Estimation of size and number density of microbubbles based on analysis of frequency-dependent attenuation

Abstract

A method of estimating the size and number density of microbubbles in suspension is proposed, which matches the theoretically calculated frequency dependent attenuation coefficient with the experimental data. Assuming that the size distribution of bubbles is given by a log-normal function, three parameters (expected value and standard deviation of radius and the number density of bubbles) of Sonazoid® in the steady flow were estimated. Bubbles are exposed to ultrasound with a center frequency of 5 MHz and mechanical indices of 0.4, 0.5, 0.7, and 1.1. The expected value and standard deviation for the size distribution were estimated to be 70–85 and 45–60% of the reference values in the case of a lower mechanical index, respectively. The number density was estimated to be 20–30 times smaller than the reference values. This fundamental examination indicates that the number density of bubbles can be qualitatively evaluated by the proposed method.