Depth-resolved reflectance instrument and method for its use
A reflectance instrument illuminates the surface of tissue with light of a selected wavelength and light emanating from the tissue due to reflectance is collected. The angle of illumination of tissue surface and/or collection of reflections is changed to probe at various depths beneath the surface of the tissue. The reflectance instrument may be used in a method for measuring the optical properties of a two layer diffuse media such as epithelial tissues.
1. A method for calculating the scattering and absorption characteristics of two layers of tissue, the steps comprising:
a) acquiring a first set of diffuse reflectance measurements from a top layer of said two layers of tissue using an instrument which limits the reflectance measurements to a shallow depth beneath the surface of the tissue;
b) calculating the absorption coefficient μ a and scattering coefficient μ s of the top layer of tissue using the measurements acquired in step a);
c) acquiring a second set of diffuse reflectance measurements from a deeper layer of said two layers of tissue using an instrument which limits the reflectance measurements primarily to a depth below the top layer of tissue; and
d) calculating the absorption coefficient μ a and scattering coefficient μ s of the deeper of said two tissue layers and the thickness of the top tissue layer using the top layer coefficients calculated in step b) and the diffuse reflectance measurements acquired in step c).
2. The method as recited in claim 1 in which step b) is performed using a single layer model of tissue and step d) is performed using a two layer model of tissue.
3. The method as recited in claim 2 in which the models used in steps b) and d) are Monte Carlo-based models.