Physiological outflow boundary conditions methodology for small arteries with multiple outlets: A patient-specific hepatic artery haemodynamics case study

2015 ◽  
Vol 229 (4) ◽  
pp. 291-306 ◽  
Author(s):  
Jorge Aramburu ◽  
Raúl Antón ◽  
Nebai Bernal ◽  
Alejandro Rivas ◽  
Juan Carlos Ramos ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Hepatic Artery ◽  
Patient Specific ◽  
Small Arteries ◽  
Outflow Boundary Conditions ◽  
Outflow Boundary

Tuning a Multiscale Model of Abdominal Aortic Hemodynamics to Incorporate Patient-Specific Features of Flow and Pressure Waveforms

2009 ◽  
Author(s):  
Ryan L. Spilker ◽  
Charles A. Taylor
Keyword(s):  
Boundary Conditions ◽  
Computational Models ◽  
Multiscale Model ◽  
Patient Specific ◽  
Vascular Walls ◽  
Outflow Boundary Conditions ◽  
Abdominal Aortic ◽  
Cardiovascular Models ◽  
Outflow Boundary ◽  
Aortic Hemodynamics

Computational models enable the calculation of quantities that are impractical or impossible to measure and the prediction of physiological changes due to interventions. In order to be useful, cardiovascular models must be both rooted in physical principles and designed such that measured or otherwise desired features of the cardiovascular system are reproduced. The former requirement has motivated the development of image-based anatomic models, patient-specific inflow boundary conditions, deformable vascular walls, outflow boundary conditions that represent the influence of the downstream circulation, and multiscale models. The development of approaches to address the latter requirement, reproducing desired features of the circulation, is a critical area of modeling research that has received comparatively little attention.

scholarly journals The impact of scaled boundary conditions on wall shear stress computations in atherosclerotic human coronary bifurcations

2016 ◽  
Vol 310 (10) ◽  
pp. H1304-H1312 ◽  
Author(s):  
Jelle T. C. Schrauwen ◽  
Janina C. V. Schwarz ◽  
Jolanda J. Wentzel ◽  
Antonius F. W. van der Steen ◽  
Maria Siebes ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Boundary Conditions ◽  
Scaling Laws ◽  
Coronary Intervention ◽  
Patient Specific ◽  
Outflow Boundary Conditions ◽  
Wall Shear ◽  
Outflow Boundary ◽  
The Impact

The aim of this study was to determine if reliable patient-specific wall shear stress (WSS) can be computed when diameter-based scaling laws are used to impose the boundary conditions for computational fluid dynamics. This study focused on mildly diseased human coronary bifurcations since they are predilection sites for atherosclerosis. Eight patients scheduled for percutaneous coronary intervention were imaged with angiography. The velocity proximal and distal of a bifurcation was acquired with intravascular Doppler measurements. These measurements were used for inflow and outflow boundary conditions for the first set of WSS computations. For the second set of computations, absolute inflow and outflow ratios were derived from geometry-based scaling laws based on angiography data. Normalized WSS maps per segment were obtained by dividing the absolute WSS by the mean WSS value. Absolute and normalized WSS maps from the measured-approach and the scaled-approach were compared. A reasonable agreement was found between the measured and scaled inflows, with a median difference of 0.08 ml/s [−0.01; 0.20]. The measured and the scaled outflow ratios showed a good agreement: 1.5 percentage points [−19.0; 4.5]. Absolute WSS maps were sensitive to the inflow and outflow variations, and relatively large differences between the two approaches were observed. For normalized WSS maps, the results for the two approaches were equivalent. This study showed that normalized WSS can be obtained from angiography data alone by applying diameter-based scaling laws to define the boundary conditions. Caution should be taken when absolute WSS is assessed from computations using scaled boundary conditions.

scholarly journals Structured Tree Impedance Outflow Boundary Conditions for 3D Lung Simulations

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Andrew Comerford ◽  
Christiane Förster ◽  
Wolfgang A. Wall
Keyword(s):  
Boundary Conditions ◽  
Flow Distribution ◽  
Left Lobe ◽  
Patient Specific ◽  
Outflow Boundary Conditions ◽  
Human Lungs ◽  
Clinical Scenarios ◽  
Mean Pressure ◽  
Acceleration And Deceleration ◽  
Outflow Boundary

In this paper, we develop structured tree outflow boundary conditions for modeling the airflow in patient specific human lungs. The utilized structured tree is used to represent the nonimageable vessels beyond the 3D domain. The coupling of the two different scales (1D and 3D) employs a Dirichlet–Neumann approach. The simulations are performed under a variety of conditions such as light breathing and constant flow ventilation (which is characterized by very rapid acceleration and deceleration). All results show that the peripheral vessels significantly impact the pressure, however, the flow is relatively unaffected, reinforcing the fact that the majority of the lung impedance is due to the lower generations rather than the peripheral vessels. Furthermore, simulations of a hypothetical diseased lung (restricted flow in the superior left lobe) under mechanical ventilation show that the mean pressure at the outlets of the 3D domain is about 28% higher. This hypothetical model illustrates potential causes of volutrauma in the human lung and furthermore demonstrates how different clinical scenarios can be studied without the need to assume the unknown flow distribution into the downstream region.

MRI-Based Inflow Boundary Conditions for Patient Specific Fluid Structure Interaction Modeling of Abdominal Aortic Aneurysms

2012 ◽  
Author(s):  
Santanu Chandra ◽  
Samarth Raut ◽  
Anirban Jana ◽  
Robert W. Biederman ◽  
Mark Doyle ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Wall Thickness ◽  
Wall Stress ◽  
Patient Specific ◽  
Structure Interaction ◽  
Outflow Boundary Conditions ◽  
Abdominal Aortic ◽  
Outflow Boundary ◽  
Fully Coupled

Rupture of abdominal aortic aneurysm (AAA) is the 10th leading cause of death for men over age of 50 in US. The decision for surgical intervention is currently based on aneurysm diameter or its expansion rate. However, the use of these criteria for all patients is debatable. For example, small aneurysms do rupture or become symptomatic before reaching the critical diameter. Computationally predicted mechanical wall stress is considered a viable alternative criterion for rupture risk assessment. Hence, it is important to evaluate the effect of different modeling approaches on the accuracy of the predicated AAA wall stress. For computational solid stress (CSS) analysis or finite element analysis (FEA), a uniform static or transient intraluminal pressure is generally applied on the wall-lumen surface whereas in fluid-structure interaction (FSI) modeling the wall-lumen surface experiences transient and non-uniform fluid stress. An earlier comparison on idealized AAA models [1] revealed that static and transient CSS underestimate the peak wall stress (PWS) by an average 20–30% for variable wall thickness and 10% for uniform wall thickness when compared to fully coupled FSI. However, FSI-predicted stresses and strains were observed to be sensitive to inflow and outflow boundary conditions, warranting further study on a more accurate approach for FSI modeling. Though significant work has been performed on modeling outflow boundary conditions [2], studies on the sensitivity of computed stress or strain to the type of FSI inflow boundary condition is scarce [2–4]. We hypothesize that a FSI framework with a patient specific velocity boundary condition derived from magnetic resonance imaging (MRI) data applied to patient specific AAA geometry would provide better accuracy of PWS calculations compared to a FEA model. In this work, we present a framework where the AAA geometry is reconstructed from computed tomography (CT) images, on which FSI simulations were performed with inlet velocity components extracted from patient MR images of the abdominal aorta. Fully coupled FSI simulations were performed and results were compared with CSS simulations with uniform transient pressure boundary conditions.

MRI Based Quantification of Outflow Boundary Conditions for Computational Fluid Dynamics of Stenosed Human Carotid Arteries

2010 ◽  
Author(s):  
Harald C. Groen ◽  
Lenette Simons ◽  
E. Marielle H. Bosboom ◽  
Frans van de Vosse ◽  
Anton F. W. van der Steen ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Boundary Conditions ◽  
Carotid Arteries ◽  
Patient Specific ◽  
Murray's Law ◽  
Murray’S Law ◽  
Outflow Boundary Conditions ◽  
Outflow Boundary ◽  
Human Carotid

Many studies have been performed to investigate the contribution of wall shear stress (WSS) to pathophysiological processes related to atherosclerosis (Groen, et al., 2007; Kaazempur-Mofrad, et al., 2004; Ku, et al., 1985). To investigate these relationships in stenosed human carotid arteries, accurate assessment of WSS is required. WSS can be calculated in vivo by coupling medical imaging and computational fluid dynamics (CFD). However, often patient specific in- and outflow information is unavailable. Therefore flow through the common (CCA), internal (ICA) and external (ECA) carotid artery needs to be estimated. Murray’s law (Murray, 1926) is often used for that purpose, but it is unclear whether this law holds for stenosed arteries. The goal of this study was to determine outflow boundary conditions for WSS calculations in stenosed carotid bifurcations. Therefore we first quantified the flow (Q) in carotid arteries with different degrees of area stenosis using phase-contrast MRI and determined an empirical relation between outflow-ratios and degree of area stenosis. Secondly we compared the estimated flow ratio based on Murray’s law to the ones measured by MRI. Finally we analyzed the influence of the outflow conditions on the calculated WSS using CFD.

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