A Simple Em Model for Determining the Scat- Tered Magnetic Resonance Radiofrequency Field of an Implanted Medical Device

A radiofrequency field (RF) field exists inside body tissue during magnetic resonance imaging (MRI). If any implanted medical device is present, there can be a very intense concentration of the scattered RF field in the tissue surrounding certain parts of the implant. This causes tissue heating that can reach dangerous levels. Scattered field considerations show that it is possible to neglect the loading effect of the implant on the MR RF source. This leads to an incident field simplification. The presence of the implant in nonhomogeneous tissue increases the complexity of the scattering problem. An approach is presented that makes the computational problem considerably smaller. A method of moments (MoM) formulation of the EM model is presented. The relevant issues that arise during a finite element method (FEM) formulation are also discussed. The methods are illustrated by solving the problem for typical implants using MoM as well as FEM.