Acoustic cavitation is a typical non-thermal phenomenon induced in liquids and biotissues by the exposure of ultrasound. It will disturb transmitting ultrasonic energy and thus should be avoided between the ultrasonic source and the target. Moreover, because of the potential tissue damage through its chemical or mechanical effects, cavitation should especially be avoided in diagnostic application. Techniques for suppression of acoustic cavitation is needed to control the cavitational phenomena in such undesirable situations. Reducing agents, such as sulfites are sometimes used to suppress cavitation in water for ultrasound coagulation therapy. However, it seems that three are no reports on quantitative results about their effects. We developed an experimental system which is suitable for measuring the effects of sulfites on suppressing cavitation with an optical detector, (fig.2). The effect of sodium sulfite (1M) on suppressing cavitation was investigated in water saturated with air or nitrogen (fig.3). Sodium sulfite increased the cavitation threshold about 1.7 times in both air saturated and nitrogen saturated water. Considering to apply chemical agents for suppressing cavitation in human body, we investigated a lesstoxic reducing agent, sodium ascorbate (vitamin C). Sodium ascorbate was found to be more effective than sodium sulfite in suppressing cavitation. The cavitation threshold in water in the presence of sodium ascorbate (1M) was about 2.5 times higher than in the absence. (Fig. 4-a). Our findings indicate the possibility of chemical agents for suppressing cavitation not only in acoustic coupling fluid but also in vivo because the low toxicity of sodium ascorbate.
