Threshold of fragmentation for ultrasonic contrast agents.

Ultrasound contrast agents are small microbubbles that can be readily destroyed with sufficient acoustic pressure, typically, at a frequency in the low megaHertz range. Microvascular flow rate may be estimated by destroying the contrast agent in a vascular bed, and estimating the rate of flow of contrast agents back into the vascular bed. Characterization of contrast agent destruction provides important information for the design of this technique. In this paper, high-speed optical observation of an ultrasound contrast agent during acoustic insonation is performed. The resting diameter is shown to be a signifi- cant parameter in the prediction of microbubble destruction, with smaller diameters typically correlated with destruction. Pressure, cen- ter frequency, and transmission phase are each shown to have a sig- nificant effect on the fragmentation threshold. A linear prediction for the fragmentation threshold as a function of pressure, when normal- ized by the resting diameter, has a rate of change of 300 kPa/mm for the range of pressures from 310 to 1200 kPa, and a two-cycle excita- tion pulse with a center frequency of 2.25 MHz. A linear prediction for the fragmentation threshold as a function of frequency, when nor- malized by the resting diameter, has a rate of change of ˛1.2 MHz/mm for a transmission pressure of 800 kPa, and a two-cycle excitation pulse with a range of frequencies from 1 to 5 MHz. © 2001 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1352752)