MR-induced heating of pacemaker leads: A parameter study of contributing factors based on multi-scale modeling

Other conference contribution, 2011

Magnetic resonance imaging (MRI) is a valuable tool for diagnostic imaging in healthcare and the number of examinations using this imaging modality increases each year. At the same time, pacemakers and other types of active implantable medical devices (AIMD) are getting increasingly common. Unfortunately, patients with an AIMD are currently deprived of the benefits of MRI due to the potentially harmful interactions of the implant with the electromagnetic fields present during MRI. In particular, currents induced by the radio frequency (RF) field can give rise to excessive heating near sharp corners and edges of the implant. The occurrence of such heating at the electrodes of a pacemaker lead can result in reduction or loss of the pacemaker’s pacing ability. As a consequence, there is a need for MR-safe pacemaker systems. Experiments and numerical modeling have been frequently used for investigations of the heating phenomenon. Such modeling is difficult due to the heterogeneity of the human body, the multi-scale nature of the problem, and inter-patient variations in factors like implant configuration. In this work, we model a wide range of length scales of the problem simultaneously. The modeled MRI birdcage antenna and the human-body phantom have sizes of approximately one fifth of a wavelength whereas the helix-shaped conducting wires of the bi-polar pacemaker lead vary on a length scale of roughly one thousandth of a wavelength. The model being entirely parameterized, we perform parameter studies to investigate how the heating is influenced by different factors, including the dielectric constants of the phantom material, the number of wire turns of the conductors, and the radii of the helices. Furthermore, implications of these results for the design of MR-safe pacemaker leads are discussed.