Untargeted microbubbles are injected intravenously into the systemic circulation in a small bolus. The microbubbles remain in the systemic circulation

for a certain period of time. During that time, ultrasound waves are directed on the area of interest. When microbubbles in the blood flow past the

imaging window, the microbubbles’ compressible gas cores oscillate in response to the high frequency sonic energy field. The microbubbles reflect a

unique echo that stands in stark contrast to the surrounding tissue due to the orders of magnitude mismatch between microbubble and tissue echogenicity.

The ultrasound system converts the strong echogenicity into a contrast-enhanced image of the area of interest. In this way, the bloodstream’s echo is

enhanced, thus allowing the clinician to distinguish blood from surrounding tissues.

Current untargeted microbubbles are Optison and Levovist. Optison is a FDA-approved microbubble made by GE Healthcare, has an albumin shell and

octafluoropropane gas core. The second FDA-approved microbubble, Levovist, made by Schering, has a lipid/galactose shell and an air core.

The table below gives a summary of ultrasound microbubbles: