Zero-crossing tracking technique for noninvasive ultrasonic temperature estimation

Objective: The purpose of this study was to investigate the feasibility of a zero-crossing tracking (ZCT) technique for temperature estimation using ultrasound images. Methods: The backscattered ultrasound radio frequency (RF) echo from a heated region experiences time shifts, which have been identified as causing a gross effect on sound speed changes and thermal expansion. The ZCT technique tracks the shifts in the zero-crossing instants between preheated and postheated A-lines to estimate the echo shifts caused by local temperature changes. Compared to the conventional cross-correlation (CCR) technique, ZCT does not require intensive computational loadings for correlation operations; hence, the computational efficiency could be improved. Phantom experiments were performed to compare the results of temperature estimation by using the ZCT and CCR techniques. Results: The imaging probe was a commercial linear array, and a high-intensity focused ultrasound transducer was used as a heating source. The acquired RF echo data were processed using the ZCT and CCR techniques. The estimation results of both techniques were similar. However, the ZCT technique yielded up to 7-fold better computational efficiency than the CCR technique. Conclusions: The ZCT technique has the ability to monitor temperature changes with superior processing speed. This method could be an alternative signal-processing technique for ultrasonic temperature estimation.