A specific feature of the procedure for determination of optical properties of turbid biological tissues and media in calculation for noninvasive medical spectrophotometry

Abstract

In contemporary medical engineering industry, oneof the key problems of development of methods, apparatuses, and devices for optical spectroscopy of biologicaltissues is the compilation of effective computation algorithms providing maximal accuracy and reliability ofdetermination of initial optical properties of the object ofinterest from experimental data [14, 18]. Optical properties of biological tissues can be determined from radiationfluxes measured experimentally by solving inverse problems of scattering [11], which employ different methodsof description of radiation propagation medium. In turbidlightscattering biological media (most biological mediaare turbid [22]), numerical models of transition theoryand lightscattering in turbid media should be used [8,20]. The models have a limited number of solutions.Therefore, approximate solutions are often used for practical purposes in photometry of turbid media. For example, flux Kubelka–Munk (KM) approaches are widelyused in the practice of noninvasive spectrophotometry,because they are simple and illustrative. Moreover, theKM models allow the final calculation equations to bederived in explicit analytical form [8, 12, 17, 18, 2124].In terms of transition theory and KM models, internaloptical properties of turbid media are completely characterized by linear optical extinction and scattering coefficients. The linear optical extinction and scattering coefficients are determined coefficients of differential equations describing the model. In optics, the KM models are purely photometricand phenomenological models based on heuristic principles providing separation of radiation field into discreterectangular fluxes. The principles also support the validity of linear equation of energy balance for each flux inmedium element [2, 48, 24]. In the simplest case, twoonedimensional flux KM models are considered. Suchmodel represents onedimensional radiation propagationmedium with two oppositely directed fluxes