Session S94.6

Numerical Modeling of Current Distribution in and near the Tips of Cardiac Pacemaker Electrodes during Magnetic Resonance Imaging

SA Seitz*, O Dössel

Karlsruhe Institute of Technology
Karlsruhe, Germany

The number of patients with pacemakers and implanted defibrillators is constantly increasing due to the demographic development. At the same time, for this type of patients, Magnetic Resonance Imaging (MRI) is one of the most valuable diagnostic tools. But several studies describe hazardous effects caused by the interaction of the occurring RF fields and the pacemaker-electrode system during MRI procedures. The most significant are malfunctions of the sensing electronics and heating at the tip of the electrode, in some cases leading to coagulation of the surrounding cardiac tissue. This may for example result in a reduced stimulus efficacy. Aim of the presented study was the development of high-resolution electrode computer models to examine the occurring current distributions inside the electrodes and on the boundaries between electrode and cardiac tissue. The examined models consisted of straight wires and of realistic reproductions of commercially available electrodes containing multiple helix shaped and straight wires. A birdcage coil comparable to a RF-coil in MRI devices generated the stimulating rotating B-field with 64 MHz as used in 3 T systems. The electrodes were placed in a saline filled plexiglass box to provide dielectric properties similar to human tissue. All simulations were carried out with Finite Difference Time Domain software. The presented simulation setup allowed the detailed examination of different electrode configurations to adapt to the variety of electrodes used in clinical practice. As a result it is demonstrated that the skin effect has a strong influence on impedance and current distribution in the pacemaker electrode wires and at the electrode tip.

(Abstract Control Number: 204)