A system-based simulation model of the ultrasound signal backscattered by blood

A simulation model is proposed to study the ultrasound signal backscattered by non-aggregating and aggregating red blood cells (RBCs). It is a linear modeling approach taking into account the tissue scattering properties as well as the characteristics of the ultrasound system. The ultrasound signal is described by the convolution of a transducer transfer function, and a function characterizing the shape of RBCs and their spatial arrangement. The modeling of the spatial arrangement of RBCs was based on the packing factor theory for non-aggregating RBCs. In the case of RBC aggregation, a rheological simulation model was developed to predict the size and spatial arrangement of RBCs. The backscattered power was simulated as a function of the hematocrit, and shear rate. For aggregating RBCs, the backscattered power was maximum at 40% hematocrit, rather than around 15% hematocrit for non-aggregating RBCs. The power was maximum at 0.1 s/sup -1/. However, the size of the aggregates increased with the hematocrit and decreased as a function of the shear rate (0.05 s/sup -1/ to 10 s/sup -1/). These results suggest that the backscattered power is not simply proportional to the size of the aggregates.