Prediction of peripheral nerve stimulation thresholds of MRI gradient coils using coupled electromagnetic and neurodynamic simulations

Abstract

Our simulation framework allows accurate prediction of gradient coil PNS thresholds and provides detailed information on location and "next nerve" thresholds that are not available experimentally. As such, we hope that PNS simulations can have a potential role in the design phase of high performance MRI gradient coils.

Peripheral nerve stimulation limits of a high amplitude and slew rate magnetic field gradient coil for neuroimaging

“…The simulations did not include a nerve model like that performed elsewhere, which potentially could have allowed for a linear integration along specific nerve bundles to provide better anatomical specificity. In this study, male PNS thresholds were slightly higher, contrary to another head‐gradient study . However, in our study, the differences were deemed to be small, especially in contrast to the effects due to age and positioning.…”

“…Although these regulatory safety guidelines apply in general to all MRI gradient systems, the need for PNS studies is especially important for MRI systems capable of higher gradient amplitude and slew rates. More recently, attempts to include human body and nerve models have been used by electromagnetic field simulations to estimate PNS thresholds . When compared with PNS experiments, these simulations provided good agreement with the location, magnitude, and orientation in whole body and head gradients, and can be a powerful way to validate PNS studies and to improve gradient designs.…”

“…More recently, attempts to include human body and nerve models have been used by electromagnetic field simulations to estimate PNS thresholds . When compared with PNS experiments, these simulations provided good agreement with the location, magnitude, and orientation in whole body and head gradients, and can be a powerful way to validate PNS studies and to improve gradient designs. They also confirm higher electric field (E‐field) amplitudes with whole‐body gradients (primarily in the torso regions) than with head gradients (in head and upper torso regions).…”

“…To first‐order, the PNS characteristics of MAGNUS are expected to be similar to the C3T, which had significantly higher Δ G min and SR min than whole‐body systems and were most sensitive in the x‐axis (left–right); it was also shown with a head‐rotation experiment that the PNS sensitivity was dependent on anatomy rather than on the gradient coil. Another head gradient of different design was also most sensitive in the x‐axis . One rationale for this is that the head in a supine position has a larger conductive area normal to the sagittal plane as compared with the coronal plane, which results in larger loops and increased induced E‐field.…”

“…Another head gradient of different design was also most sensitive in the x-axis. 19 One rationale for this is that the head in a supine position has a larger conductive area normal to the sagittal plane as compared with the coronal plane, which results in larger loops and increased induced E-field. This rationale and generalization of x-axis sensitivity may not be valid, however, as another head-gradient design with a symmetric folded coil instead showed higher -y-axis (anterior-posterior) sensitivity than the x-axis.…”