The effects of varying ultrasound parameters on oxygen scavenging via acoustic droplet vaporization

Abstract

Acoustic droplet vaporization (ADV) is a process that phase transitions liquid droplets into gas microbubbles via ultrasound. ADV results in oxygen scavenging from the surrounding fluid into the microbubbles. The objective of this study was to determine the effect of ultrasound parameters on oxygen scavenging. A microfluidic device was used to produce perfluoropentane droplets with a modal diameter of 1.14 ± 0.04 μm and a polydispersity index of 0.08 ± 0.02. Droplets were diluted to a concentration of 4.7 × 10−4 ± 0.4 × 10−5 ml/ml in 95% oxygenated water. The oxygen partial pressure (pO2) of the water was measured before and during ADV. An EkoSonic ultrasound catheter (2.35 MHz, 1.5 MPa peak negative pressure, 47 W pulse average power) nucleated ADV while either varying burst period or pulse duration (n = 5). Pre-ADV pO2 was 558 ± 5 mm Hg for all experiments. Peri-ADV pO2 dropped to 294 ± 6, 316 ± 10, and 356 ± 12 mmHg for a pulse duration of 17 μs and burst periods of 0.450 ms, 0.725 ms, and 1.000 ms, respectively. The peri-ADV pO2 dropped to 331 ± 14, 342 ± 10, 313 ± 10 mmHg for a burst period of 1.000 ms and pulse durations of 17.0, 23.4, and 37.9 μs, respectively. A significant difference was seen between the amount of oxygen scavenging for the lowest and highest burst periods (p = 0.0012) and pulse durations (p = 0.027).