Pulse duration dependence of cavitation emissions and loss of echogenicity from ultrasound contrast agents insonified by Doppler pulses

Careful determination of stable and inertial cavitation thresholds of UCAs exposed to pulsed ultrasound is required for their safe use in diagnostic and therapeutic applications. Echogenic liposomes and Definity® were diluted in porcine plasma and pumped through a physiological flow phantom. UCAs were insonified with pulsed Doppler ultrasound at three pulse durations (3.33 µs, 5.83 µs and 8.33 µs) over a range of peak rarefactional pressure amplitudes (0.06-1.9 MPa). A 10-MHz focused passive cavitation detector (PCD) was used to record cavitation emissions. PCD signals and B-mode images of UCAs and degassed water were acquired during insonation. Thresholds of stable and inertial cavitation, and loss of echogenicity were determined by piecewise linear fits of the cavitation powers and mean gray scale values, respectively. The stable cavitation thresholds were found to be lower than the inertial cavitation thresholds at each pulse duration setting. The thresholds of loss of echogenicity and stable and inertial cavitation were found to be dependent on pulse duration. The relationship between loss of echogenicity and cavitation emissions will be discussed in the context of using onscreen echogenicity to indirectly monitor cavitation during ultrasound-mediated therapy with UCAs. [Supported by NIH R01 HL059586.]