Measurement of internal tissue optical properties at ultraviolet and visible wavelengths: Development and implementation of a fiberoptic-based system.

A novel, multi-wavelength, fiberoptic system was constructed, evaluated and implemented to determine internal tissue optical properties at ultraviolet A (UVA) and visible (VIS) wavelengths. Inverse modeling was performed with a neural network to estimate absorption and reduced scattering coefficients based on spatially-resolved reflectance distributions. The model was calibrated with simulated reflectance datasets generated using a condensed Monte Carlo approach with absorption coefficients up to 85 cm(-1) and reduced scattering coefficients up to 118 cm(-1). After theoretical and experimental evaluations of the system, optical properties of porcine bladder, colon, esophagus, oral mucosa, and liver were measured at 325, 375, 405, 445 and 532 nm. These data provide evidence that as wavelengths decrease into the UVA, the dominant tissue chromophore shifts from hemoglobin to structural proteins such as collagen. This system provides a high level of accuracy over a wide range of optical properties, and should be particularly useful for in situ characterization of highly attenuating biological tissues in the UVA-VIS.