Ultrasonic Visualization of Dynamic Behavior of Red Blood Cells in Flowing Blood
It is well known that the scatter of ultrasound by blood is mainly attributed to red blood cells (RBCs) and RBC aggregation. In the present review, researches of hemodynamic influence on RBC aggregation and ultrasound backscatter from blood were overviewed. A mock flow loop and a cylindrical chamber were employed to produce various blood flows, such as pulsatile, oscillatory, and rotational flow. The "black hole" (BLH), a dark hole at the tube center surrounded by bright zone in the cross sectional B-mode image and "bright collapsing ring" (BRCR) phenomena, appearance of bright ring at the periphery and collapse of it at the center during a pulsatile cycle, were observed under pulsatile flow. The combined effects of shear rate and flow acceleration on RBC aggregation were suggested as a possible mechanism for these phenomena. The stroke volume-dependence of the "bright ring" phenomenon under oscillatory flow could also be explained by flow acceleration. The enveloped echo images from rotational flow in a compact blood chamber showed the spatial and temporal variations of RBC aggregation, which varied with the mammalian species. In the stenotic model, it was found that the echogenic variation increased locally at a distance of three tube diameters downstream from the stenosis during decelerating period, which was proposed to be mainly due to flow turbulence. The similar 'bright ring' was also observed from in vivo human carotid artery in harmonic imaging.
ultrasonic visualization hemodynamics shear rate flow acceleration flow turbulence blood echogenicity red blood cell aggregation