Effect of boundary constraints and hydrostatic pressure on the vaporization threshold of low boiling-point phase-change contrast agents

Phase-change contrast agents (PCCAs) can be vaporized using ultrasound for therapeutic and diagnostic applications. It has been previously reported that the in vivo vaporization threshold is higher than in vitro. Here, we explore the role of boundary constraints and increased hydrostatic pressure on the vaporization threshold of PCCAs. Vaporization was performed in tubes of different inner diameters and a chamber under different hydrostatic pressures. Additionally, the vaporization threshold was found in the kidneys of rats. The results show that the vaporization threshold increases with a decreasing tube diameter, and that hydrostatic pressure has no effect of the pressure required for vaporization. The in vivo threshold that was found was higher than the in vitro experiments, but the effect of boundary constraints does not account for all the difference between in vivo and in vitro.