Reduction of threshold for producing sonodynamic tissue damage by second-harmonic superimposition

Induction of acoustic cavitation of progressive waves is known to require much higher ultrasonic intensity than by standing waves. It has been found that acoustic cavitation can be an order of magnitude enhanced by superimposing the second harmonic on the fundamental. Synergistic effects between the fundamental and the second harmonic in the progressive wave mode were investigated using exteriorized mouse livers suspended in degassed saline. The intensity threshold for the production of focal tissue damage paired with fractional harmonic emission was significantly lowered by second-harmonic superimposition especially when a sonochemically active porphyrin had been administered to the mouse. Insonation with second-harmonic superimposition in combination with such a sonochemically active agent may have potential use for selective tumor treatment.