Measurement of tissue optical properties by the use of oblique-incidence optical fiber reflectometry

Fiber-optic-based oblique-incidence reflectometry is a simple and accurate method for measuring the absorption and reduced scattering coefficients μ_a and μ_s’ of semi-infinite turbid media. Obliquely incident light produces a spatial distribution of diffuse reflectance that is not centered about the point of light entry. The amount of shift in the center of diffuse reflectance is directly related to the medium’s diffusion length D. We developed a fiber-optic probe to deliver light obliquely and sample the relative profile of diffuse reflectance. Measurement in absolute units is not necessary. From the profile, it was possible to measure D, perform a curve fit for the effective attenuation coefficient μ_eff, and then calculate μ_a and μ_s’. This method was verified with Monte Carlo simulations and tested on tissue phantoms. Our measurements of D and μ_eff had an accuracy of approximately 5%, thus giving us 10% and 5% accuracy for μ_a and μ_s’, respectively.