Type:
Educational Exhibit
Keywords:
Vascular, Cardiovascular system, Arteries / Aorta, Ultrasound, Experimental, Education, Technical aspects, Diagnostic procedure, Education and training, Developmental disease
Authors:
A. Goddi1, Y. Du2, A. Dell'Era2, R. novario1; 1Varese/IT, 2Shenzhen/CN
DOI:
10.26044/ecr2019/C-0436
Background
Some studies have been performed to analyze the flow in the carotid arteries and to establish the correlations between plaque formation and complex flow patterns [1].
It has been shown that blood flow characteristics are involved in the development of atherosclerosis in the carotid bifurcation [2].
Local modifications in blood flow patterns are associated with vessel geometry variation at bends and bifurcations,
and adverse pressure gradient and significant flow decelerations,
as seen in the carotid bifurcation [3].
Model flow studies of the carotid bifurcation have shown that a large area of flow separation develops along the outer wall of the carotid sinus.
The region of separation is not merely a zone of stasis and recirculation but is instead an area of flow instability,
with multiple eddies and counter-eddies,
and of complex secondary flow patterns,
including counter-rotating helical trajectories and slow fluid movement upstream [4].
Different types of mechanical forces are also involved in the development of atherosclerosis in the carotid bifurcation [2].
Blood flowing through a vessel exerts a physical force which generates two principal stress vectors on the vessel wall.
One is the stress perpendicular to the vessel wall,
defined as tensile stress,
which represents the dilating force exerted by the blood pressure on the vessel wall.
The other is the stress parallel to the vessel wall,
defined as shear stress,
which represents the frictional force exerted on the endothelial surface [5].
The nature and magnitude of shear stress at a given location within the vasculature plays a vital role in the long-term health of the blood vessel [6].
An unsteady WSS,
associated with local non-laminar blood flow,
promotes endothelial dysfunction allowing plaque development.
It has been shown that plaque development is related to the regions where the WSS oscillates.
The position of the maximum WSS oscillation varies,
but it is always in the point where the difference in velocity vectors between the forward and the backflow during the cardiac cycle is most significant [7].
Therefore,
the prerequisites for early diagnosis and risk stratification are the ability to:
- analyze blood flow patterns,
- detect flow disturbances,
which duration is limited to short time intervals,
- identify the recirculation regions,
- calculate the WSS variation.
Despite the attempts,
it has not been possible to obtain a quick and precise measurement of WSS in the clinic for many years [5].
This is primarily due to the resolution limits of imaging modalities such as Spectral Doppler [8] and MRI [9].