Marie-Bernadette Barrau

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

RATIONALE AND OBJECTIVESThe basic characteristics of BR1, a novel echo contrast agent based on stabilized sulfur hexafluoride (SF6) microbubbles have been evaluated. METHODSThe 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. RESULTSBR1 is formulated as a lyophilized product, which after addition of saline, provides a suspension containing 2 × 108 SF6 microbubbles/mL with a number mean diameter of 2.5 µm. More than 90% of the bubbles are below 8 µm. 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. CONCLUSIONSConsidering its high echogenicity, outstanding stability, and resistance to pressure changes, BR1 is a very promising ultrasound contrast agent.

POLYMERIC MICROBALLOONS AS ULTRASOUND CONTRAST AGENTS : PHYSICAL AND ULTRASONIC PROPERTIES COMPARED WITH SONICATED ALBUMIN

Air-filled polymeric microballoons were prepared with number-mean diameters of approximately 3 microns, volume-mean diameters of approximately 5 microns, and narrow particle-size distributions (standard deviation [SD] = 1.2 microns in number and SD = 2.0 microns in volume). More than 99% of the particles were below 8 microns. These particles were found to be highly echogenic for ultrasound, showing backscatter coefficients at 7.5 MHz, similar to the ones obtained with sonicated albumin microspheres. However, at 2.25 MHz, microballoons were less echogenic than albumin microspheres. These results are consistent with ultrasound attenuation measurements, which showed a maximum at 8 to 9 MHz for the microballoons compared with a reported value of 3.5 to 4.5 MHz for albumin microbubbles. Polymeric microballoons were found to be stable in plasma or under applied pressure as evidenced by unchanged particle concentration and echogenicity. Albumin microspheres were particularly unstable to applied pressure (150 mm Hg) and showed a rapid decrease in both particle counts and echogenicity.