Electromagnetic and Electrophysiological Modeling of Cardiac Stimulation Thresholds in 13 MRI Gradient Systems and 56 Body Models

ABSTRACT Purpose The MRI safety standard IEC 60601‐2‐33 limits the maximum dB / dt and E‐field induced by MRI gradients to protect patients from cardiac stimulation (CS). Those limits were set in the early 2000s based on a compilation of electrode stimulation measurements in animals as well as electromagnetic calculations in a homogeneous ellipsoid. We re‐evaluate CS in MRI using state‐of‐the‐art electromagnetic and electrophysiological modeling in realistic body models and gradient coils. Methods We predicted CS thresholds in 56 realistic body models and 13 commercial gradient systems for trapezoidal waveforms with rise times (the time during which the gradient amplitude is ramped from zero to maximum) ranging from 0.1 to 5.0 ms. We used threshold predictions in individual body models to estimate the gradient field amplitude below which the probability of occurrence of a CS adverse event is 5.5X higher than the IEC CS limit. Conclusion Detailed simulations in a large population of realistic body models and gradient coils indicate that the IEC CS limit is substantially lower (more conservative) than the predicted gradient amplitude associated with a 2‐ppb probability for CS.