Acoustical Imaging of Individual Microbubbles

Abstract

This paper describes an acoustical approach for imaging the behavior of individual microbubbles in ultrasound fields. The experimental set-up includes a tank where small concentrations of encapsulated microbubbles are suspended in distilled water. When insonified by a programmable transmitter (TX), each microbubble is pushed away by the US radiation force to an extent which depends on its size and composition as well as on the TX parameters. For each transmitted ultrasound burst, the RF echo-signals backscattered by microbubbles over the ROI are processed in a high-speed digital board. The acquired data is used to produce two real-time displays. Tests performed in different experimental conditions clearly show bubbles accelerating in the focal region and moving slower elsewhere. It is seen in particular that all velocities measured for a full population of microbubbles are lower than- or equal to- the maximum velocities predicted for resonating bubbles. Finally, the destruction of a bubble is identified by a sudden interruption of the corresponding trace in the M-mode display. By controlling the TX parameters and monitoring the bubble movements, information about their dimension and elastic features can be obtained.