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Atherosclerosis involves an inflammatory response due to plaque formation within the arteries, which can lead to ischemic stroke and heart disease. It is one of the leading causes of death worldwide, with various contributing factors such as hyperlipidemia, hypertension, obesity, diabetes, and smoking. Wall shear stress (WSS) is also known as a contributing factor of the formation of atherosclerotic plaques. Since the causes of atherosclerosis cannot be attributed to a single factor, clearly understanding the mechanisms and causes of its occurrence is crucial for preventing the disease and developing effective treatment strategies. To better understand atherosclerosis and define the correlation between various contributing factors, computational fluid dynamics (CFD) analysis is primarily used. CFD simulates WSS, the frictional force caused by blood flow on the vessel wall with various hemodynamic changes. Using apolipoprotein E knockout (ApoE-KO) mice subjected to partial ligation and a high-fat diet at 1-week, 2-week, and 4-week intervals as an atherosclerosis model, CFD analysis was conducted along with the reconstruction of carotid artery blood flow via magnetic resonance imaging (MRI) and compared to the inflammatory factors and pathological staining. In this experiment, a comparative analysis of the effects of high WSS and low WSS was conducted by comparing the standard deviation of time-averaged wall shear stress (TAWSS) at each point within the vessel wall. As a novel approach, the standard deviation of TAWSS within the vessel was analyzed with the staining results and pathological features. Since the onset of atherosclerosis cannot be explained by a single factor, the aim was to find the correlation between the thickness of atherosclerotic plaques and inflammatory factors through standard deviation analysis. As a result, the gap between low WSS and high WSS widened as the interval between weeks in the atherosclerosis mouse model increased. This finding not only linked the occurrence of atherosclerosis to WSS differences but also provided a connection to the causes of vulnerable plaques. [ABSTRACT FROM AUTHOR]

Aortic dissection is a catastrophic failure of the endothelial wall that could lead to malperfusion or rupture. Computational modelling tools may help detect arterial damage. Technological advancements have led to more sophisticated forms of modelling being made available to low-grade computers. These devices can create 3D models with clinical data, where the clinical blood pressure waveforms' model can be used to form boundary conditions for assessing hemodynamic parameters, modelling blood flow propagation along the aorta to predict the development of cardiovascular disease. This study presents patient-specific data for a rare case of severe Type A aortic dissection. CT scan images were taken nine months apart, consisting of the artery both before and after dissection. The results for the pre-dissection CT showed that the pressure waveform at the ascending aorta was higher, and the systolic pressure was lagging at the descending aorta. For the post-dissection analysis, we observed the same outcome; however, the amplitude for the waveform (systolic pressure) at the ascending aorta increased in the false lumen by 25% compared to the true lumen by 3%. Also, the waveform peak (systolic) was leading by 0.01 s. The hemodynamic parameter of wall shear stress (WSS) predicted the aneurysm's existence at the ascending aorta, as well as potential aortic dissection. The high WSS contours were located at the tear location at the peak blood flow of 0.14 s, which shows the potential of this tool for earlier diagnosis of aortic dissection. [ABSTRACT FROM AUTHOR]

Abstract Coronary artery disease is the leading global cause of mortality and Fractional Flow Reserve (FFR) is widely regarded as the gold standard for assessing coronary artery stenosis severity. However, due to the limitations of invasive FFR measurements, there is a pressing need for a highly accurate virtual FFR calculation framework. Additionally, it’s essential to consider local haemodynamic factors such as time-averaged wall shear stress (TAWSS), which play a critical role in advancement of atherosclerosis. This study introduces an innovative FFR computation method that involves creating five patient-specific geometries from two-dimensional coronary angiography images and conducting numerical simulations using computational fluid dynamics with a three-element Windkessel model boundary condition at the outlet to predict haemodynamic distribution. Furthermore, four distinct boundary condition methodologies are applied to each geometry for comprehensive analysis. Several haemodynamic features, including velocity, pressure, TAWSS, and oscillatory shear index are investigated and compared for each case. Results show that models with average boundary conditions can predict FFR values accurately and observed errors between invasive FFR and virtual FFR are found to be less than 5%.

Coronary artery disease is the leading global cause of mortality and Fractional Flow Reserve (FFR) is widely regarded as the gold standard for assessing coronary artery stenosis severity. However, due to the limitations of invasive FFR measurements, there is a pressing need for a highly accurate virtual FFR calculation framework. Additionally, it’s essential to consider local haemodynamic factors such as time-averaged wall shear stress (TAWSS), which play a critical role in advancement of atherosclerosis. This study introduces an innovative FFR computation method that involves creating five patient-specific geometries from two-dimensional coronary angiography images and conducting numerical simulations using computational fluid dynamics with a three-element Windkessel model boundary condition at the outlet to predict haemodynamic distribution. Furthermore, four distinct boundary condition methodologies are applied to each geometry for comprehensive analysis. Several haemodynamic features, including velocity, pressure, TAWSS, and oscillatory shear index are investigated and compared for each case. Results show that models with average boundary conditions can predict FFR values accurately and observed errors between invasive FFR and virtual FFR are found to be less than 5%. [ABSTRACT FROM AUTHOR]

In this study, the effect of patient's physical activity in terms of the heart rate on the growth of the thoracic aortic aneurysm (TAA) is studied. Using medical images of the patient, a patient-specific geometry model is constructed. Then the hemodynamic parameters of the blood flow are numerically analyzed for different heart rate conditions. The simulation results show that the maximum wall shear stress, the maximum velocity, and the maximum pressure during a cardiac cycle increase by 19.1, 12.7, and 50%, respectively, as the heart rate increases from 60 to 174 beats per minute. Results also indicate that an increase in the heart rate leads to reduction of the time-averaged wall shear stress and simultaneously to an increase in the wall shear stress oscillations. According to the literature, these hemodynamic conditions are undesirable and can increase the likelihood of aneurysm development and aortic rupture. [ABSTRACT FROM AUTHOR]

Background: Understanding the risk factors leading to intracranial aneurysm (IA) rupture have still not been fully clarified. They are vital for proper medical guidance of patients harboring unruptured IAs. Clarifying the hemodynamics associated with the point of rupture could help could provide useful information about some of the risk factors. Thus far, few studies have studied this issue with often diverging conclusions. Methods: We identified a point of rupture in patients operated for an IAs during surgery, using a combination of preoperative computed tomography (CT) and computed tomography angiography (CTA). Hemodynamic parameters were calculated both for the aneurysm sac as a whole and the point of rupture. In two cases, the results of CFD were compared with those of the experiment using particle image velocimetry (PIV). Results: We were able to identify 6 aneurysms with a well-demarcated point of rupture. In four aneurysms, the rupture point was near the vortex with low wall shear stress (WSS) and high oscillatory shear index (OSI). In one case, the rupture point was in the flow jet with high WSS. In the last case, the rupture point was in the significant bleb and no specific hemodynamic parameters were found. The CFD results were verified in the PIV part of the study. Conclusion: Our study shows that different hemodynamic scenarios are associated with the site of IA rupture. The numerical simulations were confirmed by laboratory models. This study further supports the hypothesis that various pathological pathways may lead to aneurysm wall damage resulting in its rupture. [ABSTRACT FROM AUTHOR]

Aortic aneurysm is the narrowing of the aortic valve. Treatment for unruptured Abdominal Aortic Aneurysm (AAA) that does not require surgery involves exposing patients to specific physiological threshold conditions like maximal diameter and keeping a check over the expansion rate. Despite these thresholds, there are chances of rupture. Thus, it is crucial to find more accurate indicators of rupture risk and include their assessment in therapeutic decisionmaking. This study employs Computational Fluid Dynamics (CFD) to investigate pulsatile flow characteristics in generalized AAA models. It prioritizes rebuilding the intricate aspects of fluid dynamics that cannot be directly quantified in vivo, specifically focusing on how varied degrees of dilations influence these aspects. Thus, a numerical analysis uses a finite volume approach in order to investigate three-dimensional symmetric, incompressible, laminar, and transient flow characteristics in analyzing and exploring rupture potential. It is observed that the shear stress had a low magnitude within the aneurysm segment of the blood vessel, while the distal constriction of the aneurysm displayed localized peak values. It is observed that the WSS is lowered from 40% in the steady flow conditions to 20% in the dilated pipe for transient conditions, indicating that wall shear stress can also be considered a factor for analyzing aneurysmal conditions. Authors' findings also show that mapping the geographical and temporal development of flow patterns and vorticity reveals regions with low shear stress. These observations can help in clinical decision-making. [ABSTRACT FROM AUTHOR]

Traditionally, coronary angiography was restricted to visual estimation of contrast-filled lumen in coronary obstructive diseases. Over the previous decades, considerable development has been made in quantitatively analyzing coronary angiography, significantly improving its accuracy and reproducibility. Notably, the integration of artificial intelligence (AI) and machine learning into quantitative coronary angiography (QCA) holds promise for further enhancing diagnostic accuracy and predictive capabilities. In addition, non-invasive fractional flow reserve (FFR) indices, including computed tomography-FFR, have emerged as valuable tools, offering precise physiological assessment of coronary artery disease without the need for invasive procedures. These innovations allow for a more comprehensive evaluation of disease severity and aid in guiding revascularization decisions. This review traces the development of QCA technologies over the years, highlighting key milestones and current advancements. It also explores prospects that could revolutionize the field, such as AI integration and improved imaging techniques. By addressing both historical context and future directions, the article underscores the ongoing evolution of QCA and its critical role in the accurate assessment and management of coronary artery diseases. Through continuous innovation, QCA is poised to remain at the forefront of cardiovascular diagnostics, offering clinicians invaluable tools for improving patient care.

Aortic dissection is a catastrophic failure of the endothelial wall that could lead to malperfusion or rupture. Computational modelling tools may help detect arterial damage. Technological advancements have led to more sophisticated forms of modelling being made available to low-grade computers. These devices can create 3D models with clinical data, where the clinical blood pressure waveforms’ model can be used to form boundary conditions for assessing hemodynamic parameters, modelling blood flow propagation along the aorta to predict the development of cardiovascular disease. This study presents patient-specific data for a rare case of severe Type A aortic dissection. CT scan images were taken nine months apart, consisting of the artery both before and after dissection. The results for the pre-dissection CT showed that the pressure waveform at the ascending aorta was higher, and the systolic pressure was lagging at the descending aorta. For the post-dissection analysis, we observed the same outcome; however, the amplitude for the waveform (systolic pressure) at the ascending aorta increased in the false lumen by 25% compared to the true lumen by 3%. Also, the waveform peak (systolic) was leading by 0.01 s. The hemodynamic parameter of wall shear stress (WSS) predicted the aneurysm’s existence at the ascending aorta, as well as potential aortic dissection. The high WSS contours were located at the tear location at the peak blood flow of 0.14 s, which shows the potential of this tool for earlier diagnosis of aortic dissection.

BackgroundUnderstanding the risk factors leading to intracranial aneurysm (IA) rupture have still not been fully clarified. They are vital for proper medical guidance of patients harboring unruptured IAs. Clarifying the hemodynamics associated with the point of rupture could help could provide useful information about some of the risk factors. Thus far, few studies have studied this issue with often diverging conclusions.MethodsWe identified a point of rupture in patients operated for an IAs during surgery, using a combination of preoperative computed tomography (CT) and computed tomography angiography (CTA). Hemodynamic parameters were calculated both for the aneurysm sac as a whole and the point of rupture. In two cases, the results of CFD were compared with those of the experiment using particle image velocimetry (PIV).ResultsWe were able to identify 6 aneurysms with a well-demarcated point of rupture. In four aneurysms, the rupture point was near the vortex with low wall shear stress (WSS) and high oscillatory shear index (OSI). In one case, the rupture point was in the flow jet with high WSS. In the last case, the rupture point was in the significant bleb and no specific hemodynamic parameters were found. The CFD results were verified in the PIV part of the study.ConclusionOur study shows that different hemodynamic scenarios are associated with the site of IA rupture. The numerical simulations were confirmed by laboratory models. This study further supports the hypothesis that various pathological pathways may lead to aneurysm wall damage resulting in its rupture.

A transient transport flow model is adopted in a renal bifurcated artery with different stenosis cases to examine the flow phenomena when the non-Newtonian blood flow regime within the three-dimensional space domain is chosen as a pulsatile nature. The nonlinear governing equations are solved using the Finite Element Method with suitable initial-boundary conditions. During numerical computation, distinct hemodynamic parameters including Wall shear stress, Reynolds number, power law index are evaluated based on different stenosis severities (0%, 25%, and 50%) and stenosis lengths (0mm, 0.5mm, and 1mm). For 0%, 25%, and 50% stenosis, the approximate values of velocity and pressure profiles are estimated at t = 5s at various positions, and achieved the highest velocities that were around 0.07m/s, 0.08m/s, and 0.13m/s respectively. The unsteady response of the stress due to stenosis-induced shear on the outside wall is described as a result of stenosis at t = 0.1s, 0.2s, 5s. The flow is severely restricted by constriction, which increases wall movement and produces stress, depending on the amount of stenosis. As pulsatile flow time increases due to the presence of stenosis, the wall shear stress decreases gradually. The impact of Reynolds numbers on pressure profiles and velocity profiles are displayed for Re = 100, 300, 500, and 700, and found that both velocity and pressure outlines increase significantly. In order to identify the flow phenomena, the influences of the power law index for n = 0.1, 0.3568, 0.5 are presented on the velocity and pressure profiles. Shear-thinning flow occurs for 0

This study investigates the hemodynamic impacts of localized aortic valve calcification, utilizing immersed boundary-finite element (IBFE) method simulations with realistic inflow patterns of uniform and helical blood flow from the left ventricular outflow tract (LVOT). We modeled the aortic valve leaflets with varying grades of calcification, assessing their influence on valve performance, including transvalvular hemodynamics, wall shear stress (WSS) indices, and vortical structures. The findings highlighted that calcification significantly restricts leaflet motion, diminishes the orifice area, disrupts flow efficiency, and consequently increases the left ventricular workload. Advanced calcification resulted in elevated WSS, especially at the leaflet tips, which indicates a heightened risk of endothelial damage and further calcification. Asymmetrical calcifications redirect flow towards the ascending aorta wall, potentially inducing structural damage and increased stress on the remaining healthy leaflets. Calcification was also found to alter the naturally occurring helical blood flow patterns, affecting the system's fluid transport efficiency and possibly contributing to cardiovascular disease progression. The study revealed a significant alteration in vortex formation, with calcification causing distorted and complex vortex structures, which may influence the dynamics of blood flow and valve function. These insights into the hemodynamic changes induced by calcification contribute to a better understanding of the progression of aortic valve diseases and could inform more effective diagnostic and treatment strategies. [ABSTRACT FROM AUTHOR]

ObjectiveArterial stiffness is an important tissue biomarker of the progression of atherosclerotic diseases. Brachial-ankle pulse wave velocity (ba-PWV) is a gold standard of arterial stiffness measurement widely used in Asia. Changes in vascular wall shear stress (WSS) lead to artery wall remodeling, which could give rise to an increase in arterial stiffness. The study aimed to explore the association between ba-PWV and common carotid artery (CCA) WSS measured by a newly invented vascular vector flow mapping (VFM) technique.MethodsWe included 94 subjects free of apparent cardiovascular disease (CVD) and divided them into a subclinical atherosclerosis (SA) group (N = 47) and non subclinical atherosclerosis (NSA) group (N = 47). CCA WSS was measured using the VFM technique. Bivariate correlations between CCA WSS and other factors were assessed with Pearson's, Spearman's, or Kendall's coefficient of correlation, as appropriate. Partial correlation analysis was conducted to examine the influence of age and sex. Multiple linear stepwise regression was used for the analysis of independent determinants of CCA WSS. Receiver operating characteristic (ROC) analysis was performed to find the association between CCA WSS and 10-year CVD risk.ResultsThe overall subjects had a mean age of 47.9 ± 11.2 years, and males accounted for 52.1%. Average systolic CCA WSS was significantly correlated with ba-PWV (r = −0.618, p

Background Glagov et al. showed that no reduction in vessel lumen occurred until the atherosclerotic plaque burden exceeded 40% of the vessel area. Most major adverse cardiac events occurring in the first 4 years after a myocardial infarction arise from untreated angiographically mild, non-flow-limiting lesions at the time of the index event. We report how computed tomography (CT) coronary angiography (CCTA) can be used to non-invasively risk stratify a patient with non-obstructive coronary artery disease (CAD) and guide further management. Case summary A 69-year-old non-smoking female with hypertension, dyslipidaemia, and hypothyroidism presented with atypical chest pain. Electrocardiogram and left ventricular ejection fraction were normal. Her lipidic profile was normal. CCTA showed a lipid-rich plaque with very low attenuation (<30 HU) in the left main stem (LMS) extending into the proximal left anterior descending (LAD) and in the mid LAD artery. The maximum plaque burden in the LMS was 67% with a remodelling index of 1.375, and an area stenosis of 22%. Tissue characterization showed a lipid-rich plaque with a thin fibrous cap. The perivascular fat attenuation index (FAI) in the proximal LAD was suggestive of (−69 HU) inflamed perivascular fat. Shear stress analysis of the LMS plaque showed normal wall shear stress (WSS); however, the axial plaque stress was high. Her medications were intensified to rosuvastatin 20 mg once daily (OD) and ezetimibe 10 mg OD. The patient remained asymptomatic at 6 months follow-up. Discussion Our case exemplifies the value of CCTA as a diagnostic 'one-stop shop' (CCTA, finite element analysis, computed tomographic density [CTD], tissue characterization analysis, FAI analysis, WSS and wall strain, and etc.) when stratifying a patient with non-obstructive CAD. With further development of novel potent anti-lipidaemic and anti-inflammatory drugs, non-obstructive lesions with adverse plaque and haemodynamic parameters will have the opportunity to be treated with additional preventive pharmacological therapy. [ABSTRACT FROM AUTHOR]

We investigated differences in haemodynamic forces between carotid arteries that underwent primary closure (PC) or patch angioplasty (PA) using computational fluid dynamics (CFD). A total of 30 subjects were enrolled in this study, consisting of 10 subjects who underwent PC, 10 who underwent PA and 10 healthy subjects. Three-dimensional models of carotid arteries were reconstructed using patient-specific computed tomography angiography images. The conventional Navier-Stokes, continuity equation and constitutive stress-strain law with a stabilized Petrov-Galerkin scheme were solved with Newtonian and incompressible assumptions. The boundary conditions employed patient-specific velocity profiles as the inflow and lumped parameters of the three-element Windkessel model as the outflow with a rigid wall assumption. Thus, the CFD results exhibited good agreement with measurements from the subjects (r = .78). The carotid arteries of the PC group were exposed to abnormal haemodynamic forces related to building atherosclerosis in a smaller (p .05) to healthy arteries. The morphological characteristics of the carotid artery were significantly associated with the area exposed to abnormal haemodynamic forces. We identified that abnormal haemodynamic forces could be avoided by selecting appropriate surgical techniques that produce less bifurcation expansion.

Flow diverter stents (FDS) are increasingly used for the treatment of complex intracranial aneurysms such as fusiform, giant, or wide-neck aneurysms. The primary goal of these devices is to reconstruct the diseased vascular segment by diverting blood flow from the aneurysm. The resulting intra-aneurysmal flow reduction promotes progressive aneurysm thrombosis and healing of the disease. In the present study, a numerical investigation was performed for modeling blood flow inside a patient-specific intracranial aneurysm virtually treated with FDS. The aim of the study is to investigate the effects of FDS placement prior to the actual endovascular treatment and to compare the effectiveness of devices differing in porosity. Numerical simulations were performed under pulsatile flow conditions, taking into account the non-Newtonian behavior of blood. Two possible post-operative conditions with virtual stent deployment were simulated. Hemodynamic parameters were calculated and compared between the pre-operative (no stent placement) and post-operative (virtual stent placement) aneurysm models. FDS placement significantly reduced intra-aneurysmal flow velocity and increased the Relative Residence Time (RRT) on the aneurysm, thus promoting thrombus formation within the dilatation and aneurysm occlusion. The results highlighted an increase in the effectiveness of FDS as its porosity increased. The proposed analysis provides pre-operative knowledge on the impact of FDS on intracranial hemodynamics, allowing the selection of the most effective treatment for the specific patient. [ABSTRACT FROM AUTHOR]

Aortic aneurysm is one of the most common aortic diseases that can lead to unfortunate consequences. Numerical simulations have an important role in the prediction of the aftereffects of vascular diseases including aneurysm. In this research, numerical simulation of pulsatile blood flow is performed for a 3-dimensional patient-specific model of a thoracic aortic aneurysm (TAA). Since the choice of blood viscosity model may have a significant impact on the simulation results, the effects of four non-Newtonian models of blood viscosity namely Carreau, Casson, Herschel-Bulkley, power low, and the Newtonian model on the wall shear stress (WSS) distribution, shear rate, and oscillatory shear index (OSI) have been analyzed. Simulation results showed that all the non-Newtonian and Newtonian models generally, predict similar patterns for blood flow and shear rate. At high flow rates in the cardiac cycle, the WSS value for all the models are similar to each other except for the power-law model due to the shear thinning behavior. All models predict high values of OSI on the inner wall of the ascending aorta and broad areas of the inner wall of the aneurysm sac. However, the Newtonian model predicts the OSI less than the non-Newtonian models in some areas of the aneurysm sac. Results indicated that the Newtonian model generally can predict the hemodynamic parameters of the blood flow similar to the non-Newtonian but for more precise analysis and to predict the regions prone to rupture and atherosclerosis, choosing a proper non-Newtonian model is recommended. [ABSTRACT FROM AUTHOR]

This study investigates the hemodynamic impacts of localized aortic valve calcification, utilizing immersed boundary-finite element (IBFE) method simulations with realistic inflow patterns of uniform and helical blood flow from the left ventricular outflow tract (LVOT). We modeled the aortic valve leaflets with varying grades of calcification, assessing their influence on valve performance, including transvalvular hemodynamics, wall shear stress (WSS) indices, and vortical structures. The findings highlighted that calcification significantly restricts leaflet motion, diminishes the orifice area, disrupts flow efficiency, and consequently increases the left ventricular workload. Advanced calcification resulted in elevated WSS, especially at the leaflet tips, which indicates a heightened risk of endothelial damage and further calcification. Asymmetrical calcifications redirect flow towards the ascending aorta wall, potentially inducing structural damage and increased stress on the remaining healthy leaflets. Calcification was also found to alter the naturally occurring helical blood flow patterns, affecting the system’s fluid transport efficiency and possibly contributing to cardiovascular disease progression. The study revealed a significant alteration in vortex formation, with calcification causing distorted and complex vortex structures, which may influence the dynamics of blood flow and valve function. These insights into the hemodynamic changes induced by calcification contribute to a better understanding of the progression of aortic valve diseases and could inform more effective diagnostic and treatment strategies.

Objective: This study seeks to evaluate the value of the high-frame-rate vector flow imaging technique in assessing the hemodynamic changes of carotid atherosclerotic stenosis in aging people (>60 years old). Methods: Aging patients diagnosed with carotid atherosclerotic stenosis who underwent carotid high-frame-rate vector flow imaging examination were prospectively enrolled. A Mindray Resona7s ultrasound machine equipped with high-frame-rate vector flow function was used for ultrasound evaluation. First, B mode ultrasound and color Doppler flow imaging were used to evaluate carotid stenosis. Then, the vector arrows and flow streamline detected by V Flow were analyzed and the wall shear stress values (Pa) at the carotid stenosis site were measured. All patients were divided into symptomatic and asymptomatic groups according to whether they had acute/subacute stroke or other clinical symptoms within 2 weeks before ultrasound examination. The results of digital subtraction angiography or computed tomography angiography were used as the gold standard. The stenosis rate was calcified, according to North American Symptomatic Carotid Endarterectomy Trial criteria. The diagnostic values of wall shear stress, conventional ultrasound, and the combined diagnosis in carotid atherosclerotic stenosis were compared. Results: Finally, 88 patients with carotid atherosclerotic plaque were enrolled (71 males (80.7%), mean age 67.6 ± 5.4 years). The success rate of high-frame-rate vector flow imaging was 96.7% (88/91). The WSS value of symptomatic carotid stenosis (1.4 ± 0.15 Pa) was significantly higher than that of asymptomatic carotid stenosis (0.80 ± 0.08 Pa) (p < 0.05). Taking the wall shear stress value > 0.78 Pa as the diagnostic criteria for symptomatic carotid atherosclerotic plaque, the area under receiver operating characteristic curves was 0.79 with 87.1% sensitivity and 69.6% specificity. The area under receiver operating characteristic curves of the combined diagnosis (0.966) for differentiating severe carotid atherosclerotic stenosis was significantly higher than that of conventional ultrasound and WSS value, with 89.7% sensitivity and 93.2% specificity (p < 0.05). Conclusion: As a non-invasive imaging method, the high-frame-rate vector flow imaging technique showed potential value in the preoperative assessment of the symptomatic carotid atherosclerotic stenosis and diagnosing carotid atherosclerotic stenosis in aging patients. [ABSTRACT FROM AUTHOR]

Background and aims: The shape of a stent could influence focal hemodynamics and subsequently plaque growth or in-stent restenosis in intracranial atherosclerotic stenosis (ICAS). In this preliminary study, we aim to investigate the associations between stent shapes and focal hemodynamics in ICAS, using computational fluid dynamics (CFD) simulations with manually manipulated stents of different shapes. Methods: We built an idealized artery model, and reconstructed four patient-specific models of ICAS. In each model, three variations of stent geometry (i.e., enlarged, inner-narrowed, and outer-narrowed) were developed. We performed static CFD simulation on the idealized model and three patient-specific models, and transient CFD simulation of three cardiac cycles on one patient-specific model. Pressure, wall shear stress (WSS), and low-density lipoprotein (LDL) filtration rate were quantified in the CFD models, and compared between models with an inner- or outer-narrowed stent vs. an enlarged stent. The absolute difference in each hemodynamic parameter was obtained by subtracting values from two models; a normalized difference (ND) was calculated as the ratio of the absolute difference and the value in the enlarged stent model, both area-averaged throughout the arterial wall. Results: The differences in focal pressure in models with different stent geometry were negligible (ND<1% for all cases). However, there were significant differences in the WSS and LDL filtration rate with different stent geometry, with ND >20% in a static model. Observable differences in WSS and LDL filtration rate mainly appeared in area adjacent to and immediately distal to the stent. In the transient simulation, the LDL filtration rate had milder temporal fluctuations than WSS. Conclusions: The stent geometry might influence the focal WSS and LDL filtration rate in ICAS, with negligible effect on pressure. Future studies are warranted to verify the relevance of the changes in these hemodynamic parameters in governing plaque growth and possibly in-stent restenosis in ICAS. [ABSTRACT FROM AUTHOR]

In atherosclerosis, low wall shear stress (WSS) is known to favor plaque development, while high WSS increases plaque rupture risk. To improve plaque diagnostics, WSS monitoring is crucial. Here, we propose wall shear imaging (WASHI), a noninvasive contrast-free framework that leverages high-frame-rate ultrasound (HiFRUS) to map the wall shear rate (WSR) that relates to WSS by the blood viscosity coefficient. Our method measures WSR as the tangential flow velocity gradient along the arterial wall from the flow vector field derived using a multi-angle vector Doppler technique. To improve the WSR estimation performance, WASHI semiautomatically tracks the wall position throughout the cardiac cycle. WASHI was first evaluated with an in vitro linear WSR gradient model; the estimated WSR was consistent with theoretical values (an average error of 4.6% $\pm ~12.4$ %). The framework was then tested on healthy and diseased carotid bifurcation models. In both scenarios, key spatiotemporal dynamics of WSR were noted: 1) oscillating shear patterns were present in the carotid bulb and downstream to the internal carotid artery (ICA) where retrograde flow occurs; and 2) high WSR was observed particularly in the diseased model where the measured WSR peaked at 810 $\text{s}^{-{1}}$ due to flow jetting. We also showed that WASHI could consistently track arterial wall motion to map its WSR. Overall, WASHI enables high temporal resolution mapping of WSR that could facilitate investigations on causal effects between WSS and atherosclerosis. [ABSTRACT FROM AUTHOR]

We investigated differences in haemodynamic forces between carotid arteries that underwent primary closure (PC) or patch angioplasty (PA) using computational fluid dynamics (CFD). A total of 30 subjects were enrolled in this study, consisting of 10 subjects who underwent PC, 10 who underwent PA and 10 healthy subjects. Three-dimensional models of carotid arteries were reconstructed using patient-specific computed tomography angiography images. The conventional Navier-Stokes, continuity equation and constitutive stress-strain law with a stabilized Petrov-Galerkin scheme were solved with Newtonian and incompressible assumptions. The boundary conditions employed patient-specific velocity profiles as the inflow and lumped parameters of the three-element Windkessel model as the outflow with a rigid wall assumption. Thus, the CFD results exhibited good agreement with measurements from the subjects (r =.78). The carotid arteries of the PC group were exposed to abnormal haemodynamic forces related to building atherosclerosis in a smaller (p.05) to healthy arteries. The morphological characteristics of the carotid artery were significantly associated with the area exposed to abnormal haemodynamic forces. We identified that abnormal haemodynamic forces could be avoided by selecting appropriate surgical techniques that produce less bifurcation expansion. [ABSTRACT FROM AUTHOR]

The effect of stenosis for a carotid artery bifurcation with elastic and rigid walls is investigated numerically. In the present study, the blood flow is considered as a laminar pulsatile flow. The effect of fluid-solid interaction is carried out using ANSYS-FLUENT software. The results show that the maximum wall shear stress in the stenosed artery is three times higher than that of a healthy artery. The shear stress gradient in elastic arteries Is lower than in rigid arteries. For rigid artery, the return flow and separation length in the diastolic phase is lower than the systolic phase. [ABSTRACT FROM AUTHOR]

ObjectivesTo investigate the feasibility of the vector flow imaging (V Flow) technique to measure peripheral arterial hemodynamic parameters, including wall shear stress (WSS) and turbulence index (Tur) in healthy adults, and compare the results in different arteries.Materials and methodsFifty-two healthy adult volunteers were recruited in this study. The maximum and mean values of WSS, and the Tur values at early-systole, mid-systole, late-systole, and early diastole for total 156 normal peripheral arteries [common carotid arteries (CCA), subclavian arteries (SCA), and common femoral arteries (CFA)] were assessed using the V Flow technique.ResultsThe mean WSS values for CCA, SCA, and CFA were (1.66 ± 0.68) Pa, (0.62 ± 0.30) Pa, and (0.56 ± 0.27) Pa, respectively. The mean Tur values for CCA, SCA, and CFA were (0.46 ± 1.09%), (20.7 ± 9.06%), and (24.63 ± 17.66%), respectively. The CCA and SCA, as well as the CCA and CFA, showed statistically significant differences in the mean WSS and the mean Tur (P < 0.01). The mean Tur values had a negative correlation with the mean WSS; the correlation coefficient between log(Tur) and WSS is −0.69 (P < 0.05).ConclusionV Flow technique is a simple, practical, and feasible quantitative imaging approach for assessing WSS and Tur in peripheral arteries. It has the potential to be a useful tool for evaluating atherosclerotic plaques in peripheral arteries. The results provide a new quantitative foundation for future investigations into diverse arterial hemodynamic parameters.

Flow diverter stents (FDS) are increasingly used for the treatment of complex intracranial aneurysms such as fusiform, giant, or wide-neck aneurysms. The primary goal of these devices is to reconstruct the diseased vascular segment by diverting blood flow from the aneurysm. The resulting intra-aneurysmal flow reduction promotes progressive aneurysm thrombosis and healing of the disease. In the present study, a numerical investigation was performed for modeling blood flow inside a patient-specific intracranial aneurysm virtually treated with FDS. The aim of the study is to investigate the effects of FDS placement prior to the actual endovascular treatment and to compare the effectiveness of devices differing in porosity. Numerical simulations were performed under pulsatile flow conditions, taking into account the non-Newtonian behavior of blood. Two possible post-operative conditions with virtual stent deployment were simulated. Hemodynamic parameters were calculated and compared between the pre-operative (no stent placement) and post-operative (virtual stent placement) aneurysm models. FDS placement significantly reduced intra-aneurysmal flow velocity and increased the Relative Residence Time (RRT) on the aneurysm, thus promoting thrombus formation within the dilatation and aneurysm occlusion. The results highlighted an increase in the effectiveness of FDS as its porosity increased. The proposed analysis provides pre-operative knowledge on the impact of FDS on intracranial hemodynamics, allowing the selection of the most effective treatment for the specific patient.

• FSI model including anisotropic hyperelastic stented arterial region was implemented. • Three different stent geometries and their susceptibility to restenosis were analyzed. • The SIMPLE stent model is the most susceptible to restenosis. • Stress-strain state depends on a proper choice of boundary conditions. Atherosclerotic lesions of coronary arteries (stenosis) are caused by the buildup of lipids and blood-borne substances within the artery wall. Their qualitative and rapid assessment is still a challenging task. The primary therapy for this pathology involves implanting coronary stents, which help to restore the blood flow in atherosclerosis-prone arteries. In-stent restenosis is a stenting-procedure complication detected in about 10-40% of patients. A numerical study using 2-way fluid-structure interaction (FSI) assesses the stenting procedure quality and can decrease the number of negative post-operative results. Nevertheless, boundary conditions (BCs) used in simulation play a crucial role in implementation of an adequate computational analysis. Three CoCr stents designs were modelled with the suggested approach. A multi-layer structure describing the artery and plaque with anisotropic hyperelastic mechanical properties was adopted in this study. Two kinds of boundary conditions for a solid domain were examined - fixed support (FS) and remote displacement (RD) - to assess their impact on the hemodynamic parameters to predict restenosis. Additionally, the influence of artery elongation (short-artery model vs. long-artery model) on numerical results with the FS boundary condition was analyzed. The comparison of FS and RD boundary conditions demonstrated that the variation of hemodynamic parameters values did not exceed 2%. The analysis of short-artery and long-artery models revealed that the difference in hemodynamic parameters was less than 5.1%, and in most cases, it did not exceed 2.5%. The RD boundary conditions were found to reduce the computation time by up to 1.7–2.0 times compared to FS. Simple stent model was shown to be susceptible to restenosis development, with maximum WSS values equal to 183 Pa, compared to much lower values for other two stents. The study revealed that the stent design significantly affected the hemodynamic parameters as restenosis predictors. Moreover, the stress-strain state of the system artery–plaque–stent also depends on a proper choice of boundary conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

The pulsatile flow rate (PFR) in the cerebral artery system and shunt ratios in bifurcated arteries are two patient-specific parameters that may affect the hemodynamic characteristics in the pathobiology of cerebral aneurysms, which needs to be identified comprehensively. Accordingly, a systematic study was employed to study the effects of pulsatile flow rate (i.e., PFR−I, PFR−II, and PFR−III) and shunt ratio (i.e., 75:25 and 64:36) in bifurcated distal arteries, and transient cardiac pulsatile waveform on hemodynamic patterns in two internal carotid artery sidewall aneurysm models using computational fluid dynamics (CFD) modeling. Numerical results indicate that larger PFRs can cause higher wall shear stress ( W S S ) in some local regions of the aneurysmal dome that may increase the probability of small/secondary aneurysm generation than under smaller PFRs. The low W S S and relatively high oscillatory shear index ( O S I ) could appear under a smaller PFR, increasing the potential risk of aneurysmal sac growth and rupture. However, the variances in PFRs and bifurcated shunt ratios have rare impacts on the time-average pressure ( T A P ) distributions on the aneurysmal sac, although a higher PFR can contribute more to the pressure increase in the ICASA−1 dome due to the relatively stronger impingement by the redirected bloodstream than in ICASA−2. CFD simulations also show that the variances of shunt ratios in bifurcated distal arteries have rare impacts on the hemodynamic characteristics in the sacs, mainly because the bifurcated location is not close enough to the sac in present models. Furthermore, it has been found that the vortex location plays a major role in the temporal and spatial distribution of the WSS on the luminal wall, varying significantly with the cardiac period. [ABSTRACT FROM AUTHOR]

Wall shear stress (WSS) is an important contributor to vessel wall remodeling and atherosclerosis. However, image-based WSS estimation from 4D Flow MRI underestimates true WSS values, and the accuracy is dependent on spatial resolution, which is limited in 4D Flow MRI. To address this, we present a deep learning algorithm (WSSNet) to estimate WSS trained on aortic computational fluid dynamics (CFD) simulations. The 3D CFD velocity and coordinate point clouds were resampled into a 2D template of 48 × 93 points at two inward distances (randomly varied from 0.3 to 2.0 mm) from the vessel surface (“velocity sheets”). The algorithm was trained on 37 patient-specific geometries and velocity sheets. Results from 6 validation and test cases showed high accuracy against CFD WSS (mean absolute error 0.55 ± 0.60 Pa, relative error 4.34 ± 4.14%, 0.92 ± 0.05 Pearson correlation) and noisy synthetic 4D Flow MRI at 2.4 mm resolution (mean absolute error 0.99 ± 0.91 Pa, relative error 7.13 ± 6.27%, and 0.79 ± 0.10 Pearson correlation). Furthermore, the method was applied on in vivo 4D Flow MRI cases, effectively estimating WSS from standard clinical images. Compared with the existing parabolic fitting method, WSSNet estimates showed 2–3 × higher values, closer to CFD, and a Pearson correlation of 0.68 ± 0.12. This approach, considering both geometric and velocity information from the image, is capable of estimating spatiotemporal WSS with varying image resolution, and is more accurate than existing methods while still preserving the correct WSS pattern distribution.

Tissue degradation plays a crucial role in the formation and rupture of aneurysms. Using numerical computer simulations, we study the combined effects of blood flow and tissue degradation on intra-aneurysm hemodynamics. Our computational analysis reveals that the degradation-induced changes of the time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) within the aneurysm dome are inversely correlated. Importantly, their correlation is enhanced in the process of tissue degradation. Regions with a low TAWSS and a high OSI experience still lower TAWSS and higher OSI during degradation. Furthermore, we observed that degradation leads to an increase of the endothelial cell activation potential index, in particular, at places experiencing low wall shear stress. These findings are robust and occur for different geometries, degradation intensities, heart rates and pressures. We interpret these findings in the context of recent literature and argue that the degradation-induced hemodynamic changes may lead to a self-amplification of the flow-induced progressive damage of the aneurysmal wall. [ABSTRACT FROM AUTHOR]

Tissue degradation plays a crucial role in the formation and rupture of aneurysms. Using numerical computer simulations, we study the combined effects of blood flow and tissue degradation on intra-aneurysm hemodynamics. Our computational analysis reveals that the degradation-induced changes of the time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) within the aneurysm dome are inversely correlated. Importantly, their correlation is enhanced in the process of tissue degradation. Regions with a low TAWSS and a high OSI experience still lower TAWSS and higher OSI during degradation. Furthermore, we observed that degradation leads to an increase of the endothelial cell activation potential index, in particular, at places experiencing low wall shear stress. These findings are robust and occur for different geometries, degradation intensities, heart rates and pressures. We interpret these findings in the context of recent literature and argue that the degradation-induced hemodynamic changes may lead to a self-amplification of the flow-induced progressive damage of the aneurysmal wall.

Mechanical factors, especially wall shear stress (WSS) and circumferential strain (CS), play an important role in the progression and rupture of atherosclerotic plaques. Previous studies have shown that the temporal phase angle between WSS and CS, referred to as the stress phase angle (SPA) may be a biomarker for plaque development and vulnerability. Since the SPA is influenced by the severity and length of the stenosis, a multifactorial relationship between local hemodynamic variables and plaque morphology can be hypothesized. However, due to ethical restrictions and the difficulty of developing animal models, there is little experimental data to support such a hypothesis about the biomarker function of SPA. In this study, a novel non-invasive ultrasound-based method for investigating the relationship between local hemodynamics and plaque morphology is developed and investigated in-vitro and in-vivo with an apolipoprotein deficient mouse model. In the in-vitro experiments, using polyvinyl alcohol cryogel (PVA-c) phantoms, we have observed that the SPA becomes more negative and the wall shear rate (WSR) rises, as the severity of the stenosis increases. Conversely, SPA becomes more positive and WSR falls with increasing plaque length. These changes in plaque morphology have little effect on CS. The in-vivo experiments show that, as the severity of the plaque increases, the SPA becomes more negative and WSR tends to more positive values; whereas, the CS drops. We conclude that these local hemodynamic parameters such as SPA, WSR and CS, as suggested by others, can be regarded as prognostic markers for the assessment of plaque vulnerability.

Abstract Background Diseases of the descending aorta have emerged as a clinical issue in Marfan syndrome following improvements in proximal aorta surgical treatment and the consequent increase in life expectancy. Although a role for hemodynamic alterations in the etiology of descending aorta disease in Marfan patients has been suggested, whether flow characteristics may be useful as early markers remains to be determined. Methods Seventy-five Marfan patients and 48 healthy subjects were prospectively enrolled. In- and through-plane vortexes were computed by 4D flow cardiovascular magnetic resonance (CMR) in the thoracic aorta through the quantification of in-plane rotational flow and systolic flow reversal ratio, respectively. Regional pulse wave velocity and axial and circumferential wall shear stress maps were also computed. Results In-plane rotational flow and circumferential wall shear stress were reduced in Marfan patients in the distal ascending aorta and in proximal descending aorta, even in the 20 patients free of aortic dilation. Multivariate analysis showed reduced in-plane rotational flow to be independently related to descending aorta pulse wave velocity. Conversely, systolic flow reversal ratio and axial wall shear stress were altered in unselected Marfan patients but not in the subgroup without dilation. In multivariate regression analysis proximal descending aorta axial (p = 0.014) and circumferential (p = 0.034) wall shear stress were independently related to local diameter. Conclusions Reduced rotational flow is present in the aorta of Marfan patients even in the absence of dilation, is related to aortic stiffness and drives abnormal circumferential wall shear stress. Axial and circumferential wall shear stress are independently related to proximal descending aorta dilation beyond clinical factors. In-plane rotational flow and circumferential wall shear stress may be considered as an early marker of descending aorta dilation in Marfan patients.

Background: Studying the relationship between hemodynamics and local intracranial aneurysm (IA) pathobiology can help us understand the natural history of IA. We characterized the relationship between the IA wall appearance, using intraoperative imaging, and the hemodynamics from CFD simulations. Methods: Three-dimensional geometries of 15 IAs were constructed and used for CFD. Two-dimensional intraoperative images were subjected to wall classification using a machine learning approach, after which the wall type was mapped onto the 3D surface. IA wall regions included thick (white), normal (purple-crimson), and thin/translucent (red) regions. IA-wide and local statistical analyses were performed to assess the relationship between hemodynamics and wall type. Results: Thin regions of the IA sac had significantly higher WSS, Normalized WSS, WSS Divergence and Transverse WSS, compared to both normal and thick regions. Thicker regions tended to co-locate with significantly higher RRT than thin regions. These trends were observed on a local scale as well. Regression analysis showed a significant positive correlation between WSS and thin regions and a significant negative correlation between WSSD and thick regions. Conclusion: Hemodynamic simulation results were associated with the intraoperatively observed IA wall type. We consistently found that elevated WSS and WSSNorm were associated with thin regions of the IA wall rather than thick and normal regions.

Acute cerebral ischemic events and thrombosis are associated with the rupture/erosion of carotid atherosclerotic plaques. The aim of the present study was to determine the impact of calcification deposition on the wall shear stress (WSS) and stresses within the plaques using 3D fluid–structure interaction (FSI) models. Six patients with calcified carotid atherosclerosis underwent multisequence magnetic resonance imaging (MRI) and were divided into three groups according to the calcification volume. To evaluate the role of the calcification deposition on the stresses, the calcification content was replaced by lipids and arterial tissue, respectively. By comparing the results from the simulation with calcification, and when changing it to lipids there was a significant increment in the stresses at the fibrous cap (p = 0.004). Instead, by changing it to arterial tissue, there was no significant difference (p = 0.07). The calcification shapes that presented the highest stresses were thin concave arc-shaped (AS1) and thin convex arc-shaped (AS3), with mean stress values of 107 ± 54.2 and 99.6 ± 23.4 kPa, respectively. It was also observed that, the calcification shape has more influence on the level of stress than its distance to the lumen. Higher WSS values were associated with the presence of calcification. Calcification shape plays an important role in producing high stresses in the plaque. This work further clarifies the impact of calcification on plaque vulnerability. [ABSTRACT FROM AUTHOR]

Background: Wall shear stress (WSS) is related to the pathogenesis of atherosclerosis. WSS is affected by a variety of hemodynamic factors, and there is still a lack of accurate and objective methods for measuring it. This study sought to evaluate hemodynamic changes in WSS maximum (max) , WSS mean , WSS minimum (min) in the common carotid artery of healthy adults of different ages using vascular vector flow mapping (VFM)., Methods: A retrospective analysis was conducted on 70 healthy volunteers aged 20-89 years who were recruited from our Ultrasound Department between February 2021 and June 2021. An ultrasound system with a 3-15 MHz probe was used to determine regions of interest (ROIs) of the common carotid artery. VFM-based WSS measurements were obtained by selecting ROIs with optimal image quality from three full cardiac cycles. The participants were divided into the following seven age groups: the 20s group, the 30s group, the 40s group, the 50s group, the 60s group, the 70s group, and the 80s group. The WSS parameters were compared among the age groups. An analysis of variance or a Kruskal-Wallis test was used to evaluate the difference among the groups, and a Pearson analysis and linear regression were used for the correlation and trend analysis., Results: The WSS parameters were quantified using vascular VFM software. The WSS max , WSS mean , WSS min differed among the age groups and gradually decreased with age, the elderly were significantly lower than the young. The Pearson correlation coefficient of the WSS max and age was -0.556 (P<0.001), that of the WSS mean and age was -0.461 (P<0.001), and that of the WSS min and age was -0.308 (P<0.001). The WSS parameters with age are negatively correlated the carotid intima-media thickness differed between the groups., Conclusions: The carotid WSS max , WSS mean , WSS min can be quantitatively and visually analyzed using the vascular VFM technique. In healthy adults of different ages, the carotid WSS max , WSS mean , WSS min decreased with age. Our findings about the normal values of carotid WSS maybe have clinical reference value for future studies., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://cdt.amegroups.com/article/view/10.21037/cdt-24-134/coif). F.C. serves as an unpaid editorial board member of Cardiovascular Diagnosis and Therapy from September 2023 to August 2025. All authors report that this work was supported by Shanghai Municipal Health Commission Health Industry Clinical Research Project (No. 202340181) and Shanghai Xuhui District-Academia Collaborative Project (Life and Health Sciences) (No. 23XHYD-22). Y.F. is employed by FUJIFILM Healthcare. The authors have no other conflicts of interest to declare., (2024 Cardiovascular Diagnosis and Therapy. All rights reserved.)

Background: Atherosclerosis manifests as a focal disease, often affecting areas with complex hemodynamics such as the carotid bifurcation. The magnitude and regularity of the hemodynamic shear stresses acting on the vessel wall are thought to generate risk patterns unique to each patient and play a role in the pathogenesis of atherosclerosis. The involvement of different expressions of shear stress in the pathogenesis of carotid atherosclerosis highlights the need to characterize and compare the differential impact of the various expressions of shear stress in the atherosclerotic carotid bifurcation. Therefore, the aim of this study is to characterize and compare hemodynamic wall shear stresses (WSS) in the carotid arteries of subjects with asymptomatic atherosclerotic plaques. Shear stresses were also compared against vessel diameter and bifurcation angle to examine the relationships with the geometry of the carotid bifurcation.Methods: 4D Flow MRI and contrast-enhanced MRA data were acquired for 245 subjects with atherosclerotic plaques of at least 2.7 mm in conjunction with the Swedish CArdioPulmonary bioImage Study (SCAPIS). Following automatic segmentation and geometric analysis, time-resolved WSS and near-wall turbulent kinetic energy (nwTKE) were derived from the 4D Flow data. Whole-cycle parameters including time-averaged WSS and nwTKE, and the oscillatory shear index (OSI) were calculated. Pairwise Spearman rank-correlation analyses were used to investigate relationships among the hemodynamic as well as geometric parameters.Results: One hundred and seventy nine subjects were successfully segmented using automated tools and subsequently geometric and hemodynamic analyses were performed. Temporally resolved WSS and nwTKE were strongly correlated, ρ = 0.64. Cycle-averaged WSS and nwTKE were moderately correlated, ρ = 0.57. Cycle-average nwTKE was weakly correlated to OSI (ρ = −0.273), revealing that nwTKE provides information about disturbed flow on the vessel wall that OSI does not. In this cohort, there was large inter-individual variation for both WSS and nwTKE. Both WSS and nwTKE varied most within the external carotid artery. WSS, nwTKE, and OSI were weakly correlated to vessel diameter and bifurcation angle.Conclusion: The turbulent and mean component of WSS were examined together in vivo for the first time, and a strong correlation was found between them. nwTKE presents the opportunity to quantify turbulent wall stresses in vivo and gain insight into the effects of disturbed flow on the vessel wall. Neither vessel diameter nor bifurcation angle were found to be strongly correlated to the turbulent or mean component of WSS in this cohort.

The initiation and progression of atherosclerosis, which is the main cause of cardiovascular diseases, correlate with local haemodynamic factors such as wall shear stress (WSS). Numerical simulations such as computational fluid dynamics (CFD) based on medical imaging have been employed to analyse blood flow in different arteries with and without luminal stenosis. Patient-specific CFD models, however, have assumptions on blood rheology. The differences in the calculated haemodynamic factors between different rheological models have not been fully evaluated. In this study, carotid magnetic resonance imaging (MRI) was performed on six patients with different degrees of carotid stenosis and two healthy volunteers. Using the 3D reconstructed carotid geometries and the patient-specific boundary conditions, CFD simulations were performed by applying a Newtonian and four non-Newtonian models (Carreau, Cross, Quemada and Power-law). WSS descriptors and pressure gradient were analysed and compared between the models. The differences in the maximum and the average oscillatory shear index between the Newtonian and the non-Newtonian models were lower than 12.7% and 12%, respectively. The differences in pressure gradient were also within 15%. The differences in the mean time-averaged WSS (TAWSS) between the Newtonian and Cross, Carreau and Power-law models were lower than 6%. In contrast, a higher difference (26%) was found in Quemada. For the low TAWSS, the differences from the Newtonian to the non-Newtonian models were much larger, in the range of 0.4–31% for Carreau, 3–22% for Cross, 5–51% for Quemada and 10–41% for Power-law. The study suggests that the assumption of a Newtonian model is reasonable when the overall flow pattern or the mean values of the WSS descriptors are investigated. However, the non-Newtonian model is necessary when the low TAWSS region is the focus, especially for arteries with severe stenosis. [ABSTRACT FROM AUTHOR]

Flow behavior at the arterial bifurcations has significant implications on the plaque formation. It depends on the vessel size, two bifurcation angles, i.e. angle between the mother and daughter vessels and their relative magnitudes. In this study, hemodynamics for steady and pulsatile flow of blood has been investigated in an idealized carotid artery bifurcation having all the vessels in the same plane for a range of bifurcation angles for symmetric and asymmetric bifurcation. The simulations reveal the presence of a pair of helical vortices, symmetric about the bifurcation plane, in each daughter tube near the bifurcation. [ABSTRACT FROM AUTHOR]