Lipid-coated ultrastable microbubbles as a contrast agent in neurosonography.

Lipid-coated microbubbles can be synthesized from selected lipid monolayer systems for use as ultrasonic contrast. These microbubbles have the property of longevity of weeks in vitro (ultrastability) and longevity of hours in vivo. The bubbles can be manufactured with a mean diameter of approximately 2 microns in a tight diameter distribution; all are less than 6 microns and 99% are smaller than 4.5 microns. The current study compared the in vivo survival characteristics of these lipid-coated microbubbles with microbubbles produced by saline. The comparison was made in the rat brain using direct intraparenchymal injections and injections into a previously created cyst/coagulum. The echogenic enhancement by the lipid-coated microbubbles persisted in vivo for over 24 hours in both the intraparenchymal environment and in the cyst/coagulum. The saline bubble echos were not detectable by 3 hours in a cyst/coagulum, and not detectable in the parenchyma after 2 hours. The sonographic characteristics and longevity of lipid-coated microbubbles make this agent a potentially useful clinical contrast material for neurosonography.