Effect of focal spot scanning method in agarose gel and chicken breast on heating efficiency in cavitation-enhanced ultrasonic heating

Abstract

High-intensity focused ultrasound (HIFU) treatment is a non-invasive method of cancer treatment. In a HIFU treatment, ultrasound is focused on a target tumor tissue leading to temperature rise that coagulates the tissue. The treatment has a problem of long treatment time because a tumor is usually larger than the focal spot of HIFU. To reduce the treatment time, cavitation bubbles can be used for accelerating ultrasonic heating. Additionally, the heat conducting away from a focal spot can be utilized by properly scanning the focus. In this study, three sequences of scanning the focus to form six foci were compared by observing cavitation bubbles and measuring temperature rise in an excised chicken breast tissue and an agarose gel as well as a thin slice of tissue sandwiched between agarose gels. The results showed that there were differences in the behavior of bubbles and the efficient sequence between the tissue and the gel.

Effect of intended shift in propagation direction of cavitation generation position on coagulation position in bubble-enhanced ultrasonic heating

“…2) and chicken breast tissue were used as HIFU exposure targets. The sliced tissue phantom was created by combining low-mp agarose gel and chicken breast tissue, modified from a method described in a previous study, 33) in order to optically observe bubble behavior in the tissue during HIFU exposure using a high-speed camera. First, a half-layer of 0.8% low-mp agarose gel was prepared by dissolving lowmp agarose (Nippon Gene, Agarose XP) in 0.9% saline solution, pouring it into a mold, and refrigerating it for 2 h. The surface of the gel was then melted with a heated aluminum block, and a 2 mm thick slice of chicken breast was placed on the surface of the gel that had become liquid.…”

“…Previous studies have investigated the heating efficiency of bubble-enhanced ultrasonic heating using tissue-mimicking gels. [31][32][33] Bubbles generated in a tissue were observed by using a hybrid phantom consisting of tissue and agarose gel. 33) However, temporal changes in the region of cavitation bubble generation in bubble-enhanced ultrasonic heating have not been studied.…”

“…[31][32][33] Bubbles generated in a tissue were observed by using a hybrid phantom consisting of tissue and agarose gel. 33) However, temporal changes in the region of cavitation bubble generation in bubble-enhanced ultrasonic heating have not been studied. The effect of shifting the focus of the trigger pulse in the direction of ultrasound propagation to adjust the bubble-generation region was investigated on the coagulation region for a single focal shift distance, 34,35) but it has not been studied for various focal shift distances.…”

Determination of thermal and mechanical indices of an ultrasound probe with an inclined beam-axis in accordance with the new JIS (or IEC Standards)

“…Research on ultrasonic diagnosis [1][2][3][4][5][6][7][8][9][10][11][12][13] and ultrasonic therapy 14,15) are important in developing safe and highperformance medical ultrasonic equipment. As for ultrasonic diagnostic equipment, precise and practical test methods for the determination of thermal and mechanical indices related to medical diagnostic ultrasonic fields are required to ensure the safety of patients in diagnosis.…”

Cavitation threshold pressure of focused ultrasound observed with sonochemiluminescence

“…The heating induced by cavitating bubbles enhances tissue coagulation, which helps to damage a lesion. 5,6) Numerous studies have been performed to establish the threshold of sound pressure for cavitaion inception. [7][8][9][10][11][12] Apfel and Holland 13) obtained the theoretical threshold pressure required for cavitation to occur as a function of preexisting nuclei radius.…”