Modeling the Geometry, Hemodynamics and Tissue Mechanics of Cerebral Aneurysms

2004 ◽  
Author(s):  
Baoshun Ma ◽  
Robert Harbaugh ◽  
Jia Lu ◽  
Madhavan Raghavan
Keyword(s):  
Shear Stress ◽  
Mechanical Stress ◽  
Cerebral Aneurysm ◽  
Residence Time ◽  
Cerebral Aneurysms ◽  
Lesion Size ◽  
Tissue Mechanics ◽  
Particle Residence Time ◽  
Aneurysm Wall ◽  
Geometric Size

The relationship between cerebral aneurysm geometry and biomechanics was investigated. Human cerebral aneurysm geometry was reconstructed from computed tomography angiography (CTA) and refined. Various indices of global geometric (size and shape) features were computed based on differential and computational geometry techniques. Computational fluid dynamics (CFD) simulations were performed to model both steady and pulsatile blood flow in the aneurysm and surrounding vasculature. Hemodynamic indices such as wall shear stress, pressure and particle residence time were obtained. Nonlinear finite element method (FEM) and a reported finite strain constitutive model were employed to estimate the distribution of mechanical stress in the aneurysm wall under static pressure. Shear stress, sac pressure and mechanical stress correlated better with lesion shape while particle residence time correlated better with lesion size.

A Theoretical Model for Saccular Cerebral Aneurysm Growth: Deformation and Stress Analysis

2007 ◽  
Author(s):  
Martin Kroon ◽  
Gerhard Holzapfel
Keyword(s):  
Cerebral Aneurysm ◽  
Cerebral Aneurysms ◽  
Structural Features ◽  
Constitutive Behavior ◽  
Patient Specific ◽  
Western World ◽  
Specific Information ◽  
Aneurysm Wall ◽  
Aneurysm Growth ◽  
Size Criterion

Aneurysms are abnormal dilatations of arteries, and these lesions are found almost exclusively in humans. Saccular cerebral aneurysms occur most frequently in the Circle of Willis, which is a circuit of arteries supplying the brain with blood. Aneurysms of this kind appear in a few percent of the human population in the Western world. Only a few percent of these lesions do actually rupture, but once rupture occurs the consequences are severe, often with death as outcome. Once a cerebral aneurysm is detected, clinicians need to decide whether operation is required or not. These decisions are mainly based on the size of the aneurysm, where larger aneurysms are considered to be more critical than smaller ones. This size criterion is, however, not very reliable, and criteria based on mechanical fields (stress or strain) of the aneurysm should be taken into account in the decision. This, however, requires knowledge of the constitutive behavior of the aneurysm wall, together with patient-specific information regarding geometry and boundary conditions. In order to be able to model the constitutive behavior of an aneurysm, the structural features of the aneurysm wall need to be determined. Knowledge of the etiology of the aneurysm may here provide important insights.

Effects of blood flow characteristics on rupture of cerebral aneurysm: Computational study

2021 ◽  
pp. 2150143
Author(s):  
Xiao-Yong Shen ◽  
M. Barzegar Gerdroodbary ◽  
Amin Poozesh ◽  
Amir Musa Abazari ◽  
S. Misagh Imani
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
High Risk ◽  
Wall Shear Stress ◽  
Flow Pattern ◽  
Cerebral Aneurysm ◽  
Computational Study ◽  
Fluid Dynamic ◽  
Aneurysm Wall ◽  
Wall Shear

In recent decades, cardiovascular disease and stroke are recognized as the most important reason for the high death rate. Irregular bloodstream and the circulatory system are the main reason for this issue. In this paper, Computational Fluid dynamic method is employed to study the impacts of the flow pattern inside the cerebral aneurysm for detection of the hemorrhage of the aneurysm. To achieve a reliable outcome, blood flow is considered as a non-Newtonian fluid with a power-law model. In this study, the influence of the blood viscosity and velocity on the pressure distribution and average wall shear stress (AWSS) are comprehensively studied. Moreover, the flow pattern inside the aneurysm is investigated to obtain the high-risk regions for the rupture of the aneurysm. Our results indicate that the wall shear stress (WSS) increases with increasing blood flow velocity. Furthermore, the risk of aneurysm rupture is considerably increased when the AWSS increases more than 0.6. Indeed, the blood flow with high viscosity expands the high-risk region on the wall of the aneurysm. Blood flow indicates that the angle of the incoming bloodstream is substantially effective in the high-risk region on the aneurysm wall. The augmentation of the blood velocity and vortices considerably increases the risk of hemorrhage of the aneurysm.

Colocalization of thin-walled dome regions with low hemodynamic wall shear stress in unruptured cerebral aneurysms

2013 ◽  
Vol 119 (1) ◽  
pp. 172-179 ◽  
Author(s):  
Laith M. Kadasi ◽  
Walter C. Dent ◽  
Adel M. Malek
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Wall Shear Stress ◽  
Cerebral Aneurysms ◽  
Pressure Differential ◽  
Time Dependent ◽  
Aneurysm Wall ◽  
Thin Walled ◽  
Wall Shear ◽  
Unruptured Cerebral Aneurysms

Object Wall shear stress (WSS) plays a role in regulating endothelial function and has been suspected in cerebral aneurysm rupture. The aim of this study was to evaluate the spatial relationship between localized thinning of the aneurysm dome and estimated hemodynamic factors, hypothesizing that a low WSS would correlate with aneurysm wall degeneration. Methods Steady-state computational fluid dynamics analysis was performed on 16 aneurysms in 14 patients based on rotational angiographic volumes to derive maps of WSS, its spatial gradient (WSSG), and pressure. Local dome thickness was estimated categorically based on tissue translucency from high-resolution intraoperative microscopy findings. Each computational model was oriented to match the corresponding intraoperative view and numerically sampled in thin and normal adjacent dome regions, with controls at the neck and parent vessel. The pressure differential was computed as the difference between aneurysm dome points and the mean neck pressure. Pulsatile time-dependent confirmatory analysis was carried out in 7 patients. Results Matched-pair analysis revealed significantly lower levels of WSS (0.381 Pa vs 0.816 Pa; p < 0.0001) in thin-walled dome areas than in adjacent baseline thickness regions. Similarly, log WSSG and log WSS × WSSG were both lower in thin regions (both p < 0.0001); multivariate logistic regression analysis identified lower WSS and higher pressure differential as independent correlates of lower wall thickness with an area under the curve of 0.80. This relationship was observed in both steady-state and time-dependent pulsatile analyses. Conclusions Thin-walled regions of unruptured cerebral aneurysms colocalize with low WSS, suggesting a cellular mechanotransduction link between areas of flow stasis and aneurysm wall thinning.

scholarly journals Disruption of P2X4 purinoceptor and suppression of the inflammation associated with cerebral aneurysm formation

2019 ◽  
pp. 1-13 ◽  
Author(s):  
Miyuki Fukuda ◽  
Shunichi Fukuda ◽  
Joji Ando ◽  
Kimiko Yamamoto ◽  
Naohiro Yonemoto ◽  
...  
Keyword(s):  
Shear Stress ◽  
Cerebral Aneurysm ◽  
Arterial Wall ◽  
Quantitative Polymerase Chain Reaction ◽  
Cerebral Aneurysms ◽  
Artery Ligation ◽  
Hemodynamic Stress ◽  
Aneurysm Formation ◽  
Aneurysm Development ◽  
Cox 2

OBJECTIVEThere are no effective therapeutic drugs for cerebral aneurysms, partly because the pathogenesis remains unresolved. Chronic inflammation of the cerebral arterial wall plays an important role in aneurysm formation, but it is not clear what triggers the inflammation. The authors have observed that vascular endothelial P2X4 purinoceptor is involved in flow-sensitive mechanisms that regulate vascular remodeling. They have thus hypothesized that shear stress–associated hemodynamic stress on the endothelium causes the inflammatory process in the cerebral aneurysm development.METHODSTo test their hypothesis, the authors examined the role of P2X4 in cerebral aneurysm development by using P2X4−/− mice and rats that were treated with a P2X4 inhibitor, paroxetine, and subjected to aneurysm-inducing surgery. Cerebral aneurysms were induced by unilateral carotid artery ligation and renovascular hypertension.RESULTSThe frequency of aneurysm induction evaluated by light microscopy was significantly lower in the P2X4−/− mice (p = 0.0488) and in the paroxetine-treated male (p = 0.0253) and female (p = 0.0204) rats compared to control mice and rats, respectively. In addition, application of paroxetine from 2 weeks after surgery led to a significant reduction in aneurysm size in the rats euthanized 3 weeks after aneurysm-inducing surgery (p = 0.0145), indicating that paroxetine suppressed enlargement of formed aneurysms. The mRNA and protein expression levels of known inflammatory contributors to aneurysm formation (monocyte chemoattractant protein–1 [MCP-1], interleukin-1β [IL-1β], tumor necrosis factor–α [TNFα], inducible nitric oxide synthase [iNOS], and cyclooxygenase-2 [COX-2]) were all significantly elevated in the rats that underwent the aneurysm-inducing surgery compared to the nonsurgical group, and the values in the surgical group were all significantly decreased by paroxetine administration according to quantitative polymerase chain reaction techniques and Western blotting. Although immunolabeling densities for COX-2, iNOS, and MCP-1 were not readily observed in the nonsurgical mouse groups, such densities were clearly seen in the arterial wall of P2X4+/+ mice after aneurysm-inducing surgery. In contrast, in the P2X4−/− mice after the surgery, immunolabeling of COX-2 and iNOS was not observed in the arterial wall, whereas that of MCP-1 was readily observed in the adventitia, but not the intima.CONCLUSIONSThese data suggest that P2X4 is required for the inflammation that contributes to both cerebral aneurysm formation and growth. Enhanced shear stress–associated hemodynamic stress on the vascular endothelium may trigger cerebral aneurysm development. Paroxetine may have potential for the clinical treatment of cerebral aneurysms, given that this agent exhibits efficacy as a clinical antidepressant.

Flow changes caused by the sequential placement of stents across the neck of sidewall cerebral aneurysms

2005 ◽  
Vol 103 (5) ◽  
pp. 891-902 ◽  
Author(s):  
Gádor Cantón ◽  
David I. Levy ◽  
Juan C. Lasheras ◽  
Peter K. Nelson
Keyword(s):  
Shear Stress ◽  
Velocity Field ◽  
Cerebral Aneurysms ◽  
Parent Artery ◽  
Shear Stresses ◽  
Content Type ◽  
Aneurysm Neck ◽  
Aneurysm Wall ◽  
Aneurysm Model ◽  
Fine Print

Object. The goal of this study was to quantify the reduction in velocity, vorticity, and shear stresses resulting from the sequential placement of stents across the neck of sidewall cerebral aneurysms. Methods. A digital particle image velocimetry (DPIV) system was used to measure the pulsatile velocity field within a flexible silicone sidewall intracranial aneurysm model and at the aneurysm neck–parent artery interface in this model. The DPIV system is capable of providing an instantaneous, quantitative two-dimensional measurement of the velocity vector field of “blood” flow inside the aneurysm pouch and the parent vessel, and its changes at varying stages of the cardiac cycle. The corresponding vorticity and shear stress fields are then computed from the velocity field data. Three Neuroform stents (Boston Scientific/Target), each with a strut thickness between 60 and 65 µm, were subsequently placed across the neck of the aneurysm model and measurements were obtained after each stent had been placed. The authors measured a consistent decrease in the values of the maximal averaged velocity, vorticity, and shear stress after placing one, two, and three stents. Measurements of the circulation inside the sac demonstrated a systematic reduction in the strength of the vortex due to the stent placement. The decrease in the magnitude of the aforementioned quantities after the first stent was placed was remarkable. Placement of two or three stents led to a less significant reduction than placement of the first stent. Conclusions. The use of multiple flexible intravascular stents effectively reduces the strength of the vortex forming in an aneurysm sac and results in a decrease in the magnitude of stresses acting on the aneurysm wall.

scholarly journals Expression of NF-κB, MCP-1 and MMP-9 in a Cerebral Aneurysm Rabbit Model

2014 ◽  
Vol 41 (2) ◽  
pp. 200-205 ◽  
Author(s):  
Yan fei Liu ◽  
Yongqiang Zhang ◽  
Dawei Dai ◽  
Zheng Xu
Keyword(s):  
Cerebral Aneurysm ◽  
Elastic Fiber ◽  
Rabbit Model ◽  
Smooth Muscles ◽  
Cerebral Aneurysms ◽  
Inflammatory Cells ◽  
Elastic Fibers ◽  
Control Group ◽  
Brain Aneurysm ◽  
Aneurysm Wall

Objective:We explored the early expression of NF-κB, MCP-1 and -MMP 9 in a rabbit carotid aneurysm model, and investigated the possible mechanism of aneurysm.Methods:twenty four adult new Zealand rabbits were divided into four groups. normal control (group a); rabbits received elastase induction for 1, 2 3 weeks (group b, C and d respectively); hematoxylin-eosin stains were performed for observation. the mrna and protein expression of NF-κB, MCP-1 and MMP-9 were analyzed using RT-PCR and immunohistochemical methods.Results:the expression of NF-κB and MCp-1 reached their peaks after induction for one week, then decreased. their expression in week 1 and week 2 had no statistical difference. the expression of MMP-9 increased after induction. We observed the highest expression at week 3. as the induction time increased, the number of smooth muscles reduced. endothelial cells were damaged; the aneurysm wall elastic layer was damaged.Conclusion:activation of NF-κB may be one of the initiating factors contributing to the occurrence and development of cerebral aneurysm. MCP-1 induced macrophage adhesion and infiltration in the artery wall of cerebral aneurysms, and contributed to the occurrence and development of brain aneurysm. damage to elastic fibers is one of the key factors for aneurysm formation. increased infiltration of inflammatory cells and the secretion of MMP-9 are the main reasons for elastic fiber damage.

Identification of Quantifiable Hemodynamic Factors in the Assessment of Cerebral Aneurysm Behavior On behalf of the Subcommittee on Biorheology of the Scientific and Standardization Committee of the ISTH

1996 ◽  
Vol 76 (01) ◽  
pp. 118-123 ◽  
Author(s):  
Arrmelle C Burleson ◽  
Vincent T Turitto
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cerebral Aneurysm ◽  
Flow Recirculation ◽  
Treatment Techniques ◽  
Aneurysm Wall ◽  
Wall Shear ◽  
Intravascular Treatment ◽  
Experimental And Theoretical Studies

SummaryPrevious experimental and theoretical studies on the hemodynamics of saccular intracranial aneurysms have provided evidence that aneurysms tend to grow, thrombose and rupture when (1) wall shear stress and mural tension are increased compared to normal values, and (2) flow deviates from a laminar unidirectional pattern (for example flow recirculation). Aneurysm wall shear stress, however, is the only hemodynamic factor which has received special attention in terms of estimation. Additional flow-related parameters exist which could potentially bring increased insight into mechanisms for cerebral aneurysm behavior; they could also help categorize the severity of such malformations and design effective intravascular treatment techniques. The purpose of this paper is thus to present an overview of such hemodynamic factors that could assist in determining the geometries which present the greatest risks to patients. These parameters include (1) hemodynamic shear stress, (2) pressure and related stresses, (3) impingement force on the aneurysm wall, (4) inflow rate into the aneurysm, and (5) residence time of blood within the aneurysmal sac. In addition, these factors can also be currently estimated in an in vitro setting.

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.

scholarly journals Hemodynamic and morphological characteristics of a growing cerebral aneurysm

2019 ◽  
Vol 47 (1) ◽  
pp. E13 ◽  
Author(s):  
Mahsa Dabagh ◽  
Priya Nair ◽  
John Gounley ◽  
David Frakes ◽  
L. Fernando Gonzalez ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cerebral Aneurysm ◽  
Predictive Value ◽  
Patient Specific ◽  
Growth Stages ◽  
Data Set ◽  
Recirculating Flow ◽  
Aneurysm Wall ◽  
Wall Shear

The growth of cerebral aneurysms is linked to local hemodynamic conditions, but the driving mechanisms of the growth are poorly understood. The goal of this study was to examine the association between intraaneurysmal hemodynamic features and areas of aneurysm growth, to present the key hemodynamic parameters essential for an accurate prediction of the growth, and to gain a deeper understanding of the underlying mechanisms. Patient-specific images of a growing cerebral aneurysm in 3 different growth stages acquired over a period of 40 months were segmented and reconstructed. A unique aspect of this patient-specific case study was that while one side of the aneurysm stayed stable, the other side continued to grow. This unique case enabled the authors to examine their aims in the same patient with parent and daughter arteries under the same inlet flow conditions. Pulsatile flow in the aneurysm models was simulated using computational fluid dynamics and was validated with in vitro experiments using particle image velocimetry measurements. The authors’ detailed analysis of intrasaccular hemodynamics linked the growing regions of aneurysms to flow instabilities and complex vortex structures. Extremely low velocities were observed at or around the center of the unstable vortex structure, which matched well with the growing regions of the studied cerebral aneurysm. Furthermore, the authors observed that the aneurysm wall regions with a growth greater than 0.5 mm coincided with wall regions of lower (< 0.5 Pa) time-averaged wall shear stress (TAWSS), lower instantaneous (< 0.5 Pa) wall shear stress (WSS), and high (> 0.1) oscillatory shear index (OSI). To determine which set of parameters can best identify growing and nongrowing aneurysms, the authors performed statistical analysis for consecutive stages of the growing CA. The results demonstrated that the combination of TAWSS and the distance from the center of the vortical structure has the highest sensitivity and positive predictive value, and relatively high specificity and negative predictive value. These findings suggest that an unstable, recirculating flow structure within the aneurysm sac created in the region adjacent to the aneurysm wall with low TAWSS may be introduced as an accurate criterion to explain the hemodynamic conditions predisposing the aneurysm to growth. The authors’ findings are based on one patient’s data set, but the study lays out the justification for future large-scale verification. The authors’ findings can assist clinicians in differentiating stable and growing aneurysms during preinterventional planning.

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