Real-time monitoring of high intensity focused ultrasound focal damage based on transducer driving signal

Abstract

Real-time monitoring of high intensity focused ultrasound (HIFU) focal region is a key problem in clinical treatment of focused ultrasound. At present, the change of strong echo in B-ultrasound image is often used in clinical practice to monitor tissue damage in the focal area. However, the strong echo in B-ultrasound image is mostly related to cavitation and boiling bubbles in the focal area, which cannot monitor the treatment status accurately or in real time. In the HIFU treatment, the focal area tissue will be accompanied by changes in temperature, cavitation, boiling, and tissue characteristics. The acoustic load on the surface of the transducer is also constantly changing. To solve this problem, a real-time detection platform of transducer voltage and current is built in this work, which can sense the change of focal area tissue state by measuring the electrical parameters of the transducer. The experimental results show that the stability of the phase difference of the transducer driving signal will be different (the fluctuation amplitude will be different) when different media are placed on the surface of the transducer to change the acoustic load on the surface of the transducer. The fluctuation amplitude of the phase difference of the driving signal will be larger than that in the water when the iron plate is placed in the focal plane. However, the phase fluctuation amplitude will be much smaller than that in the water where the beef liver is placed. This shows that different acoustic loads can cause the electrical parameters of the transducer to change. The isolated bovine liver tissue is used as the HIFU irradiation object, and the results of the phase difference change are compared with the results of the isolated bovine liver tissue damage. The experimental results show that the phase of the transducer voltage and current will change from relatively stable to large fluctuations during the HIFU irradiation. At this time, obvious damage can be seen in the focal region when the irradiation is stopped, and the grayscale of B-ultrasound image has no significant change. In addition, when the cavitation occurs in the focal region, the fluctuation amplitude and range will turn larger. The damage area of the lower focal area under the monitoring method is smaller than that under B-ultrasonic monitoring, and the over input of radiation dose can be avoided. This method can provide a new research scheme and means for HIFU focal area tissue damage monitoring.