Flow in the Stenotic Carotid Bifurcation

2002 ◽  
Author(s):  
Stanley A. Berger ◽  
Vitaliy L. Rayz
Keyword(s):  
Plaque Rupture ◽  
Three Dimensional ◽  
Carotid Bifurcation ◽  
Atherosclerotic Plaques ◽  
Flow Conditions ◽  
Artery Wall ◽  
Plaque Development ◽  
Irregular Geometries ◽  
A Site ◽  
Realistic Geometries

The carotid artery bifurcation is prone to the development of atherosclerotic plaques, and is a site where the consequences of this development can be severe. The most immediate effects are changes in lumenal cross-section, volumetric blood flow, and forces on the wall. The end result may be plaque rupture, possibly resulting in a stroke. Plaque development, and plaque rupture, are likely both strongly influenced by the changes of the shear stress, and possibly normal stress, at the artery wall [1]. Numerical simulations of the flow in the carotid bifurcation can elucidate the influence of the flow on the plaque and vice versa. The irregular geometries of severely stenotic vessels make numerical modeling of these flows particularly challenging [2, 3]. We describe simulations in fully three-dimensional, realistic geometries under steady and pulsatile flow conditions.

scholarly journals Quantifying Effects of Plaque Structure and Material Properties on Stress Distributions in Human Atherosclerotic Plaques Using 3D FSI Models

2005 ◽  
Vol 127 (7) ◽  
pp. 1185-1194 ◽  
Author(s):  
Dalin Tang ◽  
Chun Yang ◽  
Jie Zheng ◽  
Pamela K. Woodard ◽  
Jeffrey E. Saffitz ◽  
...  
Keyword(s):  
Material Properties ◽  
Plaque Rupture ◽  
Three Dimensional ◽  
Mechanical Analysis ◽  
Atherosclerotic Plaques ◽  
Plaque Vulnerability ◽  
Stress Strain ◽  
Maximal Stress ◽  
Good Potential ◽  
Stress Variations

Background: Atherosclerotic plaques may rupture without warning and cause acute cardiovascular syndromes such as heart attack and stroke. Methods to assess plaque vulnerability noninvasively and predict possible plaque rupture are urgently needed. Method: MRI-based three-dimensional unsteady models for human atherosclerotic plaques with multi-component plaque structure and fluid-structure interactions are introduced to perform mechanical analysis for human atherosclerotic plaques. Results: Stress variations on critical sites such as a thin cap in the plaque can be 300% higher than that at other normal sites. Large calcification block considerably changes stress/strain distributions. Stiffness variations of plaque components (50% reduction or 100% increase) may affect maximal stress values by 20–50 %. Plaque cap erosion causes almost no change on maximal stress level at the cap, but leads to 50% increase in maximal strain value. Conclusions: Effects caused by atherosclerotic plaque structure, cap thickness and erosion, material properties, and pulsating pressure conditions on stress/strain distributions in the plaque are quantified by extensive computational case studies and parameter evaluations. Computational mechanical analysis has good potential to improve accuracy of plaque vulnerability assessment.

Plaque Rupture in the Carotid Artery: A Combined Imaging, Computational and Histological Analysis

2009 ◽  
Author(s):  
Giulia Soloperto ◽  
Niall Keenan ◽  
Mary Sheppard ◽  
Nigel Wood ◽  
Dudley J. Pennell ◽  
...  
Keyword(s):  
Shear Stress ◽  
Carotid Arteries ◽  
Histological Analysis ◽  
Plaque Rupture ◽  
Thrombus Formation ◽  
Atherosclerotic Plaques ◽  
Matrix Degradation ◽  
Vascular Events ◽  
Plaque Development ◽  
Combined Imaging

Cerebro-vascular events are often related to the rupture of vulnerable atherosclerotic plaques and thrombus formation in the carotid arteries. Haemodynamically significant stenoses experience increased wall shear stress (WSS) in the entrance region but in the post-stenotic region, instead the flow decelerates and tends to become unstable, with separation and recirculation. The high WSS tends to promote processes leading to matrix degradation, with potential rupture, whilst processes stimulated in the post-stenotic zone might be expected to promote further plaque development [1].

Haemorheological Effects on Thrombocyte Adhesion and Aggregation Found Under Controlled Flow Conditions

1979 ◽  
Author(s):  
P.D. Richardson
Keyword(s):  
Rate Of Change ◽  
Continuous Observation ◽  
Flow Conditions ◽  
Wide Range ◽  
Stream Migration ◽  
Local Shear ◽  
Videotape Recording ◽  
Controlled Flow ◽  
A Site

Thrombocyte adhesion and aggregation in a vessel or on a chamber wall can be measured most readily if the flow is controlled and steady, and continuous observation is used. Videotape recording is very helpful for subsequent quantification of the dynamics. The adhesion of each thrombocyte can occur for a finite time interval:this interval has been observed to have a wide range. Platelets which escape often leave open a site which attracts other platelets preferentially. The rate of change of adhesion density (platelets/mm2) is affected by the local shear rate and the shear history upstream. Aggregation is affected similarly, and also proceeds with some platelet turnover. The role of erythrocytes in facilitating cross-stream migration of thrombocytes (which can enhance the growth rate of large thrombi) appears due in part to convective flow fields induced by the motion of erythrocytes in a shear flow, which can be demonstrated theoretically and experimentally. Observations of the phenomenlogy of adhesion and aggregation under controlled flow conditions and comparison with fLu id-dynamically based theory allows representation in terras of a small number of parameters with prospects of prediction of behaviour over a wide range of haemodynamic conditions; biochemical changes lead to changes in values of the parameters, so that activating agents and inhibiting agents modify values in different directions.

scholarly journals Three-Dimensional Site Characterization Model of Bangalore Using Support Vector Machine

2012 ◽  
Vol 2012 ◽  
pp. 1-10
Author(s):  
Pijush Samui
Keyword(s):  
Support Vector Machine ◽  
Three Dimensional ◽  
Site Characterization ◽  
Standard Penetration Test ◽  
Support Vector ◽  
Characterization Model ◽  
Svm Model ◽  
Input Variables ◽  
Learning Machine ◽  
A Site

The main objective of site characterization is the prediction of in situ soil properties at any half-space point at a site based on limited tests. In this study, the Support Vector Machine (SVM) has been used to develop a three dimensional site characterization model for Bangalore, India based on large amount of Standard Penetration Test. SVM is a novel type of learning machine based on statistical learning theory, uses regression technique by introducing ε-insensitive loss function. The database consists of 766 boreholes, with more than 2700 field SPT values () spread over 220 sq km area of Bangalore. The model is applied for corrected () values. The three input variables (, , and , where , , and are the coordinates of the Bangalore) were used for the SVM model. The output of SVM was the data. The results presented in this paper clearly highlight that the SVM is a robust tool for site characterization. In this study, a sensitivity analysis of SVM parameters (σ, , and ε) has been also presented.

Early changes in coronary artery wall structure detected by microcomputed tomography in experimental hypercholesterolemia

2007 ◽  
Vol 293 (3) ◽  
pp. H1997-H2003 ◽  
Author(s):  
Xiang-Yang Zhu ◽  
Michael D. Bentley ◽  
Alejandro R. Chade ◽  
Erik L. Ritman ◽  
Amir Lerman ◽  
...  
Keyword(s):  
Vascular Endothelial Growth Factor ◽  
Coronary Artery ◽  
Growth Factor ◽  
Three Dimensional ◽  
Wall Structure ◽  
Vascular Endothelial ◽  
Micro Ct ◽  
Artery Wall ◽  
Coronary Artery Wall ◽  
Endothelial Growth Factor

Changes in the structure of the artery wall commence shortly after exposure to cardiovascular risk factors, such as hypercholesterolemia (HC), but may be difficult to detect. The ability to study vascular wall structure could be helpful in evaluation of the factors that instigate atherosclerosis and its pathomechanisms. The present study tested the hypothesis that early morphological changes in coronary arteries of hypercholesterolemic (HC) pigs can be detected using the novel X-ray contrast agent OsO4 and three-dimensional micro-computed tomography (CT). Two groups of pigs were studied after they were fed a normal or an HC (2% cholesterol) diet for 12 wk. Hearts were harvested, coronary arteries were injected with 1% OsO4 solution, and cardiac samples (6-μm-thick) were scanned by micro-CT. Layers of the epicardial coronary artery wall, early lesions, and perivascular OsO4 accumulation were determined. Leakage of OsO4 from myocardial microvessels was used to assess vascular permeability, which was correlated with immunoreactivity of vascular endothelial growth factor in corresponding histological cross sections. OsO4 enhanced the visualization of coronary artery wall layers and facilitated detection of early lesions in HC in longitudinal tomographic sections of vascular segments. Increased density of perivascular OsO4 in HC was correlated with increased vascular endothelial growth factor expression and suggested increased microvascular permeability. The use of OsO4 as a contrast agent in micro-CT allows three-dimensional visualization of coronary artery wall structure, early lesion formation, and changes in vascular permeability. Therefore, this technique can be a useful tool in atherosclerosis research.

scholarly journals A Voxel-Map Quantitative Analysis Approach for Atherosclerotic Noncalcified Plaques of the Coronary Artery Tree

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Ying Li ◽  
Wei Chen ◽  
Kaijun Liu ◽  
Yi Wu ◽  
Yonglin Chen ◽  
...  
Keyword(s):  
Coronary Artery ◽  
Three Dimensional ◽  
Coronary Intervention ◽  
Quantitative Information ◽  
Atherosclerotic Plaques ◽  
Anatomical Location ◽  
Contrast Enhanced ◽  
Percutaneous Coronary ◽  
Map Analysis ◽  
Coronary Artery Tree

Noncalcified plaques (NCPs) are associated with the presence of lipid-core plaques that are prone to rupture. Thus, it is important to detect and monitor the development of NCPs. Contrast-enhanced coronary Computed Tomography Angiography (CTA) is a potential imaging technique to identify atherosclerotic plaques in the whole coronary tree, but it fails to provide information about vessel walls. In order to overcome the limitations of coronary CTA and provide more meaningful quantitative information for percutaneous coronary intervention (PCI), we proposed a Voxel-Map based on mathematical morphology to quantitatively analyze the noncalcified plaques on a three-dimensional coronary artery wall model (3D-CAWM). This approach is a combination of Voxel-Map analysis techniques, plaque locating, and anatomical location related labeling, which show more detailed and comprehensive coronary tree wall visualization.

scholarly journals Carotid Bifurcation Hemodynamics in Older Adults: Effect of Measured Versus Assumed Flow Waveform

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Yiemeng Hoi ◽  
Bruce A. Wasserman ◽  
Edward G. Lakatta ◽  
David A. Steinman
Keyword(s):  
Magnetic Resonance ◽  
Older Adult ◽  
Blood Flow Rate ◽  
Carotid Bifurcation ◽  
Flow Waveform ◽  
Flow Conditions ◽  
Flow Rates ◽  
Relative Residence Time ◽  
Contrast Magnetic Resonance ◽  
Dynamics Models

Recent work has illuminated differences in carotid artery blood flow rate dynamics of older versus young adults. To what degree flow waveform shape, and indeed the use of measured versus assumed flow rates, affects the simulated hemodynamics of older adult carotid bifurcations has not been elucidated. Image-based computational fluid dynamics models of N=9 normal, older adult carotid bifurcations were reconstructed from magnetic resonance angiography. Subject-specific hemodynamics were computed by imposing each individual’s inlet and outlet flow rates measured by cine phase-contrast magnetic resonance imaging or by imposing characteristic young and older adult flow waveform shapes adjusted to cycle-averaged flow rates measured or allometrically scaled to the inlet and outlet areas. Despite appreciable differences in the measured versus assumed flow conditions, the locations and extents of low wall shear stress and elevated relative residence time were broadly consistent; however, the extent of elevated oscillatory shear index was substantially underestimated, more by the use of assumed cycle-averaged flow rates than the assumed flow waveform shape. For studies of individual vessels, use of a characteristic flow waveform shape is likely sufficient, with some benefit offered by scaling to measured cycle-averaged flow rates. For larger-scale studies of many vessels, ranking of cases according to presumed hemodynamic or geometric risk is robust to the assumed flow conditions.

Lab-on-a-Chip System for Developing and Fluorescence Imaging a Three-Dimensional Model of Pancreatic Islets Under Flow Conditions

2021 ◽  
Vol MA2021-01 (55) ◽  
pp. 1396-1396
Author(s):  
Zbigniew Brzozka ◽  
Patrycja Sokołowska ◽  
Kamil Zukowski ◽  
Justyna Janikiewicz ◽  
Ekzbieta Jastrzebska ◽  
...  
Keyword(s):  
Pancreatic Islets ◽  
Fluorescence Imaging ◽  
Three Dimensional ◽  
Lab On A Chip ◽  
Dimensional Model ◽  
Flow Conditions ◽  
Three Dimensional Model
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