Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session RL: Biofluids: Physiological Cerebral |
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Chair: Alison Marsden, University of California, San Diego Room: Long Beach Convention Center 202A |
Tuesday, November 23, 2010 3:05PM - 3:18PM |
RL.00001: Blending CFD simulations with clinical measurements Vitaliy Rayz, Gabriel Acevedo-Bolton, Loic Boussel, David Saloner Patient-specific CFD models accurately capture complex flows in aneurysmal arteries and predict flow-derived parameters affecting disease progression, such as wall shear stress (WSS). A disadvantage of CFD is convergence time. Blood flow can also be measured in vivo with phase-contrast magnetic resonance velocimetry (PC-MRV). This method provides time-resolved 3D velocity field at the time of imaging, but it lacks accuracy required for WSS calculations. In this study we combine PC-MRV with CFD in order to quickly achieve an accurate solution. PC-MRV data obtained for 3 cerebral aneurysm patients were used as initial and boundary conditions for CFD simulations carried out in the same geometries. Lower-resolution MR data were interpolated into a finer computational mesh. Simulation time was reduced in all cases and excellent agreement was observed between the flow fields obtained with this technique and those obtained with fully convergent simulations started from zero initial conditions. The proposed method can help clinicians obtain relevant quantitative data in just a few hours after imaging. [Preview Abstract] |
Tuesday, November 23, 2010 3:18PM - 3:31PM |
RL.00002: Cerebral aneurysms: relations between geometry, hemodynamics and aneurysm location in the cerebral vasculature Tiziano Passerini, Alessandro Veneziani, Laura Sangalli, Piercesare Secchi, Simone Vantini In cerebral blood circulation, the interplay of arterial geometrical features and flow dynamics is thought to play a significant role in the development of aneurysms. In the framework of the Aneurisk project, patient-specific morphology reconstructions were conducted with the open-source software VMTK (www.vmtk.org) on a set of computational angiography images provided by Ospedale Niguarda (Milano, Italy). Computational fluid dynamics (CFD) simulations were performed with a software based on the library LifeV (www.lifev.org). The joint statistical analysis of geometries and simulations highlights the possible association of certain spatial patterns of radius, curvature and shear load along the Internal Carotid Artery (ICA) with the presence, position and previous event of rupture of an aneurysm in the entire cerebral vasculature. Moreover, some possible landmarks are identified to be monitored for the assessment of a Potential Rupture Risk Index. [Preview Abstract] |
Tuesday, November 23, 2010 3:31PM - 3:44PM |
RL.00003: A Mathematical Model of Intracranial Saccular Aneurysms: Evidence of Hemodynamic Instability Michael Calvisi, Stephen Davis, Michael Miksis Intracranial saccular aneurysms tend to form at the apex of arterial bifurcations and often assume a nominally spherical shape. In certain cases, the aneurysm growth can become unstable and lead to rupture. While the mechanisms of instability are not well understood, hemodynamics almost certainly play an important role. In this talk, a mathematical model of a saccular aneurysm is presented that describes the shape deformations of an initially spherical membrane interacting with a viscous fluid in the interior. The governing equations are derived from the equations of a thin shell supplemented with a constitutive model that is representative of aneurysmal tissue. Among the key findings are that two families of free vibration modes exist and, for certain values of the membrane properties, one family of nonspherical, axisymmetric modes is unstable to small perturbations. In addition, the presence of a vortical interior flow of sufficient strength can excite resonance of the membrane -- an unstable phenomenon that might cause eventual rupture. [Preview Abstract] |
Tuesday, November 23, 2010 3:44PM - 3:57PM |
RL.00004: Volumetric Velocity Measurements of Pulsating Flow through a Model Aneurysm Daniel Troolin, Devesh Amatya, Ellen Longmire Volumetric 3-component velocimetry (V3V) was used to examine the flow structure inside of a scaled-up transparent urethane model of a saccular aneurysm.~ The model was fabricated to match the geometry of an in vivo case. Index matching was used to minimize optical distortions caused by the curved walls of the model. The model and a surrounding visualization box were integrated into a custom-built pulse duplicator system with in-line flow meter and pressure transducers.~ The pulsing frequency and amplitude were controlled independently to generate two flow conditions each having a non-dimensional peak Reynolds (Re) and Womersley (Wo) Number: Re = 250, Wo = 10.4 and Re = 125, Wo = 7.4.~ Phase-locked and instantaneous measurements of the pulsatile flow upstream, downstream, and within the aneurysm reveal significant three-dimensional features including zones of separation, recirculation, impingement, and relative inactivity.~ Plots and movies will be shown, and a detailed discussion of the flow and various experimental considerations will be included. [Preview Abstract] |
Tuesday, November 23, 2010 3:57PM - 4:10PM |
RL.00005: Validation of Blood Flow Simulations in Intracranial Aneurysms Yue Yu, Tomer Anor, Hyoungsu Baek, Mahesh Jayaraman, Joseph Madsen, George Karniadakis Catheter-based digital subtraction angiography (DSA) is the most accurate diagnostic procedure for investigating vascular anomalies and cerebral blood flow. Here we describe utilization of DSA in a patient with an intracranial aneursysm to validate corresponding spectral element simulations. Subsequently, we examine via visualization the structure of flow in internal carotid arteries laden with three different types of aneurysms: (1) a wide-necked saccular aneurysm, (2) a narrower-necked saccular aneurysm, and (3) a case with two adjacent saccular aneurysms. We have found through high resolution simulations that in cases (1) and (3) in physiological conditions a hydrodynamic instability occurs during the decelerating systolic phase resulting in a high frequency oscillation (20-50 Hz). We use the {\em in-silico} dye visualization to discriminate among different physical mechanisms causing the instability and contrast their effect with case (2) for which an instability arises only at much higher flowrates. [Preview Abstract] |
Tuesday, November 23, 2010 4:10PM - 4:23PM |
RL.00006: Control volume based hydrocephalus research; analysis of human data Benjamin Cohen, Timothy Wei, Abram Voorhees, Joseph Madsen, Tomer Anor Hydrocephalus is a neuropathophysiological disorder primarily diagnosed by increased cerebrospinal fluid volume and pressure within the brain. To date, utilization of clinical measurements have been limited to understanding of the relative amplitude and timing of flow, volume and pressure waveforms; qualitative approaches without a clear framework for meaningful quantitative comparison. Pressure volume models and electric circuit analogs enforce volume conservation principles in terms of pressure. Control volume analysis, through the integral mass and momentum conservation equations, ensures that pressure and volume are accounted for using first principles fluid physics. This approach is able to directly incorporate the diverse measurements obtained by clinicians into a simple, direct and robust mechanics based framework. Clinical data obtained for analysis are discussed along with data processing techniques used to extract terms in the conservation equation. Control volume analysis provides a non-invasive, physics-based approach to extracting pressure information from magnetic resonance velocity data that cannot be measured directly by pressure instrumentation. [Preview Abstract] |
Tuesday, November 23, 2010 4:23PM - 4:36PM |
RL.00007: Effect of Parent Artery Geometry on Flow Through Cerebral Aneurysm Morgan Nowak, Hiroshi Higuchi, Toshio Nakayama, Makoto Ohta The significance of parent artery geometry in aneurysm secondary flow is studied experimentally using PIV techniques. Several generalized models are used to obtain fundamental information on secondary flow structures, vortex dynamics and wall shear stress under a pulsatile flow. Time-dependent flow field through a model with the aneurysm on the lateral side of a curved parent artery is compared with that through a straight parent artery. The different wall shear stresses and fundamental structures seen within the aneurysm confirm the importance of the parent artery configuration in the development of aneurysm secondary flow. The experimental results are analyzed and compared with the numerical simulations. [Preview Abstract] |
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