Peripheral Nerve Stimulation 

Rapidly changing magnetic fields of gradient coils can induce electric fields in human tissue causing stimulation of peripheral nerves. Magnetic gradient coils are necessary component of every MRI system used to spatial encode the MRI signal. Recent advances in gradient amplifier technology over the last few years has produced gradient sub-systems that can readily induce peripheral nerve stimulation (PNS) in humans.

PNS is not considered to be a significant danger in MRI.  At threshold levels, PNS is experienced as a mild sensation such as a light vibration or poking of the skin.  Exposure at levels ~50% higher than threshold produces painful response.  At even higher levels, stimulation of vital organs and tissues such as the heart and diaphagm is possible. Fortunately, the thresholds for respiratory and cardiac stimulation are at least an order of magnitude or more greater than the PNS thresholds accessible by typical operational parameters used for MR imaging.

Therefore, PNS sets a fundamental limit for gradient performance for magnetic resonance imaging and the exposure criteria have been based on a wealth of literature that studied direct electrical stimulation of the nerves. This research has been directed at examining PNS using both magnetic and electric field stimulation in order to compare their thresholds.

Our Research Objective

To experimentally obtain electric and magnetic field stimulation data in a cohort of human volunteers in order to compare the thresholds for PNS for these two sets of data.  


Our Contribution

We have measured the PNS threshold from both electric and magnetic stimulation in a group of twenty two human subjects.  The average chronaxie times (a measure of stimulation threshold) were determined for both modes of stimulation and inter-compared.


  1. B.J. Recoskie, T.J. Scholl, B.A. Chronik 2009Discrepancy between human peripheral nerve chronaxie times as measured using magnetic and electric field stimuli: relevance to MRI gradient coil safety, Physics in Medicine and Biology 54, 5965-5979. [PDF]

  2.  B.J. Recoskie, T.J. Scholl, C.M. Collins, B.A. Chronik.  "Inconsistency between gradient coil nerve stimulation parameters as measured using electric and magnetic fields".  ISMRM Workshop on MR Safety, Virginia, MA, November 5, 2005.

Key Questions

  • Is there a difference for the chronaxie times for electric and magnetic stimulation of the peripheral nerve system in a paired subject population?
  • Are the PNS limits for MRI determined from electric field exposure data different than those determined from thresholds observed from the stimulation due to switched magnetic fields?