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


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 1.5 T, 4 T, and 7 T. 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 approximately 0.5-1.0 m axially away from the cryostat end for field strengths between 1.5-7 T to limit the exposure according to the standards when moving at a nominal 1 m second(-1).


CONCLUSIONS
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.
School of Information Technology & Electric Engineering, The University of Queensland, Brisbane, Australia. stuart@itee.uq.edu.au
Trakic
Adnan
A
Wang
Hua
H
Liu
Feng
F
D001822:Body Burden; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics / Q000295:instrumentation*; D008503:Medical Staff; D008954:Models, Biological; D009068:Movement; D016273:Occupational Exposure / Q000032:analysis*; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods; D012062:Relative Biological Effectiveness; D014915:Whole-Body Counting / Q000379:methods*