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.

scholarly journals Morphological and Hemodynamic Changes during Cerebral Aneurysm Growth

2021 ◽  
Vol 11 (4) ◽  
pp. 520
Author(s):  
Emily R. Nordahl ◽  
Susheil Uthamaraj ◽  
Kendall D. Dennis ◽  
Alena Sejkorová ◽  
Aleš Hejčl ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Kinetic Energy ◽  
Swirling Flow ◽  
Morphological Changes ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Aneurysm Wall ◽  
Aneurysm Growth ◽  
Computational Fluid Dynamics Cfd

Computational fluid dynamics (CFD) has grown as a tool to help understand the hemodynamic properties related to the rupture of cerebral aneurysms. Few of these studies deal specifically with aneurysm growth and most only use a single time instance within the aneurysm growth history. The present retrospective study investigated four patient-specific aneurysms, once at initial diagnosis and then at follow-up, to analyze hemodynamic and morphological changes. Aneurysm geometries were segmented via the medical image processing software Mimics. The geometries were meshed and a computational fluid dynamics (CFD) analysis was performed using ANSYS. Results showed that major geometry bulk growth occurred in areas of low wall shear stress (WSS). Wall shape remodeling near neck impingement regions occurred in areas with large gradients of WSS and oscillatory shear index. This study found that growth occurred in areas where low WSS was accompanied by high velocity gradients between the aneurysm wall and large swirling flow structures. A new finding was that all cases showed an increase in kinetic energy from the first time point to the second, and this change in kinetic energy seems correlated to the change in aneurysm volume.

Investigation on a Relationship Between Hemodynamics and Wall-Thinning in an Unruptured Human Cerebral Aneurysm

2012 ◽  
Author(s):  
Yasutaka Tobe ◽  
Takanobu Yagi ◽  
Sara Takahashi ◽  
Yuki Iwabuchi ◽  
Momoko Yamanashi ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Aneurysm ◽  
Medical Images ◽  
Cerebral Aneurysms ◽  
Flow Simulation ◽  
Patient Specific ◽  
Thin Walled Structures ◽  
Aneurysm Wall ◽  
Thin Walled ◽  
The Relationship

Recent studies of cerebral aneurysms are held using the blood flow simulation with patient-specific luminal geometries. In the study of development of cerebral aneurysms, wall shear stress (WSS) is focused as one of the key factors1–2. But the answer to the relationship between the extension of aneurysm and the theory of low WSS and high WSS still remains a question. One reason this question remains unsolved is because the current research about the cerebral aneurysms are held only using the vascular geometry developed from the medical images. From the intra-operative observation of cerebral aneurysms, the appearance of the cerebral aneurysm is not unified. Certain parts of the cerebral aneurysm have thin-walled structures where the blood flow of the aneurysm can be observed through the aneurysm wall. These differences in the wall structures cannot be predicted from the medical images. The purpose of this study is to see the relationship between hemodynamic patterns and thin-walled structure in human cerebral aneurysms.

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.

Influence of Medial Collagen Organization and Axial In Situ Stretch on Saccular Cerebral Aneurysm Growth

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Thomas Eriksson ◽  
Martin Kroon ◽  
Gerhard A. Holzapfel
Keyword(s):  
Middle Cerebral Artery ◽  
Cerebral Aneurysm ◽  
Cerebral Artery ◽  
Collagen Fibers ◽  
Circumferential Direction ◽  
Thickness Increase ◽  
Aneurysm Wall ◽  
Aneurysm Growth ◽  
The Media

A model for saccular cerebral aneurysm growth, proposed by Kroon and Holzapfel (2007, “A Model for Saccular Cerebral Aneurysm Growth in a Human Middle Cerebral Artery,” J. Theor. Biol., 247, pp. 775–787; 2008, “Modeling of Saccular Aneurysm Growth in a Human Middle Cerebral Artery,” ASME J. Biomech. Eng., 130, p. 051012), is further investigated. A human middle cerebral artery is modeled as a two-layer cylinder where the layers correspond to the media and the adventitia. The immediate loss of media in the location of the aneurysm is taken to be responsible for the initiation of the aneurysm growth. The aneurysm is regarded as a development of the adventitia, which is composed of several distinct layers of collagen fibers perfectly aligned in specified directions. The collagen fibers are the only load-bearing constituent in the aneurysm wall; their production and degradation depend on the stretch of the wall and are responsible for the aneurysm growth. The anisotropy of the surrounding media was modeled using the strain-energy function proposed by Holzapfel et al. (2000, “A New Constitutive Framework for Arterial Wall Mechanics and a Comparative Study of Material Models,” J. Elast., 61, pp. 1–48), which is valid for an elastic material with two families of fibers. It was shown that the inclusion of fibers in the media reduced the maximum principal Cauchy stress and the maximum shear stress in the aneurysm wall. The thickness increase in the aneurysm wall due to material growth was also decreased. Varying the fiber angle in the media from a circumferential direction to a deviation of 10 deg from the circumferential direction did, however, only show a little effect. Altering the axial in situ stretch of the artery had a much larger effect in terms of the steady-state shape of the aneurysm and the resulting stresses in the aneurysm wall. The peak values of the maximum principal stress and the thickness increase both became significantly higher for larger axial stretches.

scholarly journals Computational Fluid Dynamics for Cerebral Aneurysms in Clinical Settings

2021 ◽  
pp. 27-32
Author(s):  
Fujimaro Ishida ◽  
Masanori Tsuji ◽  
Satoru Tanioka ◽  
Katsuhiro Tanaka ◽  
Shinichi Yoshimura ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Clinical Settings ◽  
Geometry Model ◽  
Aneurysm Wall ◽  
3D Ct Angiography ◽  
Specific Geometry ◽  
Computational Fluid Dynamics Cfd

AbstractHemodynamics is thought to play an important role in the pathogenesis of cerebral aneurysms and recent development of computer technology makes it possible to simulate blood flow using high-resolution 3D images within several hours. A lot of studies of computational fluid dynamics (CFD) for cerebral aneurysms were reported; therefore, application of CFD for cerebral aneurysms in clinical settings is reviewed in this article.CFD for cerebral aneurysms using a patient-specific geometry model was first reported in 2003 and it has been revealing that hemodynamics brings a certain contribution to understanding aneurysm pathology, including initiation, growth and rupture. Based on the knowledge of the state-of-the-art techniques, this review treats the decision-making process for using CFD in several clinical settings. We introduce our CFD procedure using digital imaging and communication in medicine (DICOM) datasets of 3D CT angiography or 3D rotational angiography. In addition, we review rupture status, hyperplastic remodeling of aneurysm wall, and recurrence of coiled aneurysms using the hemodynamic parameters such as wall shear stress (WSS), oscillatory shear index (OSI), aneurysmal inflow rate coefficient (AIRC), and residual flow volume (RFV).

On Non-Newtonian Effects in Cerebral Aneurysms: A Computational Study on 12 Patient Specific Aneurysms

2012 ◽  
Author(s):  
Øyvind Evju ◽  
Kent-Andre Mardal ◽  
Kristian Valen-Sendstad
Keyword(s):  
Subarachnoid Hemorrhage ◽  
High Risk ◽  
Mortality Rate ◽  
Cerebral Aneurysm ◽  
Computational Study ◽  
Cerebral Aneurysms ◽  
Life Time ◽  
Patient Specific

The rupture of a cerebral aneurysm may cause subarachnoid hemorrhage (SAH), a type of stroke associated with a high risk of morbidity, and a mortality rate as high as 50% within 30 days. Cerebral aneurysms are relatively common. Roughly 6% of the population develop such during a life-time ([1]) and the average age of SAH is 51 years.

Hemodynamics of Cerebral Aneurysms: Connecting Medical Imaging and Biomechanical Analysis

2020 ◽  
Vol 22 (1) ◽  
pp. 231-256 ◽  
Author(s):  
Vitaliy L. Rayz ◽  
Aaron A. Cohen-Gadol
Keyword(s):  
Disease Progression ◽  
Cerebral Aneurysm ◽  
Clinical Decision Making ◽  
Treatment Guidelines ◽  
Flow Analysis ◽  
Cerebral Aneurysms ◽  
Biomechanical Analysis ◽  
Morphological Data ◽  
Risk Scores ◽  
Patient Specific

In the last two decades, numerous studies have conducted patient-specific computations of blood flow dynamics in cerebral aneurysms and reported correlations between various hemodynamic metrics and aneurysmal disease progression or treatment outcomes. Nevertheless, intra-aneurysmal flow analysis has not been adopted in current clinical practice, and hemodynamic factors usually are not considered in clinical decision making. This review presents the state of the art in cerebral aneurysm imaging and image-based modeling, discussing the advantages and limitations of each approach and focusing on the translational value of hemodynamic analysis. Combining imaging and modeling data obtained from different flow modalities can improve the accuracy and fidelity of resulting velocity fields and flow-derived factors that are thought to affect aneurysmal disease progression. It is expected that predictive models utilizing hemodynamic factors in combination with patient medical history and morphological data will outperform current risk scores and treatment guidelines. Possible future directions include novel approaches enabling data assimilation and multimodality analysis of cerebral aneurysm hemodynamics.

Annual rupture risk of growing unruptured cerebral aneurysms detected by magnetic resonance angiography

2012 ◽  
Vol 117 (1) ◽  
pp. 20-25 ◽  
Author(s):  
Takashi Inoue ◽  
Hiroaki Shimizu ◽  
Miki Fujimura ◽  
Atsushi Saito ◽  
Teiji Tominaga
Keyword(s):  
Magnetic Resonance Angiography ◽  
Mr Angiography ◽  
Cerebral Aneurysms ◽  
Rupture Risk ◽  
Aneurysm Wall ◽  
Short Period ◽  
Aneurysm Growth ◽  
Unruptured Cerebral Aneurysms ◽  
Aneurysm Diameter

Object In this paper, the authors' goals were to clarify the characteristics of growing unruptured cerebral aneurysms detected by serial MR angiography and to establish the recommended follow-up interval. Methods A total of 1002 patients with 1325 unruptured cerebral aneurysms were retrospectively identified. These patients had undergone follow-up evaluation at least twice. Aneurysm growth was defined as an increase in maximum aneurysm diameter by 1.5 times or the appearance of a bleb. Results Aneurysm growth was observed in 18 patients during the period of this study (1.8%/person-year). The annual rupture risk after growth was 18.5%/person-year. The proportion of females among patients with growing aneurysms was significantly larger than those without growing aneurysms (p = 0.0281). The aneurysm wall was reddish, thin, and fragile on intraoperative findings. Frequent follow-up examination is recommended to detect aneurysm growth before rupture. Conclusions Despite the relatively short period, the annual rupture risk of growing unruptured cerebral aneurysms detected by MR angiography was not as low as previously reported. Surgical or endovascular treatment can be considered if aneurysm growth is detected during the follow-up period.

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.

Hemodynamics of Elastase-Induced Aneurysms in Rabbit: A New High Flow Bifurcation Model

2011 ◽  
Author(s):  
Zijing Zeng ◽  
David F. Kallmes ◽  
Yong Hong Ding ◽  
Ramanathan Kadirvel ◽  
Debra A. Lewis ◽  
...  
Keyword(s):  
Animal Models ◽  
Pathological Condition ◽  
Cerebral Arteries ◽  
Cerebral Aneurysms ◽  
Vascular Wall ◽  
Patient Specific ◽  
Aneurysm Wall ◽  
Risk Of Rupture ◽  
The Impact

An intracranial aneurysm (IA) is a pathological condition of cerebral arteries characterized by local enlargements of the arterial wall, typically into a saccular shape. Rupture of the aneurysm sac can result in devastating cerebral hemorrhage. Hemodynamic factors are believed to play an important role in initiation, development and rupture of IAs [1–3]. However, the coupling between hemodynamics and aneurysm pathophysiology is complex and remains poorly understood. Patient specific diagnostics regarding risk of rupture can be substantially advanced by improving our understanding of the in-vivo response of the aneurysm wall to intra-saccular hemodynamic stresses. A mechanism for fundamental studies of the impact of chronically altered WSS on the intact vascular wall is provided by animal models. However, cerebral aneurysms have not been shown to occur naturally in animals. Thus, a number of animal models have been created for studying aneurysm pathogenesis including those in mice, rats, rabbits, canines, swine and primates. To make meaningful use of these models, it is important to evaluate their relevance to human biomechanics and pathophysiology.

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