Exploring High Frequency Temporal Fluctuations in the Terminal Aneurysm of the Basilar Bifurcation

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Matthew D. Ford ◽  
Ugo Piomelli
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
High Frequency ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Disturbed Flow ◽  
Frequency Fluctuations ◽  
Wall Shear ◽  
Inflow Jet

Cerebral aneurysms are a common cause of death and disability. Of all the cardiovascular diseases, aneurysms are perhaps the most strongly linked with the local fluid mechanic environment. Aside from early in vivo clinical work that hinted at the possibility of high-frequency intra-aneurysmal velocity oscillations, flow in cerebral aneurysms is most often assumed to be laminar. This work investigates, through the use of numerical simulations, the potential for disturbed flow to exist in the terminal aneurysm of the basilar bifurcation. The nature of the disturbed flow is explored using a series of four idealized basilar tip models, and the results supported by four patient specific terminal basilar tip aneurysms. All four idealized models demonstrated instability in the inflow jet through high frequency fluctuations in the velocity and the pressure at approximately 120 Hz. The instability arises through a breakdown of the inflow jet, which begins to oscillate upon entering the aneurysm. The wall shear stress undergoes similar high-frequency oscillations in both magnitude and direction. The neck and dome regions of the aneurysm present 180 deg changes in the direction of the wall shear stress, due to the formation of small recirculation zones near the shear layer of the jet (at the frequency of the inflow jet oscillation) and the oscillation of the impingement zone on the dome of the aneurysm, respectively. Similar results were observed in the patient-specific models, which showed high frequency fluctuations at approximately 112 Hz in two of the four models and oscillations in the magnitude and direction of the wall shear stress. These results demonstrate that there is potential for disturbed laminar unsteady flow in the terminal aneurysm of the basilar bifurcation. The instabilities appear similar to the first instability mode of a free round jet.

Differential Gene Expression of Endothelial Cells Under High Wall Shear Stress and Spatial Gradients

2010 ◽  
Author(s):  
Jennifer Dolan ◽  
Song Liu ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Spatial Gradient ◽  
Flow Acceleration ◽  
Spatial Gradients ◽  
Wall Shear

In both human and animal models, cerebral aneurysms tend to develop at the apices of bifurcations in the cerebral vasculature. Due to the focal nature of aneurysm development it has long been speculated that hemodynamics are an important factor in aneurysm susceptibility. The local hemodynamics of bifurcations are complex, being characterized by flow impingement causing a high frictional force on the vessel wall known as wall shear stress (WSS) and significant flow acceleration or deceleration, manifested as the positive or negative spatial gradient of WSS (WSSG). In vivo studies have recently identified that aneurysm initiation occurs at areas of the vessel wall that experience a combination of both high WSS and positive WSSG [1,2]

Positive and Negative Wall Shear Stress Gradients Have Different Effects on Endothelial Phenotype Under High Wall Shear Stress

2011 ◽  
Author(s):  
Jennifer Dolan ◽  
Frasier Sim ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Spatial Gradient ◽  
Cerebral Vasculature ◽  
High Wall Shear Stress ◽  
Wall Shear

In both human and animal models, cerebral aneurysms tend to develop at the apices of bifurcations in the cerebral vasculature where the blood vessel wall experiences complex hemodynamics. In vivo studies have recently revealed that the initiation of cerebral aneurysms is confined to a well-defined hemodynamic microenvironment [1,2]. Metaxa et al. [2] found that early aneurysm remodeling initiates where the vessel wall experiences high wall shear stress (WSS) and flow is accelerating, thus creating a positive spatial gradient in WSS (WSSG). Closer examination of such in vivo studies reveals that exposure of the vessel wall to equally high WSS in the presence of decelerating flow, that is, negative WSSG, does not result in aneurysm-like destruction.

A New Hexahedral Mesher for a Numerically Efficient Patient Specific Analysis of Arterial Blood Flow and Wall Shear Stress

2010 ◽  
Author(s):  
G. De Santis ◽  
P. Mortier ◽  
M. De Beule ◽  
P. Segers ◽  
P. Verdonck ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Imaging Techniques ◽  
Arterial Blood Flow ◽  
Patient Specific ◽  
Arterial Tree ◽  
Arterial Blood ◽  
Current Measuring ◽  
Wall Shear

Atherosclerosis depends on systemic risk factors but manifests itself as geometrically focal plaques, which appear in regions of the arterial tree experiencing low and/or oscillating Wall Shear Stress (WSS) such as outer edges of vessels bifurcations and highly curved vessels. Because direct measurements of WSS (differential quantity) in vivo are difficult due to limited spatial resolution offered by current measuring technologies (ultrasound, phase contrast MRI), an indirect approach is often taken, integrating medical imaging techniques (biplane angiography, CT, MRI) with Computational Fluid Dynamics (CFD) for patient specific WSS profiling.

Differential Responses of Endothelial Cells to Positive and Negative Wall Shear Stress Gradients

2010 ◽  
Author(s):  
Jennifer Dolan ◽  
Sukhjinder Singh ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Fluid Shear Stress ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Outer Side ◽  
Fluid Shear ◽  
Wall Shear

Cerebral aneurysms tend to develop at bifurcation apices or the outer side of curved vessels where the blood vessel wall experiences complex hemodynamics. In vivo studies have recently revealed that the initiation of cerebral aneurysms is confined to a well-defined hemodynamic microenvironment. Specifically aneurysms form where the vessel wall experiences high fluid shear stress (wall shear stress, WSS) and flow is accelerating, so that the wall is exposed to a positive spatial gradient in the fluid shear stress (wall shear stress gradient, WSSG)[1,2]. Closer examination of such in vivo studies reveals that exposure of the vessel wall to equally high WSS in the presence of decelerating flow, that is, negative WSSG, does not result in aneurysm-like remodeling.

scholarly journals Assessment of turbulent blood flow and wall shear stress in aortic coarctation using image-based simulations

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Romana Perinajová ◽  
Joe F. Juffermans ◽  
Jonhatan Lorenzo Mercado ◽  
Jean-Paul Aben ◽  
Leon Ledoux ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flows ◽  
Patient Specific ◽  
4D Flow Mri ◽  
4D Flow ◽  
Local Flow ◽  
Flow Mri ◽  
Wall Shear

AbstractIn this study, we analyzed turbulent flows through a phantom (a 180$$^{\circ }$$ ∘ bend with narrowing) at peak systole and a patient-specific coarctation of the aorta (CoA), with a pulsating flow, using magnetic resonance imaging (MRI) and computational fluid dynamics (CFD). For MRI, a 4D-flow MRI is performed using a 3T scanner. For CFD, the standard $$k-\epsilon $$ k - ϵ , shear stress transport $$k-\omega $$ k - ω , and Reynolds stress (RSM) models are applied. A good agreement between measured and simulated velocity is obtained for the phantom, especially for CFD with RSM. The wall shear stress (WSS) shows significant differences between CFD and MRI in absolute values, due to the limited near-wall resolution of MRI. However, normalized WSS shows qualitatively very similar distributions of the local values between MRI and CFD. Finally, a direct comparison between in vivo 4D-flow MRI and CFD with the RSM turbulence model is performed in the CoA. MRI can properly identify regions with locally elevated or suppressed WSS. If the exact values of the WSS are necessary, CFD is the preferred method. For future applications, we recommend the use of the combined MRI/CFD method for analysis and evaluation of the local flow patterns and WSS in the aorta.

Inter-Operator Segmentation Differences Impact Wall Shear Stress Distributions in Patient-Specific Computational Fluid Dynamic Models

2009 ◽  
Author(s):  
Ian C. Campbell ◽  
William W. Sprague ◽  
Marina Piccinelli ◽  
Alessandro Veneziani ◽  
John N. Oshinski
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Dynamic Models ◽  
Fluid Dynamic ◽  
Cfd Modeling ◽  
Patient Specific ◽  
Wall Thickening ◽  
Cross Sectional ◽  
Wall Shear

The link between hemodynamic forces, notably wall shear stress (WSS), and atherogenesis is well established. Patient-specific computational fluid dynamics (CFD) modeling of human vasculature has attracted recent attention because it allows investigators to determine areas at risk for plaque formation and subsequent rupture [1]. Non-invasive in vivo imaging methods such as magnetic resonance (MR) angiography allow acquisition of vascular geometry and cross-sectional velocity such that a CFD model can determine the spatial distribution of WSS. WSS may then be correlated with phenomena such as wall thickening.

Hemodynamics in growing and stable cerebral aneurysms

2015 ◽  
Vol 8 (4) ◽  
pp. 407-412 ◽  
Author(s):  
Daniel M Sforza ◽  
Kenichi Kono ◽  
Satoshi Tateshima ◽  
Fernando Viñuela ◽  
Christopher Putman ◽  
...  
Keyword(s):  
Shear Stress ◽  
Logistic Regression ◽  
Wall Shear Stress ◽  
Statistical Models ◽  
Three Dimensional ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Unruptured Aneurysms ◽  
Aspect Ratios ◽  
Wall Shear

ObjectiveThe detailed mechanisms of cerebral aneurysm evolution are poorly understood but are important for objective aneurysm evaluation and improved patient management. The purpose of this study was to identify hemodynamic conditions that may predispose aneurysms to growth.MethodsA total of 33 intracranial unruptured aneurysms longitudinally followed with three-dimensional imaging were studied. Patient-specific computational fluid dynamics models were constructed and used to quantitatively characterize the hemodynamic environments of these aneurysms. Hemodynamic characteristics of growing (n=16) and stable (n=17) aneurysms were compared. Logistic regression statistical models were constructed to test the predictability of aneurysm growth by hemodynamic features.ResultsGrowing aneurysms had significantly smaller shear rate ratios (p=0.01), higher concentration of wall shear stress (p=0.03), smaller vorticity ratios (p=0.01), and smaller viscous dissipation ratios (p=0.01) than stable aneurysms. They also tended to have larger areas under low wall shear stress (p=0.06) and larger aspect ratios (p=0.18), but these trends were not significant. Mean wall shear stress was not significantly different between growing and stable aneurysms. Logistic regression models based on hemodynamic variables were able to discriminate between growing and stable aneurysms with a high degree of accuracy (94–100%).ConclusionsGrowing aneurysms tend to have complex intrasaccular flow patterns that induce non-uniform wall shear stress distributions with areas of concentrated high wall shear stress and large areas of low wall shear stress. Statistical models based on hemodynamic features seem capable of discriminating between growing and stable aneurysms.

Cerebral aneurysm rupture status classification using statistical and machine learning methods

2021 ◽  
pp. 095441192110004
Author(s):  
Nicolás Amigo ◽  
Alvaro Valencia ◽  
Wei Wu ◽  
Sourav Patnaik ◽  
Ender Finol
Keyword(s):  
Machine Learning ◽  
Shear Stress ◽  
Random Forest ◽  
Wall Shear Stress ◽  
Confusion Matrix ◽  
Cerebral Aneurysms ◽  
Machine Learning Algorithms ◽  
Size Ratio ◽  
Patient Specific ◽  
Wall Shear

Morphological characterization and fluid dynamics simulations were carried out to classify the rupture status of 71 (36 unruptured, 35 ruptured) patient specific cerebral aneurysms using a machine learning approach together with statistical techniques. Eleven morphological and six hemodynamic parameters were evaluated individually and collectively for significance as rupture status predictors. The performance of each parameter was inspected using hypothesis testing, accuracy, confusion matrix, and the area under the receiver operating characteristic curve. Overall, the size ratio exhibited the best performance, followed by the diastolic wall shear stress, and systolic wall shear stress. The prediction capability of all 17 parameters together was evaluated using eight different machine learning algorithms. The logistic regression achieved the highest accuracy (0.75), whereas the random forest had the highest area under curve value among all the classifiers (0.82), surpassing the performance exhibited by the size ratio. Hence, we propose the random forest model as a tool that can help improve the rupture status prediction of cerebral aneurysms.

Abstract WP83: Wall Shear Stress Strength Over the Cerebral Aneurysm is Drastically Affected by Aneurysm Location While the Magnitude of Disturbed Flow is Closely Related to Aneurysm Size and Surface Area

Stroke ◽  
2017 ◽  
Vol 48 (suppl_1) ◽  
Author(s):  
Shunichi Fukuda ◽  
Yuji Shimogonya
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cerebral Aneurysm ◽  
Surface Area ◽  
Cerebral Aneurysms ◽  
Disturbed Flow ◽  
Rupture Rate ◽  
Aneurysm Size ◽  
Significant Difference ◽  
Wall Shear

Background and purpose: The rupture rate of cerebral aneurysms varies according to the aneurysm size and location. Although several reports suggest hemodynamic involvement in the mechanisms, there still remains to be clarified. Using computational fluid dynamics, we elucidated here differences in hemodynamics according to size and location of human cerebral aneurysms. Methods: Patient-specific inflow velocities and arterial geometries of 39 MCA aneurysms and anterior communicating artery (Acom) aneurysms were acquired from patients who consented to participate in the multi-institutional prospective clinical study, CFD ABO Study. Pulsatile blood flow was simulated using ANSYS-CFX, based on the Navier-Stokes equations for incompressible fluid. Aneurysms were divided into 3 groups by their size; less than 5mm, less than 7mm and more than 5mm, and more than 7mm. Results: Wall shear stress (WSS) was significantly lower in Acom aneurysms than MCA aneurysms (p=0.00075) while there was no significant difference in WSS according to aneurysm size. In contrast, indicators for disturbed flow, oscillatory shear index (OSI) and normalized transverse WSS (NtransWSS) were significantly higher over the aneurysms of the size less than 7mm and more than 5mm compared to those less than 5mm (p=0.021 and 0.014, respectively). Moreover, there were strong or moderate positive correlations between aneurysm surface area and OSI and NtransWSS, but not WSS. However, there was no significant difference in OSI or NtransWSS between MCA and Acom aneurysms. Conclusions: The data suggest that WSS strength over the cerebral aneurysm is drastically affected by the aneurysm location while the magnitude of disturbed flow is closely related to aneurysm size and surface area. A significant lower WSS in Acom aneurysms compared to MCA aneurysms may be associated with higher rupture rate in Acom aneurysms. In contrast, disturbed flow may be involved in aneurysm enlargement.

Relating Wall Shear Stress, Bleb Formation and Rupture of Cerebral Aneurysms: Image-Based Modeling and Clinical Observations

2008 ◽  
Author(s):  
Juan R. Cebral ◽  
Christopher M. Putman
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Computational Models ◽  
Cerebral Aneurysms ◽  
Clinical Observations ◽  
History Of ◽  
Wall Shear ◽  
Blood Flow Patterns

Cerebral aneurysms are widely believed to form and grow as a result of the interactions of hemodynamics and wall mechano-biology. Researchers have used a variety of tools to study these complex multi-factorial mechanisms including animal, in vitro, and computational models. The goal of these experiments has been to approximate the in vivo environment so that theories about the natural history of brain aneurysms can be developed and tested in realistic systems. Studying the link between hemodynamics and clinical observations of aneurysm progression is necessary to reach an understanding of the relative importance of the different mechanisms involved in these processes [1]. The objective of our research is to investigate the possible relationship between wall shear stress (WSS) — which is known to regulate mechano-biological processes at the arterial wall — produced by different blood flow patterns and the evolution and rupture of cerebral aneurysms.

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