RESUMO
High-resolution three-dimensional simulations (involving 100 million degrees of freedom) were employed to study transient turbulent flow in a carotid arterial bifurcation with a stenosed internal carotid artery (ICA). The geometrical model was reconstructed from MRI images, and in vivo velocity measurements were incorporated in the simulations to provide inlet and outlet boundary conditions. Due to the high degree of the ICA occlusion and the variable flow rate, a transitional and intermittent flow between laminar and turbulent states was established. Time- and space-window proper orthogonal decomposition (POD) was applied to quantify the different flow regimes in the occluded artery. A simplified version of the POD analysis that utilizes 2D slices only--more appropriate in the clinical setting--was also investigated.
Assuntos
Velocidade do Fluxo Sanguíneo , Pressão Sanguínea , Artérias Carótidas/fisiopatologia , Estenose das Carótidas/fisiopatologia , Modelos Cardiovasculares , Reologia/métodos , Simulação por Computador , Humanos , Dinâmica não Linear , Resistência ao CisalhamentoRESUMO
Proper orthogonal decomposition (POD), Kriging interpolation, and smoothing are applied to reconstruct gappy and noisy data of blood flow in a carotid artery. While we have applied these techniques to clinical data, in this paper in order to rigorously evaluate their effectiveness we rely on data obtained by computational fluid dynamics (CFD). Specifically, gappy data sets are generated by removing nodal values from high-resolution 3-D CFD data (at random or in a fixed area) while noisy data sets are formed by superimposing speckle noise on the CFD results. A combined POD-Kriging procedure is applied to planar data sets mimicking coarse resolution "ultrasound-like" blood flow images. A method for locating the vessel wall boundary and for calculating the wall shear stress (WSS) is also proposed. The results show good agreement with the original CFD data. The combined POD-Kriging method, enhanced by proper smoothing if needed, holds great potential in dealing effectively with gappy and noisy data reconstruction of in vivo velocity measurements based on color Doppler ultrasound (CDUS) imaging or magnetic resonance angiography (MRA).
Assuntos
Artefatos , Artérias Carótidas/fisiologia , Análise de Componente Principal/métodos , Fluxo Pulsátil , Processamento de Sinais Assistido por Computador , Velocidade do Fluxo Sanguíneo , Aumento da Imagem/métodos , Imageamento Tridimensional/métodos , Análise dos Mínimos Quadrados , Angiografia por Ressonância Magnética/métodos , Modelos Cardiovasculares , Reprodutibilidade dos Testes , Resistência ao Cisalhamento , Ultrassonografia Doppler em Cores/métodosRESUMO
A pulsatile laminar flow of a viscous, incompressible fluid through a stenosed artery was simulated by an immersed-boundary method. The method allows the use of a simple (rectangular) computational domain in order to simulate a flow around a complex geometry obstacle with surface irregularities (roughness). The influence of the shape and the surface roughness on the flow resistance was explored. The obtained numerical results were validated by comparison with published experimental and numerical results. We show that the surface irregularities have no significant influence on the flow resistance across an obstacle for a physiological range of Reynolds numbers. Notwithstanding, an accurate representation of irregularities allows investigation of the near-wall effects of a realistic flow such as fluid recirculation. We show that a detailed study of flow patterns in the immediate vicinity of the irregular surface can be performed using the immersed boundary method.
