T-matrix computations of light scattering by red blood cells

• The electromagnetic far field, as well as near field, originating from light interaction with a red blood cell (RBC) volume equivalent spheroid, were analyzed utilizing T-matrix theory. This method is a powerful tool which enables the influence of cell shape on the angular distribution of scattered light to be studied. General observations were that the three-dimensional shape, as well as optical thickness apparent to the incident field, affect the forward scattering. The back scattering was influenced by the shape of the surface facing the incident beam. Furthermore, sphering as well as elongation of an oblate shaped RBC into a volume equivalent sphere or prolate shaped spheroid, respectively, were theoretically modeled in order to imitate physiological phenomena caused, e.g., by sphering agents, heat or increased shear stress of flowing blood. Both sphering and elongation were shown to decrease the intensity of the forward directed scattering, thus yielding lower g-factors. The sphering made the scattering pattern independent of the azimuthal scattering angle φs, while the elongation induced more apparent φs-dependent patterns. The light scattering by an RBC volume equivalent spheroid, was thus found to be highly influenced by the shape of the scattering object. A near-field radius, rnf, was evaluated as the distance to which the maximum intensity of the total near field had decreased to 2.5 times that of the incident field. It was estimated to 2-24.5 times the maximum radius of the scattering spheroid, corresponding to 12-69 µm. When the absorption properties of a red blood cell were incorporated in the computations, the near-field radius was only slightly reduced by 0.2-0.6 times the maximum radius. As the near-field radius was shown to be larger than a simple estimation of the distance between the RBCs in whole blood, the assumption of independent scattering, frequently employed in optical measurements on whole blood, seems inappropriate. This also indicates that results obtained from diluted blood, cannot be extrapolated to whole blood, by multiplying with a simple concentration factor.

Ämnesord

NATURVETENSKAP  -- Fysik -- Atom- och molekylfysik och optik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Atom and Molecular Physics and Optics (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

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