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Purpose: Modern high‐amplitude gradient systems can be limited by the International Electrotechnical Commission 60601‐2‐33 cardiac stimulation (CS) limit, which was set in a conservative manner based on electrode experiments and E‐field simulations in uniform ellipsoidal body models. Here, we show that coupled electromagnetic‐electrophysiological modeling in detailed body and heart models can predict CS thresholds, suggesting that such modeling might lead to more detailed threshold estimates in humans. Specifically, we compare measured and predicted CS thresholds in eight pigs. Methods: We created individualized porcine body models using MRI (Dixon for the whole body, CINE for the heart) that replicate the anatomy and posture of the animals used in our previous experimental CS study. We model the electric fields induced along cardiac Purkinje and ventricular muscle fibers and predict the electrophysiological response of these fibers, yielding CS threshold predictions in absolute units for each animal. Additionally, we assess the total modeling uncertainty through a variability analysis of the 25 main model parameters. Results: Predicted and experimental CS thresholds agree within 19% on average (normalized RMS error), which is smaller than the 27% modeling uncertainty. No significant difference was found between the modeling predictions and experiments (p < 0.05, paired t‐test). Conclusion: Predicted thresholds matched the experimental data within the modeling uncertainty, supporting the model validity. We believe that our modeling approach can be applied to study CS thresholds in humans for various gradient coils, body shapes/postures, and waveforms, which is difficult to do experimentally. [ABSTRACT FROM AUTHOR]

Magnetic fields switching at kilohertz frequencies induce electric fields in the body that can cause peripheral nerve stimulation (PNS). Magnetically induced PNS, i.e. magnetostimulation, has been extensively studied below 10 kHz. It is widely characterized using a hyperbolic strength-duration curve (SDC), where the PNS thresholds monotonically decrease with frequency. The very few studies performed at higher frequencies found significant deviations from the hyperbolic SDC above ~ 25 kHz, however, those measurements are sparse and show large variability. We fill the gap in the data by measuring PNS in the head of 8 volunteers using a solenoidal coil at 16 frequencies between 200 Hz and 88.1 kHz. Contrary to the hyperbolic SDC, PNS thresholds did not decrease monotonically with frequency, but reached a minimum ~ 25 kHz. The thresholds then increased by 39% from 25 kHz to 88.1 kHz on average across subjects. Our measurements can be used for guidance and validation of neurodynamic models and to inform PNS limits of magnetic resonance imaging (MRI) gradient coils and magnetic particle imaging (MPI) systems. The observed deviation of the experimentally measured thresholds from the hyperbolic SDC calls for further study of the underlying biological mechanisms of magnetostimulation beyond 25 kHz., Competing Interests: Competing Interests Statement The author(s) declare no competing interests.