## 4 Discussion  
Flow diverters have been accepted as standalone implants for the treatment of intracranial aneurysms in lieu of other conventional treatment methods, including clipping, embolic coil, and stent-assisted coiling, in particular for wide-neck aneurysms [27]. However, effective flow diversion by the implant for aneurysm healing is considerably dependent on the velocity reduction within the aneurysm sac [28]. The current study used a PIV optical fluid dynamics measurement technique to evaluate the flow diversion effect of a new generation of the eCLIPs flow diverter and compare the results to those of previous eCLIPs coil retaining implants and the PED flow diverter. The deployment of all devices caused a flow-diverting effect in the aneurysm dome. However, the level of flow diversion and reduction of aneurys velocity compared with the baseline were different across the implants and configurations. The results showed that there is a strong correlation between metal coverage density and flow reduction. This finding was in agreement with previously published studies [15; 16; 17]. For instance, the eBRS and eB implants both reduced the velocity within the aneurysm, with metal densities of 26% and 21%, respectively. [PERSON] et al. [29] experimentally investigated the effect of stent porosity in reducing cerebral sidewall aneurysm flow using PIV. They reported that to effectively dampen the flow in an aneurysm, the stent porosity should be kept around 60% (40% metal coverage), and for a porosity of 64% (36% metal coverage), the velocity decreased by 98% in the aneurysm [29]. The eBFD was manufactured with 35% metal coverage. It had the highest flow reduction amongst the implants, with a mean flow reduction of 98%, concordant with results by [PERSON] et al. [29]. Their observation that a 26% density yielded a mean velocity of 0.0048 m/s in the aneurysm is comparable to the mean velocity of 0.0049 m/s observed for the eBRS (also 26% density). Thus, [PERSON]'s data provide a measure of validity to the results obtained in this report. A jet and large recirculation was observed in the sidewall anatomy (Figure 4f) with no device across the neck. A computational study by [PERSON] et al. [30] showed similar fluid dynamics in a cerebral bifurcation without an implant at peak systole. As expected, the PED implant in sidewall configuration significantly reduced the flow in the aneurysm dome (Figure 4g)--a result of the high density of the braided mesh influencing the fluid dynamics in the aneurysm dome. The PED has been widely accepted as an effective flow diverter for the treatment of sidewall intracranial aneurysms. A review by [PERSON] et al. [6] of PED flow diverters' clinical outcomes reported that the PED is an effective implant to treat wide-necked, fusiform, large, and giant unruptured aneurysms, with 5% of patients experiencing permanent major morbidity and mortality. However, they emphasized a lack of understanding of the flow diverter's effect at bifurcations. While the PED has 30% metal coverage, as reported in the device's instruction for use, the PED in the bifurcation configuration showed higher velocity entering the aneurysm (mean velocity 0.0075 m/s) than either the eBRS (0.0049 m/s) or eBFD (0.0014 m/s) and effectively the same as the eB implant (0.0077 m/s) with 21% density (Table 2). The higher PED mean velocity in the bifurcation geometry over a device that fully bridges the neck, such as eCLIPs implants, may be explained by the PED bending at the transition between the parent artery and daughter branch, leading to mesh stretching and higher porosity. In addition, the PED in the bifurcation configuration only partially covers the aneurysm neck, potentially leading to a Venturi effect and high velocity at the neck. While not quantified, visual inspection showed an obvious, and expected, reduction of the outflow into the contralateral branch. This observation was highlighted by [PERSON] et al.