Induction of electric fields due to gradient switching: a numerical approach

Since the first observations of peripheral nerve stimulation in MRI, it has been clear that the underlying mechanism is the activation of the nervous system by induced electric fields. However, compared to experimental investigations little work has been done on calculating these electric fields with adequate accuracy. In this article a numerical analysis of the electric fields induced by a complete whole body gradient system is presented. The calculations were carried out on three human body models of different complexities. The numerical results correlate better to the experimental observations with a body model that resembles the human body. Applying a model with inhomogeneous conductivity, numerical stability was not reached. The results were compared to the limits given in the upcoming IEC 60601-2-33 standard. The comparison shows that the derived peak electric fields depend substantially on the body model used, which dictates that limits have to refer to a body model that is exactly defined.