1. A method for calculating the scattering and absorption characteristics of tissue, the steps comprising: a) acquiring, with an optical spectroscopy system that includes an optical probe having at least one illumination fiber and at least one collection fiber, a set of diffuse reflectance measurements from the tissue; b) establishing a set of tissue optical parameters; c) calculating model reflectance values using the set of tissue optical parameters and a model which relates diffuse reflectance to tissue optical parameters, and further including: i) acquiring information relating to the locations of the at least one illumination and at least one collection fibers within the optical probe; and ii) determining a probability that a photon emitted by the at least one illumination fiber is collected by the at least one collection fiber using the information acquired in step c)i); d) calculating the sum of squares error between the measured diffuse reflectance and the model reflectance values; e) repeatedly updating optical parameters and repeating steps c) and d) until the sum of squares error is substantially minimized; f) calculating the scattering and absorption characteristics of the tissue from the updated optical parameters that yield a minimum sum of squares error; and wherein step c)ii) includes performing a convolution to integrate between the at least one illumination and at least one collection fiber.