MRI scanner-independent specific absorption rate measurements using diffusion coefficients

Objective: The purpose of this study was to measure specific absorption rate (SAR) during MRI scanning using a human torso phantom through quantification of diffusion coefficients independently of those reported by the scanner software for five 1.5 and 3 T clinical MRI systems from different vendors. Methods: A quadrature body coil transmitted the RF power and a body array coil received the signals. With diffusion tensor imaging, SAR values for three MRI sequences were measured on the five scanners and compared to the nominal values calculated by the scanners. Results: For the GE 1.5 T MRI system, the MRI scanner-reported SAR value was 1.58 W kg^-1 and the measured SAR value was 1.38 W kg^-1. For the Philips 1.5 T MRI scanner, the MRI system-reported SAR value was 1.48 W kg^-1 and the measured value was 1.39 W kg^-1. For the Siemens 3 T MRI system, the reported SAR value was 2.5 W kg^-1 and the measured SAR value was 1.96 W kg^-1. For two Philips 3 T MRI scanners, the reported SAR values were 1.5 W kg^-1 and the measured values were 1.94 and 1.96 W kg^-1. The percentage differences between the measured and reported SAR values on the GE 1.5 T, Philips 1.5 T, Siemens 3 T, and Philips 3 T were 13.5, 6.3, 24.2, 25.6, and 26.6% respectively. Conclusion: The scanner-independent SAR measurements using diffusion coefficients described in this study can play a significant role in estimating accurate SAR values as a standardized method.