An All-Ultrasound-Based System for Real-Time Monitoring and Sonication of Temperature Change and Ablation

Previously, we introduced a new harmonic motion imaging (HMI) technique for simultaneous monitoring and generation of ultrasound therapy treatment using a single element focused-ultrasound and one pulse-echo transducer. The new HMI technique uses an amplitude-modulated beam (instead of using two beams) that has a stable focal zone for the applied harmonic radiation force. The harmonic radiation force was generated by a 4.68 MHz focused transducer and a 7.5 MHz pulse-echo transducer was used to acquire RF echoes. The RF echoes were recorded and used to estimate tissue displacements during sonication. The new HMI technique has been shown to provide tissue displacement information during ultrasound therapy. In this paper, a study on the temperature dependence of the new HMI method is presented. The sonication time used applied was approximately equal to 80 seconds at maximum acoustic intensity of 658 W/cm² at the focus. The experiments were performed on bovine tissues in vitro. The results show that the temperature elevation at the focal zone during sonication rises rapidly until it reaches a temperature higher than 50degC, which produces tissue damage. The new HMI technique provides temperature-related tissue displacement changes using the same transducer, which makes it simple for monitoring temperature rise and lesions formation during high intensity focused ultrasound (HIFU) treatment