An intracranial aneurysm is a vascular disorder estimated to affect up to 5% of the global population. The use of flow diverting stents for treatment of intracranial aneurysms leads to ischemic complications. It is hypothesized that alteration in hemodynamics after placement of stents plays a vital role in ischemia (vessel occlusion). This project uses Computational Fluid Dynamics to study the alterations in hemodynamics before and after placement of stent with respect to the relative diameter of the bifurcating arteries on idealized geometries using ANSYS-CFX 15.0. Pressure and flow rate waveforms were extracted from a 1D model of the arterial tree to simulate hemodynamic conditions correctly. The results show that there are significant changes in hemodynamics (pressure and wall shear stress) before and after placement of stent. These changes are also affected by the relative diameters of the bifurcating arteries. The trends observed in hemodynamics can be interpreted by clinicians to study vessel occlusion and its relation to the relative diameters of arteries. The results have a potential to assist in treatment of aneurysms without ischemic complications.
Table of Contents
1 INTRODUCTION
1.1 Clinical Background/ Theory
1.2 Motivation
1.3 Hemodynamic variables
1.4 Computational Fluid Dynamics (CFD)
2 THESIS
2.1 Literature Review
2.2 Preliminary Work
2.2.1 Steady state analysis and Laminar flow
2.2.2 Geometry
2.2.3 Properties of Blood
2.2.4 Parabolic velocity profile
2.2.5 Rigid walls assumption
2.2.6 Mesh structure
2.2.7 Boundary conditions
2.3 Porosity model
2.4 Methodology
3 RESULTS
3.1 Unstented
3.1.1 Pressure
3.1.2 Wall Shear Stress
3.2 Stented
3.2.1 WSS Average 1
3.2.2 WSS Average 2
3.2.3 Pressure Inlet
3.2.4 Average Pressure 1
3.2.5 Average Pressure 2
3.3 Stented vs Unstented
3.3.1 Stent Small Artery (A2) vs Unstented
3.3.2 Stent Big Artery (A1) vs Unstented
4 Validation
4.1 Mesh independency
4.2 Wall Shear Stress
5 DISCUSSION
6 CONCLUSION
Research Objectives and Topics
The primary aim of this project is to investigate the effects of flow-diverting stents on intracranial artery bifurcations, specifically analyzing how the relative diameter of bifurcating vessels impacts hemodynamics and the potential risk of vessel occlusion. The research utilizes Computational Fluid Dynamics (CFD) to model these complex interactions and determine key variables that may assist clinicians in improving treatment outcomes and preventing ischemic complications.
- Analysis of hemodynamics in intracranial arterial bifurcations.
- Evaluation of the impact of bifurcating vessel diameter ratios on flow.
- Use of CFD and porous media modeling for stent simulation.
- Investigation of Wall Shear Stress (WSS) and pressure alterations.
- Comparison of stented versus unstented arterial geometries.
Excerpt from the Book
1.1 Clinical Background/ Theory
An intracranial aneurysm (brain aneurysm) can be defined as the weakening of the walls of an artery that causes a localised dilation or ballooning of the blood vessel (1). If an aneurysm ruptures it causes blood to leak into the spaces around the brain that can lead to various ischemic complications such as nausea, vomiting and loss of consciousness (1) . In more severe cases it can lead to death of the patient almost immediately after rupture. Hence treatment without ischemic complications is vital.
Intracranial aneurysms are commonly found around the Circle of Willis, a circulatory connection of arteries in the brain. Almost a third of the aneurysms are present around MCA bifurcations (2). Aneurysms of such topography pose most difficulties to endovascular surgeons. They often demand retreatment and present complications during and after surgery.
Flow diverting stents (FDS) offer a valid alternative in treatment of intracranial aneurysms at bifurcations, when other endovascular procedures such as coiling are not possible (3). FDS operate in a way where they divert blood flow away from the aneurysm sac which reduces growth of the aneurysm (4).
Side branch (SB) occlusion after placement of stent is a serious difficulty. The ischemic complications could lead to detrimental outcomes such as cardiac death. This effect does not seem to be dependent on the FDS model. Hence, it is hypothesized that other factors such as hemodynamics and its influence on clinically relevant effects such as alterations of pressure and wall shear stress (WSS) could be the reason for vessel occlusion. Understanding the mutual significance of all variables at play could help in treatment without ischemic complications. However, no large-scale study has investigated this issue.
Summary of Chapters
1 INTRODUCTION: This chapter introduces the clinical relevance of intracranial aneurysms and the motivation for using Computational Fluid Dynamics to study hemodynamic effects of flow-diverting stents.
2 THESIS: This section details the methodology, including literature review, geometric modeling, blood properties, and the implementation of the porosity model to simulate stents.
3 RESULTS: This chapter presents the data obtained from simulations, comparing pressure and Wall Shear Stress distributions in unstented and stented models across various diameter ratios.
4 Validation: This section confirms the accuracy of the CFD simulations by performing a mesh independency study and comparing the results against theoretical Poiseuille flow calculations.
5 DISCUSSION: This chapter interprets the findings, linking hemodynamic alterations—specifically pressure gradients and shear stress—to the risk of arterial occlusion.
6 CONCLUSION: This chapter summarizes the project's achievements, noting that stent placement significantly alters hemodynamics and highlighting the need for further patient-specific research.
Keywords
Intracranial aneurysm, Flow diverting stents, Hemodynamics, Computational Fluid Dynamics, Wall Shear Stress, Vessel occlusion, Bifurcation, Arterial geometry, Murray’s law, Pressure gradient, Endothelial cells, Porosity model, Windkessel model, Ischemic complications, CFD simulation.
Frequently Asked Questions
What is the core subject of this research?
The research examines the hemodynamic impact of placing flow-diverting stents on intracranial artery bifurcations and how vessel diameter ratios influence the risk of arterial occlusion.
What are the primary fields of study?
The study integrates biomechanics, fluid dynamics, and clinical neurology to understand the vascular behavior and treatment risks associated with brain aneurysms.
What is the central research question?
The project asks how the placement of flow-diverting stents and the relative diameters of bifurcating vessels alter pressure and shear stress, and whether these changes contribute to vessel occlusion.
Which scientific method is utilized in this work?
The researcher uses Computational Fluid Dynamics (CFD), specifically ANSYS-CFX 15.0, to model fluid behavior, using a porous medium to represent the stent structure.
What does the main body cover?
The main body covers the theoretical background, the setup of idealized arterial geometries, mesh generation, boundary conditions, and a comparative result analysis between stented and unstented models.
Which keywords define the research?
Key terms include Hemodynamics, Intracranial Aneurysms, Flow Diverting Stents, CFD, Wall Shear Stress, and Bifurcation mechanics.
How does the Windkessel model assist in the study?
The Windkessel model is used to simulate the peripheral resistance of the arterial system at the outlets, allowing for a realistic distribution of flow and pressure across the bifurcating vessels.
Why are endothelial cells relevant to these results?
Endothelial cells are highly sensitive to Wall Shear Stress (WSS); the study speculates that altered WSS after stenting can trigger destructive remodeling, which may lead to vessel occlusion.
How does Murray's law relate to the experiment?
Murray's law provides the theoretical basis for selecting the range of bifurcating artery diameters used in the simulations to ensure the modeled geometries are physiologically relevant.
- Quote paper
- Sarthak Khandelwal (Author), 2015, Effect of flow diverting stents on intracranial artery bifurcations with a focus on bifurcating vessels diameter on hemodynamics and occlusion, Munich, GRIN Verlag, https://www.grin.com/document/311665
