Reconstruction of carotid bifurcation hemodynamics and wall thickness using computational fluid dynamics and MRI

Abstract

A thorough understanding of the relationship between local hemodynamics and plaque progression has been hindered by an inability to prospectively monitor these factors in vivo in humans. In this study a novel approach for noninvasively reconstructing artery wall thickness and local hemodynamics at the human carotid bifurcation is presented. Three-dimensional (3D) models of the lumen and wall boundaries, from which wall thickness can be measured, were reconstructed from blackblood magnetic resonance imaging (MRI). Along with time-varying inlet/outlet flow rates measured via phase contrast (PC) MRI, the lumen boundary was used as input for computational fluid dynamic (CFD) simulation of the subject-specific flow patterns and wall shear stresses (WSSs). Results from a 59-yearold subject with early, asymptomatic carotid artery disease show good agreement between simulated and measured velocities, and demonstrate a correspondence between wall thickening and low and oscillating shear at the carotid bulb. High shear at the distal internal carotid artery (ICA) was also colocalized with higher WSS; however, a quantitative general relationship between WSS and wall thickness was not found. Similar results were obtained from a 23-year-old normal subject. Wall shear stress (WSS) is widely believed to play a key role in the development and progression of atherosclerotic plaques. Studies comparing human post-mortem distributions of plaque to in vitro fluid dynamic models have perhaps provided the most direct observational evidence for the relationship between WSS and the focal development of atherosclerotic lesions (1-4). The mechanisms by which shear stresses alter endothelial function at the cellular, molecular, and genetic level are also now being elucidated (5). Despite these advances, however, many questions still remain regarding the role of fluid dynamics in the development and progression of atherosclerosis. One reason for this has been the difficulty of identifying and monitoring the relationships between local fluid dynamic factors and plaque development on a subject-specific basis.In principle, both MR and ultrasound imaging can be used to measure wall thickness (a marker for atherosclerotic burden) and blood velocities (from which WSSs are derived) directly. However, difficulties associated with the quantification of blood velocities in regions of complex flow have in the past limited the application of such an "imaging-only" approach to relatively straight sections of the abdominal aorta (6), femoral artery (7), and common carotid artery (8 -10). While these studies were able to confirm an inverse relationship between mean or peak shear and intimal or intima-media thickness, it is not yet possible to use imaging techniques alone to map WSS in the regions of complex flow where plaques are known to localize, such as at the carotid bifurcation. Recent work by Stokholm et al. (11) suggests that WSS from individual slices at the carotid bifurcation itself can be quantified in vivo by sophisticated postprocessing of ph...

Feasibility of in vivo measurement of carotid wall shear rate using spiral fourier velocity encoded MRI

“…The peak systolic WSR values measured in vivo with the proposed method are higher than those typically reported in the literature for the common carotid arteries (11,(13)(14)(15)(16)20,22) but within the range of normal values in healthy individuals (1,3,21,(28)(29)(30)(31). Reported ranges of carotid WSR and WSS values in healthy volunteers vary significantly across the literature, in particular when comparing different techniques (11).…”

“…PC is not currently capable of providing accurate absolute measurements of WSS (18) and has been shown to underestimate blood flow velocities in the carotid bifurcation by 31-39% (19). An alternative approach for estimating WSS is to reconstruct a complex flow field via computational fluid dynamics (CFD) simulation, using vascular geometries and input/output functions derived from noninvasive imaging data (20)(21)(22). This approach is computationally intense and may be sensitive to many assumptions and simplifications that are frequently made about the properties of blood and endothelium.…”

Comparison of 2D and multislab 3D magnetic resonance techniques for measuring carotid wall volumes

“…Blood signal is suppressed by DIR. Using this technique, a theoretical maximum slab thickness of 5 cm has been suggested (17), although slow recirculating blood in the carotid bulb may still be problematic (29). Some additional techniques may prove useful to mitigate these limitations.…”

Assessment of Carotid Flow Using Magnetic Resonance Imaging and Computational Fluid Dynamics

“…Harloff et al (2010) used CFD image-based modeling as an option to improve the accuracy of MRI-based WSS and OSI estimation, with the purpose of correlating atherogenic low WSS and high OSI with the localization of aortic plaques. Steinman et al (2002) used a novel approach for noninvasively reconstructing artery wall thickness and local hemodynamics at the human carotid bifurcation. Three-dimensional models of the lumen and wall boundaries, from which wall thickness can be measured, were reconstructed from black blood MRI.…”

“…An alternative approach for cardiovascular flow assessment is to reconstruct a complex flow field via CFD simulation, using vascular geometries and input/output functions derived from non-invasive imaging data (Kim et al, 2006;Papathanasopoulou et al, 2003;Steinman et al, 2002). The accuracy of conventional CFD routines hinges on many modeling assumptions that are not strictly true for in vivo vascular flow, including rigid vessel walls and uniform blood viscosity.…”