Evaluation of SAR in a finite element human body model imposed to magnetic fields generated by a MRI bird cage coil

Abstract

There has been increasing public concern about the adverse health effects of human exposure to electromagnetic (EM) waves in magnetic resonance imaging (MRI). The safety recommendations given in a number of general publications on EM radiation include the maximum permissible whole-body specific absorption rates (SAR). In this paper theoretical analysis indicates other factors that may have an even higher impact on the potential heating of tissue, e.g. in the vicinity of implanted devices. A new finite element human body at millimeter resolution has been used to estimate local SAR in MRI scanners. The radio frequency (RF) transmitter coil has been modelled to provide circular polarized B1 field and E-field components based on tuned electrical circuits and on physical locations and values of the discrete capacitors distributed throughout the RF transmitter coil. SAR values are calculated for all tissue types included in the human body model. The results presented at the surface of various organs SAR distribution are non-trivial functions of the irradiated frequency as well as the geometry, shape, homogeneity, and material properties of the tissue and organ under consideration. It has been found that the flexibility of grid sizing in finite elements calculations leads to an order of magnitude in time savings compared to FDTD algorithms used in other studies. © 2009 Springer-Verlag.