Observations of microbubble translation near vessel walls.

Abstract

To exploit the potential clinical applications of ultrasound contrast agents, it is important to understand the basic physics of bubble-vessel interactions. In this work, high-speed micrography was used to investigate the dynamics of microbubbles inside vessels from ex vivo rat mesentery under the exposure of a single ultrasound pulse. The study included arterioles and venules. The ultrasound pulses were about 2 μs long with a center frequency of 1 MHz and peak negative pressures between 1 and 7 MPa. High-speed photographs reveal that interactions between microbubbles and vessels caused bubbles to move away from nearby vessel walls. The motion depended upon the standoff distance between the bubble and the nearest vessel wall, where a normalized standoff γ can be defined as the ratio of the standoff distance to the maximum bubble radius. For γ <1, obvious bubble movement away from the nearby vessel wall was observed during collapse. At γ=0.3, a bubble inside a venule was observed to translate over 16 μm during 1.5 μs, achieving velocities over 10 m/s. Bubble translation away from the vessel wall may be caused by the rebound of the vessel wall that was distended during bubble expansion. [Work supported by NIH Grants EB00350, AR053652, DK43881, and DK070618.]