Effect of static pressure on acoustic transmittance of Albunex microbubble suspensions

Albunex (ALX), an albumin-stabilized microbubble echo contrast agent, is sensitive to pressures similar to those produced by the heart. The tested hypothesis was that the acoustic transmittance of ALX suspensions will increase with increasing hydrostatic pressure (Ps). The test involved an acoustic setup analogous to a spectrophotometer. The acoustic transmittance of microbubble suspensions was strongly Ps dependent. Transmittance at 1 MHz was essentially zero at ambient pressure, increasing to approximately 50%, approximately 63%, and nearly 100% at Ps of 80, 120, and 400 mm Hg, respectively. The ultrasound pulses used to interrogate samples were without measurable effect on the acoustic transmittance of suspensions maintained at ambient pressure during experimental measurements. The data indicate that many of the microbubbles are destroyed at Ps comparable to those produced by the heart.