Haithem Babiker

Computational Fluid Dynamics to Evaluate the Management of a Giant Internal Carotid Artery Aneurysm

BACKGROUND Giant intracranial aneurysms are rare lesions that present uniquely complex therapeutic challenges. Computational fluid dynamics (CFD) has been used to simulate the hemodynamic environments of developing and ruptured cerebral aneurysms. In this study, we use CFD to examine retrospectively hemodynamic changes during the complicated clinical course of a giant carotid aneurysm. OBJECTIVE To take an innovative, CFD-based approach to retrospective analysis of the surgical management and clinical course of a giant carotid aneurysm. METHODS Pre- and posttreatment image data were first segmented to produce computational aneurysm models. Flow within the models was then simulated using CFD. Simulated flow and wall shear stress (WSS) profiles were analyzed and used to examine hemodynamic changes during the clinical course of the patient, after 2 independent treatments. RESULTS Greater WSS magnitudes and a more localized flow impingement region were observed at the distal portion of the aneurysm after both clinical interventions. These relative, acute changes in hemodynamic features at the distal aneurysm wall were greatest after the second intervention and may have preceded rupture of the aneurysm in that region. CONCLUSIONS The application of CFD to the management of a giant intracranial aneurysm showed unexpected posttreatment changes in flow and WSS profiles. The simulation results offer a viable explanation for the observed clinical course. This study demonstrates potential for the use of CFD preoperatively for decision-making in the surgical and endovascular management of intracranial aneurysms.

Hemodynamic characterization of geometric cerebral aneurysm templates

Hemodynamics are currently considered to a lesser degree than geometry in clinical practices for evaluating cerebral aneurysm (CA) risk and planning CA treatment. This study establishes fundamental relationships between three clinically recognized CA geometric factors and four clinically relevant hemodynamic responses. The goal of the study is to develop a more combined geometric/hemodynamic basis for informing clinical decisions. Flows within eight idealized template geometries were simulated using computational fluid dynamics and measured using particle image velocimetry under both steady and pulsatile flow conditions. The geometric factor main effects were then analyzed to quantify contributions made by the geometric factors (aneurysmal dome size (DS), dome-to-neck ratio (DNR), and parent-vessel contact angle (PV-CA)) to effects on the hemodynamic responses (aneurysmal and neck-plane root-mean-square velocity magnitude (Vrms), aneurysmal wall shear stress (WSS), and cross-neck flow (CNF)). Two anatomical aneurysm models were also examined to investigate how well the idealized findings would translate to more realistic CA geometries. DNR made the greatest contributions to effects on hemodynamics including a 75.05% contribution to aneurysmal Vrms and greater than 35% contributions to all responses. DS made the next greatest contributions, including a 43.94% contribution to CNF and greater than 20% contributions to all responses. PV-CA and several factor interactions also made contributions of greater than 10%. The anatomical aneurysm models and the most similar idealized templates demonstrated consistent hemodynamic response patterns. This study demonstrates how individual geometric factors, and combinations thereof, influence CA hemodynamics. Bridging the gap between geometry and flow in this quantitative yet practical way may have potential to improve CA evaluation and treatment criteria. Agreement among results from idealized and anatomical models further supports the potential for a template-based approach to play a useful role in clinical practice.

Simulation and Experimental Characterization of Microscopically Accessible Hydrodynamic Microvortices

Single-cell studies of phenotypic heterogeneity reveal more information about pathogenic processes than conventional bulk-cell analysis methods. By enabling high-resolution structural and functional imaging, a single-cell three-dimensional (3D) imaging system can be used to study basic biological processes and to diagnose diseases such as cancer at an early stage. One mechanism that such systems apply to accomplish 3D imaging is rotation of a single cell about a fixed axis. However, many cell rotation mechanisms require intricate and tedious microfabrication, or fail to provide a suitable environment for living cells. To address these and related challenges, we applied numerical simulation methods to design new microfluidic chambers capable of generating fluidic microvortices to rotate suspended cells. We then compared several microfluidic chip designs experimentally in terms of: (1) their ability to rotate biological cells in a stable and precise manner; and (2) their suitability, from a geometric standpoint, for microscopic cell imaging. We selected a design that incorporates a trapezoidal side chamber connected to a main flow channel because it provided well-controlled circulation and met imaging requirements. Micro particle-image velocimetry (micro-PIV) was used to provide a detailed characterization of flows in the new design. Simulated and experimental results

Influence of Stent Configuration on Cerebral Aneurysm Fluid Dynamics

Embolic coiling is the most popular endovascular treatment available for cerebral aneurysms. Nevertheless, the embolic coiling of wide-neck aneurysms is challenging and, in many cases, ineffective. Use of highly porous stents to support coiling of wide-neck aneurysms has become a common procedure in recent years. Several studies have also demonstrated that high porosity stents alone can significantly alter aneurysmal hemodynamics, but differences among different stent configurations have not been fully characterized. As a result, it is usually unclear which stent configuration is optimal for treatment. In this paper, we present a flow study that elucidates the influence of stent configuration on cerebral aneurysm fluid dynamics in an idealized wide-neck basilar tip aneurysm model. Aneurysmal fluid dynamics for three different stent configurations (half-Y, Y and, cross-bar) were first quantified using particle image velocimetry and then compared. Computational fluid dynamics (CFD) simulations were also conducted for selected stent configurations to facilitate validation and provide more detailed characterizations of the fluid dynamics promoted by different stent configurations. In vitro results showed that the Y stent configuration reduced cross-neck flow most significantly, while the cross-bar configuration reduced velocity magnitudes within the aneurysmal sac most significantly. The half-Y configuration led to increased velocity magnitudes within the aneurysmal sac at high parent-vessel flow rates. Experimental results were in strong agreement with CFD simulations. Simulated results indicated that differences in fluid dynamic performance among the different stent configurations can be attributed primarily to protruding struts within the bifurcation region.

E-061 Towards the Pre-Surgical Treatment Planning of Cerebral Aneurysms Using High Fidelity Simulations

Over the last decade, advances in medical imaging have led to a 75% increase in early diagnosis of cerebral aneurysms (CAs) along with a growing arsenal of medical devices that can now treat a wider range of CA cases. Endovascular treatment planning has shown limited progress. Current treatment planning is driven by prior training, convention and experience. Despite the best of plans, the process can involve an element of trial and error during treatment that increases procedural time, treatment costs, and the risk of procedural complications. Further, treatment planning can be unsuccessful in many cases with recurrence rates as high as 21.9% and retreatment rates of 11.0%. Therefore, there is a critical need to improve endovascular treatment planning. Here we present a novel simulation algorithm that enhances clinical capabilities for personalised pre-surgical treatment planning. In the first step of the algorithm, a computational anatomy is generated from MR or CT image data. Next, the computational anatomy is used to simulate treatment using novel device-specific finite element (FE) models that consider the structural properties of the treatment device, its mechanics, and the clinical deployment strategy. Changes in blood flow are then simulated using computational fluid dynamics (CFD). Lastly, mechanical and fluid dynamic simulation results are used to evaluate the outcomes of different treatment options. The simulation algorithm was validated against in-vitro deployments of embolic coils, stents, and the Pipeline embolization device in 3 idealised and 2 anatomical CA models. Results showed excellent agreement between FE device simulations and physical device deployments. Fluid dynamics were also compared between CFD simulations and in-vitro flow velocity and pressure measurements in the treated CA models. Results showed good agreement in mean aneurysmal velocity magnitude and intra-aneurysmal pressure. Detailed 3D structural validations against microCT data will also be presented. The value of the simulation algorithm for treatment planning is demonstrated for 3 patient cases. In case 1, stent-assisted coiling (Figure 1a) and flow diverter treatment options (Figure 1b) are evaluated for a wide-neck posterior communicating artery (PCA) aneurysm (Figure 1). In case 2, the simulation algorithm is used to predict changes in fluid dynamics after 12 coil deployments in a large basilar-tip aneurysm. Clinical and simulations results of that case showed a persisting flow jet into the aneurysmal sac after treatment. In case 3, the simulation algorithm is used to compare stent-assisted coiling and coiling-alone in a basilar tip aneurysm. Abstract E-061 Figure 1 Disclosures B. Chong: 1; C; Mayo Clinic Center for Individualised Medicine, Arizona State University. 4; C; Endovantage LLC. H. Babiker: 4; C; Endovantage LLC. D. Frakes: 4; C; Endovantage, LLC. J. Ryan: 5; C; Endovantage LLC. F. Gonzalez: 4; C; Endovantage LLC.

E-036 Predicting Flow Diverter Deployments and Clinical Validation

Introduction Flow diverters (FDs) are sized to the recipient vessel during pre-treatment planning. However, sizing can be challenging because of large changes in vessel curvature and diameter. Further, FDs can elongate by more than 50% of their labeled length after deployment, which complicates sizing. Significant complications can result from over- or under- sized devices. Here we present a finite element (FE) modelling approach for evaluating FD size and compare that approach to clinical deployments to determine its accuracy in predicting device length, diameter, and apposition. Methods Ten patient cases treated with the pipeline embolization device were acquired from two hospitals. Pre- and post- treatment CT image data were segmented then reconstructed to form computational models of the devices and vessels. A library of pipeline FE models, which was previously validated against physical devices, was used to simulate deployment of the same devices into the pre-treatment vessels. The pipeline models were first navigated via a virtual microcatheter to the landing zones observed in the post-treatment vessels. A “push-pull” algorithm was then used to simulate device unsheathing. Three post-deployment metrics were compared: device apposition to the vessel wall along the vessel centerline, device diameter along the stent centerline, and device length. Results Simulated and clinical deployments showed good agreement both qualitatively and quantitatively (Figure 1). Simulations captured regions where the device poorly apposed to the vessel wall and poorly covered the aneurysm neck. Mean errors between simulated and clinical deployments (as a percentage of the clinical value) were less than 5% for device length and 9% for device apposition and diameter.Abstract E-036 Figure 1 Conclusion FE simulations captured post-deployment FD shape and apposition. Less than a 9% mean error was found between simulated and clinical deployment metrics. These results provide additional support for the use of FE for evaluating device size during pre-treatment planning. Disclosures B. Chong: 4; C; Endovantage, LLC. H. Babiker: 4; C; Endovantage, LLC. Y. Kalani: None. C. Baccin: None. M. Mortensen: 5; C; Endovantage, LLC. M. Levitt: None. C. McDougall: None. D. Frakes: 4; C; Endovantage, LLC. F. Albuquerque: 4; C; Endovantage, LLC.

O-012 The Effect of Pipeline Embolisation Device on Intra-Aneurysmal Pressures: In-Vitro Study

Introduction Pipeline (PED) has become commonly used to treat cerebral aneurysms, studies have found that 1% of cases that use the device result in devastating subarachnoid haemorrhage due to aneurysm rupture. The cause of these complications is still unclear, and some hypothesise it may be due to the effect the PED has on the intra-aneurysmal pressure. Materials and Methods We performed in vitro studies on two patient-specific models of cerebral aneurysms (fig 1). While both aneurysms were similar in size they had different fundamental geometries, as the first was a basilar tip and the other a side wall. In order to measure the intra-aneurysmal pressure a 0.42 mm tap was drilled into the model and a 0.40 mm micro-catheter was thread into the hole and attached to a pressure transducer (Harvard Apparatus, Holliston, MA, USA). pressure measurements were acquired and collected with Labview Signal Express (National Instruments, Austin, TX, USA). Along with the intra-aneurysmal pressure, pressure measurements were also collected at the inlet and outlet of the model. In conjunction with the pressure measurements, particle image velocimetry, a flow visualisation technique, was used to observe the haemodynamic flow patterns within the aneurysm. Results Results from the sidewall aneurysm showed that the deployment of the PED led to a dampening of the pulsatile waveform within the aneurysm. However, the PED also led to an increase in average intra-aneurysmal pressure of over 7 mmHg (fig. 2). In contrast, the BTA model did not show an increase in intra-aneurysmal pressure. This difference is likely related to the fact that the sidewall aneurysm is a closed system (only one inlet and outlet), while the BTA has an additional untreated outflow. In fact the BTA model also showed an increase in pressure drop across the untreated vessel during PED deployment, which indicates that the blood flow is being directed in that direction. The flow visualisation patterns of both models indicated a reduction in the velocities within the aneurysm, indicating that the PED is leading to reductions in fluid dynamic activity, making the increase in pressure of even greater interest. Conclusion The results of this study, while preliminary, give insight into the intra-aneurysmal pressure changes associated after deployment of the PED. Our results indicate that the PED does lead to haemodynamic changes in pressure within the aneurysm that could lead to ruptured. Abstract O-012 Figure 1 Disclosures F. Gonzalez: None. B. Roszelle: None. H. Babiker: None. D. Frakes: None.

Comparison of the Effects of Embolic Coils and a Low Porosity Stent on Cerebral Aneurysm Fluid Dynamics

Wide-neck cerebral aneurysms are difficult to treat with embolic coils. Concerns over the stability of coils within the aneurysmal sac often lead to incomplete filling of the sac, which may cause recurrence [1]. To overcome this challenge, clinicians may deploy a high porosity stent in a staged process to act as a supporting bridge for coils. The stent is commonly deployed 6–8 week prior to coil embolization, which lengthens the treatment period [2].Copyright

Experimental fluid dynamic investigation of a novel hyper-elastic thin film for cerebral aneurysm treatment

Wide-neck and giant cerebral aneurysms are difficult to treat with conventional endovascular or surgical means [1]. Recently, stand-alone stent treatment has been explored as a viable treatment option for these aneurysms. Two goals of standalone stent design are to permit flexible conformation of the stent through tortuous vessels and to provide sufficient coverage across the aneurysmal neck [2]. Stents that achieve those goals can facilitate the long-term physiological processes that exclude the aneurysmal sac from circulation. Thrombosis within the sac is an important intermediate step, which may begin with the elimination of aneurysmal inflow [3].Copyright

The Effects of High Porosity Stent Configurations on Cerebral Aneurysm Hemodynamics

Coil embolization is the most common endovascular treatment for cerebral aneurysms at many centers [1]. Nevertheless, the coiling of wide-neck aneurysms is a challenge. Incomplete filling of the aneurysmal sac due to coil configuration challenges and aneurysmal growth can often lead to recurrence. To assist treatment with coils, clinicians may deploy a high porosity stent in a staged process to act as a supporting bridge for coils. The stent is first deployed across the aneurysmal neck, and multiple coils are then deployed into the aneurysmal sac 6–8 weeks later [2]. Under certain circumstances, coil deployment is not possible and high porosity stents alone are used for treatment [2–3].Copyright