Apport de la méthode des ondelettes continues à l'analyse du signal ultrasonore rétrodiffusé par des suspensions de globules rouges agrégésContribution of the continuous wavelet method to the analysis of the ultrasound signal backscattered from suspensions of aggregated red blood cells

Many studies have already been conducted to better understand blood flow in human vessels. Various techniques, in particular ultrasonic methods such as ultrasonic imaging and Doppler velocimetry have been used. Some microcirculatory disturbances found in human being could be explained by a bad distribution of blood in the capillary network, due to an increase of aggregation and a decrease of deformability of red blood cells (RBC). In the present work, the structure of aggregated RBC suspensions were approached by processing of the ultrasonic backscattering signal using the continuous wavelet transform (CWT) method. Under our experimental conditions, the CWT provides three types of parameters: first, a characteristic time of sedimentation of red blood cells and aggregates, second, characteristic frequencies of fluctuations of the number and density of red blood cells and, third ponderation coefficients of the wavelet transform. Ponderation of the wavelet coefficients was used to calculate the first four statistical moments providing information on the aggregate geometry. Experiences providing from suspensions of normal red blood cells, for various hematocrit from 5% to 35%, aggregated by using dextran 70 (70,000Da) at concentration of 30 g l^–1, show that the calculated statistical moments are useful to characterize the size distribution of aggregates.