Hemodynamic characteristics at anterior communicating artery before aneurysm initiation using patient-specific finite element blood flow simulations

The anterior communicating artery (AComA) is a unique vascular location that receives blood from two sources of inflow and redistributes it toward the anterior part of the brain through two efferent arteries. It is widely accepted that complexity in the flow pattern is associated with the high rate of aneurysm formation in that location observed in large studies. A previous computational hemodynamic study showed a possible association between high maximum intraaneurysmal wall shear stress (WSS) at the systolic peak with rupture in a cohort of AComA aneurysms. In another study it was observed a connection between location of aneurysm blebs and regions of high WSS in models where blebs were virtually removed. The purpose of this work is to study associations between hemodynamic patterns and AComA aneurysm initiation by comparing hemodynamics between the aneurysm models and the normal model where the aneurysm was computationally removed. Vascular models of both right and left circulation were independently reconstructed from three-dimensional rotational angiography images using deformable models after image registration of both images, and later fused using a surface merging algorithm. Afterwards, the geometric models were used to generate high-quality volumetric finite element grids composed several million tetrahedral elements with an advancing front technique. For each patient the second anatomical model was created by digitally removing the aneurysm. It was iteratively achieved by applying a Laplacian smoothing filter and remeshing the surface. Finite element blood flow numerical simulations were performed for both the pathological and normal models under the same flow conditions. Personalized pulsatile flow conditions were imposed at the inlets of both models with use of the Womersley solution. The Navier-Stokes equations were numerically integrated by using a fully implicit finite-element formulation. From analysis of WSS distributions it was observed that aneurysms initiated in regions of high and moderate WSS in the counterpart normal models. Adjacent or close to those regions, low WSS portions of the arterial wall were not affected by the disease. These results are in line with previous reported observations at other vascular locations.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. George Mason University; Estados UnidosFil: Putman, Christopher M.. Inova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Hemodynamic characteristics at anterior communicating artery before aneurysm initiation using patient-specific finite element blood flow simulations

The anterior communicating artery (AComA) is a unique vascular location that receives blood from two sources of inflow and redistributes it toward the anterior part of the brain through two efferent arteries. It is widely accepted that complexity in the flow pattern is associated with the high rate of aneurysm formation in that location observed in large studies. A previous computational hemodynamic study showed a possible association between high maximum intraaneurysmal wall shear stress (WSS) at the systolic peak with rupture in a cohort of AComA aneurysms. In another study it was observed a connection between location of aneurysm blebs and regions of high WSS in models where blebs were virtually removed. The purpose of this work is to study associations between hemodynamic patterns and AComA aneurysm initiation by comparing hemodynamics between the aneurysm models and the normal model where the aneurysm was computationally removed. Vascular models of both right and left circulation were independently reconstructed from three-dimensional rotational angiography images using deformable models after image registration of both images, and later fused using a surface merging algorithm. Afterwards, the geometric models were used to generate high-quality volumetric finite element grids composed several million tetrahedral elements with an advancing front technique. For each patient the second anatomical model was created by digitally removing the aneurysm. It was iteratively achieved by applying a Laplacian smoothing filter and remeshing the surface. Finite element blood flow numerical simulations were performed for both the pathological and normal models under the same flow conditions. Personalized pulsatile flow conditions were imposed at the inlets of both models with use of the Womersley solution. The Navier-Stokes equations were numerically integrated by using a fully implicit finite-element formulation. From analysis of WSS distributions it was observed that aneurysms initiated in regions of high and moderate WSS in the counterpart normal models. Adjacent or close to those regions, low WSS portions of the arterial wall were not affected by the disease. These results are in line with previous reported observations at other vascular locations.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. George Mason University; Estados UnidosFil: Putman, Christopher M.. Inova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Effects of Casson rheology on aneurysm wall shear stress

It is widely accepted that wall shear stress plays an important role in cerebral aneurysm initiation, progress and rupture. Previous works have shown strong evidence in support of the high wall shear stress as a risk factor associated to those biomechanical processes. Patient-specific imagebased computational hemodynamic modeling of vascular systems harboring cerebral aneurysms has demonstrated to be a fast and reliable way to compute quantities difficult or impossible to be measured in-vivo. The accuracy of the simulation results have been successfully validated in the past. Additionally, most model assumptions have shown no impact on the flow characterization whose association with the mentioned processes was investigated. Particularly, the incorporation of the blood rheology in large arterial systems containing aneurysms resulted in similar hemodynamic characterizations for most aneurysms. However, large aneurysms, especially those containing blebs are expected to have flow rates in the range where Newtonian and non-Newtonian models exhibit the largest differences. In order to study the impact of blood rheology in vascular systems harboring specific intracranial aneurysms, unsteady finite element blood flow simulations were carried out over patient-specific models. Those models were reconstructed from rotational angiographic images using region growing and deformable model algorithms. Unstructured finite element meshes were generated using and advancing front technique. Walls were assumed as rigid, traction-free boundary conditions were imposed at the outlets of the models, and a flow rate wave form was imposed at the inlets after scaling according to the Murray's Law for optimal arterial networks. The Casson model was incorporated as a velocity gradient dependent apparent viscosity and the results were compared to those using the Newtonian rheology. Regions with differentiated wall shear stress values and orientations were studied.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Secretaria de Ciencia y Técnica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Maria Carolina. Universidad Favaloro. Facultad de Ingeniería y Ciencias Exactas y Naturales; ArgentinaFil: Putman, Christopher M.. Innova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Effects of Casson rheology on aneurysm wall shear stress

It is widely accepted that wall shear stress plays an important role in cerebral aneurysm initiation, progress and rupture. Previous works have shown strong evidence in support of the high wall shear stress as a risk factor associated to those biomechanical processes. Patient-specific imagebased computational hemodynamic modeling of vascular systems harboring cerebral aneurysms has demonstrated to be a fast and reliable way to compute quantities difficult or impossible to be measured in-vivo. The accuracy of the simulation results have been successfully validated in the past. Additionally, most model assumptions have shown no impact on the flow characterization whose association with the mentioned processes was investigated. Particularly, the incorporation of the blood rheology in large arterial systems containing aneurysms resulted in similar hemodynamic characterizations for most aneurysms. However, large aneurysms, especially those containing blebs are expected to have flow rates in the range where Newtonian and non-Newtonian models exhibit the largest differences. In order to study the impact of blood rheology in vascular systems harboring specific intracranial aneurysms, unsteady finite element blood flow simulations were carried out over patient-specific models. Those models were reconstructed from rotational angiographic images using region growing and deformable model algorithms. Unstructured finite element meshes were generated using and advancing front technique. Walls were assumed as rigid, traction-free boundary conditions were imposed at the outlets of the models, and a flow rate wave form was imposed at the inlets after scaling according to the Murray's Law for optimal arterial networks. The Casson model was incorporated as a velocity gradient dependent apparent viscosity and the results were compared to those using the Newtonian rheology. Regions with differentiated wall shear stress values and orientations were studied.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Secretaria de Ciencia y Técnica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Maria Carolina. Universidad Favaloro. Facultad de Ingeniería y Ciencias Exactas y Naturales; ArgentinaFil: Putman, Christopher M.. Innova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Changes in cerebral aneurysm hemodynamics after virtual endarterectomy

Cerebral aneurysm hemodynamics depends on flow conditions at and geometry of parents vessels. Wall shear stress distributions and extreme values are widely accepted to be responsible for aneurysm initiation, growth and rupture. Those aneurysms may coexist with a proximal artery stenosis in a small number of patients. In those cases, that poses a challenge for interventional neuroradiologists and neurosurgeons to make the best treatment decision. For low and mild stenoses, flow alterations in the aneurysm sacs are limited when the aneurysms is located far downstream in the same circulation. However, for distal aneurysms close to the stenosis, intra-aneurysmal hemodynamics may be significantly affected by the stenosis. In this work we studied the changes in the wall shear stress distributions after virtual intervention in both ideal and patient-specific models. Three-dimensional rotational angiographic images were segmented using region growing and deformable model algorithms. Isosurface of the boundary was used to generate a volumetric mesh of tetrahedra in the domain using an advancing front technique. Numerical integration of the Navier-Stoke's equations was performed using a time dependent finite element formulation. Personalized inflow wave forms were imposed at the inlets and hemodynamic forces were studied at the systolic peak. Wall shear stress difference between and after virtual intervention were computed for different stenosis grades and different aneurysm locations.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires. Secretaria de Ciencia y Técnica; Argentina. George Mason University; Estados UnidosFil: Peloc, Nora Luz. Universidad Favaloro. Facultad de Ingeniería y Ciencias Exactas y Naturales; ArgentinaFil: Putman, Christopher M.. Innova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Effects of Stenotic Plaques in Realistic Carotid Artery Aneurysm Models: a CFD Study

Cerebral aneurysms may rarely coexist with a proximal artery stenosis. In that small percent of patients, such coexistence poses a challenge for interventional neuroradiologists and neurosurgeons to make the best treatment decision. According to previous studies, the incidence of cerebral aneurysms in patients with internal carotid artery stenosis is not greater than 5%, where the aneurysm is usually incidentally detected, being 2% for aneurysms and stenoses in the same cerebral circulation. Those cases pose a difficult management decision for the physician. Case reports showed patients who died due to aneurysm rupture months after endarterectomy but before aneurysm clipping, while others did not show any change in the aneurysm after plaque removal, having optimum outcome after aneurysm coiling. The aim of this study is to investigate the intraaneurysmal hemodynamic changes before and after treatment of stenotic plaque. Virtually created moderate stenoses in vascular models of internal carotid artery aneurysm patients were considered in a number of cases reconstructed from three dimensional rotational angiography images. The strategy to create those plaques was based on parameters analyzed in a previous work where idealized models were considered, including relative distance and stenosis grade. Ipsilateral and contralateral plaques were modeled. Wall shear stress and velocity pattern were computed from finite element pulsatile blood flow simulations. The results may suggest that relative angular position may change the wall shear stress within the aneurysm sac.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. George Mason University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Peloc, Nora Luz. Universidad Favaloro; ArgentinaFil: Putman, Christopher M.. Inova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido