On the Importance of Assumptions for Bulk Flow in Hemodynamic Models of the Carotid Bifurcation

2011 ◽  
Author(s):  
Umberto Morbiducci ◽  
Diana Massai ◽  
Diego Gallo ◽  
Raffaele Ponzini ◽  
Marco A. Deriu ◽  
...  
Keyword(s):  
Vessel Wall ◽  
Carotid Bifurcation ◽  
Flow Fields ◽  
Transport Processes ◽  
Bulk Flow ◽  
Arterial System ◽  
Vortical Flow ◽  
Primary Role ◽  
4D Flow ◽  
The Impact

It is widely accepted that the local hemodynamics in the arterial system affects the atherogenic process. In particular the hemodynamic environment at the carotid artery bifurcation has been widely studied due to its predilection for atherosclerosis. Much effort has been spent in the past on image-based CFD carotid bifurcation models to assess the sensitivity to several assumptions of wall shear stress (WSS)-based parameters as indicators of abnormal flow. This luminal-surface-oriented approach was historically driven by histological observations on samples of the vessel wall. The consequence for this was that the reduction of the complexity of 4D flow fields focused mainly on WSS. However, few studies have provided adequate insights into the influence of these assumptions in order to confidently model the 4D hemodynamics within the bifurcation. Only recently the interest in the role played by the bulk flow in the development of the arterial disease has grown dramatically. This is the consequence of the emerging awareness that arterial hemodynamics, being an intricate process that involves interaction, reconnection and continuous re-organization of structures, could play a primary role in the regulation of mass transfer, and of its athero-protective/susceptible effect. Earlier works [1] pointed out the existence of a relationship between helical/vortical flow patterns and transport processes that could affect blood-vessel wall interaction, and might cause alterations in the residence time of atherogenic particles involved in the initiation of inflammatory response. Recently we introduced robust quantitative descriptors of bulk flow that can “reduce” the inherent complexity associated with 4D flow fields in arteries [1]. Here we present a study on the impact of assumptions on blood rheology and outflow boundary conditions (BCs) on bulk flow features within healthy carotid bifurcations, by using 4D flow descriptors. The final goal is to provide adequate insights not only to complement and to integrate, but also to extend with a quantitative characterization of the bulk flow the description currently adopted to classify altered hemodynamics.

Comparison of Prospective and Retrospective Gated 4D Flow Cardiac MR Image Acquisitions in the Carotid Bifurcation

2021 ◽  
Author(s):  
Elliott R. Hurd ◽  
Mengjiao Han ◽  
Jason K. Mendes ◽  
J. Rock Hadley ◽  
Chris R. Johnson ◽  
...  
Keyword(s):  
Cardiac Mri ◽  
Carotid Bifurcation ◽  
Bulk Flow ◽  
External Carotid ◽  
Retrograde Flow ◽  
4D Flow ◽  
Velocity Magnitude ◽  
Prospective Gating ◽  
Flow Features ◽  
Temporal Coverage

Abstract The superior temporal coverage of retrospective versus prospective gating in 4D flow cardiac MRI (cMRI) imaging offers advantages in comprehensively evaluating the hemodynamic environment across the complete cardiac cycle; however, retrospective acquisitions may result in temporal smoothing. Thus, the purpose of this study was to evaluate the agreement of 4D flow cMRI-derived bulk flow features and fluid (blood) velocities in the carotid bifurcation using prospective and retrospective gating techniques. Prospective and retrospective ECG-gated three-dimensional (3D) cine phase-contrast cardiac MRI with three-direction velocity encoding (i.e., 4D flow cMRI) data were acquired in ten carotid bifurcations from men (n = 3) and women (n = 2) that were cardiovascular disease-free. Velocity magnitude data were extracted from the fluid domain within the image volumes and evaluated across the entire volume or at defined anatomic planes (common, internal, external carotid arteries). Vector magnitudes were decomposed into components to quantify flow direction and disturbances, including retrograde flow. Flow streamlines encoded for velocity magnitude and velocity profiles were generated. Qualitative and quantitative agreement was observed in bulk flow features and fluid velocity magnitudes derived from either prospective or retrospective ECG-gated 4D flow cMRI. No significant differences in velocity magnitudes or components (υr, υθ, υz) were observed. Importantly, retrospective acquisitions captured increased retrograde flow in the internal carotid artery (i.e., carotid sinus) compared to prospective acquisitions. Prospective and retrospective ECG-gated 4D flow cMRI acquisitions provide comparable evaluations of the hemodynamic environment in the carotid bifurcation. However, the increased temporal coverage of retrospective acquisitions depicts disturbed blood flow patterns not captured by the prospective gating technique.

scholarly journals Exploring the Relationships Between Hemodynamic Stresses in the Carotid Arteries

2021 ◽  
Vol 7 ◽  
Author(s):  
Magnus Ziegler ◽  
Jesper Alfraeus ◽  
Elin Good ◽  
Jan Engvall ◽  
Ebo de Muinck ◽  
...  
Keyword(s):  
Vessel Wall ◽  
Carotid Arteries ◽  
Carotid Bifurcation ◽  
Vessel Diameter ◽  
Atherosclerotic Plaques ◽  
Shear Stresses ◽  
Strongly Correlated ◽  
4D Flow ◽  
Bifurcation Angle

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.

scholarly journals 2D Projection Maps of WSS and OSI Reveal Distinct Spatiotemporal Changes in Hemodynamics in the Murine Aorta during Ageing and Atherosclerosis

Biomedicines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 1856
Author(s):  
Kristina Andelovic ◽  
Patrick Winter ◽  
Thomas Kampf ◽  
Anton Xu ◽  
Peter Michael Jakob ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Aortic Arch ◽  
Vessel Wall ◽  
Radial Strain ◽  
4D Flow ◽  
Spatially Resolved ◽  
Potential Marker ◽  
Biomechanical Forces ◽  
The Impact ◽  
Over Time

Growth, ageing and atherosclerotic plaque development alter the biomechanical forces acting on the vessel wall. However, monitoring the detailed local changes in wall shear stress (WSS) at distinct sites of the murine aortic arch over time has been challenging. Here, we studied the temporal and spatial changes in flow, WSS, oscillatory shear index (OSI) and elastic properties of healthy wildtype (WT, n = 5) and atherosclerotic apolipoprotein E-deficient (Apoe−/−, n = 6) mice during ageing and atherosclerosis using high-resolution 4D flow magnetic resonance imaging (MRI). Spatially resolved 2D projection maps of WSS and OSI of the complete aortic arch were generated, allowing the pixel-wise statistical analysis of inter- and intragroup hemodynamic changes over time and local correlations between WSS, pulse wave velocity (PWV), plaque and vessel wall characteristics. The study revealed converse differences of local hemodynamic profiles in healthy WT and atherosclerotic Apoe−/− mice, and we identified the circumferential WSS as potential marker of plaque size and composition in advanced atherosclerosis and the radial strain as a potential marker for vascular elasticity. Two-dimensional (2D) projection maps of WSS and OSI, including statistical analysis provide a powerful tool to monitor local aortic hemodynamics during ageing and atherosclerosis. The correlation of spatially resolved hemodynamics and plaque characteristics could significantly improve our understanding of the impact of hemodynamics on atherosclerosis, which may be key to understand plaque progression towards vulnerability.

scholarly journals Sensitivity Analysis of Unsteady Flow Fields and Impact of Measurement Strategy

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Takashi Misaka ◽  
Shigeru Obayashi
Keyword(s):  
Sensitivity Analysis ◽  
Data Assimilation ◽  
Three Dimensional ◽  
Measurement Data ◽  
Flow Fields ◽  
Vortical Flow ◽  
Measurement Strategy ◽  
The Difference ◽  
Flow Variables ◽  
The Impact

Difficulty of data assimilation arises from a large difference between the sizes of a state vector to be determined, that is, the number of spatiotemporal mesh points of a discretized numerical model and a measurement vector, that is, the amount of measurement data. Flow variables on a large number of mesh points are hardly defined by spatiotemporally limited measurements, which poses an underdetermined problem. In this study we conduct the sensitivity analysis of two- and three-dimensional vortical flow fields within a framework of data assimilation. The impact of measurement strategy, which is evaluated by the sensitivity of the 4D-Var cost function with respect to measurements, is investigated to effectively determine a flow field by limited measurements. The assimilation experiment shows that the error defined by the difference between the reference and assimilated flow fields is reduced by using the sensitivity information to locate the limited number of measurement points. To conduct data assimilation for a long time period, the 4D-Var data assimilation and the sensitivity analysis are repeated with a short assimilation window.

scholarly journals The Impact of Microclimate on the Reproductive Phenology of Female Populus tomentosa in a Micro-Scale Urban Green Space in Beijing

2021 ◽  
Vol 13 (6) ◽  
pp. 3518
Author(s):  
Xiaoyi Xing ◽  
Li Dong ◽  
Cecil Konijnendijk ◽  
Peiyao Hao ◽  
Shuxin Fan ◽  
...  
Keyword(s):  
Seed Dispersal ◽  
Spatial Variation ◽  
Air Temperature ◽  
Green Space ◽  
Populus Tomentosa ◽  
Early Spring ◽  
Reproductive Phenology ◽  
Primary Role ◽  
Micro Scale ◽  
The Impact

The spatial variation of poplars’ reproductive phenology in Beijing’s urban area has aggravated the threat of poplar fluff (cotton-like flying seeds) to public health. This research explored the impact of microclimate conditions on the reproductive phenology of female Populus tomentosa in Taoranting Park, a micro-scale green space in Beijing (range <1 km). The observed phenophases covered flowering, fruiting, and seed dispersal, and ENVI-MET was applied to simulate the effect of the microclimate on SGS (start day of the growing season). The results showed that a significant spatial variation in poplar reproductive phenology existed at the research site. The variation was significantly affected by the microclimate factors DMT (daily mean temperature) and DMH (daily mean heat transfer coefficient), with air temperature playing a primary role. Specifically, the phenology of flowering and fruiting phenophases (BBB, BF, FF, FS) was negatively correlated with DMT (−0.983 ≤ r ≤ −0.908, p <0.01) and positively correlated with DMH (0.769 ≤ r ≤ 0.864, p < 0.05). In contrast, DSD (duration of seed dispersal) showed a positive correlation with DMT (r = 0.946, p < 0.01) and a negative correlation with DMH (r = −0.922, p < 0.01). Based on the findings, the increase in air convection with lower air temperature and decrease in microclimate variation in green space can be an effective way to shorten the seed-flying duration to tackle poplar fluff pollution in Beijing’s early spring.

scholarly journals Stent interventions for pulmonary artery stenosis improve bi-ventricular flow efficiency in a swine model

2021 ◽  
Vol 23 (1) ◽  
Author(s):  
Ryan J. Pewowaruk ◽  
Gregory P. Barton ◽  
Cody Johnson ◽  
J. Carter Ralphe ◽  
Christopher J. Francois ◽  
...  
Keyword(s):  
Ejection Fraction ◽  
Pulmonary Artery ◽  
Ventricular Function ◽  
Intervention Group ◽  
Left Ventricular ◽  
Pulmonary Artery Stenosis ◽  
Swine Model ◽  
4D Flow ◽  
4D Flow Cmr ◽  
The Impact

Abstract Background Branch pulmonary artery (PA) stenosis (PAS) commonly occurs in patients with congenital heart disease (CHD). Prior studies have documented technical success and clinical outcomes of PA stent interventions for PAS but the impact of PA stent interventions on ventricular function is unknown. The objective of this study was to utilize 4D flow cardiovascular magnetic resonance (CMR) to better understand the impact of PAS and PA stenting on ventricular contraction and ventricular flow in a swine model of unilateral branch PA stenosis. Methods 18 swine (4 sham, 4 untreated left PAS, 10 PAS stent intervention) underwent right heart catheterization and CMR at 20 weeks age (55 kg). CMR included ventricular strain analysis and 4D flow CMR. Results 4D flow CMR measured inefficient right ventricular (RV) and left ventricular (LV) flow patterns in the PAS group (RV non-dimensional (n.d.) vorticity: sham 82 ± 47, PAS 120 ± 47; LV n.d. vorticity: sham 57 ± 5, PAS 78 ± 15 p < 0.01) despite the PAS group having normal heart rate, ejection fraction and end-diastolic volume. The intervention group demonstrated increased ejection fraction that resulted in more efficient ventricular flow compared to untreated PAS (RV n.d. vorticity: 59 ± 12 p < 0.01; LV n.d. vorticity: 41 ± 7 p < 0.001). Conclusion These results describe previously unknown consequences of PAS on ventricular function in an animal model of unilateral PA stenosis and show that PA stent interventions improve ventricular flow efficiency. This study also highlights the sensitivity of 4D flow CMR biomarkers to detect earlier ventricular dysfunction assisting in identification of patients who may benefit from PAS interventions.

scholarly journals Intracranial arterial aneurysms in childhood: case report

2006 ◽  
Vol 64 (3a) ◽  
pp. 676-680 ◽  
Author(s):  
Fernando Campos Gomes Pinto ◽  
Leandro Valiengo ◽  
Pedro Paulo Mariani Lima Santos ◽  
Hamilton Matushita ◽  
José Píndaro Pereira Plese
Keyword(s):  
Case Report ◽  
Cerebral Aneurysm ◽  
Operative Technique ◽  
Vessel Wall ◽  
Internal Carotid ◽  
Carotid Bifurcation ◽  
Early Surgery ◽  
Arterial Aneurysm ◽  
Intraoperative Rupture ◽  
Arterial Aneurysms

A case of an intracranial arterial aneurysm at internal carotid bifurcation in a 10-year-old girl is described with the special features of cerebral aneurysm which occur in children, comparing with the adults. We alert for the necessity of carefully operative technique in order to avoid damage and intraoperative rupture of the aneurysm due to the very thin vessel wall that this population can develop. Our recommendation is early surgery in these patients.

Cancer patients’ awareness about clinical research in the era of social media and “fake news”: Preliminary results from ELPIS Study.

2021 ◽  
Vol 39 (15_suppl) ◽  
pp. e24121-e24121
Author(s):  
Celeste Cagnazzo ◽  
Veronica Franchina ◽  
Giuseppe Toscano ◽  
Franca Fagioli ◽  
Tindara Franchina ◽  
...  
Keyword(s):  
Informed Consent ◽  
Clinical Research ◽  
Cancer Patients ◽  
Experimental Therapy ◽  
Average Score ◽  
Trial Participation ◽  
Primary Role ◽  
Fake News ◽  
Patient Awareness ◽  
The Impact

e24121 Background: Barriers for low recruitment in clinical trials have been classified based on three main sources: physician, patient, system. A primary role is played by a low patient awareness, which often leads to a lack of confidence in science and a substantial inability to estimate the benefits deriving from trial participation, aggravated by the spread of fake news. A prospective observational study was conducted to investigate the views of cancer patients on aspects of clinical research, their expectations, the level of comprehensibility of informed consent and the impact of the fake news phenomenon. Methods: From January 2018, after Ethics Committees approval, the ELPIS study was initiated in 9 Italian Medical Oncology Units. After signing the informed consent, patients were asked to complete a questionnaire, consisting of a set of multiple choice and Likert-score questions. Results: As of January 2021, 115 patients were enrolled, with a balanced sex distribution and a prevalence of subjects older than 55-years (79.8%). Regarding the previous knowledge about clinical research, the average score was 3.9 (range 1-5). The vast majority of respondents (91.3%) had already started experimental therapy and many of them constantly used internet (65.2%) and social networks (34.8%). More than half (53.9%) stated the interview with the physician was sufficient for a full understanding of informed consent. In case of doubt, the majority seeked support in the clinician (39.1%) while very few (1.7%) relied on the web. The average score attributed to doctor-patient relationship was equal to 8.89 (range 1-10). Respondents were quite confident in their ability to independently search for information on their disease, discriminate fake news and identify reliable sites (average score 3.26, 3.27, 3.09 respectively, over a range of 1-5). The scores related to the presumed ability to understand the results of a clinical study and to actively collaborate to produce research were high (average score 4.72 and 4.39 over a range of 1-5). Conclusions: Preliminary data from our research show a good level of patient awareness and a fine ability to understand information, discerning real from fake news. Continuing and implementing the training initiatives of the population in the health sector will certainly contribute to further improvement, hopefully obtaining an even greater involvement of patients in the early phases of research.

A Numerical Investigation of the Effect of Inlet Preswirl Ratio on Rotordynamic Characteristics of Labyrinth Seal

2017 ◽  
Author(s):  
Tomohiko Tsukuda ◽  
Toshio Hirano ◽  
Cori Watson ◽  
Neal R. Morgan ◽  
Brian K. Weaver ◽  
...  
Keyword(s):  
Flow Model ◽  
Three Dimensional ◽  
Axial Direction ◽  
Labyrinth Seal ◽  
Flow Fields ◽  
Bulk Flow ◽  
The Other ◽  
Circumferential Velocity ◽  
Stiffness Coefficients ◽  
Inlet Swirl

Full three-dimensional CFD simulations are carried out using ANSYS CFX to obtain the detailed flow field and to estimate the rotordynamic coefficients of a labyrinth seal for various inlet swirl ratios. Flow fields in the labyrinth seal with the eccentricity of the rotor are observed in detail and the detailed mechanisms that increase the destabilizing forces at high inlet swirl ratios are discussed based on the fluid governing equations associated with the flow fields. By evaluating the contributions from each term of the governing equation to cross coupled force, it is found that circumferential velocity and circumferential distribution of axial mass flow rate play key roles in generating cross coupled forces. In the case that circumferential velocity is high and decreases along the axial direction, all contributions from each term are positive cross coupled force. On the other hand, in the case that circumferential velocity is low and increases along the axial direction, one contribution is positive but the other is negative. Therefore, cross coupled force can be negative in the local chamber depending on the balance even if circumferential velocity is positive. CFD predictions of cross coupled stiffness coefficients and direct damping coefficients show better agreement with experimental results than a bulk flow model does by considering the force on the rotor in the inlet region. Cross coupled stiffness coefficients derived from the force on the rotor in the seal section agree well with those of the bulk flow model.

scholarly journals Mass transport of contaminated soil released into surface water by landslides (Göta River, SW Sweden)

2012 ◽  
Vol 16 (7) ◽  
pp. 1879-1893 ◽  
Author(s):  
G. Göransson ◽  
M. Larson ◽  
D. Bendz ◽  
M. Åkesson
Keyword(s):  
Surface Water ◽  
Contaminated Soil ◽  
Suspended Particle ◽  
Transport Processes ◽  
Landslide Risk ◽  
Suspended Sediment Transport ◽  
River Stretch ◽  
Landslide Mass ◽  
Exposure Pathway ◽  
The Impact

Abstract. Landslides of contaminated soil into surface water represent an overlooked exposure pathway that has not been addressed properly in existing risk analysis for landslide hazard, contaminated land, or river basin management. A landslide of contaminated soil into surface water implies an instantaneous exposure of the water to the soil, dramatically changing the prerequisites for the mobilisation and transport of pollutants. In this study, an analytical approach is taken to simulate the transport of suspended matter released in connection with landslides into rivers. Different analytical solutions to the advection-dispersion equation (ADE) were tested against the measured data from the shallow rotational, retrogressive landslide in clayey sediments that took place in 1993 on the Göta River, SW Sweden. The landslide encompassed three distinct events, namely an initial submerged slide, followed by a main slide, and a retrogressive slide. These slides generated three distinct and non-Gaussian peaks in the online turbidity recordings at the freshwater intake downstream the slide area. To our knowledge, this registration of the impact on a river of the sediment release from a landslide is one of few of its kind in the world and unique for Sweden. Considering the low frequency of such events, the data from this landslide are highly useful for evaluating how appropriate the ADE is to describe the effects of landslides into surface water. The results yielded realistic predictions of the measured variation in suspended particle matter (SPM) concentration, after proper calibration. For the three individual slides it was estimated that a total of about 0.6% of the total landslide mass went into suspension and was transported downstream. This release corresponds to about 1 to 2% of the annual suspended sediment transport for that river stretch. The studied landslide partly involved an industrial area, and by applying the analytical solution to estimate the transport of metals in the sediments, it was found that landslides may release a significant amount of pollutants if large contaminated areas are involved. However, further studies are needed to develop more detailed descriptions of the transport processes. There is also a need to increase the knowledge on possible environmental consequences in the near and far field, in a short- and long-time perspective. In summary, the release of pollutants should not be neglected in landslide risk assessments.

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