Determination of Optical Characteristics of Highly Scattering Biological Medium Based on Enhanced Diffusion Model of Radiation Transport

Abstract

IntroductionLaser radiation is used in studies of biological media and tissues [1 5].The problem of laser radiation propagation through strongly scattering media (SSM) is very important. Scattering dominates over absorption during laser radia tion propagation through biological tissues. Therefore, the model of purely absorbing medium is not appropriate in this case, in contrast to the transmission X ray tomo graphy algorithm. Laser radiation interaction with SSM includes both scattering and absorption. The equation of radiation transition (ERT) with regard to scattering describes laser radiation propagation through biological tissues. ERT has no analytical solution, so an approxi mate solution is required. The classical diffusion model (CDM) is presently used [6 8]. In some cases, this model provides an ERT solution, but it has substantial disadvan tages limiting the area of its application. The main disad vantage of CDM is substitution of monodirectional radi ation source (laser) by an isotropic source embedded in the medium. The enhanced diffusion model (EDM) is an alterna tive to the CDM [9]. In this work, numerical simulation of laser radiation propagation through SSM and results of experimental testing of the EDM are discussed. The EDM is superior to the CDM in terms of laser pulse propagation through thin layer SSM and medium with small scattering. The EDM is comparable to the CDM in terms of description of laser pulse propagation through thick layer SSM and medium with strong scattering. TheoryThe ETDM is a particle (energy) balance equation in closed volume and nonstationary form [6,7]:is scattering coefficient; ν is radiation propagation veloc ity module.The numerical and experimental comparison of two models of laser pulse propagation through highly scattering medium, namely a classical diffusion model and an enhanced diffusion model, is given. It is shown that the results obtained for the two models correspond to experimental data. The enhanced diffusion model more pre cisely describes the propagation of laser radiation through scattering layers with thickness about the length of mean path of photons.