High-resolution organ dosimetry for human exposure to low-frequency magnetic fields

Electric fields and current densities induced in an anatomically realistic, high-resolution model of the human body are computed. The results are given for various organs in terms of average and maximum values for 60-Hz uniform magnetic fields in three orthogonal orientations. The effects of variations in the tissue conductivity are evaluated. The data presented can he linearly scaled to frequencies up to 100 kHz without an appreciable error, provided that the changes in tissue conductivity with frequency are taken into account. The scalar potential finite difference (SPFD) method with an appropriate matrix preconditioner and a conjugate gradient solver were used to model the problem. This approach resulted in a high computational efficiency that facilitated high-resolution (3.6 mm voxels) modeling involving 1 736 872 unknowns. All computations were performed on a Hewlett-Packard 9000/735 Unix workstation using under 200 MB of physical memory. Typical computation times were of the order of 25 h. The results show that conductivity variations, source orientation, and model realism can significantly affect the dosimetry values, particularly in comparison with more simplistic models. They also show that the maximum current density in several tissues can exceed 10 mA m^-2 in a 60-Hz, 0.5-mT uniform magnetic field