Optical properties of living tissues determined in vivo using a thin fiber optic probe

When light interacts with tissue, it can be absorbed, scattered or reflected by tissue. Detection of the interaction between light and tissue can be used to characterize the optical properties of tissue. The aims of this research were to develop a fiber optic probe with a small source-detector separation to (1) determine hemoglobin oxygen saturation (sO₂) values from living tissues based on optical reflectance data (500–600 nm), (2) determine the reduced scattering coefficient (μ_s ′) from living tissues based on optical reflectance data (700–850 nm), and (3) associate light scattering with particle sizes within tissues.; To address the first aim, a non-linear curve fitting algorithm was developed to extract sO₂ values from the reflectance spectra, producing deviations between the simulated curves and the analytical model of 5% for both 0% and 100% sO₂ cases. The analytical model was validated through Monte Carlo simulations and laboratory in vitro experiments. The validated model was used to extract sO₂ values from in vivo reflectance spectra of the human finger and brain tissues.; To address the second aim, simultaneous μ_s′ and optical reflectance measurements were obtained from in vitro experiments using a standard Oximeter and a fiber optic probe coupled with a portable spectrometer, respectively. A qualitative relationship between μ_s′ and optical reflectance was developed using both Monte Carlo simulations and empirical calibrations. After being tested with laboratory phantoms, the developed algorithm was used to determine μ_s′ values of human skin and in vivo rat brain tissue. Quantification of tissue μ_s ′ is consistent between white matter of animal brains taken in vitro and in vivo.; To address the third aim, the Rayleigh-Gans approximation was used to develop a direct relationship between the slope of ln(μ_s ′(λ)) versus ln(wavelength) at various particle sizes. Detailed analysis demonstrated that a sinusoidal relationship exists between the slope and particle size as particle size varies. Thus, caution should be exercised when determining particle sizes using the slope of logarithmic scattering spectroscopy. Another approach using optimization may be possible to quantify the mean size of light scattering particles, given accurate determination of relative refractive index.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirement: Microsoft Office.