Hemodynamics of human carotid artery bifurcations: computational studies with models reconstructed from magnetic resonance imaging of normal subjects. J Vasc Surg

Imaging Research Laboratories, John P. Robarts Research Institute, London, Ontario, Canada.
Journal of Vascular Surgery (Impact Factor: 3.02). 08/1998; 28(1):143-56. DOI: 10.1016/S0741-5214(98)70210-1
Source: PubMed

ABSTRACT The precise role played by hemodynamics, particularly wall shear stress, in the development and progression of vascular disease remains unclear, in large part because of a lack of in vivo studies with humans. Although technical challenges remain for noninvasively imaging wall shear stresses in humans, vascular anatomy can be imaged with sufficiently high resolution to allow reconstruction of three-dimensional models for computational hemodynamic studies. In this paper we present an entirely noninvasive magnetic resonance imaging (MRI) protocol that provides carotid bifurcation geometry and flow rates from which the in vivo hemodynamics can be computed. Maps of average, oscillatory, and gradients of wall shear stress are presented for two normal human subjects, and their data are compared with those computed for an idealized carotid bifurcation model.
An MRI protocol was developed to acquire all necessary image data in scan times suitable for patient studies. Three-dimensional models of the carotid bifurcation lumen were reconstructed from serial black blood MR images of two normal volunteers. Common and internal carotid artery flow rate waveforms were determined from MRI phase-contrast velocity imaging in the same subjects and were used to impose fully developed velocity boundary conditions for the computational model. Subject-specific time-resolved velocities and wall shear stresses were then computed with a finite element-based Navier-Stokes equation solver.
Models reconstructed from in vivo MRI of two subjects showed obvious differences in branch angle, bulb size and extent, and three-dimensional curvature. Maps of a variety of wall shear stress indices showed obvious qualitative differences in patterns between the in vivo models and between the in vivo models and the idealized model. Secondary, helical flow patterns, induced primarily by the asymmetric and curved in vivo geometries, were found to play a key role in determining the resulting wall shear stress patterns. The use of in vivo flow rate waveforms was found to play a minor but noticeable role in some of the wall shear stress behavior observed.
Conventional "averaged" carotid bifurcation models mask interesting hemodynamic features observed in realistic models derived from noninvasive imaging of normal human subjects. Observation of intersubject variations in the in vivo wall shear stress patterns supports the notion that more conclusive evidence regarding the role of hemodynamics in vascular disease may be derived from such individual studies. The techniques presented here, when combined with subject-specific MRI measurements of carotid artery plaque thickness and composition, provide the tools necessary for entirely noninvasive, prospective, in vivo human studies of hemodynamics and the relationship of hemodynamics to vascular disease.

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    • "The first image-based patient-specific methodology for blood flow computational fluid dynamic simulations under realistic flow conditions were presented in 1998 by Taylor et al. [50] and Milner et al. [51]. A few years later, sophisticated image processing and vascular reconstruction algorithms were incorporated to model complex geometries like the whole circle of Willis [52] and the posterior circulation with a giant intracranial aneurysm [53]. "
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    ABSTRACT: About a decade ago, the first image-based computational hemodynamic studies of cerebral aneurysms were presented. Their potential for clinical applications was the result of a right combination of medical image processing, vascular reconstruction, and grid generation techniques used to reconstruct personalized domains for computational fluid and solid dynamics solvers and data analysis and visualization techniques. A considerable number of studies have captivated the attention of clinicians, neurosurgeons, and neuroradiologists, who realized the ability of those tools to help in understanding the role played by hemodynamics in the natural history and management of intracranial aneurysms. This paper intends to summarize the most relevant results in the field reported during the last years.
    07/2013; 2013(1). DOI:10.5402/2013/602707
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    • "The boundary condition for a compliant vessel including a carotid bifurcation has been systematically addressed by Formaggia et al. (2001, 2003, 2009), using 1D and 0D approximations of vasculatures at the exit. Milner et al. (1998), Ford et al. (2005) and Wake et al. (2009) among others studied the effect of the inlet velocity condition on carotid flow field. As outflow conditions, CFD studies were used to apply measured flow or velocity rate or normal traction-free conditions (Moyle et al. 2006; Lee et al. 2008; Wake et al. 2009), whereas for FSI computations, pressure (Tang et al. 2008) or combined velocity/pressure conditions (Gao et al. 2009) were used. "
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    ABSTRACT: In this study, we develop structured tree outflow boundary conditions for modelling the human carotid haemodynamics. The model geometry was reconstructed through computerised tomography scan. Unsteady-state computational fluid dynamic analyses were performed under different conditions using a commercial software package ADINA R&D, Inc., (Watertown, MA, USA) in order to assess the impact of the boundary conditions on the flow variables. In particular, the results showed that the peripheral vessels massively impact the pressure while the flow is relatively unaffected. As an example of application of these outflow conditions, an unsteady fluid-structure interaction (FSI) simulation was carried out and the dependence of the wall shear stress (WSS) on the arterial wall compliance in the carotid bifurcation was studied. In particular, a comparison between FSI and rigid-wall models was conducted. Results showed that the WSS distributions were substantially affected by the diameter variation of the arterial wall. In particular, even similar WSS distributions were found for both cases, and differences in the computed WSS values were also found.
    Computer Methods in Biomechanics and Biomedical Engineering 02/2013; 17(11). DOI:10.1080/10255842.2012.744396 · 1.77 Impact Factor
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    • "Starting from the observation that certain geometric features of vascular segments might be considered risk factors for developing atherosclerosis by virtue of their influence on flow patterns (Friedman et al., 1983; Alastruey et al., 2012), recently Lee et al. (2008) and Zhang et al. (2010) demonstrated that the susceptibility to disturbed shear at the normal carotid bifurcation can be ameliorated by the presence of vascular bending and tortuosity. Both theory (Dean, 1927; Germano, 1982,1989; Liu and Masliyah, 1993) and practice (Caro et al., 1992, 1996; Stonebridge et al., 1996; Milner et al., 1998) have demonstrated that torsion and curvature contribute to the onset and development of helical patterns in the bulk flow. Moreover, there is evidence that helical blood flow (1) elicits atheroprotective fluid–wall interaction processes, by limiting flow instabilities within the cardiovascular bed (Caro et al., 1971; Morbiducci et al., 2007, 2011a) and (2) regulates the transport of atherogenic particles at the luminal surface (Caro et al. 1996; Morbiducci et al., 2010; Liu et al., 2009, 2010). "
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    ABSTRACT: The main purpose of the study is to verify if helical flow might be a surrogate marker of the exposure to disturbed shear in normal carotid bifurcations. Based on hemodynamic simulations data of 50 carotid bifurcations, we defined appropriate helicity-based bulk flow descriptors and multivariate linear regression analysis was performed to assess the potential for a combination of helicity-based indicators in describing the exposure to disturbed shear. To select the optimal combination of helicity-based descriptors in the regression model, the Akaike information criterion was applied. The identified statistical model is composed of two bulk flow descriptors proposed here to quantify helicity intensity and the balance between counter-rotating helical flow patterns in the flow field. The model revealed the existence of a significant relationship with adjusted squared Pearson's correlation coefficient in the range 0.4-0.7 (P<0.0001). In detail, while a high helicity intensity is instrumental in suppressing flow disturbances, this protective effect could be moderated when one direction of rotation is dominant in the flow field. The in vivo quantification of the bulk flow features emerging in this study would offer a practical way to infer the presence of disturbed shear in large-scale in vivo studies of local risk factors in atherosclerosis.
    Journal of Biomechanics 07/2012; 45(14):2398-404. DOI:10.1016/j.jbiomech.2012.07.007 · 2.75 Impact Factor
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