Oxy-hemoglobin measurement in tissue layers

The results of photon diffusion modeling are applied to the measurement of oxy-hemoglobin at depths up to 10 mm in a layered tissue medium, continuous wave spectroscopy methods for measurement based on diffusion theory and the modified Lambert-Beer Law are not applicable to absorption differences in layered media. The authors examine differences in hemoglobin absorption through a finite difference solution to the Boltzmann equation for layered diffusive media. An effective photon attenuation pathlength (PAPL) is determined by matching to an analytical solution for an equivalent homogeneous medium. The PAPL provides a characterization of the optical properties in the layered medium since it is a function of the medium´s absorption and scattering coefficients. While the authors found that reflectance profiles from the layered models for biological tissue resemble those of a homogeneous medium, the effective PAPL was a unique function of the lower layer PAPL, the layered thickness, and the PAPL of the top layer. These results indicate that the PAPL can be monitored for deep tissue hemoglobin absorption when the depth and PAPL of the superficial tissue layer are measured