Comparison of Mie theory and the light scattering of red blood cells

Two important optical properties of red blood cells (RBCs), their microscopic scattering cross sections sigma(s), and the mean cosine of their scattering angles micro, contribute to the optical behavior of whole blood. Therefore, the ability of Mie theory to predict values of sigma(s) and was tested by experiment. In addition, the effect of red blood cell size on sigma(s) and micro was investigated in two ways: (1) by studying erythrocytes from the dog, goat, and human, three species known to have different RBC sizes and (2) by allowing the RBCs from each species to shrink or swell osmotically. Values of sigma(s) obtained by measuring the collimated transmittance of dilute RBC suspensions illuminated with a He-Ne laser agreed with those predicted by Mie theory. Moreover, measured as values were directly proportional to RBC volume. By contrast, values of from Mie theory were consistently greater than those obtained experimentally by making angular scattering measurements in a goniometer. Thus Mie theory appears to yield adequate values for the RBC's microscopic scattering cross section, but by treating the RBC as a sphere with an equal volume, Mie theory fails to take the RBC's anisotropy into account and thus yields spuriously high values for micro.