BR38, a New Ultrasound Blood Pool Agent

Objective: To evaluate BR38, a new microbubble-based blood pool agent for contrast-enhanced ultrasound imaging. Materials and Methods: The size characteristics of BR38 microbubbles were measured by Coulter counting. The backscatter and attenuation coefficients were determined as a function of frequency. Additional measurements included the surface charge, osmolality, viscosity, and resistance to hydrostatic pressure. Extensive pharmacological and toxicological studies were conducted on the final formulation in rats and dogs. The blood levels and elimination of the gaseous component C 4 F 10 were determined in the rabbit. Contrast-enhanced echographic examinations were performed in pigs focusing on the myocardium and the liver. Finally, safety testing and preliminary imaging experiments were performed in a Phase I clinical study in human volunteers. Results: BR38 suspensions are isotonic, nonviscous, and show a high resistance to hydrostatic pressure. Their backscatter coefficient is high at >= 2 MHz and attenuation shows a maximum at 4 MHz, slowly decreasing at higher frequencies. The no adverse effect levels of 1 mu L/kg (rats) and 5 mu L/kg (dogs) expressed as microbubble gas volume, observed in repeated toxicology studies, correspond to 50 and 250 times the expected imaging dose in human beings (0.02 mu L/kg), respectively. No effects on cardiovascular and respiratory parameters were observed in rats and dogs. C 4 F 10 is eliminated within minutes from blood and excreted in expired air. Imaging experiments showed strong and persistent enhancement of the myocardium and the liver. A late phase was observed in the liver, in animals and in human volunteers. No serious adverse events and no significant changes in vital signs, electrocardiographs, and laboratory tests were observed in Phase I human volunteers. Conclusions: BR38 shows a very good safety profile. It is characterized by a long persistence and low shadowing. BR38 is a promising ultrasound blood pool agent for noncardiac and cardiac applications including myocardial perfusion imaging.