Associations Between Hemodynamics, Shape and Atherosclerosis in M1 of Middle Cerebral Artery: Insights From 4‐Dimensional Flow Magnetic Resonance Imaging in Patients With Ischemic Stroke

BACKGROUND: Intracranial atherosclerosis is a major cause of ischemic stroke. Vascular shape affects hemodynamics and plaque development. This study aims to investigate the relationships among M1 shape, hemodynamics, plaque distribution, and stroke occurrence using 4-dimensional flow magnetic resonance imaging in patients with ischemic stroke. METHODS: This cross-sectional study included 100 patients with unilateral ischemic stroke (200 M1 segments). Time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) were measured at inner- and outer-wall sides at the most curved points and corresponding straight reference sections. Wall thickness, TAWSS, and OSI were assessed for plaque cross-sections near curved points. For plaques on straight sections, TAWSS and OSI were calculated for the thick- and thin-wall sides. In patients with bilaterally curved-shaped M1, TAWSS and OSI at the most curved cross-sections were compared between stroke and nonstroke sides. RESULTS: For curved-shaped M1, the inner-wall side showed lower TAWSS and higher OSI than the outer-wall and straight reference sections. Plaque cross-sections near curved points showed greater wall thickness and OSI but lower TAWSS at the inner wall. On straight sections, thick-wall side of plaques showed decreased TAWSS and increased OSI. In patients with bilaterally curved-shaped M1, stroke sides exhibited reduced inner-wall TAWSS and elevated outer-wall OSI than nonstroke sides. CONCLUSION: Curved M1 shape is associated with disturbed hemodynamics, favoring plaque formation at the inner wall. Local variations in TAWSS and OSI may contribute to stroke risk. Our findings enhance understanding of intracranial atherosclerosis pathophysiology and highlight the value of quantifying vascular geometry and hemodynamics for individualized stroke risk assessment.