ABSTRACT The present study concerns the modeling and analysis of ultrasound backscattering by red blood cell (RBC) aggregates, which under pathological conditions play a significant role in the rheology of blood within human vessels. A theoretical model based on the convolution between a tissue matrix and a point spread function, representing, respectively, the RBC aggregates and the characteristics of the ultrasound system, was used to examine the influence of the scatterer shape and size on the backscattered power. Both scatterers in the form of clumps of RBC aggregates and rouleaux were modeled. For all simulations, the hematocrit was kept constant at 10%, the ultrasound frequency was 10~MHz, the insonification angle was varied from 0 to 90°, and the scatterer size (diameter for clumps and length for rouleaux) ranged from 4 μm to 120 μm. Under Rayleigh scattering by assuming a Poisson distributed scatterers in space, the ultrasound backscattered power increased linearly with the particle volume. For non-Rayleigh scatterers, the intensity of the echoes diminished as the scatterer volume increased, with the exception of rouleaux at an angle of 90°. As expected, the backscattered power was angular dependent for anisotropic particles (rouleaux). The ultrasound backscattered power may not always increase with the size of the aggregates, especially when they are no longer Rayleigh scatterers. In the case of rouleaux, the anisotropy of the backscattered power is emphasized in the non-Rayleigh region.
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