High dielectric material in MRI: Numerical assessment of the reduction of the induced local power on implanted cardiac leads.

High dielectric materials (HDM) have been proposed in magnetic resonance imaging (MRI) to increase the signal-to-noise ratio (SNR) of the images acquired while reducing the radiofrequency (RF) absorption in tissue. The aim of this study is to assess the potential merit of using HDM to reduce power induced at the tip of an endocardial lead in patients undergoing MRI. Numerical simulations were performed using a commercial finite-differences time-domain (FDTD) software to model the RF field generated by a birdcage body coil at 64 MHz on a human body model. Two HDM pads were placed between the coil and the body model, and their effect was evaluated in terms of local induced power at the tip of a pacemaker lead. Two different patient imaging positions inside the coil (i.e., head & thorax) were studied. In both cases, the use of HDM allowed reducing the induced power (i.e., 57% reduction with head landmark, 68% with thorax landmark), while maintaining the same magnitude of B1 RMS at the isocenter of the coil. Additionally, when the HDM pads were placed at the head landmark, there was a significant decrease in the local-induced power at the tip of the implant path (58%). Conversely, there was only a 9% decrease when pads were placed at the thorax landmark. In conclusion, the study shows that when the implant is not included in the volume surrounded by the HDM, pads placed between the RF coil and the patient allow obtaining the same magnitude of B1-field with a lower input power of the RF coil, reducing significantly the local induced power around the implant. Conversely, if the implant is included in the volume surrounded by the HDM, the use of HDM can still reduce the input power necessary to obtain the same magnitude of B1-field, but the effect on the local induce power at the implant is lower in magnitude.