Optical parameters estimation in inhomogeneous turbid media using backscattered light: for transcutaneous scattering measurement of intravascular blood.

In our earlier research, a technique was developed to estimate the effective attenuation coefficient of subcutaneous blood vessels from the skin surface using the spatial distribution of backscattered near-infrared (NIR) light. The scattering effect in surrounding tissues was suppressed through the application of a differential principle, provided that the in vivo structure is known. In this study, a new method is proposed enabling the separate estimation of both scattering and absorption coefficients using NIR light of different wavelengths. The differential technique is newly innovated to make it applicable to the subcutaneous structure without requiring explicit geometrical information. Suppression of the scattering effect from surrounding tissue can be incorporated into the process of estimating the scattering and absorption coefficients. The validity of the proposed technique can be demonstrated through Monte Carlo simulations using both homogeneous and inhomogeneous tissue-simulating models. The estimated results exhibit good coherence with theoretical values ( r 2  = 0.988-0.999). Moreover, the vulnerability and robustness of the proposed technique against different measurement errors are verified. Optimal conditions for practical measurement are specified under various light-detection conditions. Separate estimation of scattering and absorption coefficients improves the accuracy of turbidity measurements and spectroscopy in biomedical applications considerably, particularly for noninvasive measurements and analysis of blood, lipids, and other components in subcutaneous blood vessels.