Analysis of microbubble dynamics under ultrasound exposure

Abstract

Microbubble contrast agents used in diagnosis are used in a non‐invasive configuration. However, the ultrasound parameters are not physically analyzed, which means that there is insufficient data on the parameters to explain unexpected events during diagnosis. To obtain sufficient knowledge about the parameters related to ultrasound diagnosis using microbubble contrast agents, we devised an experiment to measure the acoustic signals and capture diagnostic images and high‐speed images. With this experiment, we measured the acoustic signals from the microbubble focusing on the microbubble concentration and investigated the relationship between the microbubble concentration and the microbubble dynamics under ultrasound exposure. We used Sonazoid™ as a microbubble. The range of the ultrasound frequency is from 0.5 to 5.7 MHz. The microbubble concentration was changed from the void fraction of 0, 1.3×10−5, 1.3×−4, 0.0013 and 0.013%. As the results, the fundamental echo signals increased linearly at low void fractions, but the increasing trend weakened with the increase in the void fraction, which suggests that the transition from single bubble behavior to bubble cloud behavior occurred. In addition, the result of calculating the bubble interaction parameter β also suggests the transition.