Effect of Weight Input in Magnetic Resonance Imaging System on Radio-Frequency-Induced Heating of Metallic Implants

Abstract

Radio-frequency-(RF)-induced heating in clinical magnetic resonance imaging (MRI) may pose risks to patients with metallic implants. The specific absorption rate (SAR), a representative index for the estimation of a temperature increase, may be influenced by the weight input in the MR system. We investigate the RF-induced heating of implants as a function of the weight input in the MRI system. The employed measurement method for the implant heating conformed to the American Society for Testing and Materials (ASTM) F2182-11a criteria. Two different implants (titanium-alloy humeral nail and stainless-steel shaft) were analyzed. All experiments were performed using a clinical 1.5-T MR system. MRI was performed using a transmit/receive radio-frequency body coil at a whole-body average SAR of 2.0 W/kg for 15 min. The weight input in the system was in the range of 10–200 kg. Temperature measurements of the implant tip were performed using a fiber optic thermometer system. For a weight of 60 kg, the highest temperature changes for the humeral nail and stainless-steel shaft were 3.9 °C and 5.9 °C, respectively, while for a weight of 200 kg, the highest temperature changes were 9.9 °C and 12.4 °C, respectively. The highest temperature change increased with the weight in the range of 10–140 kg. These findings suggest that even at a permissible SAR level, there are potential risks of RF heating on patients with implants, owing to the large input weight in the MRI system.