Investigation of blood under pulsatile flow using ultrasound imaging

Abstract

Red blood cells (RBCs) stick together to form rouleaux at lower shear rate and the rouleaux break up at higher shear rate. This reversible phenomenon is known to RBC aggregation, which is responsible for a non-Newtonian fluid. This erythrocyte aggregation is also related to several pathological diseases, such as hyperlipidemia, arteriosclerosis, diabetes, obesity, and other cardiac vascular diseases. However, there are not many ways to measure and monitor this RBC aggregation noninvasively in real time. Ultrasound is a possible tool for this. In this study, a commercialized GE LOGIQ 700 Expert ultrasonic system with an M12L linear transducer was used in several in vitro and in vivo experiments for investigation of blood under pulsatile flow using B-mode and harmonic imaging. In in vitro experiments in a mock flow loop with porcine blood, two interesting phenomena, “Black Hole” (BLH) and “Bright Collapsing Ring” (BRCR), were observed in B-mode cross-sectional images. BLH is a lower echoic zone at the center stream of a tube, and BRCR refers to the appearance of a hyper-echoic ring at the periphery and its collapse to the tube center during a pulsatile flow cycle. These phenomena were investigated under well-controlled hemodynamic conditions at different flow speeds and stroke rates. Radial distribution of rouleaux was also studied at different transducer beam angles. In in vivo experiments on human carotid arteries, the BRCR was also observed from harmonic images of not 1 but 10 human subjects.