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.

Comparison of Flow Diverter Deployment Strategies for Cerebral Aneurysm Treatment: Evaluation of Hemodynamic Modifications

2013 ◽  
Author(s):  
Robert Damiano ◽  
Chris Martensen ◽  
Ding Ma ◽  
Jianping Xiang ◽  
Adnan Siddiqui ◽  
...  
Keyword(s):  
Shear Stress ◽  
Preliminary Investigation ◽  
Cerebral Aneurysms ◽  
Flow Diverter ◽  
Patient Specific ◽  
Great Success ◽  
Pipeline Embolization Device ◽  
Recent Advancement ◽  
Specific Geometry ◽  
Shed Light

Flow diversion with the Pipeline Embolization Device (PED, Covidien, Irvine, CA) represents the most recent advancement in endovascular treatment of cerebral aneurysms. Despite great success at treating previously untreatable aneurysms, complications such as delayed rupture after PED treatment raise concerns that clinical outcome is not always predictable. This is due to the lack of knowledge about the flow modifications by different configurations of PED placement in patient-specific geometry and how these affect thrombosis. To shed light on mechanisms behind these issues, this study investigated the hemodynamic modifications induced by different treatment scenarios, including (1) a single PED vs. 2 overlapping PEDs and (2) uniform vs. dense packing of a single PED. Besides flow reduction and wall shear stress (WSS) modification, we also conducted a preliminary investigation of the potential for platelet activation from high blood shear induced by PED struts.

Exploring High Frequency Temporal Fluctuations in the Terminal Aneurysm of the Basilar Bifurcation

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Matthew D. Ford ◽  
Ugo Piomelli
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
High Frequency ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Disturbed Flow ◽  
Frequency Fluctuations ◽  
Wall Shear ◽  
Inflow Jet

Cerebral aneurysms are a common cause of death and disability. Of all the cardiovascular diseases, aneurysms are perhaps the most strongly linked with the local fluid mechanic environment. Aside from early in vivo clinical work that hinted at the possibility of high-frequency intra-aneurysmal velocity oscillations, flow in cerebral aneurysms is most often assumed to be laminar. This work investigates, through the use of numerical simulations, the potential for disturbed flow to exist in the terminal aneurysm of the basilar bifurcation. The nature of the disturbed flow is explored using a series of four idealized basilar tip models, and the results supported by four patient specific terminal basilar tip aneurysms. All four idealized models demonstrated instability in the inflow jet through high frequency fluctuations in the velocity and the pressure at approximately 120 Hz. The instability arises through a breakdown of the inflow jet, which begins to oscillate upon entering the aneurysm. The wall shear stress undergoes similar high-frequency oscillations in both magnitude and direction. The neck and dome regions of the aneurysm present 180 deg changes in the direction of the wall shear stress, due to the formation of small recirculation zones near the shear layer of the jet (at the frequency of the inflow jet oscillation) and the oscillation of the impingement zone on the dome of the aneurysm, respectively. Similar results were observed in the patient-specific models, which showed high frequency fluctuations at approximately 112 Hz in two of the four models and oscillations in the magnitude and direction of the wall shear stress. These results demonstrate that there is potential for disturbed laminar unsteady flow in the terminal aneurysm of the basilar bifurcation. The instabilities appear similar to the first instability mode of a free round jet.

scholarly journals A Workflow for Patient-Individualized Virtual Angiogram Generation Based on CFD Simulation

2012 ◽  
Vol 2012 ◽  
pp. 1-24 ◽  
Author(s):  
Jürgen Endres ◽  
Markus Kowarschik ◽  
Thomas Redel ◽  
Puneet Sharma ◽  
Viorel Mihalef ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Blood Flow ◽  
Shear Stress ◽  
Cfd Simulation ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Hemodynamic Parameters ◽  
Risk Of Rupture ◽  
Computational Fluid Dynamics Cfd ◽  
Subsequent Comparison

Increasing interest is drawn on hemodynamic parameters for classifying the risk of rupture as well as treatment planning of cerebral aneurysms. A proposed method to obtain quantities such as wall shear stress, pressure, and blood flow velocity is to numerically simulate the blood flow using computational fluid dynamics (CFD) methods. For the validation of those calculated quantities, virtually generated angiograms, based on the CFD results, are increasingly used for a subsequent comparison with real, acquired angiograms. For the generation of virtual angiograms, several patient-specific parameters have to be incorporated to obtain virtual angiograms which match the acquired angiograms as best as possible. For this purpose, a workflow is presented and demonstrated involving multiple phantom and patient cases.

scholarly journals High-fidelity virtual stenting: modeling of flow diverter deployment for hemodynamic characterization of complex intracranial aneurysms

2015 ◽  
Vol 123 (4) ◽  
pp. 832-840 ◽  
Author(s):  
Jianping Xiang ◽  
Robert J. Damiano ◽  
Ning Lin ◽  
Kenneth V. Snyder ◽  
Adnan H. Siddiqui ◽  
...  
Keyword(s):  
Intracranial Aneurysms ◽  
Average Velocity ◽  
Vascular Anatomy ◽  
Flow Diverter ◽  
Turnover Time ◽  
High Fidelity ◽  
Inflow Rate ◽  
Proof Of Concept ◽  
Flow Reduction

OBJECT Flow diversion via Pipeline Embolization Device (PED) represents the most recent advancement in endovascular therapy of intracranial aneurysms. This exploratory study aims at a proof of concept for an advanced device-modeling tool in conjunction with computational fluid dynamics (CFD) to evaluate flow modification effects by PED in actual, treated cases. METHODS The authors performed computational modeling of 3 PED-treated complex aneurysm cases. The patient in Case 1 had a fusiform vertebral aneurysm treated with a single PED. In Case 2 the patient had a giant internal carotid artery (ICA) aneurysm treated with 2 PEDs. Case 3 consisted of tandem ICA aneurysms (III-a and III-b) treated by a single PED. The authors’ recently developed high-fidelity virtual stenting (HiFiVS) technique was used to recapitulate the clinical deployment process of PEDs in silico for these 3 cases. Pretreatment and posttreatment aneurysmal hemodynamics studies performed using CFD simulation were analyzed. Changes in aneurysmal flow velocity, inflow rate, wall shear stress (WSS), and turnover time were calculated and compared with the clinical outcome. RESULTS In Case 1 (occluded within the first 3 months), the aneurysm had the most drastic flow reduction after PED placement; the aneurysmal average velocity, inflow rate, and average WSS were decreased by 76.3%, 82.5%, and 74.0%, respectively, whereas the turnover time was increased to 572.1% of its pretreatment value. In Case 2 (occluded at 6 months), aneurysmal average velocity, inflow rate, and average WSS were decreased by 39.4%, 38.6%, and 59.1%, respectively, and turnover time increased to 163.0%. In Case 3, Aneurysm III-a (occluded at 6 months) had a decrease by 38.0%, 28.4%, and 50.9% in average velocity, inflow rate, and average WSS, respectively, and turnover time increased to 139.6%, which was quite similar to Aneurysm II. Surprisingly, the adjacent Aneurysm III-b had more substantial flow reduction (a decrease by 77.7%, 53.0%, and 84.4% in average velocity, inflow rate, and average WSS, respectively, and an increase to 213.0% in turnover time) than Aneurysm III-a, which qualitatively agreed with angiographic observation at 3-month follow-up. However, Aneurysm III-b remained patent at both 6 months and 9 months. A closer examination of the vascular anatomy in Case 3 revealed blood draining to the ophthalmic artery off Aneurysm III-b, which may have prevented its complete thrombosis. CONCLUSIONS This proof-of-concept study demonstrates that HiFiVS modeling of flow diverter deployment enables detailed characterization of hemodynamic alteration by PED placement. Posttreatment aneurysmal flow reduction may be correlated with aneurysm occlusion outcome. However, predicting aneurysm treatment outcome by flow diverters also requires consideration of other factors, including vascular anatomy.

A New Virtual Coiling Method and its Use in Evaluation of Combining Coiling and Flow-Diversion Treatment in a Patient-Specific Aneurysm

2014 ◽  
Author(s):  
Robert Damiano ◽  
Jianping Xiang ◽  
Elad Levy ◽  
Hui Meng
Keyword(s):  
Internal Carotid ◽  
Thrombus Formation ◽  
Artery Aneurysm ◽  
Flow Diverter ◽  
Patient Specific ◽  
Test Case ◽  
Carotid Artery Aneurysm ◽  
Internal Carotid Artery Aneurysm ◽  
Single Flow ◽  
Packing Densities

A new realistic finite element method (FEM) based endovascular coil deployment technique was developed to explore the hemodynamic modifications of coiling in addition to flow diverter (FD) treatment. A patient-specific internal carotid artery aneurysm was used as a test case, and a single flow diverter was deployed using a previously developed method [1], along with several coils using the new method. Results showed fluctuations in hemodynamic parameters at low packing densities (1–3 coils) which are unexpected. At high packing density however (6 coils), results were consistent with expectations. These results suggest that adding coils at low packing densities to FD treatment may not cause significant additional flow reduction into the aneurysm sac, but may provide a scaffold for aneurysmal thrombus formation.

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.

Hemodynamic differences between Pipeline and coil-adjunctive intracranial stents

2019 ◽  
Vol 11 (9) ◽  
pp. 908-911 ◽  
Author(s):  
Brian Thomas Jankowitz ◽  
Bradley A Gross ◽  
Santhosh Seshadhri ◽  
Gaurav Girdhar ◽  
Ashutosh Jadhav ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Metal Surface ◽  
Velocity Vector ◽  
Surface Coverage ◽  
Flow Analysis ◽  
Flow Diverter ◽  
Turnover Time ◽  
Inflow Rate ◽  
Wall Shear

IntroductionModern coil-adjunctive intracranial stent designs have increased metal surface coverage to construct putative ‘flow diverter lights.’ This is rooted in the assumption that flow diversion is linearly correlated with metal surface coverage rather than being a threshold to be reached by device porosity and design.ObjectiveTo evaluate this assumption, by performing computational flow analysis on three aneurysm models treated with low metal surface coverage stents (ATLAS and Enterprise), a Pipeline flow diverter, and the LVIS Blue stent.MethodsComputational flow analysis was performed on virtual deployment models entailing deployment of an ATLAS, Enterprise, LVIS Blue, or Pipeline. The impact of device deployment on velocity vectors at the neck, maximum wall shear stress, inflow rate into the aneurysm, and turnover time was determined.ResultsVelocity vector plots demonstrated low magnitude, localized inflow jets for Pipeline only; asymmetric, selectively high inflow jets were seen for LVIS Blue, and broader velocity vector clusters were seen for Atlas and Enterprise. Reduction in wall shear stress as compared with baseline was significant for all devices and greatest for the Pipeline. Mean peak wall shear stress was significantly lower for LVIS Blue in comparison with ATLAS or Enterprise but significantly lower for Pipeline than for LVIS Blue. Reduction of inflow rate into the aneurysm was significant for LVIS Blue and Pipeline but significantly lower for Pipeline than for LVIS Blue. Turnover time was statistically similar for ATLAS, Enterprise, and LVIS Blue, but significantly increased for Pipeline.ConclusionConsiderable differences in peak wall shear stress, inflow rates, and turnover time between flow diverters, moderate- and low-porosity stents reinforce the assumption that effective flow diversion represents a threshold in device design, encompassing metal surface coverage only in part.

Hemodynamics and the Natural History of Cerebral Aneurysms

2007 ◽  
Author(s):  
Juan R. Cebral ◽  
Marcelo A. Castro ◽  
Christopher M. Putman
Keyword(s):  
Shear Stress ◽  
Natural History ◽  
Wall Shear Stress ◽  
Intracranial Aneurysms ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
High Wall Shear Stress ◽  
Arterial Hemodynamics ◽  
History Of ◽  
Major Factors

The mechanisms responsible for the evolution and rupture of cerebral aneurysms are not well understood. This is a multi-factorial problem, and previous studies [1–3] have identified the major factors involved: a) arterial hemodynamics, b) mechanobiology and wall biomechanics, and c) peri-aneurysmal environment. In this paper we present recent results based on patient-specific computational hemodynamics models of a number of cerebral aneurysms that indicate that hemodynamics plays an important role both in the progression and rupture of intracranial aneurysms. In particular, the data seems to support the idea that mechanisms associated to high wall shear stress may be responsible for the evolution and rupture of these aneurysms [4].

scholarly journals A new imaging tool for realtime measurement of flow velocity in intracranial aneurysms

2017 ◽  
Vol 7 (3) ◽  
Author(s):  
Athanasios K. Petridis ◽  
Marius Kaschner ◽  
Jan F. Cornelius ◽  
Marcel A. Kamp ◽  
Angelo Tortora ◽  
...  
Keyword(s):  
Real Time ◽  
Fluid Velocity ◽  
Flow Diverter ◽  
Flow Dynamics ◽  
Patient Specific ◽  
Flow Profile ◽  
Injection Speed ◽  
Unruptured Aneurysms ◽  
Flow Reduction ◽  
Imaging Tool

With modern imaging modalities of the brain a significant number of unruptured aneurysms are detected. However, not every aneurysm is prone to rupture. Because treatment morbidity is about 10% it is crucial to identify unstable aneurysms for which treatment should be discussed. Recently, new imaging tools allow analysis of flow dynamics and wall stability have become available. It seems that they might provide additional data for better risk profiling. In this study we present a new imaging tool for analysis of flow dynamics, which calculates fluid velocity in an aneurysm (Phillips Electronics, N.V.). It may identify regions with high flow and calculate flow reduction after stenting of aneurysms. Contrast is injected with a stable injection speed of 2 mL/sec for 3 sec. Two clinical cases are illustrated. Velocity in aneurysms and areas of instability can be identified and calculated during angiography in real-time. After stenting and flow diverter deployment flow reduction in the internal carotid aneurysm was reduced by 60% and there was a reduction of about 65% in the posterior cerebral artery in the second case we are reporting. The dynamic flow software calculates the flow profile in the aneurysm immediately after contrast injection. It is a real-time, patient specific tool taking into account systole, diastole and flexibility of the vasculature. These factors are an improvement as compared to current models of computational flow dynamics. We think it is a highly efficient, user friendly tool. Further clinical studies are on their way.

scholarly journals In-silico trial of intracranial flow diverters replicates and expands insights from conventional clinical trials

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ali Sarrami-Foroushani ◽  
Toni Lassila ◽  
Michael MacRaild ◽  
Joshua Asquith ◽  
Kit C. B. Roes ◽  
...  
Keyword(s):  
Clinical Trials ◽  
In Silico ◽  
Flow Diverter ◽  
Patient Specific ◽  
Success Rates ◽  
Virtual Experiments ◽  
Flow Reduction ◽  
The Cost ◽  
Flow Diverting Stent ◽  
Flow Diverters

AbstractThe cost of clinical trials is ever-increasing. In-silico trials rely on virtual populations and interventions simulated using patient-specific models and may offer a solution to lower these costs. We present the flow diverter performance assessment (FD-PASS) in-silico trial, which models the treatment of intracranial aneurysms in 164 virtual patients with 82 distinct anatomies with a flow-diverting stent, using computational fluid dynamics to quantify post-treatment flow reduction. The predicted FD-PASS flow-diversion success rates replicate the values previously reported in three clinical trials. The in-silico approach allows broader investigation of factors associated with insufficient flow reduction than feasible in a conventional trial. Our findings demonstrate that in-silico trials of endovascular medical devices can: (i) replicate findings of conventional clinical trials, and (ii) perform virtual experiments and sub-group analyses that are difficult or impossible in conventional trials to discover new insights on treatment failure, e.g. in the presence of side-branches or hypertension.

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