Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session G3: Brain and Lymphatic SystemBio Fluids: Internal
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Chair: Vitaliy Rayz, Purdue University Room: 403 |
Monday, November 20, 2017 10:35AM - 10:48AM |
G3.00001: Direct observation of cerebrospinal fluid bulk flow in the brain Humberto Mestre, Jeffrey Tithof, John Thomas, Douglas Kelley, Maiken Nedergaard Cerebrospinal fluid (CSF) serves a~vital~role~in~normal brain function.~Its~adequate~flow and~exchange~with interstitial fluid~through perivascular spaces (PVS)~has been shown to be important in the clearance of toxic metabolites like amyloid-$\beta $,~and~its~disturbance~can~cause severe neurological diseases. It has long been suspected that bulk flow may transport CSF, but limitations in imaging techniques have~prevented direct observation of such flows in the PVS.~In this talk, we describe a novel approach using~high speed two~photon laser scanning microscopy which has allowed for~the first ever direct observation of~CSF flow~in the PVS of a mouse brain.~By performing~particle tracking velocimetry, we quantify the CSF bulk flow speeds and PVS geometry.~This technique enables future studies of CSF flow disturbances on a new scale and~will pave the way for evaluating the role of these fluxes in neurodegenerative disease.~ [Preview Abstract] |
Monday, November 20, 2017 10:48AM - 11:01AM |
G3.00002: Cerebrospinal fluid bulk flow is driven by the cardiac cycle Jeffrey Tithof, Humberto Mestre, John Thomas, Maiken Nedergaard, Douglas Kelley Recent discoveries have uncovered a cerebrospinal fluid (CSF) transport system in the perivascular spaces (PVS) of the mammalian brain which clears excess extracellular fluid and protein waste products. The oscillatory pattern of CSF flow has long been attributed to arterial pulsations due to cardiac contractility but limitations in imaging techniques have impeded quantitative measurement of flow rates within the PVS. In this talk, we describe quantitative measurements from the first ever direct imaging of CSF flow in the PVS of a mouse brain. We perform particle tracking velocimetry to obtain time-resolved velocity measurements. To identify the cardiac and/or respiratory dependence of the flow, while imaging, we simultaneously record the mouse's electrocardiogram and respiration. Our measurements conclusively indicate that CSF pulsatility in the arterial PVS is directly driven by the cardiac cycle and not by the respiratory cycle or cerebral vasomotion. These results offer a substantial step forward in understanding bulk flow of CSF in the mammalian brain and may have important implications related to neurodegenerative diseases. [Preview Abstract] |
Monday, November 20, 2017 11:01AM - 11:14AM |
G3.00003: Flow in cerebral aneurysms: 4D Flow MRI measurements and CFD models. Vitaliy Rayz, Susanne Schnell 4D Flow MRI is capable of measuring blood flow in vivo, providing time-resolved velocity fields in 3D. The dynamic range of the 4D Flow MRI is determined by a velocity sensitivity parameter (venc), set above the expected maximum velocity, which can result in noisy data for slow flow regions. A dual-venc 4D flow MRI technique, where both low- and high-venc data are acquired, can improve velocity-to-noise ratio and, therefore, quantification of clinically-relevant hemodynamic metrics. In this study, patient-specific CFD simulations were used to evaluate the advantages of the dual-venc approach for assessment of the flow in cerebral aneurysms. The flow in 2 cerebral aneurysms was measured in vivo with dual-venc 4D Flow MRI and simulated with CFD, using the MRI data to prescribe flow boundary conditions. The flow fields obtained with computations were compared to those measured with a single- and dual-venc 4D Flow MRI. The numerical models resolved small flow structures near the aneurysmal wall, that were not detected with a single-venc acquisition. Comparison of the numerical and imaging results shows that the dual-venc approach can improve the accuracy of the 4D Flow MRI measurements in regions characterized by high-velocity jets and slow recirculating flows. [Preview Abstract] |
Monday, November 20, 2017 11:14AM - 11:27AM |
G3.00004: In vivo and in vitro measurements of cerebral aneurysm hemodynamics Omid Amili, Mostafa Toloui, Pierre-Francois Van de Moortele, Bharathi Jagadeesan, Filippo Coletti The hemodynamics of cerebral aneurysms is thought to play a critical role in their formation, growth, and potential rupture. Our understanding in this area, however, comes mostly from~in vitro~experiments and numerical simulations, which have limited realism.~In vivo~measurements of the intracranial blood flow can be obtained by Magnetic Resonance Imaging (MRI), but they typically suffer from limited accuracy and inadequate resolution. Here we present a direct comparison between~in vivo~and~in vitro~measurements of the flow inside an internal carotid artery aneurysm. For both, we use 4D (i.e. volumetric and time-resolved) MRI velocimetry performed in a 7 Tesla magnet at sub-millimeter resolution. The~in vitro~measurements are carried out in a 3D printed aneurysm replica scaled up by a factor three, effectively increasing the spatial resolution. The patient-specific inflow waveform and the corresponding Reynolds and Womersley numbers are matched in a flow loop that mimics the impedance of the vascular bed. Direct comparison of the velocity fields allows assessing the robustness of the~in vivo~measurements, while highlighting the insight achievable~in vitro. The data also represents a comprehensive test case for numerical simulations. [Preview Abstract] |
Monday, November 20, 2017 11:27AM - 11:40AM |
G3.00005: Investigation of Patient-Specific Cerebral Aneurysm using Volumetric PIV, CFD, and \textit{In Vitro} PC-MRI Melissa Brindise, Ben Dickerhoff, David Saloner, Vitaliy Rayz, Pavlos Vlachos 4D PC-MRI is a modality capable of providing time-resolved velocity fields in cerebral aneurysms \textit{in vivo}. The MRI-measured velocities and subsequent hemodynamic parameters such as wall shear stress, and oscillatory shear index, can help neurosurgeons decide a course of treatment for a patient, e.g. whether to treat or monitor the aneurysm. However, low spatiotemporal resolution, limited velocity dynamic range, and inherent noise of PC-MRI velocity fields can have a notable effect on subsequent calculations, and should be investigated. In this work, we compare velocity fields obtained with 4D PC-MRI, computational fluid dynamics (CFD) and volumetric particle image velocimetry (PIV), using a patient-specific model of a basilar tip aneurysm. The same \textit{in vitro} model is used for all three modalities and flow input parameters are controlled. \textit{In vivo}, PC-MRI data was also acquired for this patient and used for comparison. Specifically, we investigate differences in the resulting velocity fields and biases in subsequent calculations. Further, we explore the effect these errors may have on assessment of the aneurysm progression and seek to develop corrective algorithms and other methodologies that can be used to improve the accuracy of hemodynamic analysis in clinical setting. [Preview Abstract] |
Monday, November 20, 2017 11:40AM - 11:53AM |
G3.00006: Parametric Characterization of Flow Inside Cererbal Aneurysms Treated with Flow-Diverting Stents Michael Barbour, Michael Levitt, Christian Geindreau, Luke Johnson, Keshav Chivukula, Alberto Aliseda Cerebral aneurysms are often treated with a flow-diverting stent (FDS) to reduce blood flow into the aneurysm sac, promoting the development of a stable thrombus. Successful treatment is highly dependent on the degree of flow reduction and the altered hemodynamics inside the aneurysm sac following treatment. Establishing a causal connection between hemodynamic metrics of FDS-treated CAs and long-term clinical outcomes requires a rigorous parametric characterization of this flow environment. We use 3D particle image velocimetry (PIV) to measure the flow inside idealized aneurysm models treated with FDS. Physiologically realistic Reynolds numbers and increasing levels of parent vessel curvature are analyzed to understand the effect of inertia on flow development. The flow velocity into the aneurysm and the topology of the flow inside the sac is shown to be highly dependent on parent vessel Dean number (De). The role of flow pulsatility is then added to the study via time-dependent waveforms. Velocity measurements at 2 values of parent vessel Womersley number (Wo) allow us to parameterize flow inside of CAs treated with FDS as a function of De, Re and Wo, improving the fundamental understanding of how FDS alter CA hemodynamics and aiding in the development of new treatments. [Preview Abstract] |
Monday, November 20, 2017 11:53AM - 12:06PM |
G3.00007: Modelling Ischemic Stroke and Temperature Intervention Using Vascular Porous Method Stephen Blowers, Prashant Valluri, Ian Marshall, Peter Andrews, Bridget Harris, Michael Thrippleton In the event of cerebral infarction, a region of tissue is supplied with insufficient blood flow to support normal metabolism. This can lead to an ischemic reaction which incurs cell death. Through a reduction of temperature, the metabolic demand can be reduced, which then offsets the onset of necrosis. This allows extra time for the patient to receive medical attention and could help prevent permanent brain damage from occurring. Here, we present a vascular-porous (VaPor) blood flow model that can simulate such an event. Cerebral blood flow is simulated using a combination of 1-Dimensional vessels embedded in 3-Dimensional porous media. This allows for simple manipulation of the structure and determining the effect of an obstructed vessel. Results show regional temperature increase of 1-1.5$^{\mathrm{o}}$C comparable with results from literature (in contrast to previous simpler models). Additionally, the application of scalp cooling in such an event dramatically reduces the temperature in the affected region to near hypothermic temperatures, which points to a potential rapid form of first intervention. [Preview Abstract] |
Monday, November 20, 2017 12:06PM - 12:19PM |
G3.00008: Kinetics of Transferrin and Transferrin-Receptor during Iron Transport through Blood Brain Barrier Aminul Khan, Jin Liu, Prashanta Dutta Transferrin and its receptors play an important role during the uptake and transcytosis of iron by blood brain barrier (BBB) endothelial cells to maintain iron homeostasis in BBB endothelium and brain. In the blood side of BBB, ferric iron binds with the apo-transferrin to form holo-transferrin which enters the endothelial cell via transferrin receptor mediated endocytosis. Depending on the initial concentration of iron inside the cell endocytosed holo-transferrin can either be acidified in the endosome or exocytosed through the basolateral membrane. Acidification of holo-transferrin in the endosome releases ferrous irons which may either be stored and used by the cell or transported into brain side. Exocytosis of the holo-transferrin through basolateral membrane leads to transport of iron bound to transferrin into brain side. In this work, kinetics of internalization, recycling and exocytosis of transferrin and its receptors are modeled by laws of mass action during iron transport in BBB endothelial cell. Kinetic parameters for the model are determined by least square analysis. Our results suggest that the cell's initial iron content determines the extent of the two possible iron transport pathways, which will be presented in this talk [Preview Abstract] |
Monday, November 20, 2017 12:19PM - 12:32PM |
G3.00009: Cerebral blood flow reduction in Alzheimer’s disease: impact of capillary occlusions on mice and humans Maxime Berg, Adlan Merlo, Myriam Peyrounette, Vincent Doyeux, Amy Smith, Jean Cruz-hernandez, Oliver Bracko, Mohammad Haft-javaherian, Nozomi Nishimura, Chris B. Schaffer, Yohan Davit, Michel Quintard, Sylvie Lorthois Alzheimer’s disease may be the most common form of dementia, yet a satisfactory diagnosis procedure has still to be found (Nelson JNEEN 2012). Recent studies (Iturria-Medina Nat Com 2016 & Cruz-Hernandez SFN meeting 2016) suggest that a significant decrease of cerebral blood flow, probably caused by white blood cells stalling small vessels, may be among the earliest biological markers. To assess this hypothesis we derive a blood flow model, validate it against in vitro controlled experiments and in vivo measurements made on mice. We then investigate the influence of capillary occlusions on regional perfusion (sum of all arteriole flowrates feeding the network) of large mice and humans anatomical networks. Consistent with experiments, we observe no threshold effect, so that even a small percentage of occlusions (2-4\%) leads to significant blood flow decrease (5-12\%). We show that both species share the same linear dependance, suggesting possible translation from mice to human. [Preview Abstract] |
Monday, November 20, 2017 12:32PM - 12:45PM |
G3.00010: Understanding Lymphatic Valve Function via Computational Modeling Ki Wolf, Zhanna Nepiyushchikh, Mohammad Razavi, Brandon Dixon, Alexander Alexeev The lymphatic system is a crucial part to the circulatory system with many important functions, such as transport of interstitial fluid, fatty acid, and immune cells. Lymphatic vessels' contractile walls and valves allow lymph flow against adverse pressure gradients and prevent back flow. Yet, the effect of lymphatic valves' geometric and mechanical properties to pumping performance and lymphatic dysfunctions like lymphedema is not well understood. Our coupled fluid-solid computational model based on lattice Boltzmann model and lattice spring model investigates the dynamics and effectiveness of lymphatic valves in resistance minimization, backflow prevention, and viscoelastic response under different geometric and mechanical properties, suggesting the range of lymphatic valve parameters with effective pumping performance. Our model also provides more physiologically relevant relations of the valve response under varied conditions to a lumped parameter model of the lymphatic system giving an integrative insight into lymphatic system performance, including its failure due to diseases. [Preview Abstract] |
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