Frequency dependence of simulated ultrasound signals backscattered by aggregating red blood cells

The frequency dependence of the ultrasound signal backscattered by blood was studied with a simulation model. The ultrasound backscattered signal was simulated with a linear model that considers the characteristics of the ultrasound system and the tissue scattering properties. The tissue function was described by the position and the shape of the red blood cells (RBCs). The effect of the flow on the spatial organization of aggregating RBCs was simulated with a 2D model. It is an iterative model that considers the effect of the flow and the adhesive and repulsive forces acting on each RBC. RBC aggregation was simulated at 40 % hematocrit and shear rates of 0.05 s(-1), 0.08 s(-1), 0.1 s(-1), 0.5 s(-1), and 5 s(-1). Ultrasound frequencies between 5 and 500 MHz were studied. Results suggest that in the presence of RBC aggregation, the frequency dependence may vary depending on the shear rate and the range of frequencies studied. The enhancement of the backscattered power with RBC aggregation may be more important at frequencies below 30 MHz. At higher frequencies, changes in the frequency dependence of the ultrasound backscattered power were noted in the presence of RBC aggregation. It is concluded that further studies may be necessary to understand the relationship between the ultrasound backscattered power and the spatial organization of aggregating RBCs.