Uncertainty Analysis of Computational Model to Simulate Neurostimulation Caused by Gradient Fields in MRI

Electric Stimulation, Peripheral Nerve Stimulation in MRI

MRI gradient coil, peripheral nerve stimulation, Time varying magnetic fields

The aim of this research project is to quantify the uncertainty of current state-of-the art anatomical phantoms and computational models for predicting neurostimulation induced by time-varying magnetic fields (so-called gradient fields) within the context of magnetic resonance imaging (MRI) scanners. For this purpose stimulation thresholds will be measured in a volunteer study. The measurements will provide valuable data for the development and validation of future models.

The study does not investigate any health related interventions, neither a therapy nor medical device. The study aims to provoke peripheral nerve stimulation from time varying magnetic (so-called gradient) fields in volunteers in order to measure gradient threshold levels in different configurations (different gradient coil units, different positions and postures). The experiments will provide new data regarding the interaction of gradient fields and function of the peripheral nervous system. These measurements are of general interest to quantify associated modeling uncertainties and validate current or future computational modeling techniques. The experiments will use an MR scanner to generate the gradient fields used to induce stimulation. In normal mode the maximum gradient field allowed by the manufacturer may lead to peripheral nerve stimulation in approximately 50% of subjects. However, depending on the position and posture it may induce PNS in even fewer than 50% of subjects. Therefore, for the purpose of measuring stimulation thresholds it is necessary to operate the gradient units in experimental mode (with respect to the gradient field) as described in IEC 60601-2-33, i.e. the gradient limits set by the manufacturer will be disabled. As described in the standard, the gradient field will be increased slowly from non-stimulating levels until the volunteer perceives first stimulation sensations, at which point the gradient field will be stopped. This protocol does not lead to an increased risk of cardiac muscle stimulation compared to the normal mode, but only an increased likelihood of PNS with non-painful sensations in the skin, e.g. tingling, twitching or poking. PNS is not considered a health concern. The radio-frequency (RF) field will remain switched off, i.e. there is no risk of heating (the scanner will not acquire images in this mode).

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Switzerland