Properties of coagulating blood under steady flow detected by statistical analysis of backscattered signals

Most of previous investigations on the evaluation of blood coagulation were performed from the blood under static or stirred conditions which however are far from those of in vivo cases. Hence, this study is to detect varying properties of clotting blood through ultrasonic statistical model calculated from backscattered signals under steady flow condition at a 40 s^-1 mean shear rate. The radiofrequency (RF) signals backscattered from flowing blood were measured with a 10 MHz focused transducer. A 30 ml aliquot of blood was circulated in the flow model and 3 ml of 0.5 M calcium chloride solution was added to induce blood coagulation. In each experiment, the radiofrequency signals backscattered from the blood (digitized at 100 MHz) were collected for 20 min at a temporal resolution of 50 A-lines s^-1. The Nakagami parameter was used to analyze variations in the blood during clotting. Results showed that the Nakagami parameter was approximately 0.75±0.1 for flowing blood during the initial stage of blood coagulation, and increased rapidly to its highest level of 2.6±0.5 during clotting. These experimental results demonstrate the feasibility of using the ultrasonic statistical parameter for detecting blood coagulation from flowing blood and provide a novel method for further monitor the progress of clotting and thrombosis research in vivo.