Session: 2H

sound transducer 24 mm in diameter and piezoelectrically active at both 1.0 & 2.0 MHz was used. Acoustic emission from 10% ethyl alcohol solutions were measured during insonation at acoustic intensity of 10 W/cm2 (1.0 & 2.0 MHz: 5 W/cm2 each) and the intensity of a subharmonic component at 0.5 MHz was calculated. SH phase shifting with a shift pitch not larger than 0.5 π and a shift interval time not shorter than 30 ms was effective in inducing cavitation as much as the SH phase is fixed to the optimum phase. We also studied the effect of SH phase shifting on sonodynamic tumor treatment. A focused ultrasound transducer 60 mm in diameter (F num. = 1) with a cross-beam arrangement at 0.5 & 1.0 MHz was used. In the presence of a newly synthesized sonodynamic agent, an amphiphilic derivative of rose bengal, the effect of shift interval time on the growth of tumor tissues implanted into a mouse was investigated. When ultrasound was exposed at an acoustic intensity of 20 W/cm2 (0.5 & 1.0 MHz: 10 W/cm2 each), the tumor growth was suppressed significantly at a shift interval time of 143 and 1430 ms but not at 14 ms. SH phase shifting at shift intervals longer than several ten millisecond was effective to induce cavitation both in vitro and in vivo. Using this result, SHS will show its best performance in sonodynamic tumor treatment. Part of this work was partly supported by National Research and Development Program for Medical and Welfare Apparatus under entrustment of the New Energy and Industrial Technology Development Organization (NEDO), Japan.