An MRI scanner-independent radiofrequency dosimeter for the estimation of RF power deposition with a human torso phantom

An assessment of radiofrequency (RF) power deposition independent of the information provided by MRI scanners is thus desirable. We developed a novel scanner-independent RF dosimeter based on measurements of the resistance of a thermistor that dissipates the RF power during scanning. With the RF dosimeter, the RF power deposition for four MRI sequences with specific absorption rate (SAR) values (0.1-3.3 W/kg) was measured on five different scanners and the correlation between the RF dosimeter reading and the SAR levels calculated by the scanners was investigated. The novel RF dosimeter showed a linear relationship between the RF power deposition and the scanner-reported whole-body averaged SAR for each scanner. However, there was a variability in the reading among different scanners. The RF dosimeter readings were 9.7 and 9.5 mW on GE 1.5 T (SAR=2.6 W/kg), 3.6 and 3.7 mW on Philips 1.5 T (SAR=3.3 W/kg), 9.5 and 8.6 mW on Siemens 3 T (SAR=3.0 W/kg), and 4.7 and 3.9 mW on Philips 3 T (SAR=2.6 W/kg), respectively. The scanner-independent RF dosimeter developed in this study can play a significant role in checking the accuracy of scanners’ SAR values as a standardized method for measuring the RF power deposition for MR safety.