Optimization of Strut Placement in Flow Diverter Stents for Four Different Aneurysm Configurations

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Hitomi Anzai ◽  
Jean-Luc Falcone ◽  
Bastien Chopard ◽  
Toshiyuki Hayase ◽  
Makoto Ohta
Keyword(s):  
Arterial Occlusion ◽  
Flow Simulation ◽  
Flow Diverter ◽  
Optimal Placement ◽  
Parent Artery ◽  
High Porosity ◽  
Mesh Structure ◽  
Flow Reduction ◽  
Fine Mesh ◽  
Flow Diverter Stent

A modern technique for the treatment of cerebral aneurysms involves insertion of a flow diverter stent. Flow stagnation, produced by the fine mesh structure of the diverter, is thought to promote blood clotting in an aneurysm. However, apart from its effect on flow reduction, the insertion of the metal device poses the risk of occlusion of a parent artery. One strategy for avoiding the risk of arterial occlusion is the use of a device with a higher porosity. To aid the development of optimal stents in the view point of flow reduction maintaining a high porosity, we used lattice Boltzmann flow simulations and simulated annealing optimization to investigate the optimal placement of stent struts. We constructed four idealized aneurysm geometries that resulted in four different inflow characteristics and employed a stent model with 36 unconnected struts corresponding to the porosity of 80%. Assuming intracranial flow, steady flow simulation with Reynolds number of 200 was applied for each aneurysm. Optimization of strut position was performed to minimize the average velocity in an aneurysm while maintaining the porosity. As the results of optimization, we obtained nonuniformed structure as optimized stent for each aneurysm geometry. And all optimized stents were characterized by denser struts in the inflow area. The variety of inflow patterns that resulted from differing aneurysm geometries led to unique strut placements for each aneurysm type.

Flow Simulations to Establish the Relationship Between the Inflow Zone in the Neck of a Cerebral Aneurysm and the Positions of Struts

2016 ◽  
Author(s):  
Kazuhiro Watanabe ◽  
Hitomi Anzai ◽  
Makoto Ohta
Keyword(s):  
Reduction Rate ◽  
Flow Simulation ◽  
High Flow ◽  
Parent Artery ◽  
High Porosity ◽  
Critical Area ◽  
Flow Reduction ◽  
Fine Mesh ◽  
Parent Artery Occlusion ◽  
The Relationship

Flow-diverter (FD) stent implantation is an attractive treatment for cerebral aneurysms because of its low level of invasiveness. FD stent has a fine mesh structure, and the aim of FD implantation is to reduce the blood flow in an aneurysm by covering the aneurysm orifice. However, the fine mesh of the implant poses the risk of parent artery occlusion. One approach for avoiding this risk is to use a stent with a higher porosity. Previous studies have shown that placing a strut to disturb the inflow entering an aneurysm can promote a higher reduction in aneurysm flow. However, Hirabayashi et al. reported that a high-porosity stent can be sensitive to misdeployment in flow reduction. We hypothesized that a positioning error in flow reduction was sensitive to the relative position of the strut to the inflow configuration. In this study, we performed flow simulation to investigate the relationship between the inflow zone of the aneurysm neck and the positions of struts. Lattice Boltzmann (LB) flow simulation was performed to allow a comprehensive study of strut positions. Two rectangular solids were used as the strut model. Steady flow simulation was applied to models based on ideal and realistic three-dimensional (3D) aneurysm geometry, changing two strut positions along the neck plane. For both models, velocity boundaries were imposed on the inlet and a constant pressure boundary was imposed on the outlet. Average flow velocity in an aneurysm was calculated to evaluate the dependency of the flow reduction effect on the deployment position. We analyzed aneurysm flow using the following three strategies to observe the relationship between flow configuration, strut configuration, and flow reduction. Analysis A: Flow reduction rate (Rf) with one strut. A strut was moved from the proximal to the distal neck (perpendicular deployment) or from outside to inside (parallel deployment). Analysis B: Rf with two struts. One strut (strut A) was fixed in a specific position on the neck plane. The other (strut B) was moved along the neck plane in parallel to strut A. Analysis C: Rf with two struts. Strut B was located on the distal or inner side of strut A. The distance between the two struts was changed, and the two struts were moved along the neck plane while maintaining that distance. From the results of Analyses A and B, we confirmed a critical area in the inflow zone that maintained a high flow reduction regardless of the position of the second strut. The results of Analysis C confirmed that there were several distances between the struts at which flow reduction was almost constant. This constant reduction was maintained when one of the struts was located in the critical area, whereas the reduction was disturbed if both struts were located outside the area. These results suggest that the influence of positioning errors can be reduced by constantly placing at least one strut in a critical area, resulting in a high flow reduction. This may lead to optimal stent porosity for flow reduction and robustness of deployment.

scholarly journals Selection of helical braided flow diverter stents based on hemodynamic performance and mechanical properties

2016 ◽  
Vol 9 (10) ◽  
pp. 999-1005 ◽  
Author(s):  
Takashi Suzuki ◽  
Hiroyuki Takao ◽  
Soichiro Fujimura ◽  
Chihebeddine Dahmani ◽  
Toshihiro Ishibashi ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Reduction Rate ◽  
Flow Diverter ◽  
Outer Diameter ◽  
Cfd Simulations ◽  
Flow Reduction ◽  
Radial Stiffness ◽  
Flow Diverter Stent ◽  
Hemodynamic Performance ◽  
Longitudinal Flexibility

BackgroundAlthough flow diversion is a promising procedure for the treatment of aneurysms, complications have been reported and it remains poorly understood. The occurrence of adverse outcomes is known to depend on both the mechanical properties and flow reduction effects of the flow diverter stent.ObjectiveTo clarify the possibility of designing a flow diverter stent considering both hemodynamic performance and mechanical properties.Materials and methodsComputational fluid dynamics (CFD) simulations were conducted based on an ideal aneurysm model with flow diverters. Structural analyses of two flow diverter models exhibiting similar flow reduction effects were performed, and the radial stiffness and longitudinal flexibility were compared.ResultsIn CFD simulations, two stents–Pore2-d35 (26.77° weave angle when fully expanded, 35 μm wire thickness) and Pore3-d50 (36.65°, 50 μm respectively)–demonstrated similar flow reduction rates (68.5% spatial-averaged velocity reduction rate, 85.0% area-averaged wall shear stress reduction rate for Pore2-d35, and 68.6%, 85.4%, respectively, for Pore3-d50). However, Pore3-d50 exhibited greater radial stiffness than Pore2-d35 (40.0 vs 21.0 mN/m at a 3.5 mm outer diameter) and less longitudinal flexibility (0.903 vs 0.104 N·mm bending moments at 90°). These measurements indicate that changing the wire thickness and weave angle allows adjustment of the mechanical properties while maintaining the same degree of flow reduction effects.ConclusionsThe combination of CFD and structural analysis can provide promising solutions for an optimized stent. Stents exhibiting different mechanical properties but the same flow reduction effects could be designed by varying both the weave angle and wire thickness.

Comparison of hemodynamic stress in healthy vessels after parent artery occlusion and flow diverter stent treatment for internal carotid artery aneurysm

2021 ◽  
pp. 1-8
Author(s):  
Tetsuya Tsukada ◽  
Takashi Izumi ◽  
Haruo Isoda ◽  
Masahiro Nishihori ◽  
A. Elisabeth Kropp ◽  
...  
Keyword(s):  
Flow Diverter ◽  
Artery Occlusion ◽  
Volume Flow ◽  
Parent Artery ◽  
Hemodynamic Stress ◽  
Parent Artery Occlusion ◽  
Flow Diverter Stent ◽  
Stent Treatment ◽  
Before And After ◽  
Healthy Side

OBJECTIVE De novo aneurysms generally develop in healthy vessels after parent artery occlusion for large internal carotid artery (ICA) aneurysm, possibly owing to increased hemodynamic stress in the remaining vessels. In recent years, there has been a shift toward flow diverter stent treatment. However, there is a lack of direct evidence and data that prove this change in hemodynamic stress in healthy vessels after parent artery occlusion and flow diverter stent treatment. The authors compared hemodynamic stress in healthy-side vessels before and after parent artery occlusion and flow diverter treatments. METHODS The authors included patients who underwent 3D cine phase-contrast MRI before and after large ICA aneurysm treatment. Spatially and temporally averaged volume flow rates and spatially averaged systolic wall shear stress (WSS) in healthy-side ICA distal to the posterior communicating artery (C1 segment according to Fisher’s classification) were measured before and after parent artery occlusion and flow diverter treatments. RESULTS Seventeen patients were included (5 patients in the parent artery occlusion group and 12 in the flow diverter group). At 1–2 months after treatment, median volume flow rate in healthy-side ICA increased from 5.36 ml/sec to 6.28 ml/sec (total increase 117%, p = 0.04) in the parent artery occlusion group and from 4.65 ml/sec to 4.93 ml/sec (total increase 106%, p = 0.02) in the flow diverter group. In the parent artery occlusion group, median WSS in the C1 segment of the healthy-side ICA increased from 3.91 Pa to 5.61 Pa (total increase 143%, p = 0.08); however, no significant increase was observed in the flow diverter group (4.29 Pa to 4.57 Pa [total increase 107%, p = 0.21]). CONCLUSIONS Postoperatively, volume flow rate and WSS in the C1 segment of the healthy-side ICA significantly increased in the parent artery occlusion group. Therefore, the parent artery occlusion group was more prone to de novo aneurysm than the flow diverter group.

Increasing Flow Diversion for Cerebral Aneurysm Treatment Using a Single Flow Diverter

Neurosurgery ◽  
2014 ◽  
Vol 75 (3) ◽  
pp. 286-294 ◽  
Author(s):  
Jianping Xiang ◽  
Ding Ma ◽  
Kenneth V. Snyder ◽  
Elad I. Levy ◽  
Adnan H. Siddiqui ◽  
...  
Keyword(s):  
Shear Stress ◽  
Cerebral Aneurysms ◽  
Flow Diverter ◽  
Turnover Time ◽  
Patient Specific ◽  
Uniform Mesh ◽  
Mesh Structure ◽  
Flow Reduction ◽  
Flow Stasis ◽  
Single Flow

Abstract BACKGROUND: A neurovascular flow diverter (FD), aiming at inducing embolic occlusion of cerebral aneurysms through hemodynamic changes, can produce variable mesh densities owing to its flexible mesh structure. OBJECTIVE: To explore whether the hemodynamic outcome would differ by increasing FD local compaction across the aneurysm orifice. METHODS: We investigated deployment of a single FD using 2 clinical strategies: no compaction (the standard method) and maximum compaction across the aneurysm orifice (an emerging strategy). Using an advanced modeling technique, we simulated these strategies applied to a patient-specific wide-necked aneurysm model, resulting in a relatively uniform mesh with no compaction (C1) and maximum compaction (C2) at the aneurysm orifice. Pre- and posttreatment aneurysmal hemodynamics were analyzed using pulsatile computational fluid dynamics. Flow-stasis parameters and blood shear stress were calculated to assess the potential for aneurysm embolic occlusion. RESULTS: Flow streamlines, isovelocity, and wall shear stress distributions demonstrated enhanced aneurysmal flow reduction with C2. The average intra-aneurysmal flow velocity was 29% of pretreatment with C2 compared with 67% with C1. Aneurysmal flow turnover time was 237% and 134% of pretreatment for C2 and C1, respectively. Vortex core lines and oscillatory shear index distributions indicated that C2 decreased the aneurysmal flow complexity more than C1. Ultrahigh blood shear stress was observed near FD struts in inflow region for both C1 and C2. CONCLUSION: The emerging strategy of maximum FD compaction can double aneurysmal flow reduction, thereby accelerating aneurysm occlusion. Moreover, ultrahigh blood shear stress was observed through FD pores, which could potentially activate platelets as an additional aneurysmal thrombosis mechanism.

A Computational Modelling for Hemodynamic Conditions Following Flow-Diverting Treatment in Cerebral Aneurysms

2018 ◽  
Author(s):  
Gen Fu ◽  
Alexandrina Untaroiu
Keyword(s):  
Average Velocity ◽  
Physiological State ◽  
Cerebral Aneurysms ◽  
Side Wall ◽  
Flow Diverter ◽  
Geometrical Parameters ◽  
Parent Artery ◽  
Flow Diverter Stent ◽  
Structure Of Flow ◽  
Flow Diverters

Cerebral aneurysms are abnormal dilations of blood vessels within the skull that, in some cases, may rupture and bleed. The rupture of an aneurysm can cause significant bleeding into or around the brain (a stroke). Flow diverters are specially designed low porosity stents that are deployed into the parent artery to cover the neck of the aneurysm. The dense mesh-like structure of flow diverters aims at redirecting flow from the aneurysm to the parent artery and vice versa, resulting in flow stasis in the aneurysm and promoting thrombus formation conditions. The thrombosed aneurysm is then resorbed by the body’s wound healing mechanisms-the end result of which is a remodeled vessel returned to its normal physiological state. Most previous studies have been focused on correlating the hemodynamic conditions with the outcome of the flow diverters. On the other hand, the effects of the location of the stents have not been addressed. In this study, a numerical simulation of an idealized side wall aneurysm model is used to predict the hemodynamic conditions for different flow diverter stent locations. The CFD model of the aneurysm is developed based on data from the literature and the geometrical parameters are set according to the test data. Pulsatile boundary conditions are chosen according to the normal physiological conditions. The entire stent geometry is used to model the effect of the stent on the flow characteristics. The hemodynamic conditions in the aneurysm corresponding to different stent locations are compared. The results show that the average velocity and vorticity are significantly different depending on different stent locations. Marked reduction in average velocity, average vorticity, and mean wall shear stress within the aneurysm sac have been observed even in malposition cases. The results of this study can be further used to guide the deployment of the flow diverter stent in clinical application.

Utility of VasoCT in the treatment of intracranial aneurysm with flow-diverter stents

2012 ◽  
Vol 117 (1) ◽  
pp. 45-49 ◽  
Author(s):  
Osman Kizilkilic ◽  
Naci Kocer ◽  
George Emmanuel Metaxas ◽  
Drazenko Babic ◽  
Robert Homan ◽  
...  
Keyword(s):  
Flow Diverter ◽  
Parent Artery ◽  
Flat Panel ◽  
Stent Deployment ◽  
Flat Panel Detector ◽  
Flow Diverter Stent ◽  
Low Profile ◽  
Intracranial Arteries ◽  
High Flexibility

Object The small size and tortuous anatomy of intracranial arteries require that flow-diverter stents in the intracranial vasculature have a low profile, high flexibility, and excellent trackability. However, these features limit the degree of radiopacity that can be incorporated into the stents. Visualization of these stents and the degree of stent deployment using conventional radiographic techniques is suboptimal. To overcome this drawback, the authors used a new combined angiography/CT suite that uses flat-panel detector technology for higher resolution angiography. Methods The authors present their preliminary experience in the imaging of flow-diverter stents in 31 patients in whom VasoCT was used with a new flat-panel detector angiographic system. Results Intraarterial VasoCT was performed after flow-diverter stent deployment in all cases. In 4 of these cases, balloon angioplasty or telescopic stent deployment–related decisions were made after checking VasoCT images. At 3- and 6-month follow-up in 27 patients, digital subtraction angiography was performed in 12 patients and intravenous VasoCT in 11 patients. Twenty-three of 31 patients had their aneurysm occluded during short-term follow-up, and 4 of the 31 patients still had minimal residual filling of the aneurysms. None of the 27 patients had stenosis of the parent artery. Conclusions The authors found that VasoCT provides clear visualization of flow-diverter stents. The images obtained both intraarterially and intravenously are very promising. The initial results provide a high confidence and reproducibility rate for further utilization of this new technique.

scholarly journals Giant internal carotid aneurysm: endovascular parent artery occlusion after failed treatment using a flow diverter—case report

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Dalibor Sila ◽  
Markus Lenski ◽  
Stefan Rath
Keyword(s):  
Internal Carotid ◽  
Giant Aneurysm ◽  
Flow Diverter ◽  
Artery Occlusion ◽  
Successful Outcome ◽  
Parent Artery ◽  
Vessel Occlusion ◽  
Parent Artery Occlusion ◽  
Flow Diverter Stent ◽  
Vessel Reconstruction

Abstract Treatment of giant aneurysms is challenging. While parent vessel reconstruction is the primary therapeutical target, the parent artery occlusion (PAO) is considered the next treatment option. We report a case of a 56-year-old woman with a right-sided non-ruptured giant aneurysm of the cavernous internal carotid artery. After failed aneurysm treatment by vessel remodeling through a flow diverter stent, we decided upon aneurysm coiling and PAO. Prior to the procedure, a successful balloon occlusion test (BOT) was performed, and in the second stage, just before occluding the parent artery, the BOT with induced hypotension was repeated. We achieved a good angiographic result and successful outcome without neurological deficit. In the case of failed treatment of giant aneurysm by vessel reconstruction, PAO is a therapeutical option. Prior to the vessel occlusion, a BOT with induced arterial hypotension challenge should be performed.

scholarly journals Predictive score for complete occlusion of intracranial aneurysms treated by flow-diverter stents using machine learning

2020 ◽  
pp. neurintsurg-2020-016748
Author(s):  
Alexis Guédon ◽  
Cédric Thépenier ◽  
Eimad Shotar ◽  
Joseph Gabrieli ◽  
Bertrand Mathon ◽  
...  
Keyword(s):  
Feature Selection ◽  
Test Sample ◽  
Training Sample ◽  
Flow Diverter ◽  
Side Branch ◽  
Predictive Score ◽  
Parent Artery ◽  
Complete Occlusion ◽  
Class Separation ◽  
Flow Diverter Stent

BackgroundComplete occlusion of an intracranial aneurysm (IA) after the deployment of a flow-diverter stent is currently unpredictable. The aim of this study was to develop a predictive occlusion score based on pretreatment clinical and angiographic criteria.MethodsConsecutive patients with ≥6 months follow-up were included from 2008 to 2019 and retrospectively analyzed. Each IA was evaluated using the Raymond–Roy occlusion classification (RROC) and dichotomized as occluded (A) or residual (B/C); 80% of patients were randomly assigned to the training sample. Feature selection and binary outcome prediction relied on logistic regression and threshold maximizing class separation selected by a CART tree algorithm. The feature selection was addressed by a genetic algorithm selected from the 30 pretreatment available variables.ResultsThe study included 146 patients with 154 IAs. Feature selection yielded a combination of six variables with a good cross-validated accuracy on the test sample, a combination we labeled DIANES score (IA diameter, indication, parent artery diameter ratio, neck ratio, side-branch artery, and sex). A score of more than −6 maximized the ability to predict RROC=A with sensitivity of 87% (95% CI 79% to 95%) and specificity of 82% (95% CI 64% to 96%) in the training sample. Accuracy was 86% (95% CI 79% to 94%). In the test sample, sensitivity and specificity were 89% (95% CI 77% to 98%) and 60% (95% CI 33% to 86%), respectively. Accuracy was 81% (95% CI 69% to 91%).ConclusionA score was developed as a grading scale for prediction of the final occlusion status of IAs treated with a flow-diverter stent.

scholarly journals Early angiographic changes of intra-aneurysmal flow after flow-diverter stent treatment are not predictive of therapeutic success

2016 ◽  
Vol 22 (6) ◽  
pp. 682-686 ◽  
Author(s):  
Paul-Emile Labeyrie ◽  
Benjamin Gory ◽  
Udi Sadeh-Gonike ◽  
Nazyed Huguet ◽  
Rotem Sivan-Hoffmann ◽  
...  
Keyword(s):  
Flow Diverter ◽  
Parent Artery ◽  
Technical Success ◽  
Therapeutic Success ◽  
Flow Modification ◽  
Flow Diverter Stent ◽  
Delay Times ◽  
Stent Treatment ◽  
Flow Changes

Background and purpose Flow-diverter stents (FDS) are new devices for the endovascular treatment of intracranial aneurysms (IAs) promoting progressive aneurysmal thrombosis. To date, the delay of aneurysmal exclusion remains unclear. We evaluated the correlation between angiographic changes in the first 24 hours and 12-month occlusion in aneurysms treated with FDS. Methods We retrospectively analyzed the intra-aneurysmal flow by evaluating the in-flow and out-flow delays on preoperative, immediate postoperative, 24-hour and 12-month follow-up angiography. Dichotomy of in-flow and out-flow within the aneurysm was considered as the time of contrast filling and time of contrast washing relatively to the parent artery. The delay times were compared and correlated with the therapeutic success of FDS at 12 months of follow-up. Results Out of 14 treated IAs, in 13 consecutive patients, n = 10 (71%) aneurysms showed complete occlusion at 12 months. Between immediate postoperative and 24-hour control, 10 aneurysms (71%) demonstrated in-flow modification, with eight increasing, two decreasing and four having no change. There were no statistical differences in therapeutic success in relation to the different flow-related profiles of intra-aneurysmal flux. Out-flow modifications were found in 11 aneurysms (79%) between immediate postoperative and 24-hour control, with five increasing, six decreasing and three having no change. Similar to the in-flow changes, there were no statistical differences in therapeutic success relative to the flow-related profiles. Conclusions Early angiographic changes after FDS placement are very frequent, but are not correlated with the 12-month technical success of flow-diversion techniques.

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