Contrast Agent Microbubble Jetting during Initial Interaction with 200-kHz Focused Ultrasound.

The initial response of microbubbles flowing through a 500-μm polycarbonate capillary to a burst of 200-kHz focused ultrasound, at peak-negative pressure amplitudes from 0.7-1.5 MPa, was investigated with dual-perspective high-speed imaging. Directed jetting through the acoustic focus is demonstrated according to the pressure gradients acting across the cavitating microbubbles. At lower amplitudes, repeated microbubble-jetting is accompanied by sudden, intermittent translation. At higher amplitudes a rebound jet also forms, before disintegration into a cavitation cloud.