A system-based approach to modeling the ultrasound signal backscattered byred blood cells

A system-based model is proposed to describe and simulate the ultrasound si gnal backscattered by red blood cells (RBCs). The model is that of a space- invariant linear system that takes into consideration important biological tissue stochastic scattering properties as well as the characteristics of t he ultrasound system. The formation of the ultrasound signal is described b y a convolution integral involving a transducer transfer function, a scatte rer prototype function, and a function representing the spatial arrangement of the scatterers. The RBCs are modeled as nonaggregating spherical scatte rers, and the spatial distribution of the RBCs is determined using the Perc us-Yevick packing factor. Computer simulations of the model are used to stu dy the power backscattered by RBCs as a function of the hematocrit, the vol ume of the scatterers, and the frequency of the incident wave (2-500 MHz). Good agreement is obtained between the simulations and theoretical and expe rimental data for both Rayleigh and non-Rayleigh scattering conditions. In addition to these results, the renewal process theory is proposed to model the spatial arrangement of the scatterers, The study demonstrates that the system-based model is capable of accurately predicting important characteri stics of the ultrasound signal backscattered by blood. The model is simple and flexible, and it appears to be superior to previous one- and two-dimens ional simulation studies.