Comparison of the threshold for peripheral nerve stimulation during gradient switching in whole body MR systems

Abstract

Purpose: To compare thresholds for peripheral nerve stimulation from gradient switching in whole body magnetic resonance (MR) equipment of different design. Materials and Methods: Threshold data obtained in three experiments were reformatted into a single joint data set describing thresholds for anterio-posterior (AP) gradient orientation and Echo Planar Imaging (EPI) waveforms with bipolar ramp times between 0.07 and 1.2 ms. Reformatting included the use of: a) the rate of change of the maximum field in the patient space as a measure of gradient output, b) lowest observable thresholds, c) lognormal distribution of thresholds, and d) equal standard deviation (SD) of all samples. Results: The joint data fit a hyperbolic threshold function. The residues were not significantly different between experiments. Conclusion: When expressed in appropriate format, the thresholds for peripheral nerve stimulation in volunteers for whole body MR equipment can be described with a hyperbolic threshold curve with rheobase 18.8 ± 0.6 Tesla/second and chronaxie 0.36 ± 0.02 milliseconds. © 2002 Wiley-Liss, Inc.