Evaluation of electromagnetic field distributions under 1.5 T MRI scanning within human models of a virtual family

Magnetic Resonance Imaging (MRI) has been contraindicated in patients with pacemakers or implantable cardioverter-defibrillators (ICDs) due to safety concerns, such as the heating of adjacent bodily tissue due to radio frequency (RF) induced current. The ISO/IEC 10974 Joint Working Group (JWG) has developed a tiered approach in establishing the worst case RF heating conditions that active implantable devices may experience during MRI utilizing computer simulations. According to the ISO/IEC JWG tier 2 approach, we evaluated the electric fields induced in the implant regions of pacemakers and ICDs in five human body models during 1.5 T MRI scans. The maximum electrical field (Emax) can be used as a conservative estimation to test MRI induced heating. The SEMCAD software package was used to calculate the electric field distribution due to RF fields from high pass and low pass MRI birdcage coils. The variables studied in the simulations also included circularly polarized field rotations, body positions inside RF coils (landmark positions), tissue properties, and RF coil size. The Emax and 95^th percentile electric field values were computed from the simulations at each of multiple implant regions.

1. Introduction

With the increased use of implantable medical devices, there have been concerns related to the interaction between magnetic resonance imaging (MRI) systems with these devices. These interactions include magnetic field interactions, heating, and image artifacts [1]. Notably, MRI-related heating may lead to tissue damage near implants that have elongated metallic components. Accordingly, MRI safety issues are generally characterized by following standards. Such standards are based on those appropriate test procedures presented by the International Organization for Standardization and the International Electrotechnical Commission (ISO/IEC) and American Society for Testing and Materials (ASTM) International [2].