Effect of second-harmonic phase on producing sonodynamic tissue damage

It was recently found that sonochemically active cavitation can be induced at relatively low ultrasonic intensity when the second harmonic is superimposed onto the fundamental. The intensity threshold for the production of focal damage in mouse liver tissue with emission of fractional harmonics was lowered by an order of magnitude via second-harmonic superimposition especially when a sonodynamically active agent was administered to the mouse. Such synergistic effects between the fundamental and the second-harmonic were marked in the range of second-harmonic phase giving relatively large peak rarefaction. In contrast, higher intensity thresholds were observed in the phase range giving relatively high positive peak pressure. This tendency was consistent with the theoretical prediction