Transient cavitation dynamics of vaporized perfluorocarbon nanodroplets measured with an acoustical camera

Perfluorocarbon nanodroplets are metastable phase-change contrast agents that convert into gas bubbles on demand through acoustic droplet vaporization (ADV). Their transient radial dynamics are difficult to measure without high-speed optical imaging. An acoustical camera approach characterizes post-ADV bubble dynamics acoustically. Perfluoropentane nanodroplets were activated with a 5 MHz focused pulse (peak negative pressure ≈5 MPa) and simultaneously probed at 35 MHz, with the side-scattered signal detected by an orthogonal receiver. Scattered amplitude scales with bubble radius, so the Hilbert-transformed envelope yields a relative radius-time response with microsecond resolution, revealing rapid growth and collapse consistent with transient inertial cavitation. Collapse times give a mean maximum bubble radius of 13.2 ± 1.8μm (N=475), roughly 300 times the >∼46 nm precursor radius, confirming strongly inertial overshoot. Deriving from pulse timing rather than amplitude, this estimate is independent of bubble position within the probe beam. The 35 MHz focal zone is approximately four times narrower than the 5 MHz activation zone, so the detected amplitude reflects lateral position rather than size, and only 7% of events fall within ±20% of the timing estimate. The technique offers a low-complexity route to quantifying post-ADV cavitation dynamics and comparing nanodroplet formulations.