Breast MRI in the prone position: impact on RF-induced heating of active implantable medical devices

Objective: Prone (face-down) postures, commonly used in breast examination, as well as in wrist and elbow imaging, change the the induced current path in the body and therefore the incident electric fields to the implants during MR examination, potentially leading to significant variations from risk predictions made in supine postures. The goal of this work is to investigates the impact of prone breast examination postures, compared to supine MR examination postures, on the RF-induced heating of medical implants. Approach: To assess these effects, the Virtual Population anatomical model Ella was modified with breast shapes typical of a prone examination, and posed with one or both arms raised above the head. The head was positioned either adjacent to the bore wall, typical for breast MR examinations, or centrally within the bore, similar to supine positioning. The RF-induced electric fields and worst-case power depositions were compared with those from the supine Ella model for representative generic pacemaker, deep brain stimulator (DBS), and cochlear implants, at breast imaging landmarks. Main Results: The results indicate that prone positions typical of breast examination can lead to differences in incident electric field and corresponding RF-heating of, at least, up to 5 dB at 1.5 T, and up to 2.5 dB at 3.0 T, for cochlear implants, 1-2 dB for DBS, and 1 dB for pacemakers, compared to the corresponding supine imaging landmarks. Significance: These findings underscore the importance of considering patient posture in RF safety assessments of implantable medical devices in the head and neck regions. To avoid underestimation of local RF exposure near these implants, a comprehensive posture-aware safety protocol should be designed and considered during the RF safety evaluation and labeling.