Experimental study of stability of a contrast agent in an ultrasound field

Attenuation coefficient and phase velocity measurements and direct optical observations showed that microbubbles of a contrast agent (Albunex) in 5% bovine albumin solution were not stable under ultrasonic irradiation. When the concentration of Albunex was 0.41 microL/mL and a 2.5-MHz phased array transducer of a Hewlett-Packard ultrasound imaging system (Model 77020AC) was used as the ultrasound source (the compression and rarefaction peak pressure amplitudes were, respectively, equal to 2 MPa and 1 MPa, the repetition frequency was 2.64 kHz), the attenuation coefficient at 2.5 MHz dropped from 40 dB/cm to 16 dB/cm after 2 min of continuous insonification. Under a static condition, it was shown by direct optical observations that the microbubbles shrank and aggregated to form clusters or were destroyed under insonification; pressure amplitude was estimated to be 0.5 MPa, frequency = 2.44 MHz, and the pulse repetition frequency was 5 kHz.