The role of the carotid sinus in the reduction of arterial wall stresses due to head movements—potential implications for cervical artery dissection

Computational evaluation of smoothed particle hydrodynamics for implementing blood flow modelling through CT reconstructed arteries

Simulation of blood flow in a stenosed artery using Smoothed Particle Hydrodynamics (SPH) is a new research field, which is a particle-based method and different from the traditional continuum modelling technique such as Computational Fluid Dynamics (CFD). Both techniques harness parallel computing to process hemodynamics of cardiovascular structures. The objective of this study is to develop and test a new robust method for comparison of arterial flow velocity contours by SPH with the well-established CFD technique, and the implementation of SPH in computed tomography (CT) reconstructed arteries. The new method was developed based on three-dimensional (3D) straight and curved arterial models of millimeter range with a 25% stenosis in the middle section. In this study, we employed 1,000 to 13,000 particles to study how the number of particles influences SPH versus CFD deviation for blood-flow velocity distribution. Because further increasing the particle density has a diminishing effect on this deviation, we have determined a critical particle density of 1.45 particles/mm2 based on Reynolds number (Re = 200) at the inlet for an arterial flow simulation. Using this critical value of particle density can avoid unnecessarily big computational expenses that have no further effect on simulation accuracy. We have particularly shown that the SPH method has a big potential to be used in the virtual surgery system, such as to simulate the interaction between blood flow and the CT reconstructed vessels, especially those with stenosis or plaque when encountering vasculopathy, and for employing the simulation results output in clinical surgical procedures.

Transient blood flow in elastic coronary arteries with varying degrees of stenosis and dilatations: CFD modelling and parametric study

In this paper, we have analysed pulsatile flow through partially occluded elastic arteries, to determine the haemodynamic parameters of wall shear stress (WSS), wall pressure gradient and pressure drops (ΔP), contributing to enhanced flow resistance and myocardial ischaemic regions which impair cardiac contractility and cause increased work load on the heart. In summary, it can be observed that stenoses in an artery significantly influence the haemodynamic parameters of wall shear stress and pressure drop in contrast to dilatations case. This deduces that stenosis plays a more critical role in plaque growth and vulnerability in contrast to dilatation, and should be the key element in cardiovascular pathology and diagnosis. Through quantitative analysis of WSS and ΔP, we have provided a clearer insight into the haemodynamics of atherosclerotic arteries. Determination of these parameters can be helpful to cardiologists, because it is directly implicated in the genesis and development of atherosclerosis.

BIOMECHANICAL INVESTIGATION OF PULSATILE FLOW IN A THREE-DIMENSIONAL ATHEROSCLEROTIC CAROTID BIFURCATION MODEL

It is a well-established fact that atherosclerosis in carotid bifurcation depends on flow parameters such as wall shear stress, flow pulsatility, and blood pressure. However, it is still not clearly verified how atherosclerosis can become aggravated when plaque experiences a high level of shear stress during advance stages of this disease. In this paper, fluid and structural properties in idealistic geometries are analyzed by using fluid-structure interaction (FSI). From our results, the relationship among blood pressure, stenotic compression, and deformation was established. We show that a high level of compression occurs at the stenotic apex, and can potentially be responsible for plaque progression. Moreover, wall shear stress and deformation are significantly affected by the degree of stenosis. Finally, through analysis of the FSI-based simulation results, we can better understand the parameters that influence flow through a stenotic artery and plaque aggravation, and apply the knowledge for the enhancement of clinical research and prediction of treatment outcomes.

Sparsity transform k-t principal component analysis for accelerating cine three-dimensional flow measurements

Time-resolved three-dimensional flow measurements are limited by long acquisition times. Among the various acceleration techniques available, k-t methods have shown potential as they permit significant scan time reduction even with a single receive coil by exploiting spatiotemporal correlations. In this work, an extension of k-t principal component analysis is proposed utilizing signal differences between the velocity encodings of three-directional flow measurements to further compact the signal representation and hence improve reconstruction accuracy. The effect of sparsity transform in k-t principal component analysis is demonstrated using simulated and measured data of the carotid bifurcation. Deploying sparsity transform for 8-fold undersampled simulated data, velocity root-mean-square errors were found to decrease by 52 ± 14%, 59 ± 11%, and 16 ± 32% in the common, external, and internal carotid artery, respectively. In vivo, errors were reduced by 15 ± 17% in the common carotid artery with sparsity transform. Based on these findings, spatial resolution of three-dimensional flow measurements was increased to 0.8 mm isotropic resolution with prospective 8-fold undersampling and sparsity transform k-t principal component analysis reconstruction. Volumetric data were acquired in 6 min. Pathline visualization revealed details of helical flow patterns partially hidden at lower spatial resolution.

Wall stress of the cervical carotid artery in patients with carotid dissection: a case-control study

Spontaneous internal carotid artery (ICA) dissection (sICAD) results from an intimal tear located around the distal carotid sinus. The mechanisms causing the tear are unknown. This case-control study tested the hypotheses that head movements increase the wall stress in the cervical ICA and that the stress increase is greater in patients with sICAD than in controls. Five patients with unilateral, recanalized, left sICAD and five matched controls were investigated before and after maximal head rotation to the left and neck hyperextension after 45° head rotation to the left. The anatomy of the extracranial carotid arteries was assessed by magnetic resonance imaging and used to create finite element models of the right ICA. Wall stress increased after head movements. Increases above the 80th and 90th percentile were located at the intimal side of the artery wall from 7.4 mm below to 10 mm above the cranial edge of the carotid sinus, i.e., at the same location as histologically confirmed tears in patients with sICAD. Wall stress increase did not differ between patients and controls. The present findings suggest that wall stress increases at the intimal side of the artery wall surrounding the distal edge of the carotid bulb after head movements may be important for the development of carotid dissection. The lack of wall stress difference between the two groups indicates that the carotid arteries of patients with carotid dissection have either distinct functional or anatomical properties or endured unusually heavy wall stresses to initiate dissection.

Congenital spine deformities: a new screening indication for blunt cerebrovascular injuries after cervical trauma?

Blunt cerebrovascular injuries (BCVI) carry significant morbidity if not diagnosed and treated early. A high index of clinical suspicion is needed to recognize the injury patterns associated with this condition and to order the requisite imaging studies needed to diagnose it accurately. We report of BCVI associated with a congenital cervical spine malformation after blunt trauma. We recommend inclusion of cervical spine malformations to the current Eastern Association for the Surgery of Trauma screening criteria for BCVI and explain our rationale for the same.