Use of Microbubbles as an Optical Coherence Tomography Contrast Agent

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Rationale and Objectives

Optical coherence tomography (OCT) is a technique for obtaining cross-sectional images of tissue with a resolution of approximately 10 μm and a depth of imaging of 1–2 mm (1). OCT is analogous to ultrasound (US) imaging, with reflected, near-infrared (1,300-nm) light measured instead of sound. This technique has been used to image several types of tissues, including blood vessels (2) and the eye (3). Because OCT detects light backscattered at index of refraction mismatches, it was anticipated

Materials and Methods

Phospholipid-coated perfluorobutane microbubbles (ImaRx Pharmaceutical, Tucson, Ariz) were used throughout the studies (mean diameter, 2 μm; 5 × 109 particles/mL). Images were first obtained of silicon tubing holding microbubbles in concentrations of 0%, 10%, 1%, and 0.5%. Microbubbles were diluted with carboxymethylcellulose (CMC) to retard bubble rising during the approximately 10 seconds required for each image.

To evaluate the effects of microbubbles on OCT images of blood vessels, four mice

Results

The phantom studies characterized the OCT signal obtained from microbubble solutions. Figure 1a shows a reference image of pure CMC. The tubing in Figure 1b contains 10% microbubbles. At this concentration, the microbubbles are so highly scattering that the signal from the top of the lumen is saturated, and the bottom of the lumen is shadowed. At a 1% concentration of microbubbles (Fig 1c), a uniform and bright reflection is seen throughout the tubing lumen. There is still a noticeable increase

Conclusion

This study showed that microbubbles produce a strong OCT signal and that microbubble solutions as dilute as 0.5% are distinguishable from clear fluids. Because blood and tissues also produce a fairly strong OCT signal, the effects in vivo on the visualization of blood vessels are subtle. The most significant advantage is that microbubbles allow the boundary between the blood and the vessel wall to be visualized. Because microbubbles also increase the attenuation coefficient of blood, this

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