## 4 Discussion
[9], who computationally modelled the blood flow in a bifurcation geometry pre- and post-implantation of a PED and showed a reduction of the flow rate into the contralateral branch, leading to hypoperfusion post stenting. The velocity entering the aneurysm at the bifurcation location is markedly higher than that entering at a sidewall location, as might be expected due to the flow perturbation unique to a bifurcation geometry [11], comporting with the clinical observation that a water jet phenomenon at a bifurcation is the likely cause of the higher rate of recurrence at a bifurcation [31]. The eBFD flow diverter in the bifurcation shows a reduction of mean velocity of 98%, whereas the PED has a mean reduction of mean velocity of 86% in a sidewall configuration. Possibly more importantly, the mean velocity is 0.0014 m/s within a bifurcation aneurysm with an eBFD implant and is 0.0013 m/s for a PED implant at a sidewall. [PERSON] et al. [28], using CFD simulation, studied the association of hemodynamic conditions and occlusion times after flow diversion in cerebral aneurysm. Their study reported that the threshold for early occlusion of the aneurysm (thrombosis at 3 months) is a reduction of aneurysm velocity to 0.013 m/s. Both the eBFD and PED exceeded this threshold in the bifurcation and sidewall locations, respectively, by a factor of 10. Recognizing that the PED is accepted in clinical use as a FD in sidewall applications with a mean velocity of 0.0013 m/s, the eBFD, with an aneurysm mean velocity of 0.0014 m/s, should provide the same security of early thrombus formation in a bifurcation aneurysm as PED confers in a sidewall aneurysm. The successful flow-diverting effect of the eBFD in a bifurcation aneurysm, however, would occur without obstructing the flow into either side branch. While wall shear stress (WSS) is an important parameter in the analysis of aneurysm flow diversion effects, it was not calculated in this study due to aliasing and light reflection at the lumen wall that may lead to error in the cross-correlation algorithm. CFD analysis can be implemented in the future to calculate the WSS in three dimensions and high resolution. [PERSON] et al. [32] numerically showed that the placement of the stents reduced the velocity and vortices in the aneurysm sac, which caused a reduction of the wall shear stress and shear rate. In the current study, we also observed velocity and recirculation area reductions in the aneurysm after implantation. Since the shear rate and WSS are directly proportional to the velocity gradient, it is expected that the shear rate and WSS stress are reduced, similar to the results by [PERSON] et al. [32]. While blood exhibits non-Newtonian behavior for a shear rate lower than 100 1/s, the working fluid used in this study was Newtonian. [PERSON] et al. [33] reported that the refractive index of xanthan-gum-based non-Newtonian fluid cannot be matched easily by varying NaI as it considerably changes the fluid viscosity. Failing to perfectly match the refractive index causes optical distortion in PIV analysis and bias in the cross-correlation algorithm, leading to inaccurate results. Thus, a Newtonian fluid was chosen as a blood analogue. Using a non-Newtonian blood analogue might yield improved outcomes. However, different experimental and numerical hemodynamic studies have used a Newtonian model and proved that it provides a good estimation of flow characteristics [34; 35]. [PERSON] et al. [35] numerically investigated the effect of the non-Newtonian fluid assumption on blood flow dynamics in the internal carotid artery with a saccular aneurysm. The study reported that the non-Newtonian effect on wall shear stress was only important in high-velocity-gradient areas. However, both Newtonian and non-Newtonian models showed similar wall shear stress in the aneurysm area. Blood flow has pulsatile characteristics.