Reducing MRI RF-induced heating for the external fixation using capacitive structures

Abstract

This paper presents a generic method to reduce the radiofrequency (RF) induced heating of external fixation devices during the magnetic resonance imaging (MRI) procedure. A simplified equivalent circuit model was developed to illustrate the interaction between the external fixation device and the MRI RF field. Carefully designed mechanical structures, which utilize capacitive reactance from the circuit model, were applied to the external fixation device to mitigate the coupling between the external fixation device and the MRI RF field for RF-induced heating reduction. Both numerical and experimental studies were performed to demonstrate the validity of the circuit model and the effectiveness of the proposed method. By adding capacitive structures in both the clamp-pin and rod-clamp joints, the peak specific absorption rate averaged in 1 gram (SAR1g) near the pin tips were reduced from 760.4 W kg−1 to 12.0 W kg−1 at 1.5 T and 391.5 W kg−1 to 25.2 W kg−1 at 3 T from numerical simulations. Experimental results showed that RF-induced heating was reduced from 7.85 °C to 1.01 °C at 1.5 T and from 16.70 °C to 0.32 °C at 3 T for the external fixation device studied here. The carefully designed capacitive structures can be used to detune the coupling between the external fixation device and the MRI fields to reduce the RF-induced heating in the human body for both 1.5 T and 3 T MRI systems. However, as RF-induced heating is very device and design specific all devices must be thoroughly tested based on its final design.