Numerical Analysis of RF-Induced Heating While Wearing Face Mask at Magnetic Resonance Imaging

ABSTRACT

In response to the unprecedented COVID-19 pandemic, wearing face masks in public places and common facilities has been strongly recommended to help prevent the further spread of the virus. However, conductive components of the face mask carry the potential risk of radio-frequency (RF)-induced heating when exposed to an RF electromagnetic field, particularly during magnetic resonance imaging (MRI). In this study, a realistic human head model wearing a face mask exposed to a strong RF electromagnetic field in 1.5 T, 3 T, and 7 T MRI was simulated. A nose wire in contact with the skin and a mask sheet with relatively high electrical conductivity, emulating a silver nanoparticle-coated face mask, was modeled to investigate the worst case of RF-induced heating that could occur during the MRI scan. 24 scenarios were simulated by using finite-difference time-domain (FDTD)-based electromagnetic solver and thermal-transient solver from Sim4Life commercial simulation software. According to the results, a notable enhancement in the specific absorption rate (SAR) and temperature rise was observed in the local region of the skin where the wire contacted the skin around the edge of the high-conductive mask sheet. In particular, a maximum of a 12-fold increase in mass-averaged SAR and a temperature increase of more than 8.0 degrees C occurred because of the conductive face mask at 3 T, compared to the normal polymer-based face mask with low conductivity. Our results confirmed that the degree of RF-induced heating due to the face mask could be completely different depending on the RF frequency of the MRI, location where the nose wire contacted the skin, and conductivity of the mask sheet. To the best of our knowledge, this is the first study to assess the face mask as a factor for RF-induced heating during MRI. These findings are important for providing a safety guide that allows patients to safely undergo MRI while wearing a face mask during the COVID-19 pandemic.