Effects of rose bengal on cavitation cloud behavior in optically transparent gel phantom investigated by high-speed observation

Abstract

Sonodynamic treatment is a non-thermal ultrasonic method using sonochemical effect of cavitation bubbles. Rose bengal (RB) is sonochemically active and reduces cavitation threshold and therefore has potential to be an agent for sonodynamic treatment. For the effectiveness and safety of the treatment, controlling cavitation is crucial. In our previous study, we have suggested high-intensity focused ultrasound (HIFU) employing second-harmonic superimposition, which can control cavitation cloud generation by superimposing the second harmonic onto the fundamental. In this study, to investigate the effects of RB on cavitation behavior, a polyacrylamide gel phantom containing RB was exposed to second-harmonic superimposed ultrasound and the generated cavitation bubbles were observed by a high-speed camera. The gel contained three different concentrations of RB, 0, 1, and 10 mg/L. The ultrasonic intensity and exposure duration were 40 kW/cm2 and 100 μs, respectively. The fundamental frequency was 0.8 MHz. In the results, the amount of the incepted cloud became higher and the lifetime of bubbles became longer as the RB concentration increased at high reproducibility. The observed RB concentration dependence suggests that the amount of cavitation bubbles can be controlled using second-harmonic superimposition. The observed lifetime extension of bubbles can not only promote sonochemical but also enhance thermal bioeffect.