Safety aspects of switched gradient fields.

At sufficient amplitude, gradient-induced electric fields may stimulate nerves and muscles in patients during MR examinations. This article reviews the physics, physiology, and safety aspects of nerve and muscle (including respiratory and cardiac) stimulation. This article also reviews experimental data on gradient-induced stimulation. While threshold stimulations are just perceptible, patients may experience pain at high electric field amplitudes. Safety margins required to prevent cardiac stimulation and to limit painful stimulations are investigated.