Noninvasive estimation of temperature elevations in biological tissues using acoustic nonlinearity parameter imaging

A method for noninvasively imaging temperature would assist the development of hyperthermia. In this study, the relationships between the acoustic nonlinearity parameters and the temperatures in porcine fat and liver were obtained. The temperature elevations induced by ultrasound irradiation of porcine fat and liver were then derived inversely from acoustic nonlinearity parameter imaging. These temperature elevations were compared with theoretical predictions and with those measured by a thermocouple. The temperature elevations at the focus in the fat and liver samples measured via a thermocouple were 21.1 +/- 0.8 degrees C and 15.7 +/- 0.6 degrees C, respectively, which coincided with those obtained by acoustic nonlinearity parameter imaging (22.0 +/- 1.4 degrees C in fat and 16.9 +/- 1.1 degrees C in liver). These may be compared with the theoretical predictions of elevations of 24.0 degrees C in fat and 19.7 degrees C in liver. The results of this study show that acoustic nonlinearity imaging may be a novel method for temperature evaluation in hyperthermia.