Resonance ultrasonic measurements of microscopic gas bubbles

The positive identification and location of stationary or moving bubbles in human tissue is a persisting problem in the study and management of dysbarism. Since bubbles are resonant scatterers of ultrasound, while structures such as red-cell clumps and tissue interfaces are not, it is possible in principle to identify bubbles uniquely and to determine their position and size. A pulsed, ultrasonic echo-ranging system was expressly designed to exploit the principle of bubble resonance, and was evaluated for bubble identification and location in two experiments. Echos from bubbles in a water bath were computer-processed to reveal a distinct "line-narrowing" in the Fourier domain, which is diagnostic of gas bubbles. An increase in echo signal from a dog's jugular vein upon distal bubble injecton was obtained as evidence for in vivo bubble detection. We conclude that the exploitation of the bubble resonance principle can offer a safe, noninvasive technology for micro-bubble identification, location, and size determination in many tissues. This technology appears capable of measuring stationary bubbles in tissue spaces or impacted in blood vessels as well as those moving in the vascular system.