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

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

Then 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.