Effects of arterial blood flow on walls of the abdominal aorta: distributions of wall shear stress and oscillatory shear index determined by phase-contrast magnetic resonance imaging
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Although abdominal aortic aneurysms (AAAs) occur mostly inferior to the renal artery, the mechanism of the development of AAA in relation to its specific location is not yet clearly understood. The objective of this study was to evaluate the hypothesis that even healthy volunteers may manifest specific flow characteristics of blood flow and alter wall shear or oscillatory shear stress in the areas where AAAs commonly develop. Eight healthy male volunteers were enrolled in this prospective study, aged from 24 to 27. Phase-contrast magnetic resonance imaging (MRI) was performed with electrocardiographic triggering. Flow-sensitive four-dimensional MR imaging of the abdominal aorta, with three-directional velocity encoding, including simple morphological image acquisition, was performed. Information on specific locations on the aortic wall was applied to the flow encodes to calculate wall shear stress (WSS) and oscillatory shear index (OSI). While time-framed WSS showed the highest peak of 1.14 ± 0.25 Pa in the juxtaposition of the renal artery, the WSS plateaued to 0.61 Pa at the anterior wall of the abdominal aorta. The OSI peaked distal to the renal arteries at the posterior wall of the abdominal aorta of 0.249 ± 0.148, and was constantly elevated in the whole abdominal aorta at more than 0.14. All subjects were found to have elevated OSI in regions where AAAs commonly occur. These findings indicate that areas of constant peaked oscillatory shear stress in the infra-renal aorta may be one of the factors that lead to morphological changes over time, even in healthy individuals.
KeywordsAneurysm Aorta Blood flow Wall shear stress
With regard to technical assistance for data analysis, we deeply appreciate the help of Kazutoshi Miyashita. Also, we are grateful to Hirotaka Sato, Koji Matsumoto, Masatoshi Kojima for their time-consuming efforts acquiring MRI data. Finally, we gratefully acknowledge Dr. Ken Motoori for his methodological suggestions.
Compliance with ethical standards
Conflict of interest
The authors have no conflicts of interest to declare.
This study was partially supported by the Inohana Alumni Association of the Chiba University of Medicine (12046).
Streamline in the abdominal aorta. View from the left side. Note that the aortic wall changes its size in accordance with the blood flow. After the fast flow, static looping flow remains to the renal arteries. (MPG 1766 kb)
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