| The research presented in this dissertation investigates pacemaker lead tip heating due to the radiofrequency (RF) magnetic field applied during MRI procedures for 1.5 Tesla MRI systems. The applied 64 MHz radiofrequency magnetic field induces an electric field and eddy currents in the human body which can be spatially concentrated by metallic implants. Pacemaker leads are elongated conductive structures that behave as antennas, coupling to the specific wavelength of the RF field. The RF induced heating at the pacemaker lead tip depends upon a variety of factors. This dissertation addresses conventional in vitro temperature measurements, computer modeling, and novel bench top measurements to examine the effects of lead length, termination condition, electrical conductivity, electric field strength, and lead impedance on pacemaker lead tip heating.;This dissertation has resulted in several clinically relevant findings. Firstly it shows that abandoned leads may present a higher risk for RF induced pacemaker lead tip heating than pacemaker attached leads, therefore calling into question MR procedures for patients with abandoned leads. Secondly, pacemaker lead tip heating is shown to be a function of solution conductivity at the lead tip, exhibiting peak heating between 0.2 and 0.6 Siemens/meter (S/m). Given that normal cardiac tissue has a conductivity near 0.6 S/m and scar tissue has an conductivity near 0.01 S/m, the presence of scar tissue around the pacemaker lead tip might reduce the risk of thermal damage, based on the difference in electrical conductivity between the tissue types.;This dissertation also describes new methods to examine pacemaker lead tip heating. The first such method showed that electromagnetic computational models of the RF field can be used to evaluate the average electric field along a given lead path, which in turn showed a quadratic correlation to pacemaker lead tip heating measurements. The second new method was the electrical characterization of the pacemaker leads. This method showed that pacemaker leads exhibited resonant behavior at 64, showing a strong dependence on lead length and termination condition. These findings have lead to a better understanding of several key factors that control pacemaker lead tip heating. |
