Biological effects of exposure to magnetic resonance imaging: an overview

Abstract

The literature on biological effects of magnetic and electromagnetic fields commonly utilized in magnetic resonance imaging systems is surveyed here. After an introduction on the basic principles of magnetic resonance imaging and the electric and magnetic properties of biological tissues, the basic phenomena to understand the bio-effects are described in classical terms. Values of field strengths and frequencies commonly utilized in these diagnostic systems are reported in order to allow the integration of the specific literature on the bio-effects produced by magnetic resonance systems with the vast literature concerning the bio-effects produced by electromagnetic fields. This work gives an overview of the findings about the safety concerns of exposure to static magnetic fields, radio-frequency fields, and time varying magnetic field gradients, focusing primarily on the physics of the interactions between these electromagnetic fields and biological matter. The scientific literature is summarized, integrated, and critically analyzed with the help of authoritative reviews by recognized experts, international safety guidelines are also cited.

Figure 1

Frequency dependence of relative permittivity ε (x) and conductivity σ (o); the major dispersion regions α, β and γ are indicated. The frequency range of interest for MRI devices is reported. (adapted from Ref. [16])

Figure 2

Spectrum of magnetic susceptibilities. The figure shows that the majority of human tissues is diamagnetic or weakly paramagnetic. (from Ref. [17])

Figure 3

The mean peripheral nerve stimulation thresholds and cardiac stimulation thresholds for the most sensitive population percentile estimated by Reilly. (adapted from Ref. [47])

Figure 4

Mean human nerve stimulation thresholds by z gradient; in figure are shown the experimental data and the Reilly fit. (adapted from Ref. [47])

Figure 5

Estimated probability of cardiac stimulation assuming dB/dt levels are at the mean peripheral nerve stimulation thresholds. (adapted from Ref. [47])