ИСТИНА

Blood is a highly structured heterogeneous and dynamic fluid tissue exhibiting complex rheologic and optical properties. Contemporary optical techniques are potentially capable of providing the quantitative assessment of the fundamental role and properties of the molecular and cellular components of blood in maintaining the homeostasis of life organisms or in reflecting their pathological alterations. Red blood cells (RBC) are the major scattering particles in whole blood due to their predominant volumetric concentration and high scattering crosssection. Theoretically, the angular distribution of light intensity scattered by an individual particle is determined by a scattering phase function (SPF), which can be defined either by a phenomenological formula, or calculated on the basis of certain approximations, accounting for the shape of RBC. Recent results in measurement and calculation of light scattering phase functions of large optically soft particles of different sizes, shapes, and orientations, modeling the single nondeformed, shear-deformed and aggregated RBC are discussed. Different approaches are compared to cal- culate light scattering angular distributions resulting from photon migration in multiply scattering layers of concentrated suspensions of such particles. Results are in good agreement with Monte-Carlo simulations of the similar process. Both approaches are used to model the time course of backscat- tered light intensity, related to the experimentally measured spontaneous aggregation kinetics. An overview will be given of optical techniques and their applications for the study of single RBC, RBC suspensions and whole blood structure and dynamics at both in vitro and in vivo conditions, including reversible aggregation, shear-induced deformation and radial redistribution of RBC, concentration and velocity profile alterations in bulk flow conditions, etc. Feasibility of light scattering, laser Doppler and optical coherence Doppler tomography measurements in blood in single and multiple scattering limits will be evaluated. Potentials of the discussed techniques for biomedical experimental and clinical applications including diagnostics of pathological states, and pain-free experiments will be discussed. As an example, measurements will be discussed performed with blood samples of experimental animals that help to assess the mechanisms of such pathological states as cerebral ischemia.