Direct video microscopic observation of the dynamic effects of medical ultrasound on ultrasound contrast microspheres

RATIONALE AND OBJECTIVES. Ultrasound can cause destruction of microbubble contrast agents used to enhance medical ultrasound imaging. This study sought to characterize the dynamics of this interaction by direct visual observation of microbubbles during insonification in vitro by a medical ultrasound imaging system. METHODS. Video microscopy was used to observe air-filled sonicated albumin microspheres adsorbed to a solid support during insonation. RESULTS. Deflation was not observed at lowest transmit power settings, At higher intensities, gas left the microparticle gradually, apparently dissolving into the surrounding medium. Deflation was slower for higher microsphere surface densities. Intermittent ultrasound imaging (0.5 Nz refresh rate) caused slower deflation than continuous imaging (33 Hz), CONCLUSIONS. Higher concentrations of microbubbles, lower ultrasound transmit power settings, and intermittent imaging each can reduce the rate of destruction of microspheres resulting from medical ultrasound insonation.