Gas microbubbles (MBs) are investigated as intravascular optical coherence tomography (OCT) contrast agents. Agar + intralipid scattering tissue phantoms with two embedded microtubes were fabricated to model vascular blood flow. One was filled with human blood, and the other with a mixture of human blood + MB. Swept-source structural and speckle variance (sv) OCT images, as well as speckle decorrelation times, were evaluated under both no-flow and varying flow conditions. Faster decorrelation times and higher structural and svOCT image contrasts were detected in the presence of MB in all experiments. The effects were largest in the svOCT imaging mode, and uniformly diminished with increasing flow velocity. These findings suggest the feasibility of utilizing MB for tissue hemodynamic investigations and for microvasculature contrast enhancement in OCT angiography.
In this study gas microbubbles are investigated as intravascular OCT contrast agents. Agar+Intralipid scattering tissue-like phantoms with two embedded microtubes were fabricated to model vascular blood flow. One was filled with human blood, and the other with a mixture of human blood and microbubbles. Swept-source structural and speckle variance OCT images, as well as speckle decorrelation times, were evaluated under both stationary and flow conditions. Faster decorrelation times and higher image contrast were detected in the presence of microbubbles in all experiments, and the effect was largest for speckle variance OCT ~2.3x greater contrast under flow conditions. The feasibility of utilizing microbubbles for tissue hemodynamic investigations and for microvasculature contrast enhancement in OCT angiography thus appears promising.
Optical contrast agents introduce distinct features to induce detectable changes in native tissue properties . 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  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.