Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session D15: Bio: Aneurysms |
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Chair: Alberto Aliseda, University of Washington Room: E143/144 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D15.00001: Volumetric PIV in Patient-Specific Cerebral Aneurysm Melissa Brindise, Ben Dickerhoff, David Saloner, Vitaliy Rayz, Pavlos Vlachos Cerebral aneurysms impose a unique challenge in which neurosurgeons must assess and decide between the risk of rupture and risk of treatment for each patient. Risk of rupture is often difficult to determine and most commonly assessed using geometric data including the size and shape of the aneurysm and parent vessel. Hemodynamics is thought to play a major role in the growth and rupture of a cerebral aneurysm, but its specific influence is largely unknown due to the inability of \textit{in vivo} modalities to characterize detailed flow fields and limited \textit{in vitro} studies. In this work, we use a patient-specific basilar tip aneurysm model and volumetric particle image velocimetry (PIV). \textit{In vivo}, 4-D PC-MRI measurements were obtained for this aneurysm and the extracted pulsatile waveform was used for the \textit{in vitro} study. Clinically relevant metrics including wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT), 3-D pressure contours, and pressure wave speed were subsequently computed. This is the first study to investigate \textit{in vitro} 3-D pressure fields within a cerebral aneurysm. The results of this study demonstrate how these metrics influence the biomechanics of the aneurysm and ultimately their affect on the risk of rupture. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D15.00002: ABSTRACT WITHDRAWN |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D15.00003: Proper orthogonal decomposition analyses of high-frequency transient flow instabilities in intracranial aneurysms Muhammad Owais Khan, Christophe Chnafa, Kristian Valen-Sendstad, David A. Steinman Treatment of incidentally detected intracranial aneurysms (IAs) can exceed the natural risk of rupture. Abnormal hemodynamic forces, derived from image-based CFD, have, therefore, been proposed to assess the risk of IA rupture. Although majority of the CFD-literature has shown laminar and stable flows in IAs, recent high-resolution CFD simulations have highlighted the presence of transient high-frequency flow instabilities, or turbulent-like flows, consistent with experimental evidence from early 70s and 80s. However, whether flows in IAs are turbulent is still not fully understood. We performed DNS of 6 patient-specific IAs exhibiting varying levels of "turbulence". Proper orthogonal decomposition (POD) eigenspectra revealed that $\sim$96\% of the kinetic energy was concentrated in the first mode. Time-windowed POD showed that energy in higher modes (k$>$50) was dominated by contributions from deceleration phase. Velocity fields were reconstructed from the higher modes to highlight presence of distinct flow structures. We also identified presence of discrete frequency bands by applying wavelet analyses to time-velocity traces, and used novel Fourier-based hemodynamic indices to characterize the nature of these turbulent-like flows. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D15.00004: Wall Shear Stress Distribution in a Patient-Specific Cerebral Aneurysm Model using Reduced Order Modeling. Suyue Han, Gary Han Chang, Clemens Schirmer, Yahya Modarres-Sadeghi We construct a reduced-order model (ROM) to study the Wall Shear Stress (WSS) distributions in image-based patient-specific aneurysms models. The magnitude of WSS has been shown to be a critical factor in growth and rupture of human aneurysms. We start the process by running a training case using Computational Fluid Dynamics (CFD) simulation with time-varying flow parameters, such that these parameters cover the range of parameters of interest. The method of snapshot Proper Orthogonal Decomposition (POD) is utilized to construct the reduced-order bases using the training CFD simulation. The resulting ROM enables us to study the flow patterns and the WSS distributions over a range of system parameters computationally very efficiently with a relatively small number of modes. This enables comprehensive analysis of the model system across a range of physiological conditions without the need to re-compute the simulation for small changes in the system parameters. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D15.00005: Modeling contrast agent flow in cerebral aneurysms: comparison of CFD with medical imaging Vitaliy Rayz, Alireza Vali, Monica Sigovan, Michael Lawton, David Saloner, Loic Boussel PURPOSE: The flow in cerebral aneurysms is routinely assessed with X-ray angiography, an imaging technique based on a contrast agent injection. In addition to requiring a patient's catheterization and radiation exposure, the X-ray angiography may inaccurately estimate the flow residence time, as the injection alters the native blood flow patterns. Numerical modeling of the contrast transport based on MRI imaging, provides a non-invasive alternative for the flow diagnostics. METHODS: The flow in 3 cerebral aneurysms was measured in vivo with 4D PC-MRI, which provides time-resolved, 3D velocity field. The measured velocities were used to simulate a contrast agent transport by solving the advection-diffusion equation. In addition, the flow in the same patient-specific geometries was simulated with CFD and the velocities obtained from the Navier-Stokes solution were used to model the transport of a virtual contrast. RESULTS: Contrast filling and washout patterns obtained in simulations based on MRI-measured velocities were in agreement with those obtained using the Navier-Stokes solution. Some discrepancies were observed in comparison to the X-ray angiography data, as numerical modeling of the contrast transport is based on the native blood flow unaffected by the contrast injection. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D15.00006: 4D Magnetic Resonance Velocimetry in a 3D printed brain aneurysm Omid Amili, Daniele Schiavazzi, Filippo Coletti Cerebral aneurysms are of great clinical importance. It is believed that hemodynamics play a critical role in the development, growth, and rupture of brain arteries with such condition. The flow structure in the aneurysm sac is complex, unsteady, and three-dimensional. Therefore the time-resolved measurement of the three-dimensional three-component velocity field is crucial to predict the clinical outcome. In this study magnetic resonance velocimetry is used to assess the fluid dynamics inside a 3D printed model of a giant intracranial aneurysm. We reach sub-millimeter resolution while resolving sixteen instances within the cardiac cycle. The physiological flow waveform is imposed using an in-house built pump in a flow circuit where the cardiovascular impedance is matched. The flow evolution over time is reconstructed in detail. The complex flow structure is characterized by vortical and helical motions that reside in the aneurysm for most part of the cycle. The 4D pressured distribution is also reconstructed from the velocity field. The present case study was used in a previous CFD challenge, therefore these results may provide useful experimental comparison for simulations performed by other research groups. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D15.00007: Physiologically-relevant measurements of flow through coils and stents: towards improved modeling of endovascular treatment of intracranial aneurysms Michael Barbour, Michael Levitt, Christian Geindreau, Sabine Rolland du Roscoat, Luke Johnson, Keshav Chivukula, Alberto Aliseda The hemodynamic environment in cerebral aneurysms undergoing flow-diverting stent (FDS) or coil embolization treatment plays a critical role in long-term outcomes. Standard modeling approaches to endovascular coils and FDS simplify the complex geometry into a homogenous porous volume or surface through the addition of a Darcy-Brinkman pressure loss term in the momentum equation. The inertial and viscous loss coefficients are typically derived from published \textit{in vitro} studies of pressure loss across FDS and coils placed in a straight tube, where the only fluid path is across the treatment -- an unrealistic representation of treatment apposition \textit{in vivo. }The pressure drop across FDS and coils in side branch aneurysms located on curved parent vessels is measured. Using PIV, the velocity at the aneurysm neck plane is reconstructed and used to determine loss coefficients for better models of endovascular coils or FDS that account for physiological placement and vessel curvature. These improved models are incorporated into CFD simulations and validated against \textit{in vitro} model PIV velocity, as well as compared to microCT-based coil/stent-resolving CFD simulations of patient-specific treated aneurysm flow. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D15.00008: Computational Study of Intracranial Aneurysms with Flow Diverting Stent: Correlation with Surgical Outcome Yik Sau Tang, Tin Lok Chiu, Anderson Chun On Tsang, Gilberto Ka Kit Leung, Kwok Wing Chow Intracranial aneurysm, abnormal swelling of the cerebral artery, can cause massive internal bleeding in the subarachnoid space upon aneurysm rupture, leading to a high mortality rate. Deployment of a flow diverting stent through endovascular technique can obstruct the blood flow into the aneurysm, thus reducing the risk of rupture. Patient-specific models with both bifurcation and sidewall aneurysms have been investigated. Computational fluid dynamics analysis with physiological boundary conditions has been performed. Several hemodynamic parameters including volume flow rate into the aneurysm and the energy (sum of the fluid kinetic and potential energy) loss between the inlet and outlets were analyzed and compared with the surgical outcome. Based on the simulation results, we conjecture that a clinically successful case might imply less blood flow into the aneurysm after stenting, and thus a smaller amount of energy loss in driving the fluid flow in that portion of artery. This study might provide physicians with quantitative information for surgical decision making. (Partial financial support by the Innovation and Technology Support Program (ITS/011/13 {\&} ITS/150/15) of the Hong Kong Special Administrative Region Government) [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D15.00009: A hemodynamic-based dimensionless parameter for predicting rupture of intracranial aneurysms. Hafez Asgharzadeh, Nicole Varble, Hui Meng, Iman Borazjani Rupture of an intracranial aneurysm (IA) is a disease with high rates of mortality. Given the risk associated with the aneurysm surgery, quantifying the likelihood of aneurysm rupture is essential. There are many risk factors that could be implicated in the rupture of an aneurysm. However, the hemodynamic factors are believed to be the most influential ones. Here, we carry out three-dimensional high resolution simulations on human subjects IAs to test a dimensionless number, denoted as An number, to classify the flow mode. An number is defined as the ratio of the time takes the parent artery flow transports through the expansion region to the time required for vortex formation. Furthermore, we investigate the correlation of IA flow mode and WSS/OSI on the human subject IAs. Finally, we test if An number can distinguish ruptured from unruptured IAs on a database containing 204 human subjects IAs. [Preview Abstract] |
Sunday, November 20, 2016 4:54PM - 5:07PM |
D15.00010: Towards the evaluation of the pathological state of ascending thoracic aneurysms: integration of in-vivo measurements and hemodynamic simulations Alessandro Boccadifuoco, Alessandro Mariotti, Simona Celi, Nicola Martini, Maria Vittoria Salvetti Ascending thoracic aortic aneurysms are cardiovascular diseases consisting in a dilation of the ascending thoracic aorta. Since indicating a weakness of the arterial wall, they can lead to major complications with significant mortality rate. Clinical decisions about surgery are currently based on the maximum aortic diameter, but this single index does not seem a reliable indicator of the pathological state of the aorta. Numerical simulations of the blood flow inside the aneurysm may give supplementary information by quantifying important indices that are difficult to be measured, like the wall shear stress. Our aim is to develop an efficient platform in which in-vivo measurements are used to perform the hemodynamic simulations on a patient-specific basis. In particular, we used real geometries of thoracic aorta and focused on the use of clinical information to impose accurate boundary conditions at the inlet/outlets of the computational model. Stochastic analysis was also performed, to evaluate how uncertainties in the boundary parameters affect the main hemodynamic indicators, by considering both rigid and deformable walls. Stochastic calibration of numerical parameters against clinical data is in progress and results will be possibly shown. [Preview Abstract] |
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