Determination of optical properties in highly attenuating media with an endoscope-compatible reflectance approach

Accurate in vivo optical property data in the ultraviolet to visible range are scarce for many endoscope-accessible organs, yet such information is essential for understanding light propagation and identifying dosimetry standards for biomedical optical spectroscopy. We have performed a preliminary study towards the development of a reflectance-based system for endoscopic measurement of tissue optical properties relevant to fluorescence spectroscopy. To address the constraint of instrument channel diameter and strong attenuation of light in the spectral region of interest, maximum fiber separation distance was limited to 2.5 mm. Measurements were performed on tissue phantoms for a range of optical properties relevant to gastrointestinal mucosal tissues in the ultraviolet to visible range: absorption coefficients from 1 to 256 cm-1 and reduced scattering coefficients from 5 to 25 cm-1. Neural network and partial least squares algorithms were trained on radial reflectance profiles generated by a Monte Carlo model as well as by experimental data. These routines were then used to estimate absorption and reduced scattering coefficients from reflectance data. Results are discussed in terms of the optimization of models for optical property determination