Temperature Distribution In The Medium Containing Contrast Agent Microbubbles In HIFU Field

摘要

HIFU (High Intensity Focused Ultrasound) treatment combined with microbubbles as a heat transducer has currently been investigated. It has been indicated from experimental and numerical studies that microbubbles have a potential to enhance the heat deposition around the focal region of ultrasound. In order to realize this method, it is needed that the coagulation region in the tissue which contains microbubbles is well-controlled, but the behavior of thermal energy in the tissue becomes more complicated by the addition of the microbubbles. In this study, the temperature distribution in the medium with microbubbles is analyzed in detail. This time, a thermal liquid crystal (TLC) sheet is used for the measurement of temperature distribution. The TLC is put in a polyacrylamide gel and the focused ultrasound is irradiated. In the case of no bubbles, the shape of the high temperature region was ellipse at the focal region. In the case of some bubbles, the shape grew more complicated and its area became larger. The position of the high temperature region moved to the front of the geometric focal point. The microbubbles oscillate and radiate heat energy around them, and the attenuation effect of ultrasound becomes larger. In the case of too many bubbles, the temperature at the geometric focus didn't become so high. The bubbles shield the most of ultrasound energy. It is very important to choose the optimal conditions of microbubble-enhanced HIFU treatment, considering these phenomena.