Effect of Flow-diverter Stent on In Vitro Aneurysmal Flow (original) (raw)
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Acta Neurochirurgica
Background Stent deployment across the aneurysmal neck has been established as one of the endovascular methods to treat intracranial aneurysms with or without coils. Objective The purpose is to study the possible adverse effects of deployment of the new flow-diverter stent-like devices (FD) on the flow characteristics of saccular aneurysm models. Methods Numerical simulations of the blood flow patterns in the artificial models of three aneurysms were studied. One model was designed without an FD stent, the second model with one FD stent, and the third model with two stents. Numerical simulation for incompressible laminar blood flow was conducted in the three artificial cerebral aneurysm models by means of computational fluid dynamics. Results There was a noticeable increase in the values of the circumferential pressure distributed on the walls of the aneurysm after stent deployment; this led to an increase the tension of the aneurysm surface and was considered to be an adverse effect. This pressure increase was further aggravated by the deployment of another stent. However, there is a beneficial effect of using FD stents, translating into the reduction of the flow velocity inside the aneurysm and wall shear stress at the inflow zone. This reduction decreases further with the deployment of another stent. Conclusion Aneurysms become tenser after the deployment of one flow-diverter stent and (more tense still) after after the deployment of another stent. This principle should be kept in mind when choosing which group of aneurysms is the best candidate for such a treatment strategy. This study recommends deploying several FD stents during endovascular procedures until complete arrest of the blood flow occurs during the procedure; otherwise, the aneurysm may become tenser and dangerous if a slow blood flow jet still exists inside it at the end of the procedure.
Interventional neuroradiology : journal of peritherapeutic neuroradiology, surgical procedures and related neurosciences, 2006
Stent implants placed across the neck of cerebral aneurysms are capable of reducing aneurysmal flow when coils are not used for filling the aneurysms. It is important to evaluate the effects of flow reduction caused by stent implants used for the treatment of cerebral aneurysms. Subtracted vortex centers path line method (SVC method) is one of the image post processing methods employed for quantitative flow measurement. We developed a modified SVC method by employing Cinematic Angiography (25 frames/s) and digital video recording (30 frames/s) with a commercial digital camera.We successfully compared the flow effectiveness using a tubular silicon model with a sidewall aneurysm. The result suggests that our modified SVC method is useful for a comparative examination of the effect of aneurysmal flow reduction caused by stent implants.
Medical Imaging 2004: Physiology, Function, and Structure from Medical Images, 2004
Asymmetric stents are promising new devices for endovascular treatment of cerebrovascular aneurysms. For in vitro experiment a patch made of stainless steel mesh is directly attached onto a standard stent and deployed so that the patch is placed over the aneurysm orifice. Thus we modify substantially the flow into the aneurysm and decrease the shear stress on the aneurysm walls. We used mesh-patches having different permeabilities and evaluated the flow using Particle Image Velocimetry. PIV provides instantaneous velocity vector measurements in a cross-section of flow containing reflective micro-particles. A pulsed-laser light sheet illuminates the flow in the target area and images are acquired using a CCD camera. By registering the position of the particles in two successive images the fluid velocity vectors components are calculated. From the 2D velocity field a best polynomial fit is made to obtain a smooth function of each velocity with respect to the coordinates. Using the fit, we derived the values of quantities of interest in the plane of acquisition such as: tangent shear stress, vorticity and inflow. We used four meshes of different permeabilities. We found out that by using lower permeability meshes we create better conditions for the embolization of the aneurysm.
AJNR. American journal of neuroradiology
Stent implantation alone might not be sufficient to produce definitive treatment of cerebral aneurysms. Therefore, extended experimental work is needed to improve results. We show the feasibility of using an in vitro anatomically shaped elastic model for flow evaluation before and after stent implantation. Based on human vascular casting, an anatomic elastic internal carotid artery model, including an aneurysm on the supraclinoid portion, was manufactured. The model was connected to a circulatory loop to simulate physiological flow. After visualization of the flow by using glass particles and laser sheet translumination, the digitally recorded data were transferred for computer analysis. Intra-saccular flow pattern changes and the vortex velocity reduction induced by the stent were investigated qualitatively and quantitatively. The distal neck of the aneurysm behaved as a flow divider. Therefore, it was directly exposed to the hemodynamic stress. Inside the sac, a well-defined vorte...
Frontiers in Neurology, 2021
Purpose: The flow diversion effect of an intracranial stent is closely related to its metal coverage rate (MCR). In this study, the flow diversion effects of Enterprise and low-profile visualized intraluminal support (LVIS) stents are compared with those of a Pipeline flow diverter, focusing on the MCR change. Moreover, the changes in the flow diversion effect caused by the additional manipulations of overlapping and compaction are verified using computational fluid dynamics (CFD) analysis. Methods: CFD analysis was performed using virtually generated stents mounted in an idealized aneurysm model. First, the flow diversion effects of single Enterprise, LVIS, and Pipeline devices were analyzed. The Enterprise and LVIS were sequentially overlapped and compared with a Pipeline, to evaluate the effect of stent overlapping. The effect of compacting a stent was evaluated by comparing the flow diversion effects of a single and two compacted LVIS with those of two overlapped, uncompacted LV...
Numerical analysis of stent porosity and strut geometry for intra-saccular aneurysmal flow
2011
We numerically simulate the hemodynamics of aneurysmal flow and evaluate stent design configuration based on an idealistic geometrical model. We examined large-scale swirling of blood within a significantly dilated aneurysm. Various parameters such as stent porosity and strut shape have an impact on the pressure and shear strain rate within the aneurysm. Using biofluid mechanical parameters such as pressure gradient and shear strain rate for aneurysmal arteries implanting with different stent configuration, a flow analysis framework for evaluation of stents is developed. With the application of cardiac flow analysis, we are aim to achieve a balance in the two properties in order to prevent aneurysmal rupture and thrombosis formation and give out the most suitable stent configuration for the stent implanting surgery.
2009 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, 2009
The aim of this study is to investigate the influence of stent axial orientation on saccular aneurysm hemodynamics. Two commercial stents, Neuroform stent (stent 1) and Zilver stent (stent 2) are modeled in this study. Both stents are virtually deployed with four different axial orientations to fit into the luminal surface of a patient-specific internal carotid artery (ICA) aneurysm model. Computational hemodynamic analyses are carried out in unstented and stented aneurysm models. The intra-aneurismal flows of stented aneurysm models show disturbed and complex flow patterns while the flow activities and the forces acting on the aneurysm wall are generally alleviated by stenting. The influence of the axial orientation of the stent on the aneurysm hemodynamics is more significant for stent 2 which has a larger strut size compared to stent 1. Interestingly, the flow activity in the aneurysm is rather increased when the intra-luminal scaffolding of stent is not sufficient.
Journal of neurointerventional surgery, 2015
Validation of computational fluid dynamics (CFD) in stented intracranial aneurysms (IAs) is still lacking, to reliably predict prone to occlusion hemodynamics, probing, in particular, velocity reduction, and flow pattern changes. This study compares CFD outcome with particle imaging velocimetry (PIV) for three commercial off the shelf (COTS) stents of different material densities. The recently developed uniform and high precision multi-time lag PIV method was applied to a sidewall aneurysm before and after implantation of three COTS stents with high, intermediate, and low material densities. The measured laser sheet flow patterns and velocity reductions were compared with CFD results and correlated with stent material density. Velocity reduction was in good agreement for unstented high and low porosity stented IA, while flow pattern change was fully matched for unstented and high porosity stented IA. Poor CFD-PIV matching in IA was found for intermediate porosity stents. CFD reprodu...
Intracranial Stents Being Modeled as a Porous Medium: Flow Simulation in Stented Cerebral Aneurysms
Annals of Biomedical Engineering, 2011
Intracranial aneurysms may be treated by flow diverters, alternatively to stents and coils combination. Numerical simulation allows the assessment of the complex nature of aneurismal flow. Endovascular devices present a rather dense and fine strut network, increasing the complexity of the meshing. We propose an alternative strategy, which is based on the modeling of the device as a porous medium. Two patient-specific aneurysm data sets were reconstructed using conventional clinical setups. The aneurysms selection was done so that intra-aneurismal flow was shear driven in one and inertia driven in the other. Stents and their porous medium analog were positioned at the aneurysm neck. Physiological flow and standard boundary conditions were applied. The comparison between both approaches was done by analyzing the velocity, vorticity, and shear rate magnitudes inside the aneurysm as well as the wall shear stress (WSS) at the aneurysm surface. Simulations without device were also computed. The average flow reduction reaches 76 and 41% for the shear and inertia driven flow models, respectively. When comparing the two approaches, results show a remarkable similarity in the flow patterns and magnitude. WSS, iso-velocity surfaces and velocity on a trans-sectional plane are in fairly good agreement. The root mean squared error on the investigated parameters reaches 20% for aneurysm velocity, 30.6% for aneurysm shear rate, and 47.4% for aneurysm vorticity. It reaches 20.6% for WSS computed on the aneurysm surface. The advantages of this approach reside in its facility to implement and in the gain in computational time. Results predicted by the porous medium approach compare well with the real stent geometry model and allow predicting the main effects of the device on intraaneurismal flow, facilitating thus the analysis.
Analysis on intra-aneurysmal flow influence by stenting
2010 3rd International Conference on Biomedical Engineering and Informatics, 2010
This Using numerical simulation, the evolution of vortices in an aneurysm can be tracked. We examined large-scale swirling of blood within a significantly dilated aneurysm and quantified the pressure gradient and shear strain rate. Based on these fluid mechanical parameters, we are able to identify the difference in flow effects between the untreated and stented aneurysmal arteries. This study demosntrates that the large-scale vortex, pressure gradient and blood shear strain rate within an aneurysm sac reduces after stenting.