Safety Study of RF-induced Heating Near Cardiac Stents for 5T MRI System

Ao Shen, Mir Khadiza Akter, jianfeng Zheng, Ji Chen
University of Houston


Abstract

The U.S. Food and Drug Administration (FDA) recently cleared the 5T whole-body MRI system for clinical use. However, its different field distribution and resonant wavelength pose a safety concern for patients with im-plants. This is the first study that investigates RF-induced heating near stents of varying lengths in the right common carotid artery of an anatomically accurate human model during 5T MRI whole-body scans.

Full-wave numerical simulations were performed using FDTD-based Sim4Life (version 7.2, ZMT, Switzerland). Stents of 20, 30, 40, 50, and 60 mm in length, with a 4 mm diameter, were placed in a clinically relevant position inside the right common carotid artery of an adult male model (Duke, Age: 34 years). The model, together with the implants, was placed inside a 16-port RF coil (circularly polarized) operating at 210.8 MHz, with the stent initially centered in the isocenter location (landmark 0 mm). To assess the imaging landmark effect, the model was also shifted by -200 mm, -100 mm, 100 mm, and 200 mm along the MRI bore direction. Maximum 1g-averaged SAR near the stents was evaluated under 2 W/kg whole-body SAR condition, and thermal simulations were conducted to evaluate the 15-minute temperature rise for the worst-case configuration.

For all imaging landmarks, the highest 1g-averaged SAR was observed at the edges of the stents, with the worst case at landmark 0 mm (similar to those observed for 1.5T and 3T systems). SAR increased with stent length, starting from 12.8 W/kg for the 20 mm stent and increasing to 72.9 W/kg for the 60 mm stent (near half-wavelength at 5T). After 15 minutes of RF expo-sure, the maximum temperature rise is less than 1 °C, highlighting the similar thermal risks of 5T MRI to those observed at 1.5T and 3T.