A new method to improve RF safety of implantable medical devices using inductive coupling at 3.0 T MRI

Abstract

Objective: To enhance RF safety when implantable medical devices are located within the body coil but outside the imaging region by using a secondary resonator (SR) to reduce electric fields, the corresponding specific absorption rate (SAR), and temperature change during MRI.

Materials and methods: This study was conducted using numerical simulations with an American Society for Testing and Materials (ASTM) phantom and adult human models of Ella and Duke from Virtual Family Models, along with corresponding experimental results of temperature change obtained using the ASTM phantom. The circular SR was designed with an inner diameter of 150 mm and a width of 6 mm. Experimental measurements were carried out using a 3 T Medical Implant Test System (MITS) body coil, electromagnetic (EM) field mapping probes, and an ASTM phantom.

Results: The magnitudes of B₁⁺ (|B₁⁺|) and SAR_1g were reduced by 15.2% and 5.85% within the volume of interest (VoI) of an ASTM phantom, when a SR that generates opposing electromagnetic fields was utilized. Likewise, the Δ|B₁⁺| and ΔSAR_1g were reduced by up to 56.7% and 57.5% within the VoI of an Ella model containing a copper rod when an opposing SR was used.

Conclusion: A novel method employing the designed SR, which generates opposing magnetic fields to partially shield a sample, has been proposed to mitigate the risk of induced-RF heating at the VoI through numerical simulations and corresponding experiments under various conditions at 3.0 T.

Keywords: Computational modeling; FDTD; Implantable medical device; Inductive coupling; SAR; Secondary resonator.