Acoustic size distribution analyzer for microbubbles

In this study, an acoustic size distribution measurement of the ultrasound contrast agent Definity^¿ was performed. Single lipid shelled microbubbles were insonified at 25 MHz, high above their resonance frequencies, so that their acoustic responses depend on their physical cross sections only. We calculated the size of each microbubble from the measured absolute backscattered pressures. The acoustic size measurements were compared to optical reference size measurements to test their accuracy. Our acoustic sizing method was applied to 88 individual Definity^¿ bubbles to derive a size distribution of this agent. The result showed agreement with the optical measurements of the same contrast agent population. The averaged sizes obtained acoustically differed by 26% with the optical measurement. This novel acoustic sizing method shows potential for estimating the size distribution of an ultrasound contrast agent noninvasively.