Numerical Study on MRI RF Heating for Circular External Fixators under 1.5T MRI

Tissue heating due to radio frequency (RF) energy absorption in human body for patients in a Magnetic Resonance Imaging (MRI) environment is one of the primary concerns about MRI related safety issues for patients, especially with the presence of sizable metal implants such as circular external fixation devices. This paper proposes a novel method to evaluate the MRI RF induced heating effects of circular external fixation devices utilizing an innovative leg phantom. A number of essential geometrical parameters, i.e. number of screws and wires, ring frame diameter, strut length, and insertion angle were numerically investigated to study the RF induced heating mechanism and behaviors of circular external fixation devices. Numerical results suggest that non-wire configuration with fewer screws, large ring frame size, relatively large strut length and the maximum insertion angle pointing outwards may lead to the worst case MRI RF coil induced heating. The peak spatial average specific absorption rate (SAR) over 1 gram can approach 341.3 W/kg with a 2 W/kg whole body SAR.