Feasibility study of pulse compression technique to improve accuracy of ultrasonic temperature estimation

Purpose: In this work, we propose pulse compression technique using a chirp signal to improve accuracy of parameters including thermal expansion, propagation velocity of ultrasound, and calibration curve used for converting thermal strain data into its corresponding temperature in the therapeutic ultrasound. Methods: The performance of the proposed method was experimentally demonstrated by in vitro experiments using an egg-white phantom and a sliced porcine liver. Measurement of thermal expansion and propagation velocity of ultrasound was done by transferring the specimen from a heating bath to a measuring bath per 5°C temperature resolution. The calibration curve was implemented by combining the measured thermal expansion and propagation velocity of ultrasound. Results: In two received signals from a phantom and a sliced porcine liver, the amplitudes of pulse compressed signals were about 35 and 12.5 times higher than sinusoidal signal, respectively. Therefore, core parameters including thermal expansion, propagation velocity of ultrasound, and calibration curve used for ultrasonic temperature estimation were more accurately obtained based on the high sensitivity of pulse compression technique. Conclusions: Our study indicates that increasing the amplitude of the received signal is a critical factor in order to obtain more accurate parameters such as thermal expansion, propagation velocity of ultrasound, and calibration curve. The proposed method can be one of the potential ways to increase the sensitivity of the received signal and thus, the accuracy of temperature estimation using ultrasound can be more improved.