Microbubble acoustic signatures: bubble deflation

Ultrasound Contrast Agents (UCAs) are used in medical imaging to enhance the visibility of structures, especially blood vessels and the liver. An example application of UCAs is the detection and classification of tumors. The most common UCA consist of microbubbles, which have pronounced non-linear acoustical scattering properties. Research on the characteristics of these microbubbles is still in progress. The project described in this paper is focussed on the classification of the microbubbles. The acoustic response of a single microbubble depends on the environment and the location of the microbubble. Three classes can be defined: Microbubbles floating freely, microbubbles in the neighborhood of a (vessel) wall, and clusters of interfering microbubbles. Many different bubble models are available and the most appropriate one must be selected to be used in the classification algorithms. Classification of these microbubbles using the characteristics of the received ultrasound signal is necessary to gain knowledge about the location and environment of the microbubble, which in turn represents properties of the tissue. In this paper, the deflation rate or aging of a microbubble is discussed. Because of the limited number of bubbles in the data-set at this moment, we are unable to define a relation between bubble size and deflation rate.