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Exposure of workers to pulsed gradients in MRI.

Crozier S, Wang H, Trakic A, Liu F

School of Information Technology and Electric Engineering, The University of Queensland, Brisbane, Queensland, Australia. stuart@itee.uq.edu.au

PURPOSE: To numerically evaluate the electric field/current density magnitudes and spatial distributions in healthcare workers when they are standing close to the gradient coil windings near the magnetic resonance imaging (MRI) scanner ends. MATERIALS AND METHODS: Anatomically realistic, whole-body male and female voxel phantoms are engaged to model the workers at various positions near the ends of three cylindrical gradient coils (x-, y-, and z-axis gradients). The numerical calculations of induced fields are based on an efficient, quasistatic finite-difference method. RESULTS: The simulations show that it is possible to induce electric fields/current densities above levels recommended by the International Commission for Non-ionizing Radiation Protection (ICNIRP) and the Institute of Electrical and Electronics Engineers (IEEE) standards when the workers are standing close to the gradient coils and when two or three gradients are switched simultaneously, as is often the case. CONCLUSION: The longitudinal gradient tends to induce more fields in workers than the transverse coils. The strongest levels of field exposure are observed when all three gradients are operated simultaneously and can be above regulations when the healthcare worker is close to the gradient coils. Other postures such as bending into the magnet shall be investigated in further studies.

Published 5 November 2007 in J Magn Reson Imaging, 26(5): 1236-54.
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