Motion-Induced Fields in Magnetic Resonance Imaging: Are the Dielectric Currents Really Negligible?

This paper deals with the exposure of humans moving through the stray stationary magnetic field produced by magnetic resonance imaging scanners. In particular, the work evaluates the influence of the dielectric currents, whose effects have been disregarded up to now, despite the very high permittivity values obtained by extrapolation based on the most common dispersion models of tissue properties. The analysis is carried out by considering a high-resolution anatomical model through an original numerical procedure that includes the dielectric phenomena. The results prove that the high values of the dielectric permittivity produce limited, but nonnegligible variations on the induced current density, while weakly influencing the electric field. Finally, the stability of the results with respect to variations of the dielectric permittivity practically removes the need for an accurate measurement of such a parameter that is affected by high uncertainties at very low frequencies.