BR1: a new ultrasonographic contrast agent based on sulfur hexafluoride-filled microbubbles.

Rationale And Objectives: The basic characteristics of BR1, a novel echo contrast agent based on stabilized sulfur hexafluoride (SF6) microbubbles have been evaluated.

Methods: The authors determined the physicochemical properties (bubble concentration, bubble size distribution, resistance to pressure, and stability) and the acoustic properties (backscatter and attenuation coefficients) of BR1. The diagnostic value of BR1 was evaluated further in minipigs. Left heart images were recorded before and after injection of different doses of BR1.

Results: BR1 is formulated as a lyophilized product, which after addition of saline, provides a suspension containing 2 x 10(8) SF6 microbubbles/mL with a number mean diameter of 2.5 microns. More than 90% of the bubbles are below 8 microns. The use of SF6 rather than air provides an improved resistance to pressure increases such as the ones occuring in the left heart during systole. After reconstitution, the echogenicity and the bubble characteristics are unchanged for more than 8 hours. The high echogenicity remains almost constant over the entire medical frequency range (1-10 MHz). BR1 injections in animals resulted in a homogenous, dose-dependent opacification of the left heart.

Conclusions: Considering its high echogenicity, outstanding stability, and resistance to pressure changes, BR1 is a very promising ultrasound contrast agent.