Time-frequency analysis by the wavelet method of the ultrasonic backscattering coefficient from blood: application to red blood cell aggregation

Ultrasound backscattering is a well adapted method to study red blood cell (RBC) aggregation and formation of aggregates because ultrasound waves propagate easily in soft tissues. Moreover, the sensitivity of the method to detect aggregates depends on the 6th power of the mean size of aggregates considered as spherical. So, variations of the ultrasonic backscattering intensity can be related to variations of the mean size of aggregates and then to the aggregation kinetics. The ultrasonic signal backscattered by blood being non-stationary, a time-frequency analysis of the echograms would be useful. Such an analysis of the ultrasonic signal backscattered by red blood cells sedimenting in suspension is presented by using the wavelet method. The advantage of the method is to determine locally in the suspension the frequency component of the signal related to the aggregation kinetics, and to follow it versus time with a better accuracy than the short Fourier analysis.