## 4 Discussion  
In the recent years, the endovascular techniques for treating cerebral aneurysms have shown significant advances although, they still need to be improved [22]. Intravascular stenting is presently one of the most used treatment methods even though their effect on the flow has not been completely explained from the scientific point of view. For treating cerebral aneurysms with flow diverters, a deep knowledge of the associated hemodynamic changes is always needed for optimizing the treatment performance of the stents. FDSs are considered promising for reducing blood flow into and thus occluding the aneurys sac. While in the past these devices were used in association with other techniques, many studies have demonstrated that they can be potentially used alone [8; 10; 11; 58]. Also, it has been shown that the porosity has emerged as one of the very important parameters for the success of FDS treatment [1; 7; 9]. This parameter is important to the hemodynamics changes in the artery, such as the changes in blood flow velocity and pressure, thus affecting the thrombosis. Despite many encouraging studies, the outcomes of cerebral aneurysms treated by FDSs remain uncertain and unpredictable. For example, some modifications that could be induced by the FDS for facilitating the desired hemodynamic environment are still unknown [4; 22; 50]. Very recently [PERSON] et al. [4] investigated the aneurys hemodynamic changes before and after FDS treatment; and they also examined the potential hemodynamic reduction thresholds by analysing velocity, WSS, and pressure pre- and post- stent treatments. Furthermore, they suggested a velocity reduction threshold for the aneurysm thrombosis. Unfortunately, no other hemodynamic indices have been reported in this regard. Only a few studies have analyzed the WSS related variables [50; 52] and used them in assessing aneurys rupture [22; 29]. A better understanding of the post treatment conditions would help the design of new devices for treating aneurysms. For this, in this work we have analyzed various hemodynamics quantities (velocity, pressure, TAWSS, OSI and RRT) within an idealized cerebral aneurystic artery in the presence of a new FDS design. Its performance has been compared with those of other commercial designs. The hemodynamic variables examined in this study could help identify the risk of aneurysm rupture [50]. In particular, TAWSS and OSI are recognized to be strong indicators for determining whether or not an aneurysm will rupture as reported by [PERSON] et al. [50]. Previous studies have demonstrated that low WSS and high OSI regulate endothelial surface adhesion molecules, causing dysfunction of flow-induced nitrous oxide, increasing endothelial permeability, and thus, promoting atherogenesis and inflammatory cell infiltration [60]. The inflammation process caused by this hemodynamic environment may promote degradation of the aneurysm wall, and possibly lead to the aneurysm rupture [50; 60]. In this study we also compute the RRT, which is associated with the flow blockage in the aneurysm. This parameter is directly correlated with TAWSS and OSI and has been very rarely evaluated for assessing FDS performance though it can provide the information on of the flow motion near the arterial wall. The biodegradable stent showed the largest increase in RRT despite a similar flow reduction due to its larger porosity. This would be explained by examining the OSI spatial distribution on the aneurys dome. The maximal value was found in a specific region in all started cases, the case of STENT BS showed higher values around the dome as compared to the other two cases (STENT 1 and 2). This result suggests the necessity of evaluating the variable of RRT in addition to the flow reduction. Many of previous studies have focused on the blood flow, velocity and pressure.