Real‐time passive acoustic monitoring of tissue damage during thermal ablation by high‐intensity focused ultrasound.

Abstract

This work proposes a novel method for monitoring tissue ablation by high intensity focused ultrasound (HIFU) in real time. The proposed method employs the passively acquired acoustic signal emitted from the HIFU focus throughout an exposure. A total of 161 exposures were performed in seven freshly excised ox livers using 1.067‐MHz HIFU at a 95% duty cycle. Acoustic emissions were recorded using a 15‐MHz passive detector aligned confocally and coaxially with the HIFU transducer. Lesion presence and size were ascertained by slicing the tissue in the transverse and axial focal planes post‐exposure. Results demonstrate that the successful formation of HIFU lesions in ex vivo ox liver is highly correlated with the presence of pronounced dips in the magnitude of the received signal at integer harmonics of the insonation frequency. Optimization and validation of a detection algorithm based on this observation show that the detector agrees with the post‐exposure lesioning assessment in 75% of cases overall, and that the error rate drops further for exposures shorter than 1 s or longer than 2 s. Such a detector could therefore provide a low‐cost means of effectively monitoring clinical HIFU treatments passively and in real time.