Introduction
The latest data from the Global Burden of Disease Study (GBD) shows that stroke is the primary cause of death and disability in adults in China, bringing a huge economic burden to patients and society^[1]. Atherosclerosis is the most common cause of ischemic stroke. Systemic arteries are exposed to systemic risk factors of atherosclerosis, such as age, gender, hyperlipidemia, hypertension, hyperglycemia, smoking and obesity, but atherosclerosis plaque has specific predilection sites^[2].The bifurcation of the common carotid artery is the most common location of carotid atherosclerotic plaque^[3]. In this study, 4D flow MRI was used to evaluate the carotid artery hemodynamics, and the geometric of the carotid artery was fused to explore the hemodynamic and geometric mechanism of carotid atherosclerotic plaque formation.
Methods
122 carotid arteries of 61 patients were included and divided into plaque group(N=69) and non-plaque group(N=53). The 4D flow MRI scans were performed using a 3.0T MRI scanner (Ingenia CX, Philips Healthcare, the Netherlands) with a tirty-two channel head–neck coil. The 4D flow MRI was acquired using a volumetric and a time-resolved PC method. The scanning parameters were as follows:FOV=240×240mm²,TR/TE=5.6/2.9ms,Flip angle=8°, Velocity encoding(VENC)=100cm/s, The total scan time of the 4D flow was approximately 12−15 minutes depending on the heart rate of each subject. The 4D flow datasets were imported into the CVI-42 platform (Version 5.6.6, Circle Cardiovascular Imaging, Canada) for further analysis. As displayed in Fig.1a and b, we placed plane in the bifurcation of common carotid artery to evaluate hemodynamics (Volume, Velocity_max, Axial WSS_mean, Circumferential WSS_mean, 3D WSS_max, 3D WSS_mean, PG_max, PG_mean). Measurement of carotid artery geometry based on 3D-TOF MRA as displayed in Fig.1c. The measured geometric parameters include: a) ICA/CCA-ratio: the ratio of ICA maximum inner diameter to CCA maximum inner diameter; b) Bifurcation angle: measured along two tangent lines along the outer wall of internal and external carotid arteries, using α represent; c) Tortuosity: The curvature of the carotid artery is evaluated by the ratio of the straight distance (D) to the distance along the center of the lumen (L) of CCA-ICA. Statistical analysis was performed using GraphPad Prism (version 9.0) software. Independent two sample t-tests were used to detect carotid artery geometry and hemodynamic changes among plaque group and non-plaque group. P<0.05 was considered statistically significant.
Results
122 carotid arteries of 61 patients were included and divided into plaque group(N=69) and non-plaque group(N=53). The patient demographic data were listed in Table1. Carotid artery geometry and hemodynamic of plaque group and non-plaque group were displayed in Table2. There were statistically significant differences in bifurcation angle, tortuosity, axial WSS_mean, circumferential WSS_mean, 3D WSS_max, 3D WSS_mean, PG_max and PG_mean between the two groups(P<0.05)，as displayed in Fig.2 and Fig.3.
Discussion
The high tortuosity of the carotid artery has a protective effect on patients with carotid atherosclerosis, because the increase of eddy current inhibits turbulence. A larger bifurcation angle of the CCA, a lower PG and WSS of the carotid artery are more likely to form plaques. Few studies use PG value to detect the formation of plaque. One study compared the PG value of healthy people and patients with carotid atherosclerotic stenosis, and found that the PG value of patients with stenosis was low^[4]. In addition, there are also studies that show that the PG value decreases with age, and old age is one of the risk factors for atherosclerotic plaque formation^[5]. Therefore, it indirectly indicates that low PG value can promote plaque formation. Low WSS increases the uptake of low-density lipoprotein, leading to the formation of lipid components in plaques. In addition, low WSS value changes the blood flow pattern of vascular endothelium at the molecular and cellular levels, and all these reactions promote the formation of atherosclerotic plaque^[6].
Conclusion
As an initial and exploratory study, this work showed that the large bifurcation angle of the CCA and the low tortuosity of the carotid artery are geometric risk factors for plaque formation in carotid bifurcation. Low PG and WSS are hemodynamic factors promoting plaque formation.