ИСТИНА

Laser diffractometry of erythrocytes (ektacytometry) is a fast in vitro diagnostic technique for measuring the deformability of red blood cells - erythrocytes. In ektacytometry, the erythrocytes are placed in the so-called Couette flow-chamber in a highly diluted suspension. The shear stress in the flow elongates the cells and orients them in approximately the same direction. A laser beam illuminates thousands of the cells in the flow simultaneously, and special CCD sensors measure the diffraction pattern (DP) originated by low angle single scattering of the beam by these cells. In conventional ektacytometry, the measured DP is used to calculate an average elongation of particles as a function of stepwisely increasing shear stress values. The problem of retrieving more detailed information about the shear-induced elongation of cells is of interest for medical applications. The main aim of this work is to significantly enhance the capabilities of the ektacytometry. We statistically characterize the ensemble of particles by their distribution in elongations ω (ε), where ε denotes a random value describing the relative elongation of the cells. In the first part of the work, we made analytical estimates, which relate the shape of a certain iso-intensity curve of the DP with first 3 moments of ε: average value s=<ε>, dispersion µ and asymmetry ν. The estimates are obtained under assumption that size distribution of cells has a negligibly small width; the anomalous diffraction approximation was used for modeling the light scattering by the elongated erythrocytes. The estimates lead to the new algorithm for calculating the parameters s,µ,ν. The algorithm is based on second derivatives of the iso-intensity curve in the 4 characteristic points. We experimentally tested the proposed method using the rat blood samples, which were prepared in a special way such that, in the experiment, the parameters s,µ,ν were known in advance. We recorded the diffraction pattern at a certain shear stress conditions and obtained an iso-intensity curve with level of noise not exceeding 15%. The values of s,µ,ν calculated using our algorithm differed from the corresponding experimentally preset values by less than 15%. In the second part of the work, we used the assessed parameters s,µ,ν as a priori information to obtain the whole distribution of erythrocytes in elongation ω(ε) by solving certain Fredholm integral equation of the first kind.