Numerical study of currents in workers induced by body-motion around high-ultrahigh field MRI magnets

Abstract

Purpose: To numerically evaluate the electric field/current density magnitudes and spatial distributions in healthcare workers when moving through strong, nonuniform static magnetic fields generated by the magnetic resonance imaging (MRI) system and to understand the relationship between the field characteristics and levels/distributions of induced field quantities. Materials and Methods: Tissue-equivalent, whole-body male and female voxel phantoms are engaged to model the workers at various positions and variety of body motions around three real superconducting magnets with field strengths of 1.5T, 4T, and 7T. The numerical calculations of induced fields are based on an efficient, quasistatic finite-difference scheme. Results: The simulations show that it is possible to induce electric fields/current densities above levels recommended by International Commission for Non-ionizing Radiation Protection (ICNIRP) and Institute of Electrical and Electronics Engineers (IEEE) standards when the worker is moving very close to the imager. The results indicate that the worker should be at least ∼0.5-1.0 m axially away from the cryostat end for field strengths between 1.5-7T to limit the exposure according to the standards when moving at a nominal 1 m second-1. Conclusion: To comply with international safety regulations, workers either need to be restricted in their access to certain areas around the magnet or to ensure slow movement in specified regions. © 2007 Wiley-Liss, Inc.