Development of fiber-optic probe designs and methods for depth-sensitive optical measurements

This dissertation presents a series of studies on the development of fiber-optic probe designs and Monte Carlo based methods for depth-sensitive optical measurements in layered tissues such as cervical epithelial tissues.; A Monte Carlo code that is capable of simulating both reflectance and fluorescence using various fiber-optic probe geometries was validated by phantom experiments. An equation relating the optical properties and fluorescence efficiency of individual phantom components, to those of the whole phantom was proposed to enable quantitative comparison between numerically simulated fluorescence and experimentally measured fluorescence.; Then a series of fiber-optic probe designs were evaluated for depth-sensitive optical measurements in terms of the sensitivity to a specific layer and the signal intensity using the validated Monte Carlo code. In particular, it was found that the angled probe was always sensitive to the superficial layer, while the flat tip probe was primarily sensitive to the underlying layer of a two-layered epithelial tissue model. The feasibility of performing depth-sensitive fluorescence spectroscopy with the angled probe was demonstrated experimentally on tissue phantoms.; By combining the angled fiber design and the flat-tip fiber design, a composite probe was proposed and fabricated for preferentially detecting diffuse reflectance from the top or bottom layer in a theoretical two-layered epithelial tissue model. A sequential estimation method was developed to extract the optical properties of both layers and the top layer thickness for given diffuse reflectance spectroscopy measurements. This method was validated quantitatively by independent Monte Carlo simulations and qualitatively by phantom experiments.; The angled probe design was further explored for fast estimation of reduced scattering coefficient in a moderately absorbing medium, for which the effect of absorption on measured diffuse reflectance is negligible. A lookup table method was employed to extract the reduced scattering coefficient. This method may be particularly useful for detecting the scattering properties of the epithelial layer.; In summary, the depth-sensitive probe designs and the associated models are able to obtain layer-specific information from optical measurements. Further refinement of these techniques would help advance the use of optical spectroscopy in clinical settings for early cancer detection in epithelial tissues.