Modeling and measuring cardiac magnetostimulation

Magnetic resonance imaging (MRI) employs time-varying magnetic gradient fields, which induce electric fields (E-fields) in the patient that can potentially stimulate the heart. The performance of novel gradient systems is increasingly restricted by regulatory safety limits, thus motivating a deeper understanding of cardiac stimulation (CS) in MRI. This thesis investigates the thresholds and mechanisms underlying CS using an integrative approach of modeling and measurements. First, a numerical modeling framework was developed that combines E-field simulations in computational body models with electrophysiological cardiac fiber models to predict stimulation thresholds and sites in the heart. The CS thresholds predicted for two commercial gradient systems were >10-fold higher than the regulatory limits. Second, cardiac magnetostimulation thresholds were measured in ten healthy pigs using magnetic field pulses created by capacitor discharges into a coil. The average threshold E-field in the porcine heart was 92.9 pm 13.5 V/m. CS thresholds predicted in individualized porcine models derived from MR images reproduced the measurements with deviations of