Wire-based sternal closure: MRI-related heating at 1.5 T/64 MHz and 3 T/128 MHz based on simulation and experimental phantom study.

Abstract

The paper investigates factors that affect the RF-induced heating for commonly used wire-based sternal closure under 1.5 T and 3 T MRI systems and clarifies the heating mechanisms. Numerical simulations based on the finite-difference time-domain method and experimental measurements in ASTM (American Society for Testing and Materials) phantom were used in the study. Various configurations of the wire-based sternal closure in the phantom were studied based on parameter sweeps to understand key factors related to the RF-induced heating. In vivo simulations were further performed to explore the RF-induced heating in computational human phantoms for clinically relevant scenarios. The wire-based sternal closure can lead to peak 1-g averaged spatial absorption ratio of 106.3 W/kg and 75.2 W/kg in phantom and peak 1-g averaged specific absorption rate of 32.1 W/kg and 62.1 W/kg in computational human models near the device at 1.5 T and 3 T, respectively. In phantom, the simulated maximum temperature rises for 15-minute RF exposure are 9.4°C at 1.5 T and 5.8°C at 3 T. Generally, the RF-induced heating will be higher when the electrical length of the device is close to the resonant length or when multiple components are spaced closely along the longitudinal direction. The RF-induced heating related to wire-based sternal closure can be significant due to the antenna effect and capacitive mutual coupling effect related to the specific geometries of devices.