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5 March 2015 Study optical properties of biological tissue in the presence of microbubbles
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Optical contrast agents introduce distinct features to induce detectable changes in native tissue properties [1]. In ultrasound imaging, microbubbles (MBs) – a gas-core shell-encapsulated agent – are used clinically as contrast agents. The working hypothesis of this study is that microbubbles can be employed as an intravascular contrast agent in optical imaging systems. Microbubbles can produce a refractive index mismatch which makes it distinguishable from surrounding media. In this work, the interaction of collimated light and microbubbles in a [1] biological phantom solution was investigated. The biological medium was comprised of intralipid and human blood which was constructed to cover the range of soft tissue optical properties. The effect of microbubbles on the optical properties such as reduced scattering and absorption coefficients were considered. Diffuse reflectance (DR) and total transmittance (TT) of a biological phantom solution were measured using a spectroscopic integrating sphere system in the absence and presence of Definity® microbubbles. The optical properties were computed using the inverse adding doubling (IAD) software. The presence of microbubbles increased DR and decreased TT of the phantom. In the presence of MB’s (2.5% volume concentration), the reflectance of the phantom increased by 25% in the optical window. There is no absorption event and only scattering happened after light-microbubbles interactions. The reduced scattering coefficient increased significantly (30%) indicating the potential use of MBs as optical contrast agents. In conclusion, reflectance of a media can be enhanced by adding microbubbles to increase scattering properties and more light was detected returning to the surface of tissue.
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Homa Assadi, Vincent Lee, Raffi Karshafian, and Alexandre Douplik "Study optical properties of biological tissue in the presence of microbubbles", Proc. SPIE 9321, Optical Interactions with Tissue and Cells XXVI, 93210X (5 March 2015);

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