RESUMO
Carotid endarterectomy (CEA) influences the carotid endoluminal anatomy, which results in hemodynamic changes before and after surgery. We investigated the hemodynamics of severe carotid artery stenosis before and after conventional endarterectomy with/without patch repair. An in vitro experiment utilizing carotid phantoms, which underwent a procedure that emulated CEA with/without the patch repair, was performed with a high-spatiotemporal resolution using 4D flow MRI. We evaluated an abnormal region of carotids, which consists of the normalized time-averaged wall shear stress (NTA|WSS|) and the oscillatory shear index (OSI), to account for continuous high-shear regions (high NTA|WSS| and low OSI) and chaotic low-shear regions, i.e., stenosis-prone regions (low NTA|WSS| and high OSI). The use of normalized hemodynamic parameters (e.g., NTA|WSS|) allowed comparison of diverse cases with different conditions of hemodynamics and vessel geometry. We observed that the stenosis-prone regions of the carotids with patches were noticeably larger than the corresponding regions in no-patch carotids. A large recirculating flow zone found in the stenosis-prone region of the internal carotid artery (ICA) of the postoperative carotids with patches partially blocks the flow path into ICA, and consequently the flow rate was not recovered after surgery unlike an expectation.
Assuntos
Artéria Carótida Interna/fisiopatologia , Estenose das Carótidas/cirurgia , Endarterectomia das Carótidas , Modelos Cardiovasculares , Fluxo Sanguíneo Regional/fisiologia , Idoso , Velocidade do Fluxo Sanguíneo/fisiologia , Artéria Carótida Interna/diagnóstico por imagem , Artéria Carótida Interna/cirurgia , Estenose das Carótidas/diagnóstico , Estenose das Carótidas/fisiopatologia , Humanos , Imageamento Tridimensional/métodos , Imageamento por Ressonância Magnética/métodos , Masculino , Imagens de Fantasmas , Período Pós-Operatório , Estudos Retrospectivos , Índice de Gravidade de Doença , Resistência ao Cisalhamento/fisiologia , Estresse Mecânico , Resultado do TratamentoRESUMO
Four-dimensional flow magnetic resonance imaging (4D flow MRI) is a versatile tool to obtain hemodynamic information and anatomic information simultaneously. The wall shear stress (WSS), a force exerted on a vessel wall in parallel, is one of the hemodynamic parameters available with 4D flow MRI and is thought to play an important role in clinical applications such as assessing the development of atherosclerosis. Nevertheless, the accuracy of WSS obtained with 4D flow MRI is rarely evaluated or reported in literature, especially in the in vivo studies. We propose a novel and facile criterion called Reynolds resolution to assess the accuracy of WSS estimation in 4D flow MRI studies. Reynolds resolution consists of a spatial resolution, encoding velocity, kinematic viscosity of a working fluid, and signal-to-noise ratio, which are readily accessible information in 4D flow MRI measurements. We explored the relationship between Reynolds resolution and the WSS error. To include diverse and extensive cases, we measured three circular tubing flows with a diameter of 40, 8, and 2â¯mm. The 40â¯mm tubing flow was measured by 3 Tesla (T) human MR scanner with a knee coil and spatial resolution of 0.5â¯mm. The 8 and 2â¯mm tubing flows were both measured by 4.7 T MR scanner, but the scans were performed with a conventional birdcage coil (8â¯mm tubing) and a custom-made solenoid coil (2â¯mm tubing), respectively. The spatial resolution was varied from 0.2, 0.4 or 0.8â¯mm for the 8â¯mm tubing flow, but was fixed at 0.090â¯mm for 2â¯mm tubing flow. In addition, the near-wall velocity gradient, required to be determined prior to the WSS, was calculated using two methods; these included assuming a linear velocity profile or quadratic velocity profile near wall. The accuracy of WSS obtained using each method and tubing flow was evaluated against the theoretical WSS value. As a result, we found that Reynolds resolution is in logarithmic relation to the WSS error.
Assuntos
Aumento da Imagem/métodos , Processamento de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Modelos Cardiovasculares , Velocidade do Fluxo Sanguíneo , Desenho de Equipamento , Hemodinâmica , Imagens de Fantasmas , Resistência ao Cisalhamento , Razão Sinal-Ruído , Estresse MecânicoRESUMO
Three-Dimensional network of carbon nanotubes: The 3D network of CNTs have hierarchical structures comprised of interconnected SWNTs between Si pillars in microfluidic channels. The Al(2)O(3) coated 3D networks were used for size different nanoparticles filtration and streptavidin capturing in very diluted solution. The 3D network of SWNTs systems will provide a robust multifuncitonal platform for a variety of biomedical and environmental applications.