Light propagation in a turbid medium with insonified microbubbles

Terence S Leung,Eleanor Stride,Jack E Honeysett,Jing Deng

doi:10.1117/1.jbo.18.1.015002

Abstract

Surfactant stabilized microbubbles are widely used clinical contrast agents for ultrasound imaging. In this work, the light propagation through a turbid medium in the presence of microbubbles has been investigated. Through a series of experiments, it has been found that the optical attenuation is increased when the microbubbles in a turbid medium are insonified by ultrasound. Such microbubble enhanced optical attenuation is a function of both applied ultrasound pressure and microbubble concentration. To understand the mechanisms involved, a Monte Carlo (MC) model has been developed. Under ultrasound exposure, the sizes of microbubbles vary in space and time, and their dynamics are modeled by the Rayleigh-Plesset equation. By using Mie theory, the spatially and temporally varying optical scattering and scattering efficiency of microbubbles are determined based on the bubble sizes and internal refractive indices. The MC model is shown to effectively describe a medium with rapidly changing optical scattering, and the results are validated against both computational results using an N-layered diffusion equation model and experimental results using a clinical microbubble contrast agent (SonoVue®).

Highlights

Surfactant stabilized microbubbles, with diameters of a few micrometers, are used as clinical contrast agents for ultrasound imaging
An Monte Carlo (MC) model has been developed for light propagation in a turbid medium with insonified microbubbles, and has been validated using a diffusion equation (DE) model and experiments with clinical grade microbubbles (SonoVue®)
While near infrared contrast agents such as indocyanine green have been widely used for their absorption properties,[25,26] we have shown that insonified microbubbles can be used as a “scattering” contrast agent

Summary

Introduction

Surfactant stabilized microbubbles, with diameters of a few micrometers, are used as clinical contrast agents for ultrasound imaging. While their acoustic properties have been studied extensively,[1] their optical properties are less well known. The optical scattering from an object depends on its size.[2] a microbubble’s optical scattering is expected to change during insonification. This property has enabled the application of optical measurement techniques to investigate the sizes of insonified microbubbles and their dynamics.[3] It has been suggested that the size change of insonified microbubbles can be exploited for fluorescence imaging with fluorophore labeled microbubbles.[4,5]

Methods

Results

Discussion

Conclusion