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.

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.

Image Based CFD Modeling of Coronary Artery Wall Shear Stress and Importance of Patient-Specific Velocity Boundary Conditions

2007 ◽  
Author(s):  
Kevin R. Johnson ◽  
John N. Oshinski
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Spatial Resolution ◽  
Multidetector Ct ◽  
Atherosclerotic Lesion ◽  
Cfd Modeling ◽  
Patient Specific ◽  
Lesion Development ◽  
Wall Shear ◽  
Atherosclerotic Lesion Development

Low and oscillatory arterial wall shear stress (WSS) have been shown to have an effect on many factors implicated in atherosclerotic lesion development. The majority of studies on the relationship between low or oscillating WSS and sites of intimal thickening and early atherosclerotic lesion development are based on in-vitro model studies of flow and WSS distribution. These models are based on average vessel geometries with average flow conditions and compared to average pathology distribution of lesions that may obscure the true relationship between WSS and lesion distribution[1]. Recent techniques have been developed using coronary MR angiography to create patient-specific 3D models along with velocity measurements of blood flow using phase contrast magnetic resonance (PCMR). However, these models may lack adequate spatial resolution for accurate, localized calculation of WSS[2]. Current, state-of-art multidetector CT scanners offer improvements in spatial resolution over MRI for creation of 3D vessel models.

Spatial comparison between wall shear stress measures and porcine arterial endothelial permeability

2004 ◽  
Vol 286 (5) ◽  
pp. H1916-H1922 ◽  
Author(s):  
Heather A. Himburg ◽  
Deborah M. Grzybowski ◽  
Andrew L. Hazel ◽  
Jeffrey A. LaMack ◽  
Xue-Mei Li ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Evans Blue ◽  
Fluid Dynamic ◽  
Endothelial Permeability ◽  
Blue Dye ◽  
Evans Blue Dye ◽  
Wall Shear ◽  
And Function

A better understanding of how hemodynamic factors affect the integrity and function of the vascular endothelium is necessary to appreciate more fully how atherosclerosis is initiated and promoted. A novel technique is presented to assess the relation between fluid dynamic variables and the permeability of the endothelium to macromolecules. Fully anesthetized, domestic swine were intravenously injected with the albumin marker Evans blue dye, which was allowed to circulate for 90 min. After the animals were euthanized, silicone casts were made of the abdominal aorta and its iliac branches. Pulsatile flow calculations were subsequently made in computational regions derived from the casts. The distribution of the calculated time-dependent wall shear stress in the external iliac branches was directly compared on a point-by-point basis with the spatially varying in vivo uptake of Evans blue dye in the same arteries. The results indicate that in vivo endothelial permeability to albumin decreases with increasing time-average shear stress over the normal range. Additionally, endothelial permeability increases slightly with oscillatory shear index.

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.

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.

Redox Signaling in an In Vivo Murine Model of Tailored Wall Shear Stress

2009 ◽  
Author(s):  
Nick J. Willett ◽  
John Oshinski ◽  
Don Giddens ◽  
Robert Guldberg ◽  
W. Robert Taylor
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Protein Expression ◽  
Fluid Dynamic ◽  
Inflammatory Marker ◽  
Inflammatory Protein ◽  
Wall Shear ◽  
Acute Changes ◽  
High Degree

Wall Shear Stress (WSS) has been identified as an important factor in the pathogenesis of atherosclerosis. We developed a novel murine aortic coarctation model to alter the hemodynamic environment in vivo. The model utilizes the shape memory response of nitinol clips to provide a high degree of control over aortic diameter and subsequently WSS. We employed this model to test the hypothesis that acute changes in WSS in vivo induce upregulation of inflammatory proteins mediated by Reactive Oxygen Species (ROS). WSS was mapped through a computational fluid dynamic model and correlated to inflammatory marker expression. C57B16 control mice were compared to tempol treated, apocynin treated, p47phox KO, and catalase overexpressor mice in this study. The results show that the coarctation produces low mean oscillatory WSS in the region downstream of the clip. The WSS in this region correlates to a large increase in VCAM-1 expression in wild-type mice. This WSS dependent increase in protein expression is unchanged in animal models of decreased ROS. This suggests that although the redox state is important to the overall pathogenesis of the disease, individual ROS or ROS sources may not be sufficient to inhibit a WSS dependent inflammatory response. Further analysis with this model utilizing other reagent treatments, transgenic mice, and markers will allow us to analyze the functional contribution of transcription factors, ROS, and ROS sources to WSS dependent inflammatory protein expression.

Y-Stent Coiling of Basilar Bifurcation Aneurysms Induces a Dynamic Angular Vascular Remodeling With Alteration of the Apical Wall Shear Stress Pattern

Neurosurgery ◽  
2012 ◽  
Vol 72 (4) ◽  
pp. 617-629 ◽  
Author(s):  
Bulang Gao ◽  
Merih I. Baharoglu ◽  
Alex D. Cohen ◽  
Adel M. Malek
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Dynamic Analysis ◽  
Computational Fluid Dynamic ◽  
Fluid Dynamic ◽  
Cerebral Arteries ◽  
Patient Specific ◽  
Computational Fluid Dynamic Analysis ◽  
Hemodynamic Forces ◽  
Wall Shear

Abstract BACKGROUND: Although wide-necked basilar bifurcation aneurysms are treated with Y-stent coiling, the effect of this intervention on vessel configuration and hemodynamics is unknown. OBJECTIVE: To investigate the immediate and delayed effects of Y-stenting using self-expanding microstents on basilar bifurcation architecture and hemodynamics. METHODS: Fifteen patients underwent basilar Y-stent coiling and imaging with rotational angiography. Vascular angles were measured between proximal P1 segments of the posterior cerebral arteries (α) and between the basilar artery and each P1 segment (β1,2) in the anteroposterior and γ1,2 sagittal planes. Patient-specific computational fluid dynamic analysis was used to estimate wall shear stress (WSS) changes with treatment. RESULTS: In the anteroposterior plane, Y-stenting significantly decreased angle α and increased β angles immediately after stent coiling (P < .05 and P < .01, respectively) in a continued dynamic remodeling that progressed further in later months; sagittal γ angles also decreased (P < .0001). This novel stent-induced geometric progressive remodeling resulted in effective straightening and narrowing of the basilar bifurcation angle α (150.0 degrees vs 113 degrees, P < .0001) with significant correlation (r = 0.39, P < .05) between pretreatment proximal P1 angles and maximal angular change. Computational fluid dynamic analysis showed the angular remodeling led to significant narrowing of the WSS interpeak at the apex, redirecting high WSS away from the neck transition zone with native vessel toward the inert coil mass. CONCLUSION: Y-configuration stent coiling induced immediate and, more significantly, a previously undefined delayed cerebrovascular remodeling. This progressive stent-induced angular remodeling alters perianeurysmal hemodynamics, independent of the flow-diverting properties of stent struts, thus shifting the balance of hemodynamic forces affecting aneurysm development and evolution.

scholarly journals Wall shear stress gradient is independently associated with middle cerebral artery aneurysm development: a case-control CFD patient-specific study based on 77 patients

BMC Neurology ◽  
2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Mikołaj Zimny ◽  
Edyta Kawlewska ◽  
Anna Hebda ◽  
Wojciech Wolański ◽  
Piotr Ładziński ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Middle Cerebral Artery ◽  
Cerebral Artery ◽  
Case Control ◽  
Independent Effect ◽  
Patient Specific ◽  
Aneurysm Formation ◽  
Wall Shear ◽  
Mca Aneurysm

Abstract Background Previously published computational fluid dynamics (CFD) studies regarding intracranial aneurysm (IA) formation present conflicting results. Our study analysed the involvement of the combination of high wall shear stress (WSS) and a positive WSS gradient (WSSG) in IA formation. Methods We designed a case-control study with a selection of 38 patients with an unruptured middle cerebral artery (MCA) aneurysm and 39 non-aneurysmal controls to determine the involvement of WSS, oscillatory shear index (OSI), the WSSG and its absolute value (absWSSG) in aneurysm formation based on patient-specific CFD simulations using velocity profiles obtained from transcranial colour-coded sonography. Results Among the analysed parameters, only the WSSG had significantly higher values compared to the controls (11.05 vs − 14.76 [Pa/mm], P = 0.020). The WSS, absWSSG and OSI values were not significantly different between the analysed groups. Logistic regression analysis identified WSS and WSSG as significant co-predictors for MCA aneurysm formation, but only the WSSG turned out to be a significant independent prognosticator (OR: 1.009; 95% CI: 1.001–1.017; P = 0.025). Significantly more patients (23/38) in the case group had haemodynamic regions of high WSS combined with a positive WSSG near the bifurcation apex, while in the control group, high WSS was usually accompanied by a negative WSSG (14/39). From the analysis of the ROC curve for WSSG, the area under the curve (AUC) was 0.654, with the optimal cut-off value −0.37 Pa/mm. The largest AUC was recognised for combined WSS and WSSG (AUC = 0.671). Our data confirmed that aneurysms tend to form near the bifurcation apices in regions of high WSS values accompanied by positive WSSG. Conclusions The development of IAs is determined by an independent effect of haemodynamic factors. High WSS impacts MCA aneurysm formation, while a positive WSSG mainly promotes this process.

scholarly journals Genetic correlates of wall shear stress in a patient-specific 3D-printed cerebral aneurysm model

2019 ◽  
Vol 11 (10) ◽  
pp. 999-1003 ◽  
Author(s):  
Michael R Levitt ◽  
Christian Mandrycky ◽  
Ashley Abel ◽  
Cory M Kelly ◽  
Samuel Levy ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Cerebral Aneurysm ◽  
Cell Morphology ◽  
Patient Specific ◽  
Parent Vessel ◽  
3D Printed ◽  
Wall Shear ◽  
Dynamics Simulations

ObjectivesTo study the correlation between wall shear stress and endothelial cell expression in a patient-specific, three-dimensional (3D)-printed model of a cerebral aneurysm.Materials and methodsA 3D-printed model of a cerebral aneurysm was created from a patient’s angiogram. After populating the model with human endothelial cells, it was exposed to media under flow for 24 hours. Endothelial cell morphology was characterized in five regions of the 3D-printed model using confocal microscopy. Endothelial cells were then harvested from distinct regions of the 3D-printed model for mRNA collection and gene analysis via quantitative polymerase chain reaction (qPCR.) Cell morphology and mRNA measurement were correlated with computational fluid dynamics simulations.ResultsThe model was successfully populated with endothelial cells, which survived under flow for 24 hours. Endothelial morphology showed alignment with flow in the proximal and distal parent vessel and aneurysm neck, but disorganization in the aneurysm dome. Genetic analysis of endothelial mRNA expression in the aneurysm dome and distal parent vessel was compared with the proximal parent vessels. ADAMTS-1 and NOS3 were downregulated in the aneurysm dome, while GJA4 was upregulated in the distal parent vessel. Disorganized morphology and decreased ADAMTS-1 and NOS3 expression correlated with areas of substantially lower wall shear stress and wall shear stress gradient in computational fluid dynamics simulations.ConclusionsCreating 3D-printed models of patient-specific cerebral aneurysms populated with human endothelial cells is feasible. Analysis of these cells after exposure to flow demonstrates differences in both cell morphology and genetic expression, which correlate with areas of differential hemodynamic stress.

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