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Sasaki K, Komatsu F, Miyatani K, Tanaka R, Yamada Y, Kato Y, Hirose Y. Predicting Morphological Changes to Vessel Walls Adjacent to Unruptured Cerebral Aneurysms Using Computational Fluid Dynamics. Asian J Neurosurg 2023; 18:764-768. [PMID: 38161604 PMCID: PMC10756830 DOI: 10.1055/s-0043-1771367] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024] Open
Abstract
Objective This study compared intraoperative findings with preoperative computed tomography angiography (CTA) and computational fluid dynamics (CFD) analysis of perianeurysmal findings for the indication of possible vessel wall thinning. Materials and Methods Participants comprised 38 patients with unruptured middle cerebral artery aneurysms treated by surgical clipping at our hospital between May 2020 and April 2021. We defined parent artery radiation sign (PARS) as the presence of each of the following three findings in CFD analysis based on preoperative CTA: (1) impingement of the stream line on the outer parent vessel wall of the aneurysm; (2) radiation of wall shear stress vectors outwards from the same site; and (3) increased wall pressure compared with the surrounding area. CFD analysis showing PARS was compared with intraoperative findings. Results In all nine cases with PARS, no morphological abnormalities were found in the same area on CTA. However, intraoperative findings showed thinning of the parent artery wall in one of the nine cases and formation of a very small mass in three cases, differing from CTA findings. All nine patients underwent additional clipping and/or wrapping and coating at the site of PARS. Conclusion Detecting thinning of the vessel wall or the presence of a microaneurysm may be difficult in endovascular therapy, which is based on the visualization of the vessel lumen. CFD analysis suggests the necessity of confirming findings for the vessel wall around an aneurysm by direct manipulation, as the presence of PARS may indicate partial thinning of the vessel wall or formation of a microaneurysm.
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Affiliation(s)
- Kento Sasaki
- Department of Neurosurgery, Fujita Health University, Bantane Hospital, Nagoya, Aichi, Japan
| | - Fuminari Komatsu
- Department of Neurosurgery, Fujita Health University, Bantane Hospital, Nagoya, Aichi, Japan
| | - Kyosuke Miyatani
- Department of Neurosurgery, Fujita Health University, Bantane Hospital, Nagoya, Aichi, Japan
| | - Riki Tanaka
- Department of Neurosurgery, Fujita Health University, Bantane Hospital, Nagoya, Aichi, Japan
| | - Yasuhiro Yamada
- Department of Neurosurgery, Fujita Health University, Bantane Hospital, Nagoya, Aichi, Japan
| | - Yoko Kato
- Department of Neurosurgery, Fujita Health University, Bantane Hospital, Nagoya, Aichi, Japan
| | - Yuichi Hirose
- Department of Neurosurgery, Fujita Health University, Toyoake, Aichi, Japan
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Sunderland K, Jiang J, Zhao F. Disturbed flow's impact on cellular changes indicative of vascular aneurysm initiation, expansion, and rupture: A pathological and methodological review. J Cell Physiol 2022; 237:278-300. [PMID: 34486114 PMCID: PMC8810685 DOI: 10.1002/jcp.30569] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 08/06/2021] [Accepted: 08/16/2021] [Indexed: 01/03/2023]
Abstract
Aneurysms are malformations within the arterial vasculature brought on by the structural breakdown of the microarchitecture of the vessel wall, with aneurysms posing serious health risks in the event of their rupture. Blood flow within vessels is generally laminar with high, unidirectional wall shear stressors that modulate vascular endothelial cell functionality and regulate vascular smooth muscle cells. However, altered vascular geometry induced by bifurcations, significant curvature, stenosis, or clinical interventions can alter the flow, generating low stressor disturbed flow patterns. Disturbed flow is associated with altered cellular morphology, upregulated expression of proteins modulating inflammation, decreased regulation of vascular permeability, degraded extracellular matrix, and heightened cellular apoptosis. The understanding of the effects disturbed flow has on the cellular cascades which initiate aneurysms and promote their subsequent growth can further elucidate the nature of this complex pathology. This review summarizes the current knowledge about the disturbed flow and its relation to aneurysm pathology, the methods used to investigate these relations, as well as how such knowledge has impacted clinical treatment methodologies. This information can contribute to the understanding of the development, growth, and rupture of aneurysms and help develop novel research and aneurysmal treatment techniques.
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Affiliation(s)
- Kevin Sunderland
- Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931
| | - Jingfeng Jiang
- Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931,Corresponding Authors: Feng Zhao, 101 Bizzell Street, College Station, TX 77843-312, Tel : 979-458-1239, , Jingfeng Jiang, 1400 Townsend Dr., Houghton, MI 49931, Tel: 906-487-1943
| | - Feng Zhao
- Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843,Corresponding Authors: Feng Zhao, 101 Bizzell Street, College Station, TX 77843-312, Tel : 979-458-1239, , Jingfeng Jiang, 1400 Townsend Dr., Houghton, MI 49931, Tel: 906-487-1943
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Wang H, Balzani D, Vedula V, Uhlmann K, Varnik F. On the Potential Self-Amplification of Aneurysms Due to Tissue Degradation and Blood Flow Revealed From FSI Simulations. Front Physiol 2021; 12:785780. [PMID: 34955893 PMCID: PMC8709128 DOI: 10.3389/fphys.2021.785780] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 11/09/2021] [Indexed: 11/13/2022] Open
Abstract
Tissue degradation plays a crucial role in the formation and rupture of aneurysms. Using numerical computer simulations, we study the combined effects of blood flow and tissue degradation on intra-aneurysm hemodynamics. Our computational analysis reveals that the degradation-induced changes of the time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) within the aneurysm dome are inversely correlated. Importantly, their correlation is enhanced in the process of tissue degradation. Regions with a low TAWSS and a high OSI experience still lower TAWSS and higher OSI during degradation. Furthermore, we observed that degradation leads to an increase of the endothelial cell activation potential index, in particular, at places experiencing low wall shear stress. These findings are robust and occur for different geometries, degradation intensities, heart rates and pressures. We interpret these findings in the context of recent literature and argue that the degradation-induced hemodynamic changes may lead to a self-amplification of the flow-induced progressive damage of the aneurysmal wall.
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Affiliation(s)
- Haifeng Wang
- Theory and Simulation of Complex Fluids, Department of Scale-Bridging Thermodynamic and Kinetic Simulation, Interdisciplinary Center for Advanced Materials Simulation (ICAMS), Ruhr-Universität Bochum, Bochum, Germany
| | - Daniel Balzani
- Department of Civil and Environmental Engineering, Chair of Continuum Mechanics, Ruhr-Universität Bochum, Bochum, Germany
| | - Vijay Vedula
- Department of Mechanical Engineering, Columbia University in the City of New York, New York, NY, United States
| | - Klemens Uhlmann
- Department of Civil and Environmental Engineering, Chair of Continuum Mechanics, Ruhr-Universität Bochum, Bochum, Germany
| | - Fathollah Varnik
- Theory and Simulation of Complex Fluids, Department of Scale-Bridging Thermodynamic and Kinetic Simulation, Interdisciplinary Center for Advanced Materials Simulation (ICAMS), Ruhr-Universität Bochum, Bochum, Germany
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4
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Futami K, Misaki K, Uno T, Nambu I, Kamide T, Nakada M. Morphological factors affecting vortex core instability on 4D flow MRI of unruptured cerebral aneurysms. Neurol Res 2021; 44:455-462. [PMID: 34791984 DOI: 10.1080/01616412.2021.2004365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
OBJECTIVE The spatiotemporal instability of intra-aneurysmal vortex flow may be associated with unruptured cerebral aneurysm rupture. We identified morphological factors that affect intra-aneurysmal vortex core patterns classified based on the instability on four-dimensional (4D) flow magnetic resonance imaging (MRI) and determined cutoff values for the factors to discriminate unstable core patterns. METHODS We classified vortex core patterns of 40 unruptured aneurysms on 4D flow MRI into stable, stable with a flapping tip, continuously deforming wave-or-coil-like, and non-visualized. We statistically compared nine morphological parameters among aneurysm groups with individual patterns. RESULTS The vortex cores were stable (n = 16) (group A), stable with a flapping tip (n = 15) (group B), wave-or-coil-like (n = 7) (group C), and non-visualized (n = 2) (group D). Since there were no statistically significant differences between groups A and B, we compared the difference between the groups A and B and the other groups. Multivariate logistic regression analyses found that size ratio (SR) was an only independently significant parameter (p < 0.05). The receiver-operating characteristic analysis between groups A and B and group C and between groups A and B and groups C and D revealed that the area under the curve value for SR was the highest (0.829 [95% CI, 0.642-1.0]; 0.867 [95% CI, 0.715-1.0], respectively) among morphological factors; the cutoff value for SR was 1.72 (specificity 0.714, sensitivity 0.756; specificity 0.806, sensitivity 0.778, respectively). CONCLUSION SR was an independent morphological factor contributing to vortex core instability based on the vortex core patterns on 4D flow MRI.Abbreviations: CFD: computational fluid dynamics; 3D: three-dimensional; 4D: four-dimensional; MRI: magnetic resonance imaging; MRA: magnetic resonance angiography; ICA: internal carotid artery; AR: aspect ratio; SR: size ratio; CI: confidence interval; AUC: area under the curve; ROC: receiver-operating characteristic.
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Affiliation(s)
- Kazuya Futami
- Department of Neurosurgery, Hokuriku Central Hospital of Japan Mutual Aid Association of Public School Teachers, Oyabe, Japan
| | - Kouichi Misaki
- Department of Neurosurgery, Kanazawa University School of Medicine, Kanazawa, Japan
| | - Takehiro Uno
- Department of Neurosurgery, Kanazawa University School of Medicine, Kanazawa, Japan
| | - Iku Nambu
- Department of Neurosurgery, Kanazawa University School of Medicine, Kanazawa, Japan
| | - Tomoya Kamide
- Department of Neurosurgery, Kanazawa University School of Medicine, Kanazawa, Japan
| | - Mitsutoshi Nakada
- Department of Neurosurgery, Kanazawa University School of Medicine, Kanazawa, Japan
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Khan MO, Toro Arana V, Najafi M, MacDonald DE, Natarajan T, Valen-Sendstad K, Steinman DA. On the prevalence of flow instabilities from high-fidelity computational fluid dynamics of intracranial bifurcation aneurysms. J Biomech 2021; 127:110683. [PMID: 34454331 DOI: 10.1016/j.jbiomech.2021.110683] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Revised: 07/31/2021] [Accepted: 08/09/2021] [Indexed: 11/27/2022]
Abstract
High-fidelity computational fluid dynamics (HF-CFD) has revealed the potential for high-frequency flow instabilities (aka "turbulent-like" flow) in intracranial aneurysms, consistent with classic in vivo and in vitro reports of bruits and/or wall vibrations. However, HF-CFD has typically been performed on limited numbers of cases, often with unphysiological inflow conditions or focused on sidewall-type aneurysms where flow instabilities may be inherently less prevalent. Here we report HF-CFD of 50 bifurcation aneurysm cases from the open-source Aneurisk model repository. These were meshed using quadratic finite elements having an average effective spatial resolution of 0.065 mm, and solved under physiologically-pulsatile flow conditions using a well-validated, minimally-dissipative solver with 20,000 time-steps per cardiac cycle Flow instability was quantified using the recently introduced spectral power index (SPI), which quantifies, from 0 to 1, the power associated with velocity fluctuations above those of the driving inflow waveform. Of the 50 cases, nearly half showed regions within the sac having SPI up to 0.5, often with non-negligible power into the 100's of Hz, and roughly 1/3 had sac-averaged SPI > 0.1. High SPI did not significantly predict rupture status in this cohort. Proper orthogonal decomposition of cases with highest SPIavg revealed time-varying energetics consistent with transient turbulence. Our reported prevalence of high-frequency flow instabilities in HF-CFD modelling of aneurysms suggests that care must be taken to avoid routinely overlooking them if we are to understand the highly dynamic mechanical forces to which some aneurysm walls may be exposed, and their prevalence in vivo.
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Affiliation(s)
- M O Khan
- Cardiovascular Imaging, Modelling and Biomechanics Lab, Department of Electrical, Computer and Biomedical Engineering, Ryerson University, Ontario, Canada.
| | - V Toro Arana
- Stanford University School of Medicine, Stanford, CA, USA
| | - M Najafi
- Biomedical Simulation Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
| | - D E MacDonald
- Biomedical Simulation Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
| | - T Natarajan
- Biomedical Simulation Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, Canada; Simula Research Laboratory, Lysaker Norway
| | | | - D A Steinman
- Biomedical Simulation Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
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Mahrous SA, Sidik NAC, Saqr KM. Numerical study on the energy cascade of pulsatile Newtonian and power-law flow models in an ICA bifurcation. PLoS One 2021; 16:e0245775. [PMID: 33493237 PMCID: PMC7833255 DOI: 10.1371/journal.pone.0245775] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Accepted: 01/07/2021] [Indexed: 11/18/2022] Open
Abstract
The complex physics and biology underlying intracranial hemodynamics are yet to be fully revealed. A fully resolved direct numerical simulation (DNS) study has been performed to identify the intrinsic flow dynamics in an idealized carotid bifurcation model. To shed the light on the significance of considering blood shear-thinning properties, the power-law model is compared to the commonly used Newtonian viscosity hypothesis. We scrutinize the kinetic energy cascade (KEC) rates in the Fourier domain and the vortex structure of both fluid models and examine the impact of the power-law viscosity model. The flow intrinsically contains coherent structures which has frequencies corresponding to the boundary frequency, which could be associated with the regulation of endothelial cells. From the proposed comparative study, it is found that KEC rates and the vortex-identification are significantly influenced by the shear-thinning blood properties. Conclusively, from the obtained results, it is found that neglecting the non-Newtonian behavior could lead to underestimation of the hemodynamic parameters at low Reynolds number and overestimation of the hemodynamic parameters by increasing the Reynolds number. In addition, we provide physical insight and discussion onto the hemodynamics associated with endothelial dysfunction which plays significant role in the pathogenesis of intracranial aneurysms.
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Affiliation(s)
- Samar A. Mahrous
- Department of Thermo-Fluid Universiti Teknologi Malaysia, Skudai, Malaysia
- College of Engineering and Technology, Arab Academy for Science, Technology and Maritime Transport, Alexandria, Egypt
- * E-mail:
| | - Nor Azwadi Che Sidik
- Department of Thermo-Fluid Universiti Teknologi Malaysia, Skudai, Malaysia
- Malaysia–Japan International Institute of Technology (MJIIT), University Teknologi Malaysia Kuala Lumpur, Kuala Lumpur, Malaysia
| | - Khalid M. Saqr
- College of Engineering and Technology, Arab Academy for Science, Technology and Maritime Transport, Alexandria, Egypt
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7
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Saqr KM, Rashad S, Tupin S, Niizuma K, Hassan T, Tominaga T, Ohta M. What does computational fluid dynamics tell us about intracranial aneurysms? A meta-analysis and critical review. J Cereb Blood Flow Metab 2020; 40:1021-1039. [PMID: 31213162 PMCID: PMC7181089 DOI: 10.1177/0271678x19854640] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Despite the plethora of published studies on intracranial aneurysms (IAs) hemodynamic using computational fluid dynamics (CFD), limited progress has been made towards understanding the complex physics and biology underlying IA pathophysiology. Guided by 1733 published papers, we review and discuss the contemporary IA hemodynamics paradigm established through two decades of IA CFD simulations. We have traced the historical origins of simplified CFD models which impede the progress of comprehending IA pathology. We also delve into the debate concerning the Newtonian fluid assumption used to represent blood flow computationally. We evidently demonstrate that the Newtonian assumption, used in almost 90% of studies, might be insufficient to describe IA hemodynamics. In addition, some fundamental properties of the Navier-Stokes equation are revisited in supplementary material to highlight some widely spread misconceptions regarding wall shear stress (WSS) and its derivatives. Conclusively, our study draws a roadmap for next-generation IA CFD models to help researchers investigate the pathophysiology of IAs.
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Affiliation(s)
- Khalid M Saqr
- Biomedical Flow Dynamics Laboratory, Institute of Fluid Science, Tohoku University, Sendai, Miyagi, Japan.,Department of Mechanical Engineering, College of Engineering and Technology, Arab Academy for Science, Technology and Maritime Transport, Alexandria, Egypt
| | - Sherif Rashad
- Department of Neurosurgical Engineering and Translational Neuroscience, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.,Department of Neurosurgery, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
| | - Simon Tupin
- Biomedical Flow Dynamics Laboratory, Institute of Fluid Science, Tohoku University, Sendai, Miyagi, Japan
| | - Kuniyasu Niizuma
- Department of Neurosurgical Engineering and Translational Neuroscience, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.,Department of Neurosurgery, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.,Department of Neurosurgical Engineering and Translational Neuroscience, Graduate School of Biomedical Engineering, Tohoku University, Sendai, Japan
| | - Tamer Hassan
- Department of Neurosurgery, Alexandria University School of Medicine, Azarita Medical Campus, Alexandria, Egypt
| | - Teiji Tominaga
- Department of Neurosurgery, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
| | - Makoto Ohta
- Biomedical Flow Dynamics Laboratory, Institute of Fluid Science, Tohoku University, Sendai, Miyagi, Japan
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Real-World Variability in the Prediction of Intracranial Aneurysm Wall Shear Stress: The 2015 International Aneurysm CFD Challenge. Cardiovasc Eng Technol 2018; 9:544-564. [PMID: 30203115 PMCID: PMC6290689 DOI: 10.1007/s13239-018-00374-2] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2018] [Accepted: 08/11/2018] [Indexed: 11/04/2022]
Abstract
Purpose Image-based computational fluid dynamics (CFD) is widely used to predict intracranial aneurysm wall shear stress (WSS), particularly with the goal of improving rupture risk assessment. Nevertheless, concern has been expressed over the variability of predicted WSS and inconsistent associations with rupture. Previous challenges, and studies from individual groups, have focused on individual aspects of the image-based CFD pipeline. The aim of this Challenge was to quantify the total variability of the whole pipeline. Methods 3D rotational angiography image volumes of five middle cerebral artery aneurysms were provided to participants, who were free to choose their segmentation methods, boundary conditions, and CFD solver and settings. Participants were asked to fill out a questionnaire about their solution strategies and experience with aneurysm CFD, and provide surface distributions of WSS magnitude, from which we objectively derived a variety of hemodynamic parameters. Results A total of 28 datasets were submitted, from 26 teams with varying levels of self-assessed experience. Wide variability of segmentations, CFD model extents, and inflow rates resulted in interquartile ranges of sac average WSS up to 56%, which reduced to < 30% after normalizing by parent artery WSS. Sac-maximum WSS and low shear area were more variable, while rank-ordering of cases by low or high shear showed only modest consensus among teams. Experience was not a significant predictor of variability. Conclusions Wide variability exists in the prediction of intracranial aneurysm WSS. While segmentation and CFD solver techniques may be difficult to standardize across groups, our findings suggest that some of the variability in image-based CFD could be reduced by establishing guidelines for model extents, inflow rates, and blood properties, and by encouraging the reporting of normalized hemodynamic parameters.
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Xu L, Liang F, Gu L, Liu H. Flow instability detected in ruptured versus unruptured cerebral aneurysms at the internal carotid artery. J Biomech 2018; 72:187-199. [PMID: 29602477 DOI: 10.1016/j.jbiomech.2018.03.014] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 03/03/2018] [Accepted: 03/06/2018] [Indexed: 11/30/2022]
Abstract
Flow instability has emerged as a new hemodynamic metric hypothesized to have potential value in assessing the rupture risk of cerebral aneurysms. However, diverse findings have been reported in the literature. In the present study, high-resolution hemodynamic simulations were performed retrospectively on 35 aneurysms (10 ruptured & 25 unruptured) located at the internal carotid artery (ICA). Simulated hemodynamic parameters were statistically compared between the ruptured and unruptured aneurysms, with emphasis on examining the correlation of flow instability with the status of aneurysm rupture. Pronounced flow instability was detected in 20% (2 out of 10) of the ruptured aneurysms, whereas in 44% (11 out of 25) of the unruptured aneurysms. Statistically, the flow instability metric (quantified by the temporally and spatially averaged fluctuating kinetic energy over the aneurysm sac) did not differ significantly between the ruptured and unruptured aneurysms. In contrast, low wall shear stress area (LSA) and pressure loss coefficient (PLC) exhibited significant correlations with the status of aneurysm rupture. In conclusion, the present study suggests that the presence of flow instability may not correlate closely with the status of aneurysm rupture, at least for ICA aneurysms. On the other hand, the retrospective nature of the study and the small sample size may have to some extent compromised the reliability of the conclusion, and therefore large-scale prospective studies would be needed to further address the issue.
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Affiliation(s)
- Lijian Xu
- School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Shanghai Jiao Tong University and Chiba University International Cooperative Research Centre (SJTU-CU ICRC), Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Fuyou Liang
- School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Shanghai Jiao Tong University and Chiba University International Cooperative Research Centre (SJTU-CU ICRC), Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
| | - Lixu Gu
- Shanghai Jiao Tong University and Chiba University International Cooperative Research Centre (SJTU-CU ICRC), Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Hao Liu
- School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Shanghai Jiao Tong University and Chiba University International Cooperative Research Centre (SJTU-CU ICRC), Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi, Chiba 2638522, Japan.
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Hemodynamics in a giant intracranial aneurysm characterized by in vitro 4D flow MRI. PLoS One 2018; 13:e0188323. [PMID: 29300738 PMCID: PMC5754057 DOI: 10.1371/journal.pone.0188323] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Accepted: 11/03/2017] [Indexed: 11/19/2022] Open
Abstract
Experimental and computational data suggest that hemodynamics play a critical role in the development, growth, and rupture of cerebral aneurysms. The flow structure, especially in aneurysms with a large sac, is highly complex and three-dimensional. Therefore, volumetric and time-resolved measurements of the flow properties are crucial to fully characterize the hemodynamics. In this study, phase-contrast Magnetic Resonance Imaging is used to assess the fluid dynamics inside a 3D-printed replica of a giant intracranial aneurysm, whose hemodynamics was previously simulated by multiple research groups. The physiological inflow waveform is imposed in a flow circuit with realistic cardiovascular impedance. Measurements are acquired with sub-millimeter spatial resolution for 16 time steps over a cardiac cycle, allowing for the detailed reconstruction of the flow evolution. Moreover, the three-dimensional and time-resolved pressure distribution is calculated from the velocity field by integrating the fluid dynamics equations, and is validated against differential pressure measurements using precision transducers. The flow structure is characterized by vortical motions that persist within the aneurysm sac for most of the cardiac cycle. All the main flow statistics including velocity, vorticity, pressure, and wall shear stress suggest that the flow pattern is dictated by the aneurysm morphology and is largely independent of the pulsatility of the inflow, at least for the flow regimes investigated here. Comparisons are carried out with previous computational simulations that used the same geometry and inflow conditions, both in terms of cycle-averaged and systolic quantities.
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Four-Dimensional Phase Contrast Magnetic Resonance Imaging Protocol Optimization Using Patient-Specific 3-Dimensional Printed Replicas for In Vivo Imaging Before and After Flow Diverter Placement. World Neurosurg 2017. [DOI: 10.1016/j.wneu.2017.06.042] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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12
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Jain K, Jiang J, Strother C, Mardal KA. Transitional hemodynamics in intracranial aneurysms - Comparative velocity investigations with high resolution lattice Boltzmann simulations, normal resolution ANSYS simulations, and MR imaging. Med Phys 2017; 43:6186. [PMID: 27806613 DOI: 10.1118/1.4964793] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Blood flow in intracranial aneurysms has, until recently, been considered to be disturbed but still laminar. Recent high resolution computational studies have demonstrated, in some situations, however, that the flow may exhibit high frequency fluctuations that resemble weakly turbulent or transitional flow. Due to numerous assumptions required for simplification in computational fluid dynamics (CFD) studies, the occurrence of these events, in vivo, remains unsettled. The detection of these fluctuations in aneurysmal blood flow, i.e., hemodynamics by CFD, poses additional challenges as such phenomena cannot be captured in clinical data acquisition with magnetic resonance (MR) due to inadequate temporal and spatial resolutions. The authors' purpose was to address this issue by comparing results from highly resolved simulations, conventional resolution laminar simulations, and MR measurements, identify the differences, and identify their causes. METHODS Two aneurysms in the basilar artery, one with disturbed yet laminar flow and the other with transitional flow, were chosen. One set of highly resolved direct numerical simulations using the lattice Boltzmann method (LBM) and another with adequate resolutions under laminar flow assumption were conducted using a commercially available ANSYS Fluent solver. The velocity fields obtained from simulation results were qualitatively and statistically compared against each other and with MR acquisition. RESULTS Results from LBM, ANSYS Fluent, and MR agree well qualitatively and quantitatively for one of the aneurysms with laminar flow in which fluctuations were <80 Hz. The comparisons for the second aneurysm with high fluctuations of > ∼ 600 Hz showed vivid differences between LBM, ANSYS Fluent, and magnetic resonance imaging. After ensemble averaging and down-sampling to coarser space and time scales, these differences became minimal. CONCLUSIONS A combination of MR derived data and CFD can be helpful in estimating the hemodynamic environment of intracranial aneurysms. Adequately resolved CFD would suffice gross assessment of hemodynamics, potentially in a clinical setting, and highly resolved CFD could be helpful in a detailed and retrospective understanding of the physiological mechanisms.
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Affiliation(s)
- Kartik Jain
- Simulation Techniques and Scientific Computing, University of Siegen, Hölderlinstr. 3, 57076 Siegen, Germany and Center for Biomedical Computing, Simula Research Laboratory, N-1325 Lysaker, Norway
| | - Jingfeng Jiang
- Department of Biomedical Engineering, Michigan Technological University, Houghton, Michigan 49931
| | - Charles Strother
- University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53705
| | - Kent-André Mardal
- Department of Mathematics, University of Oslo, 0316 Oslo, Norway and Center for Biomedical Computing, Simula Research Laboratory, N-1325 Lysaker, Norway
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On the quantification and visualization of transient periodic instabilities in pulsatile flows. J Biomech 2016; 52:179-182. [PMID: 28069165 DOI: 10.1016/j.jbiomech.2016.12.037] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 12/20/2016] [Accepted: 12/21/2016] [Indexed: 11/21/2022]
Abstract
Turbulent-like flows without cycle-to-cycle variations are more frequently being reported in studies of cardiovascular flows. The associated stimuli might be of mechanobiological relevance, but how to quantify them objectively is not obvious. Classical Reynolds decomposition, where the flow is separated into mean and fluctuating velocity components, is not applicable as the phase-average is zero. We therefore expanded on established techniques and present the idea, analogous to Reynolds decomposition, to decompose a flow with transient instabilities into low- versus high frequency components, respectively, to discriminate flow instabilities from the underlying cardiac pulsatility. Transient wall shear stress and velocity signals derived from computational fluid dynamic simulations were transferred to the frequency domain. A high-pass filter was applied to subtract the 99% most-energy-containing frequencies, which gave a cut-off frequency of 25Hz. We introduce here the spectral power index, and compute the fluctuating kinetic energy, based on the high-pass filtered velocity components, both being frequency-based operators. The efficacy was evaluated in an aneurysm model for multiple flow rates demonstrating transition to turbulent-like flows. The frequency-based operators were found to better correlate with the qualitatively observed flow instabilities compared to conventional descriptors, like time-averaged wall shear stress or oscillatory shear index. We demonstrate how the high frequencies beyond the physiological range could be analyzed and/or transferred back to the time domain for quantification and visualization purposes. We have introduced general frequency-based operators, easily extendable to other cardiovascular territories based on a posteriori heuristic filtering that allows for separation, isolation, and quantification of cycle-invariant turbulent-like flows.
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