internal echoes in flowing blood, blood flow echogenicity, red cell aggregation, shear rate, high resolution real-time ultrasound
The mechanism of blood flow echogenicity during ultrasonography was investigated by in vitro experiments using fresh blood circulating in tubes of various diameters (12, 9, and 6 mm). Echogenicity became maximally intense during stasis of blood and decreased as shear rate of flow increased. Echogenicity in tubes of various diameters was the same when evaluated in terms of shear rate. Shear rate, but not velocity, was a main factor determining echogenicity. Since shear rate determines the degree of red cell aggregation if other factors affecting aggregation remain constant, these experimental results provided an additional evidence that red cell aggregation is an important contributor to blood flow echogenicity. At low shear rate, red cell aggregation increased with an increased of echogenicity and at high shear rate, disaggregation occurred resulting in a reduction in echogenicity. In conclusion, the results of the present study may be helpful for determination of in vivo and in vitro red cell aggregation, detection of slow flow state or blood stasis in vessels, prediction of thrombus formation and, for hemodynamic examination of circulatory system by means of flowing echoes.