Modeling and analysis of ultrasound backscattering by spherical aggregatesand rouleaux of red blood cells

The present study concerns the modeling and analysis of ultrasound backscat tering by red blood cell (RBC) aggregates, which under pathological conditi ons 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 t he characteristics of the ultrasound system, was used to examine the influe nce of the scatterer shape and size on the backscattered power. Both scatte rers in the form of clumps of RBC aggregates and rouleaux were modeled. For all simulations, the hematocrit was kept constant at 10%, the ultrasound f requency was 10 MHz;, the insonification angle was varied from 0 to 90 degr ees, and the scatterer size (diameter for clumps and length for rouleaux) r anged from 4 mu m to 120 mu m Under Rayleigh scattering by assuming a Poiss on distributed scatterers in space, the ultrasound backscattered power incr eased linearly with the particle volume. For non-Rayleigh scatterers, the i ntensity of the echoes diminished as the scatterer volume increased, with t he exception of rouleaux at an angle of 90 degrees. As expected, the backsc attered power was angular dependent for anisotropic particles (rouleaux). T he 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 emphasiz ed in the non-Rayleigh region.