Oblique-incidence reflectometry: one relative profile measurement of diffuse reflectance yields two optical parameters

A new, simple and quick approach, oblique-incidence reflectometry, was used to measure the absorption and reduced scattering coefficients of a semi-infinite turbid medium. An obliquely incident light beam causes the center of the far diffuse reflectance to shift from the point of incidence, where the far diffuse reflectance refers to the diffuse reflectance that is several transport mean free paths away from the incident point. The amount of shift yields the diffusion constant by a simple formula, and the slope of the diffuse reflectance yields the attenuation coefficient. Only the relative profile of the diffuse reflectance is needed to deduce both optical parameters, which makes this method attractive in clinical settings because it does not require a stringent calibration for absolute quantity measurements. This method was tested theoretically by Monte Carlo simulations and experimentally by a reflectometer. Because this method can be used to measure optical properties of biological tissues quickly and requires only inexpensive equipment, it has potential clinical application to the diagnosis of disease or monitoring of treatments.