Simulation of dB/dt‐Over‐Electric Field Cardiac Magnetostimulation Safety Ratios in 75 Body Models and 18 Gradient Systems

ABSTRACT Purpose The IEC 60601‐2‐33 standard provides consensus‐based safety provisions for MRI equipment. Protection of patients against cardiac stimulation (CS) is based on limiting the maximum E‐field induced by MRI gradient coils. In practice, this is achieved by imposing a conservative dB/dt threshold on any gradient waveform. The dB/dt‐over‐E‐field conversion ratio currently used in IEC 60601‐2‐33 was derived in a homogeneous ellipsoid exposed to a uniform B‐field and is 10 (T/s)*(V/m) −1 . This limit is becoming increasingly restrictive in high performance clinical systems. We therefore evaluate dB/dt‐over‐E‐field ratios in realistic body models and coils using state‐of‐the‐art electromagnetic simulations. Methods We performed two independent simulation studies in a total of 75 realistic body models and 13 commercial gradient systems and derived dB/dt‐over‐E‐field ratios in the heart. We thresholded the E‐field maps to mitigate the impact of staircasing artifacts in boundary voxels between the myocardium and the lungs. Results Thresholding the E‐field maps at the 99th percentile E‐field value (E99) eliminates staircasing artifacts in both simulation studies. Study #1 predicts a larger range of dB/dt‐over‐E99 ratios (13–53 (T/s)*(V/m) −1 ) than study #2 (12–35 (T/s)*(V/m) −1 ). Despite differences in EM solvers, body models, coils, mesh resolution, and post‐processing, both studies find similar worst‐case ratios of dB/dt‐over‐E99 of 12–13 (T/s)*(V/m) −1 . Conclusion Our simulations of dB/dt‐over‐E‐field ratios for cardiac safety in MRI cover a large range of realistic clinical scenarios. An increase of the allowable dB/dt beyond the current CS limit in IEC 60601‐2‐33 may be feasible.