Preliminary Results on Torso PNS Thresholds at the Ultrasonic Driving Frequency of 20 kHz using a Whole-Body Gradient Coil

Motivation: For silent whole-body MRI using ultrasonic encoding at 20kHz, very high slew rates will be experienced by body parts such as the torso with PNS risk. However, PNS thresholds for these body parts at ultrasonic frequencies are not well known. Goal(s): To estimate PNS thresholds for the torso at 20kHz. Approach: We test volunteers in a whole-body gradient coil driven at 20kHz to determine when PNS occurs and compare to simulations and current IEC guidelines. Results: PNS occurs at much higher dB/dt values than predicted by IEC guidelines at 20kHz, where we found a mean threshold value of 1316T/s for the torso. Impact: PNS is a concern for body MRI using ultrasonic encoding. Here, we show much higher measured PNS thresholds than IEC guideline predictions for 20kHz gradient switching, suggesting that whole-body silent MRI at 20kHz is possible with reduced risk of PNS.