The Tissue-reduced Virtual Family Models for RF-induced Heating Evaluation of Passive Medical Implants at 1.5 T and 3 T

RF-induced heating is an important safety concern for patients with implantable medical devices under magnetic resonance imaging (MRI) scanning. The implanted device may lead to a high temperature rise near device edges and cause tissue damage. Thus, the RF-induced heating near the device needs to be properly evaluated for the safety of patients. The study in ASTM phantom and human models is adopted to evaluate the RF-induced heating near the medical implants. To make the experiment in human models more practical, the tissue-reduced virtual family models were proposed for RF-induced heating simulation and possible experiments in the future. Simplified human body models with a reduced number of tissues were developed using the Gaussian Mixture Model (GMM). Different tissues were grouped into several clusters based on the electrical parameters. Using three human body models (the Duke, the Ella, and the FATS) from the virtual family, electromagnetic simulations were conducted for the original and simplified human models under 1.5 T and 3 T MRI systems. The electric field distributions were extracted for comparison. To investigate the performance of the proposed tissue-reduced virtual family models on RF-induced heating evaluation for the passive device, some representative passive device systems were implanted in the original virtual family models, tissue-reduced virtual family models, and ASTM phantom for simulation. The studied device systems are the standalone screw system, the pedicle screw system, the plate and screw system, and the stent system. They were implanted in the clinical positions in the human models and in the fixed position in the ASTM phantom as required by the ASTM standard. The simulated results of specific absorption rate averaged to 1 gram (SAR1g) near the device at 1.5 T and 3 T in the human models and ASTM phantom were extracted for comparison.