Optical characterization of dense tissues using low-coherence interferometry

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Abstract
Reflectometers based on low-coherence interferometry are potentially useful tools for probing superficial biological structures. In this paper, we present results of theoretical and experimental investigations of the variables that affect the backscattered signals measured by low-coherence reflectometers from dense tissues. Using a single-backscatter model of a turbid biological sample, we examine the effects of the focal spot size and collection angle on the heterodyne efficiency for light backscattered over a range of sampling depths. Coherence losses resulting from multiple scattering are studied using a simple analytical model augmented by numerical simulations. Our results suggest that the single-backscatter model, which has been applied previously in atmospheric lidar and ultrasound studies, provides a good description of the relationship between the shape of the reflectance-vs-depth profiles and the optical properties of a turbid sample under certain conditions. Model predictions were tested by measuring reflectance profiles from dense suspensions of particles using a low-coherence reflectometer built in our laboratory and a commercially available fiber-optic reflectometer. Results of these measurements are compared with others obtained in vivo from human skin. To demonstrate that small structures located at depths of several hundred microns can be probed without contacting a biological specimen, we show an image of bone specimen obtained with the laboratory reflectometer.

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