Numerically-simulated induced electric field and current density within a human model located close to a z-gradient coil

Abstract

Purpose: To simulate exposure (e.g., during interventional procedures) of a worker close to an operating MR scanner by calculating electric fields and current density within an anatomically realistic body model due to a z-gradient coil and to compare results with safety guidelines and European Directive 2004/40/EC. Materials and Methods: Electric field and current density in an adult male model located at three positions within the range 0.19-0.44 m from the end of a generic z-gradient coil were calculated using the time-domain finite integration technique (FIT). Frequency scaling was used in which quasistatic conditions were assumed and results obtained at 1 MHz (assuming tissue conductivity values at 1 kHz) were scaled to 1 kHz. Results: Current density (averaged over 1 cm2) in central nervous system (CNS) tissues up to 20.6 mA m-2 and electric fields (averaged over 5 mm) up to 4.1 V m-1 were predicted for a gradient of 10 mT m-1 and slew rate of 10 T m-1 second-1. Conclusion: Compliance with 2004/40/EC, and with basic restriction values of Institute of Electrical and Electronics Engineers (IEEE) C95.6-2002, was predicted only at impracticably low gradients/slew rates in the ranges 4.9-9.1 mT m-1/4.9-9.1 T m -1 second-1 and 5-21 mT m-1/ 5-21 T m -1 second-1, respectively. © 2007 Wiley-Liss, Inc.