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

Area of Science:

• Biomedical Engineering
• Medical Physics
• Electromagnetism

Background:

• The IEC 60601-2-33 standard sets safety limits for MRI equipment to prevent patient cardiac stimulation (CS).
• Current CS protection relies on a conservative dB/dt threshold, which is becoming restrictive for advanced MRI systems.
• The existing dB/dt-over-E-field ratio was derived under simplified conditions and may not reflect real-world scenarios.

Purpose of the Study:

• To evaluate dB/dt-over-E-field ratios in realistic human body models and MRI gradient coils.
• To determine if current safety limits for cardiac stimulation in MRI are overly conservative.
• To provide data for potential revisions of the IEC 60601-2-33 standard.

Main Methods:

• Conducted two independent electromagnetic simulation studies using 75 realistic body models and 13 commercial gradient systems.
• Derived dB/dt-over-E-field ratios specifically within the heart region.
• Applied E-field map thresholding at the 99th percentile (E99) to mitigate simulation artifacts.

Main Results:

• Thresholding at E99 effectively eliminated staircasing artifacts in simulation results.
• Study #1 predicted dB/dt-over-E99 ratios ranging from 13 to 53 (T/s)*(V/m)^-1.
• Both studies converged on similar worst-case dB/dt-over-E99 ratios of 12-13 (T/s)*(V/m)^-1, despite methodological differences.

Conclusions:

• Simulations across diverse realistic clinical scenarios suggest current cardiac safety limits in MRI may be too stringent.
• An increase in the allowable dB/dt threshold beyond the existing IEC 60601-2-33 cardiac safety limit appears feasible.
• These findings support re-evaluating MRI safety standards for high-performance systems.