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Objective:To explore the hemodynamic characteristics of the middle cerebral artery (MCA) in atherosclerotic stenosis using four-dimensional flow (4D Flow) MRI, and combining high-resolution magnetic resonance vessel wall imaging (HR VW-MRI) to analyze the relationship between hemodynamics and the degree of stenosis, as well as the morphological characteristics of plaques.Methods:The study was a cross-sectional study. A total of 24 patients with middle cerebral artery(MCA) M1 atherosclerotic stenosis and 10 age and sex matched healthy controls (HC group) were prospectively recruited from September 2018 to March 2021 at Beijing Tiantan Hospital, Capital Medical University. All subjects underwent MRI examination. The hemodynamic of MCA were collected by 4D Flow MRI, and the hemodynamic parameters of proximal and distal MCA stenosis were calculated by blood flow post-processing software, including average blood flow rate (FR avg), average blood flow velocity (V avg), peak blood flow velocity (V pk), time average wall shear stress (TAWSS), minimum wall shear stress (WSS min) and oscillatory shear index (OSI). The differences in hemodynamic parameters among the proximal and distal ends of MCA stenosis and the HC group were compared using one-way ANOVA or Kruskal-Wallis H test. The stenosis rate and characteristics of MCA plaque were analyzed by HR VW-MRI, including remodeling index (RI), normalized wall index (NWI) and plaque length. Pearson or Spearman correlation analysis was used to explore the correlation between stenosis rate and hemodynamic parameters. Taking the stenosis rate as the control variable, partial correlation analysis was used to explore the correlation between plaque morphological characteristics and hemodynamic parameters. Results:There were statistically significant differences in FR avg, V avg, V pk, TAWSS, OSI, WSS min among the proximal and distal stenosis of MCA and HC groups ( P<0.05). The proximal end of the MCA stenosis had significantly higher FR avg, V avg, TAWSS and WSS min than those of the distal end of the stenosis ( P<0.01). The FR avg, V avg, V pk, TAWSS, and WSS min in the distal end of MCA stenosis were lower than those in the HC group, while the OSI was higher than that in the HC group ( P<0.01). The correlation analysis results showed that the MCA proximal V pk ( r=-0.425, P=0.027) and distal V pk ( r=-0.538, P=0.004) were negatively correlated with the diameter stenosis rate. When the stenosis rate was taken as the control factor, in the MCA proximal stenosis, V avg ( r=0.553, P=0.003), TAWSS ( r=0.543, P=0.004) and WSS min ( r=0.547, P=0.004) were positively correlated with RI, proximal OSI was negatively correlated with RI ( r=-0.492, P=0.011), and was positively correlated with the plaque length ( r=0.437, P=0.026). At the distal end of the stenosis, V pk was negatively correlated with NWI ( r=-0.556, P=0.003), OSI was negatively correlated with RI ( r=-0.511, P=0.008), NWI ( r=-0.390, P=0.049). TAWSS was positively correlated with RI ( r=0.393, P=0.047). Conclusions:The 4D Flow MRI demonstrates characteristic hemodynamic changes in the proximal and distal ends of the stenotic MCA. The local hemodynamic characteristics of the stenotic MCA are correlated with plaque morphological parameters, including lumen stenosis, plaque load, and RI. It suggests an interaction between the occurrence and development of MCA plaque and local hemodynamic changes.