IV injection of air-filled human albumin microspheres to enhance arterial Doppler signal: A preliminary study in rabbits

When air-filled human albumin microspheres are injected IV, they have been shown to traverse the pulmonary circulation and markedly influence the echogenicity of the left atrium and ventricle. We studied the possibility that the microspheres can be used to enhance the Doppler signal from systemic arteries and the portal vein. Doppler sonography of the aorta, renal artery, intrarenal branch, and portal vein was performed after the IV injection of saline or microspheres in doses of 1.0, 0.5, 0.3, and 0.1 ml in four rabbits. With appropriate blinding of the observers, subjective estimates of enhancement of the Doppler signal were made in each case. All injections of saline had no detectable effect. All four doses of microspheres enhanced the Doppler signal in the aorta in all rabbits. Signals from the renal artery enhanced in all rabbits after injections of 0.3 ml or greater, but in only two rabbits after 0.1 ml. Although the 1.0-ml dose enhanced the Doppler signal from the intrarenal arterial branch in all rabbits, the 0.5- and 0.3-ml doses enhanced signals in two and the 0.1-ml dose in one. The effect was typical for bolus IV injections. The mean time from injection to onset of enhamcement was 5 sec and the effect lasted for 12 sec. Portal venous signals were evaluated in three rabbits. Ten injections were made, four at 1.0 ml and two at each of the lesser doses. Portal vein signals enhanced after all four injections of 1.0 ml of microspheres but after only one of the six injections of lower doses. Our results show that the IV injection of air-filled human albumin microspheres enhances the Doppler signal from systemic arteries and the portal vein and that the microspheres have the potential to serve as a contrast agent for Doppler sonography in humans.