developed for modeling of electric fields and currents in electrically anisotropic and heterogeneous media. The method is useful for numerical assessment of human exposure to low-frequency electromagnetic fields, which has been typically performed using isotropic models of the human body. The method is matrix-free and based on structured voxelized grids. Numerical tests indicate that the method has all typical benefits of multigrid methods, i.e., convergence in a constant number of iterations and linear complexity in terms of the number of degrees of freedom. The developed method is applied to the dosimetry of the induced electric field in ten anatomically realistic models of the human head exposed to uniform 50-Hz magnetic fields. The models are constructed from magnetic resonance images and account for the electrical anisotropy of the brain tissues via diffusion weighted images. The dosimetry modeling shows that the tissue anisotropy leads to a small but significant increase (14% on average) of the 99th percentile induced electric field strength in the white matter of the brain. However, isotropic models can still provide sufficient accuracy for dosimetry if this slight underestimation of the 99th percentile electric field strength is accounted for.