Behavior of bubbles of slowly permeating gas used for ultrasonic imaging contrast.

RATIONALE AND OBJECTIVES: The authors predict behavior of blood cell-sized bubbles containing a foreign gas that slowly crosses a gas-liquid interface. Such bubbles are being developed for ultrasonic contrast. METHODS: Using appropriate coefficients for N2, O2, CO2, and foreign gases, the authors simulate diffusion between bubbles and blood with a numerically solved equation system. RESULTS: Within 30 seconds after intravenous injection of bubbles, entrance of endogenous gases more than doubles the radius. In vivo size and duration of the bubbles are quantitatively related to the amount of the foreign gas inside. Size and ultrasonic imaging effectiveness of the circulating bubbles become larger in lungs than in the rest of the circulation. As the foreign gas is lost, imaging effectiveness diminishes more rapidly than bubble radius. CONCLUSIONS: Bubbles of slowly permeating gas change size and composition after injection and also during their passage through different parts of the circulation.