Ultrasonic backscatter from flowing whole blood. II: Dependence on frequency and fibrinogen concentration.

Earlier studies showed that ultrasonic backscatter from erythrocytes suspended in saline is a function of hematocrit and frequency and that it can be affected by flow disturbance. The experimental data agree well with the theories. Recently, studies have been extended to flowing whole blood. The results indicated that ultrasonic backscatter from flowing whole blood differs from that from saline suspensions of erythrocytes in that it is shear-rate dependent and species dependent. In the present article, data on the dependence of ultrasonic backscatter from flowing whole blood on frequency and on fibrinogen concentration are reported. It was found that ultrasonic backscatter from flowing whole blood also depends on fibrinogen concentration when red blood cell (RBC) aggregation exists. Moreover, when the blood is under conditions that favor RBC aggregation such as low shear rates, high fibrinogen concentration, or high hematocrits, Rayleigh scattering apparently is no longer sufficient to describe its scattering behavior.