Using the vector potential in evaluating the likelihood of peripheral nerve stimulation due to switched magnetic field gradients

✍ Scribed by Martin Bencsik; Richard Bowtell; Roger M. Bowley

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 562 KB
• Volume: 50
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.10520

✦ Synopsis

Abstract

The time‐varying magnetic field gradients used in MRI can cause peripheral nerve stimulation (PNS) in human subjects, as a result of the electric fields induced in tissue. The local electric field, E, is given by E = −∂A/∂t − ∇ϕ where A, is the vector potential and ϕ is the scalar electric potential generated by charges accumulated at boundaries between regions of different conductivity. Difficulties in calculating ϕ have led some investigators to use −∂A/∂t alone as a predictor of the induced field. Here the spatial variation of −∂A/∂t and E is investigated for the case of a simple spherical conductor exposed to time‐varying gradients produced by two different gradient coils that generate identical internal magnetic fields, but very different vector potentials. The results indicate that the temporal derivative of A bears little relation to the induced electric field, and that consequently neglecting the effect of the scalar potential introduces significant errors in estimating the likelihood of PNS. Magn Reson Med 50:405–410, 2003. © 2003 Wiley‐Liss, Inc.