In the SOpHIA study, cerebral CTA was performed in all patients at baseline after an acute ischemic stroke or TIA, with a 64-slice CT scanner (Lightspeed VCT, GE Healthcare) with the following protocol: intravenous contrast (Omnipaque 300) was injected via the antecubital vein at a rate of 3–3.5 mL/s with a total volume of 70 mL, and images were obtained with 120 kVp, 550 mAs, 0.625 mm slice thickness and 0.4 s rotation ( Lan et al., 2020). We performed static cerebral blood flow simulation in three cases and transient simulation in the remaining case. In this study, we therefore aimed to investigate the differences, if any, of CFD simulation results in pressure (e.g., PR) and WSS between Newtonian and non-Newtonian fluid models, in a virtual arterial stenosis model and patient-specific ICAS models we performed static simulations on the virtual model, and both static and transient simulations on patients-specific models.įour patients with stenosed MCA recruited in the SOpHIA study ( Leng et al., 2019) were analyzed in the current study. Previous studies simulating blood flow in intracranial aneurysms, in normal aorta, and in virtual arterial stenosis models have indicated differences in the estimations of pressure and WSS based on Newtonian and non-Newtonian models ( Hippelheuser et al., 2014 Rabby et al., 2014). However, in the low-velocity areas, the true viscosity is much higher than this constant, when non-Newtonian rheological models could simulate the blood viscosity variations in different shear strain rates ( Gijsen et al., 1999 Jahangiri et al., 2017). With increasing flow velocity and shear strain rate, blood flows more smoothly ( Moon et al., 2014) and its viscosity decreases toward a constant, which has been commonly used as the viscosity of blood in a Newtonian model ( Jahangiri et al., 2017). In most of the previous CFD studies on ICAS, blood was simulated as a Newtonian fluid for simplicity ( Leng et al., 2014, 2019 Nam et al., 2016 Liu et al., 2018 Chen et al., 2020), despite the fact that blood is a non-Newtonian fluid with a shear-thinning nature ( Nader et al., 2019). Both indices have been associated with the risk of stroke relapse in patients with symptomatic ICAS: those with a lower PR (i.e., larger translesional pressure gradient) and excessively elevated focal WSS at the ICAS lesion had significantly higher risk of recurrent stroke despite optimal medical treatment ( Leng et al., 2019). On the other hand, the relative change of wall shear stress (WSS) at the stenotic throat as compared to WSS at proximal “normal” vessel segment, has also been proposed to reflect the hemodynamic impact of an ICAS lesion on plaque growth and rupture ( Lan et al., 2020). For instance, translesional pressure ratio (PR), calculated as the ratio of the pressures distal and proximal to an ICAS lesion obtained in a CFD model, has been put forward to reflect the hemodynamic significance of ICAS ( Liebeskind and Feldmann, 2013). In recent years, computational fluid dynamics (CFD) modeling based on conventional neurovascular imaging has been applied to simulate in vivo cerebral blood flow and quantify cerebral hemodynamic metrics in the presence of ICAS, which cannot be achieved with conventional neurovascular imaging alone ( Liebeskind et al., 2016 Linfang Lan, 2017 Liu et al., 2018 Chen et al., 2020).Ĭomputational fluid dynamics modeling studies have indicated that global and focal cerebral hemodynamics may play an important role in governing the risk of stroke recurrence in patients with symptomatic ICAS ( Leng et al., 2014, 2019). Intracranial atherosclerotic stenosis (ICAS) is a major cause for ischemic stroke and transient ischemic attack (TIA) in Asian populations ( Wong, 2006).
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