Intra-Aneurysmal Flow Patterns: Illustrative Comparison among Digital Subtraction Angiography, Optical Flow, and Computational Fluid Dynamics (original) (raw)
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Image-Based Computational Simulation of Flow Dynamics in a Giant Intracranial Aneurysm
2003
BACKGROUND AND PURPOSE: Blood flow dynamics are thought to play an important role in the pathogenesis and treatment of intracranial aneurysms; however, hemodynamic quantities of interest are difficult to measure in vivo. This study shows that computational fluid dynamics (CFD) combined with computed rotational angiography can provide such hemodynamic information in a patient-specific and prospective manner.
Medical Imaging 2007: Physiology, Function, and Structure from Medical Images, 2007
In this study we qualitatively compare the flow structures observed in cerebral aneurysms using conventional angiography and virtual angiograms produced from patient-specific computational fluid dynamics (CFD) models. For this purpose, high frame rate biplane angiograms were obtained during a rapid injection of contrast agent in three patients with intracranial aneurysms. Patient-specific CFD models were then constructed from 3D rotational angiography images of each aneurysm. Time dependent flow fields were obtained from the numerical solution of the incompressible Navier-Stokes equations under pulsatile flow conditions derived from phase-contrast magnetic resonance measurements performed on normal subjects. These flow fields were subsequently used to simulate the transport of a contrast agent by solving the advection-diffusion equation. Both the fluid and transport equations were solved with an implicit finite element formulation on unstructured grids. Virtual angiograms were then constructed by volume rendering of the simulated dye concentration field. The flow structures observed in the conventional and virtual angiograms were then qualitatively compared. It was found that the finite element models showed distinct flow types for each aneurysm, ranging from simple to complex. The virtual angiograms showed good agreement with the images from the conventional angiograms for all three aneurysms. Analogous size and orientation of the inflow jet, regions of flow impaction, major intraaneurysmal vortices and regions of outflow were observed in both the conventional and virtual angiograms. In conclusion, patient-specific image-based computational models of intracranial aneurysms can realistically reproduce the major intraaneurysmal flow structures observed with conventional angiography.
American Journal of Neuroradiology, 2011
BACKGROUND AND PURPOSE: Patient-specific simulations of the hemodynamics in intracranial aneurysms can be constructed by using image-based vascular models and CFD techniques. This work evaluates the impact of the choice of imaging technique on these simulations. MATERIALS AND METHODS: Ten aneurysms, imaged with 3DRA and CTA, were analyzed to assess the reproducibility of geometric and hemodynamic variables across the 2 modalities. RESULTS: Compared with 3DRA models, we found that CTA models often had larger aneurysm necks (P ϭ .05) and that most of the smallest vessels (between 0.7 and 1.0 mm in diameter) could not be reconstructed successfully with CTA. With respect to the values measured in the 3DRA models, the flow rate differed by 14.1 Ϯ 2.8% (mean Ϯ SE) just proximal to the aneurysm and 33.9 Ϯ 7.6% at the aneurysm neck. The mean WSS on the aneurysm differed by 44.2 Ϯ 6.0%. Even when normalized to the parent vessel WSS, a difference of 31.4 Ϯ 9.9% remained, with the normalized WSS in most cases being larger in the CTA model (P ϭ .04). Despite these substantial differences, excellent agreement (Ն 0.9) was found for qualitative variables that describe the flow field, such as the structure of the flow pattern and the flow complexity. CONCLUSIONS: Although relatively large differences were found for all evaluated quantitative hemodynamic variables, the main flow characteristics were reproduced across imaging modalities. ABBREVIATIONS: 3DRA ϭ 3D rotational angiography; ACA ϭ anterior cerebral artery; A N ϭ aneurysm neck area; BA ϭ basilar artery; CFD ϭ computational fluid dynamics; CTA ϭ CT angiography; ⌬ ϭ relative difference between the 3DRA and CTA models with respect to the 3DRA model; ICA ϭ internal carotid artery; LWSS A ϭ the portion of aneurysm wall under low WSS (Ͻ0.4 Pa) at end diastole; M ϭ number of cases for which the value in the CTA model was lower than in the 3DRA model; MCA ϭ middle cerebral artery; MCA M1 ϭ MCA M1 segment; MCA M1-M2 ϭ MCA M1-M2 bifurcation; MWSS A ϭ maximum WSS on the aneurysm wall at peak systole; NQ A ϭ Q A /Q P ; NWSS A ϭ WSS A /WSS P ; N90WSS A ϭ 90WSS A normalized by the mean WSS on the aneurysm at peak systole; OSI ϭ oscillatory shear index; Q A ϭ flow rate into the aneurysm; Q P ϭ flow rate in the parent vessel just proximal to the aneurysm; SE ϭ standard error; VA ϭ vertebral artery; V A ϭ aneurysm volume; 90WSS A ϭ 90th percentile value of the WSS on the aneurysm at peak systole; WSS ϭ wall shear stress; WSS A ϭ mean WSS on the aneurysm wall; WSS P ϭ mean WSS on a segment of the parent vessel just proximal to the aneurysm
2009
Hemodynamics play an important role in the pathogenesis of intracranial aneurysms and are believed to provide valuable information to predict aneurysmal rupture. Using image-based vascular models and computational fluid dynamics (CFD) techniques, the inter-aneurysmal hemodynamics can be studied in depth. In this paper, the effect of using different image-modalities is evaluated by investigating 4 middle cerebral arteries bifurcation aneurysms imaged with three-dimensional rotational angiography (3DRA) and computed tomographic angiography (CTA). The presented visualizations show that the main flow characteristics are preserved. However, there are large discrepancies in quantitative measurements.
Cardiovascular Engineering and Technology
Introduction Wall shear stress (WSS) is associated with the growth and rupture of an intracranial aneurysm. To reveal their underlying connections, many image-based computational fluid dynamics (CFD) studies have been conducted. However, the methodological validations using both in vivo medical imaging and in vitro optical flow measurements were rarely accompanied in such studies. Methods In the present study, we performed a comparative assessment on the hemodynamics of a patient-specific intracranial saccular aneurysm using in vivo 4D Flow MRI, in silico CFD, in vitro stereoscopic and tomographic particle imaging velocimetry (Stereo-PIV and Tomo-PIV) techniques. PIV experiments and CFD were conducted under steady state corresponding to the peak systole of 4D Flow MRI. Results The results showed that all modalities provided similar flow features and overall surface distribution of WSS. However, a large variation in the absolute WSS values was found. 4D Flow MRI estimated a 2- to 4-f...
Detailed knowledge of the hemodynamics in cerebral aneurysms is valuable not only for understanding their formation and rupture but also for clinical evaluation and treatment. However, important hemodynamic quantities are difficult to measure in vivo. In this paper we present a methodology for modeling patient-specific blood flows in cerebral aneurysms that combines medical image analysis and finite element methods. Intracranial aneurysms are segmented from either CTA or 3D rotational angiography images using implicit deformable models. Unstructured grids are constructed from the segmented images and computational fluid dynamics analysis are performed under realistic pulsatile flow conditions. J.R. Cebral, M. Hernández, A.F. Frangi (2003). Computational analysis of blood flow dynamics in cerebral aneurysms from CTA and 3D rotational angiography image data. In International Congress on Computational Bioengineering, M. Doblaré, M. Cerrolaza, H. Rodrigues, Zaragoza, Spain, in press.
IEEE Transactions on Medical Imaging, 2005
Hemodynamic factors are thought to be implicated in the progression and rupture of intracranial aneurysms. Current efforts aim to study the possible associations of hemodynamic characteristics such as complexity and stability of intra-aneurysmal flow patterns, size and location of the region of flow impingement with the clinical history of aneurysmal rupture. However, there are no reliable methods for measuring blood flow patterns in vivo. In this paper, an efficient methodology for patient-specific modeling and characterization of the hemodynamics in cerebral aneurysms from medical images is described. A sensitivity analysis of the hemodynamic characteristics with respect to variations of several variables over the expected physiologic range of conditions is also presented. This sensitivity analysis shows that although changes in the velocity fields can be observed, the characterization of the intra-aneurysmal flow patterns is not altered when the mean input flow, the flow division, the viscosity model, or mesh resolution are changed. It was also found that the variable that has the greater impact on the computed flow fields is the geometry of the vascular structures. We conclude that with the proposed modeling pipeline clinical studies involving large numbers cerebral aneurysms are feasible.