Stimulation of peripheral nerves by time varying magnetic field gradients during magnetic resonance tomography

Purpose: The objective of this study is to explain how peripheral nerves can be stimulated by magnetic resonance imaging (MRI) and to describe the associated potential risk. Present knowledge on the bioeffects of time-varying magnetic fields used in MRI are summarized and discussed. Material and Methods: This review summarizes current reports on peripheral nerve stimulation during MRI and studies which determine threshold values for stimulation effects. Results/Discussion: The comparison of the different studies indicates that it is reasonable to express the stimulation threshold in terms of the gradient amplitude rather than in terms of the rate of change of the magnetic field gradient. Further studies are necessary to obtain reliable threshold values for peripheral nerve stimulation during MRI and, even more important, to find out how these results can be used to define threshold values in order to avoid excitation of the myocardium during MRI. (orig.)