Scavenging dissolved oxygen via acoustic droplet vaporization

Abstract

Acoustic droplet vaporization (ADV) has been investigated for capillary hemostasis, thermal ablation, and ultrasound imaging. The maximum diameter of a microbubble produced by ADV depends on the gas saturation of the surrounding fluid. This dependence is due to diffusion of dissolved gases from the fluid into the perfluoropentane (PFP) microbubble. This study investigated the change in oxygen concentration in the surrounding fluid after ADV. Albumin-shelled PFP droplets in air-saturated saline (1:30, v/v) were continuously pumped through a flow system and insonified by a focused 2-MHz single-element transducer to induce ADV. B-mode image echogenicity was used to determine the ADV threshold pressure amplitude. The dissolved oxygen concentration in the fluid upstream and downstream of the insonation region was measured using inline sensors. Droplet size distributions were measured before and after ultrasound exposure to determine the ADV transition efficiency. The ADV pressure threshold at 2 MHz was 1.7 MPa (peak negative). Exposure of PFP droplets to ultrasound at 5 MPa peak negative pressure caused the dissolved oxygen content in the surrounding fluid to decrease from 88 ± 3% to 20 ± 4%. The implications of oxygen scavenging during ADV will be discussed.