A Feasible Method to Evaluate RF-Induced Heating Behavior of Passive Orthopedic Implants in Human Body
Magnetic resonance imaging (MRI) radio frequency (RF) -induced heating is one of the most important concerns of MRI safety for patients with implantable medical devices. Due to the difficulties of performing direct study of the RF-induced heating in human body for an implantable medical device, the current standard method is to investigate the RF-induced heating in a standard and fully controlled phantom, which is filled with a homogeneous media to mimic the human body tissues. However, the RF-induced heating in a homogeneous regular shaped media is different from that in a heterogeneous human body, especially patients with orthopedic healthcare products. Numerical studies were already conducted to illustrate the difference of RF-induced heating on medical plates between phantom and human body. It is necessary to study the intrinsic mechanism of RF-induced heating in heterogeneous human body with passive implantable medical device and evaluate it with a feasible accurate method. Numerical modeling and simulations are conducted to study the RF-induced heating for typical orthopedic implants, such bone plates, hip prosthesis, and tibia intramedullary nails, in 1.5T and 3T magnetic resonance (MR) environment. Comparison results of RF-induced heating between phantom and human body are conducted to show the disadvantages of phantom. In order to study the mechanism of RF-induced heating for passive orthopedic implants, Huygens source and heterogeneous phantom are applied which could illustrate the effect of incident field and medium, respectively. Additionally, a homogeneous human-shape phantom is applied to study the RF-induced heating for each orthopedic implant. The effect of medium electric properties on the incident electric field distribution inside phantom structure are investigated. And local low lossy medium is added to mimic the effect of human bone tissue on RF-induced heating. Based on these results and analysis, a new phantom structure is proposed to properly evaluate the RF-induced heating behavior of passive orthopedic implants. Compared to traditional ASTM phantom method, the new phantom structure could achieve the exact RF-induced heating properties for passive orthopedic implants.