Affiliations: Department of Ocean System Engineering,
Interdisciplinary Postgraduate Program in Biomedical Engineering, Jeju National
University, 66 Jejudaehakno, Jeju-si, Jeju special self-governing province,
690-756, Korea. E-mail: paeng@jejunu.ac.kr | Department of Bioengineering, University of Utah, Salt
Lake City, UT 84112, USA. E-mail: kweonho.nam@utah.edu (Corresponding author)
Abstract: 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.
