ANOMALOUS DIFFRACTION BY ARBITRARILY ORIENTED ELLIPSOIDS - APPLICATIONS IN EKTACYTOMETRY

Anomalous diffraction by an arbitrarily oriented ellipsoid with three different axes is derived. From the resulting expression the relations hip between the shape of the ellipsoid and the intensity pattern is im mediately evident: The axial ratio of the elliptical isointensity curv e equals the axial ratio of the elliptical projected area of the ellip soid. A comparison of anomalous diffraction with calculations performe d with the T-matrix method reveals that the anomalous diffraction appr oximation is highly accurate for single ellipsoidal red blood cells. A pplication of the expression for anomalous diffraction by ellipsoids t o a population of red blood cells shows that, even in a red-cell suspe nsion as examined in an ektacytometer, the axial ratio of the isointen sity curves is equal to the mean axial ratio of the red blood cells in the population. In ektacytometry this relationship between cell shape and intensity pattern is commonly assumed to hold true without refere nce to the light-scattering properties of the cells. The results prese nted here show that this assumption is valid, and we offer a profound theoretical basis for it by considering in detail the light scattering by the red blood cells.