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Korte J, Marsh LMM, Saalfeld S, Behme D, Aliseda A, Berg P. Fusiform versus Saccular Intracranial Aneurysms-Hemodynamic Evaluation of the Pre-Aneurysmal, Pathological, and Post-Interventional State. J Clin Med 2024; 13:551. [PMID: 38256685 PMCID: PMC11154261 DOI: 10.3390/jcm13020551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2023] [Revised: 01/08/2024] [Accepted: 01/11/2024] [Indexed: 01/24/2024] Open
Abstract
Minimally-invasive therapies are well-established treatment methods for saccular intracranial aneurysms (SIAs). Knowledge concerning fusiform IAs (FIAs) is low, due to their wide and alternating lumen and their infrequent occurrence. However, FIAs carry risks like ischemia and thus require further in-depth investigation. Six patient-specific IAs, comprising three position-identical FIAs and SIAs, with the FIAs showing a non-typical FIA shape, were compared, respectively. For each model, a healthy counterpart and a treated version with a flow diverting stent were created. Eighteen time-dependent simulations were performed to analyze morphological and hemodynamic parameters focusing on the treatment effect (TE). The stent expansion is higher for FIAs than SIAs. For FIAs, the reduction in vorticity is higher (Δ35-75% case 2/3) and the reduction in the oscillatory velocity index is lower (Δ15-68% case 2/3). Velocity is reduced equally for FIAs and SIAs with a TE of 37-60% in FIAs and of 41-72% in SIAs. Time-averaged wall shear stress (TAWSS) is less reduced within FIAs than SIAs (Δ30-105%). Within this study, the positive TE of FDS deployed in FIAs is shown and a similarity in parameters found due to the non-typical FIA shape. Despite the higher stent expansion, velocity and vorticity are equally reduced compared to identically located SIAs.
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Affiliation(s)
- Jana Korte
- Department of Fluid Dynamics and Technical Flows, University of Magdeburg, 39106 Magdeburg, Germany
- Research Campus STIMULATE, University of Magdeburg, 39106 Magdeburg, Germany; (L.M.M.M.); (S.S.); (D.B.); (P.B.)
| | - Laurel M. M. Marsh
- Research Campus STIMULATE, University of Magdeburg, 39106 Magdeburg, Germany; (L.M.M.M.); (S.S.); (D.B.); (P.B.)
- Department of Mechanical Engineering, George Mason University, Fairfax, VA 22030, USA
| | - Sylvia Saalfeld
- Research Campus STIMULATE, University of Magdeburg, 39106 Magdeburg, Germany; (L.M.M.M.); (S.S.); (D.B.); (P.B.)
- Department of Computer Science and Automation, Ilmenau University of Technology, 98693 Ilmenau, Germany
| | - Daniel Behme
- Research Campus STIMULATE, University of Magdeburg, 39106 Magdeburg, Germany; (L.M.M.M.); (S.S.); (D.B.); (P.B.)
- University Hospital Magdeburg, University of Magdeburg, 39106 Magdeburg, Germany
| | - Alberto Aliseda
- Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA;
| | - Philipp Berg
- Research Campus STIMULATE, University of Magdeburg, 39106 Magdeburg, Germany; (L.M.M.M.); (S.S.); (D.B.); (P.B.)
- Department of Medical Engineering, University of Magdeburg, 39106 Magdeburg, Germany
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Gaidzik F, Korte J, Saalfeld S, Janiga G, Berg P. Image-based hemodynamic simulations for intracranial aneurysms: the impact of complex vasculature. Int J Comput Assist Radiol Surg 2024:10.1007/s11548-023-03045-3. [PMID: 38206468 DOI: 10.1007/s11548-023-03045-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Accepted: 12/06/2023] [Indexed: 01/12/2024]
Abstract
PURPOSE Hemodynamics play an important role in the assessment of intracranial aneurysm (IA) development and rupture risk. The purpose of this study was to examine the impact of complex vasculatures onto the intra-vessel and intra-aneurysmal blood flow. METHODS Complex segmentation of a subject-specific, 60-outlet and 3-inlet circle of Willis model captured with 7T magnetic resonance imaging was performed. This model was trimmed to a 10-outlet model version. Two patient-specific IAs were added onto both models yielding two pathological versions, and image-based blood flow simulations of the four resulting cases were carried out. To capture the differences between complex and trimmed model, time-averaged and centerline velocities were compared. The assessment of intra-saccular blood flow within the IAs involved the evaluation of wall shear stresses (WSS) at the IA wall and neck inflow rates (NIR). RESULTS Lower flow values are observed in the majority of the complex model. However, at specific locations (left middle cerebral artery 0.5 m/s, left posterior cerebral artery 0.25 m/s), higher flow rates were visible when compared to the trimmed counterpart. Furthermore, at the centerlines the total velocity values reveal differences up to 0.15 m/s. In the IAs, the reduction in the neck inflow rate and WSS in the complex model was observed for the first IA (IA-A δNIRmean = - 0.07ml/s, PCA.l δWSSmean = - 0.05 Pa). The second IA featured an increase in the neck inflow rate and WSS (IA-B δNIRmean = 0.04 ml/s, PCA.l δWSSmean = 0.07 Pa). CONCLUSION Both the magnitude and shape of the flow distribution vary depending on the model's complexity. The magnitude is primarily influenced by the global vessel model, while the shape is determined by the local structure. Furthermore, intra-aneurysmal flow strongly depends on the location in the vessel tree, emphasizing the need for complex model geometries for realistic hemodynamic assessment and rupture risk analysis.
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Affiliation(s)
- Franziska Gaidzik
- Research Campus STIMULATE, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany.
- Laboratory of Fluid Dynamics and Technical Flows, Forschungscampus STIMULATE, Otto-von-Guericke-University Magdeburg, Universitätsplatz 2, 39106, Magdeburg, Germany.
| | - Jana Korte
- Research Campus STIMULATE, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
- Laboratory of Fluid Dynamics and Technical Flows, Forschungscampus STIMULATE, Otto-von-Guericke-University Magdeburg, Universitätsplatz 2, 39106, Magdeburg, Germany
| | - Sylvia Saalfeld
- Research Campus STIMULATE, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
- Laboratory of Simulation and Graphics, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
| | - Gábor Janiga
- Research Campus STIMULATE, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
- Laboratory of Fluid Dynamics and Technical Flows, Forschungscampus STIMULATE, Otto-von-Guericke-University Magdeburg, Universitätsplatz 2, 39106, Magdeburg, Germany
| | - Philipp Berg
- Research Campus STIMULATE, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
- Department of Medical Engineering, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany
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Yang W, Sam K, Qiao Y, Huang Z, Steinman DA, Wasserman BA. A Novel Window Into Human Vascular Remodeling and Diagnosing Carotid Flow Impairment: The Petro-Occipital Venous Plexus. J Am Heart Assoc 2023; 12:e031832. [PMID: 37830353 PMCID: PMC10757507 DOI: 10.1161/jaha.123.031832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Accepted: 09/13/2023] [Indexed: 10/14/2023]
Abstract
Background Adaptive arterial remodeling caused by flow reduction from downstream stenosis has been demonstrated in animal studies. The authors sought to determine whether inward remodeling from downstream stenosis also occurs in humans and is detectable by ex vacuo expansion of the Rektorzik venous plexus (RVP) surrounding the petrous internal carotid artery. Methods and Results The authors analyzed 214 intracranial magnetic resonance imaging examinations that included contrast-enhanced vessel wall imaging. RVP symmetry was qualitatively assessed on vessel wall imaging. RVP thickness (RVPT) was measured on the thicker side if asymmetric or randomly assigned side if symmetric. Maximum stenosis (M1 or intracranial internal carotid artery) was measured. Posterior communicating artery and A1 diameters (>1.0 mm and 1.5 mm, respectively) defined adequate collateral outflow when proximal to the stenosis. Seventy-two patients had stenosis downstream from RVPT measurements. For those without adequate outflow (38 of 72), 95.0% with RVPT ≥1.0 mm had ≥50% stenosis compared with only 5.6% with RVPT <1.0 mm. For these 72 patients, higher RVPT (RVPT ≥1.0 mm versus <1.0 mm) and absent adequate outflow were associated with greater downstream stenosis (P<0.001) using multivariate regression. For patients with downstream stenosis without adequate outflow, asymmetric RVP thickening was associated with greater ipsilateral stenosis (P<0.001, all had ≥46% stenosis) when stenosis was unilateral and greater differences in stenosis between sides (P=0.005) when stenosis was bilateral. Conclusions Inward internal carotid artery remodeling measured by RVPT or RVP asymmetry occurs as downstream stenosis approaches 50%, unless flow is preserved through a sufficiently sized posterior communicating artery or A1, and may serve as a functional measure of substantial flow reduction from downstream stenosis.
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Affiliation(s)
- Wenjie Yang
- Department of Diagnostic Radiology & Nuclear MedicineUniversity of Maryland School of MedicineBaltimoreMD
| | - Kevin Sam
- Department of Diagnostic Radiology & Nuclear MedicineUniversity of Maryland School of MedicineBaltimoreMD
| | - Ye Qiao
- Russell H. Morgan Department of Radiology and Radiological SciencesJohns Hopkins School of MedicineBaltimoreMD
| | - Zhongqing Huang
- Department of Diagnostic Radiology & Nuclear MedicineUniversity of Maryland School of MedicineBaltimoreMD
| | - David A. Steinman
- Department of Mechanical & Industrial EngineeringUniversity of TorontoCanada
| | - Bruce A. Wasserman
- Department of Diagnostic Radiology & Nuclear MedicineUniversity of Maryland School of MedicineBaltimoreMD
- Russell H. Morgan Department of Radiology and Radiological SciencesJohns Hopkins School of MedicineBaltimoreMD
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Korte J, Voß S, Janiga G, Beuing O, Behme D, Saalfeld S, Berg P. Is Accurate Lumen Segmentation More Important than Outlet Boundary Condition in Image-Based Blood Flow Simulations for Intracranial Aneurysms? Cardiovasc Eng Technol 2023; 14:617-630. [PMID: 37582997 PMCID: PMC10602961 DOI: 10.1007/s13239-023-00675-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Accepted: 07/17/2023] [Indexed: 08/17/2023]
Abstract
PURPOSE Image-based blood flow simulations are increasingly used to investigate the hemodynamics in intracranial aneurysms (IAs). However, a strong variability in segmentation approaches as well as the absence of individualized boundary conditions (BCs) influence the quality of these simulation results leading to imprecision and decreased reliability. This study aims to analyze these influences on relevant hemodynamic parameters within IAs. METHODS As a follow-up study of an international multiple aneurysms challenge, the segmentation results of five IAs differing in size and location were investigated. Specifically, five possible outlet BCs were considered in each of the IAs. These are comprised of the zero-pressure condition (BC1), a flow distribution based on Murray's law with the exponents n = 2 (BC2) and n = 3 (BC3) as well as two advanced flow-splitting models considering the real vessels by including circular cross sections (BC4) or anatomical cross sections (BC5), respectively. In total, 120 time-dependent blood flow simulations were analyzed qualitatively and quantitatively, focusing on five representative intra-aneurysmal flow and five shear parameters such as vorticity and wall shear stress. RESULTS The outlet BC variation revealed substantial differences. Higher shear stresses (up to Δ9.69 Pa), intrasaccular velocities (up to Δ0.15 m/s) and vorticities (up to Δ629.22 1/s) were detected when advanced flow-splitting was applied compared to the widely used zero-pressure BC. The tendency of outlets BCs to over- or underestimate hemodynamic parameters is consistent across different segmentations of a single aneurysm model. Segmentation-induced variability reaches Δ19.58 Pa, Δ0.42 m/s and Δ957.27 1/s, respectively. Excluding low fidelity segmentations, however, (a) reduces the deviation drastically (>43%) and (b) leads to a lower impact of the outlet BC on hemodynamic predictions. CONCLUSION With a more realistic lumen segmentation, the influence of the BC on the resulting hemodynamics is decreased. A realistic lumen segmentation can be ensured, e.g., by using high-resolved 2D images. Furthermore, the selection of an advanced outflow-splitting model is advised and the use of a zero-pressure BC and BC based on Murray's law with exponent n = 3 should be avoided.
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Affiliation(s)
- Jana Korte
- Forschungscampus STIMULATE, University of Magdeburg, Magdeburg, Germany.
- Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany.
| | - Samuel Voß
- Forschungscampus STIMULATE, University of Magdeburg, Magdeburg, Germany
- Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany
| | - Gábor Janiga
- Forschungscampus STIMULATE, University of Magdeburg, Magdeburg, Germany
- Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany
| | - Oliver Beuing
- Department of Radiology, AMEOS Hospital, Bernburg, Germany
| | - Daniel Behme
- Department of Neuroradiology, University Hospital of Magdeburg, Magdeburg, Germany
| | - Sylvia Saalfeld
- Forschungscampus STIMULATE, University of Magdeburg, Magdeburg, Germany
- Department of Computer Science and Automation, Ilmenau University of Technology, Ilmenau , Germany
| | - Philipp Berg
- Forschungscampus STIMULATE, University of Magdeburg, Magdeburg, Germany
- Department of Medical Engineering, University of Magdeburg, Magdeburg, Germany
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Mantilla D, Berod A, Ortiz AF, Vera DD, Nicoud F, Costalat V. Heterogeneous model to evaluate CFD in intracranial bifurcation aneurysms treated with the WEB device to predict angiographic outcome. Interv Neuroradiol 2023:15910199231152514. [PMID: 36734097 DOI: 10.1177/15910199231152514] [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: 02/04/2023] Open
Abstract
INTRODUCTION The Woven EndoBridge device (WEB) was developed as an alternative to treat Wide-Necked bifurcation aneurysms. It has proven to be effective and safe, however, cases of recanalization have been reported. The purpose of this study was to evaluate and quantify hemodynamic parameters and indexes with CFD of the intracranial aneurysms before and after WEB simulation and to establish their relationship to complete occlusion. MATERIALS AND METHODS Using the heterogeneous model based on the marching cubes algorithm, we created 3D representations of 27 bifurcated intracranial aneurysms treated with the single-layer WEB device to evaluate hemodynamics parameters with CFD, calculated with and without the WEB. RESULTS We observed a lower treatment entry concentration indices (ICI) (2.12 ± 1.31 versus 3.14 ± 0.93, p-value: 0.029) previous to placement of WEB and higher pre-treatment FN (7.56 ± 5.92 versus 3.35 ± 1.51, p-value: 0.018) and post-treatment FN (5.34 ± 5.89 versus 1.99 ± 0.83, p-value: 0.021) for cases with successful occlusions. Lower post-treatment SRa (197.81 ± 221.29 versus 80.02 ± 45.25, p-value: 0.044) and higher pre (0.11 ± 0.07 versus 0.25 ± 0.19, p-value: 0.011) and post-treatment MATT (0.69 ± 1.23 versus 1.02 ± 0.46, p-value: 0.006) were observed in non-occluded cases. CONCLUSIONS In our CFD analysis of the hemodynamic parameters of IA, we found lower ICI before the placement of the WEB device and higher FN pre- and post-treatment for cases with successful occlusions. Non-occluded cases had lower post-treatment SRa and higher pre-treatment and post-treatment MATT.
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Affiliation(s)
- Daniel Mantilla
- Interventional Radiology Department, 536071Fundación oftalmológica de Santander - Clínica Ardila Lülle. Floridablanca, Colombia
- Interventional Radiology Department, 27968Universidad Autónoma de Bucaramanga, Bucaramanga, Colombia
- Faculté de Sciences, 27037Université de Montpellier, Montpellier, France
| | - Alain Berod
- Sim&Cure, Montpellier, France
- Institut Montpelliérain Alexander, Grothendieck, CNRS, Univ. Montpellier, Montpellier, France
| | - Andrés F Ortiz
- Interventional Radiology Department, 536071Fundación oftalmológica de Santander - Clínica Ardila Lülle. Floridablanca, Colombia
- Interventional Radiology Department, 27968Universidad Autónoma de Bucaramanga, Bucaramanga, Colombia
| | - Daniela D Vera
- Radiology Department, Fundación oftalmológica de Santander, Clínica Ardila Lülle, Floridablanca, Colombia
| | - Franck Nicoud
- Institut Montpelliérain Alexander, Grothendieck, CNRS, Univ. Montpellier, Montpellier, France
| | - Vincent Costalat
- Neuroradiology, Hôpital Güi-de-Chauliac, 26905CHU de Montpellier, Montpellier, France
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Mantilla D, Berod A, Ortiz AF, D Vera D, Nicoud F, Costalat V. Geometry of intracranial aneurysms and of intrasaccular devices may influence aneurysmal occlusion rates after endovascular treatment. Interv Neuroradiol 2023:15910199231152504. [PMID: 36703556 DOI: 10.1177/15910199231152504] [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: 01/28/2023] Open
Abstract
INTRODUCTION The Woven EndoBridge device (WEB) is used to treat wide-neck bifurcation aneurysms. These devices are deployed inside the sac. Therefore, the mesh structure provides apposition with the aneurysm wall and induces aneurysmal thrombosis. The objective of our study was to evaluate the anatomic and device-related parameters and indexes with Computational Fluid Dynamics (CFD) of the intracranial aneurysms before and after WEB simulation and find their relationship to complete occlusion. MATERIALS AND METHODS Using the heterogeneous model based on the marching cubes algorithm, we created 3D representations of 27 bifurcated intracranial aneurysms treated with the single-layer WEB device to evaluate anatomic and device-related parameters with CFD. RESULTS In our CFD analysis, we observed higher large volumes (Va) (0.25 ± 0.18 versus 0.39 ± 0.09, p-value= 0.025) and higher volume to neck surface ratio (Ra) (1.32 ± 0.17 versus 1.54 ± 0.14, p-value= 0.021) in cases with occlusion failure. CONCLUSIONS Large aneurysm volumes (Va) and higher volume to neck surface ratio (Ra) could be associated with occlusion failure in aneurysms treated with the WEB device.
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Affiliation(s)
- Daniel Mantilla
- Interventional Radiology Department, Fundación oftalmológica de Santander - Clínica Ardila Lülle, Floridablanca, Colombia
- Interventional Radiology Department, 27968Universidad Autónoma de Bucaramanga, Bucaramanga, Colombia
| | - Alain Berod
- Sim&Cure, Montpellier, France
- Institut Montpelliérain Alexander, Grothendieck, CNRS, Univ. Montpellier, Montpellier, France
| | - Andrés F Ortiz
- Interventional Radiology Department, Fundación oftalmológica de Santander - Clínica Ardila Lülle, Floridablanca, Colombia
- Interventional Radiology Department, 27968Universidad Autónoma de Bucaramanga, Bucaramanga, Colombia
| | - Daniela D Vera
- Radiology Department, Fundación oftalmológica de Santander, Clínica Ardila Lülle, Floridablanca, Colombia
| | - Franck Nicoud
- Institut Montpelliérain Alexander, Grothendieck, CNRS, Univ. Montpellier, Montpellier, France
| | - Vincent Costalat
- Neuroradiology, Hôpital Güi-de-Chauliac, CHU de Montpellier, Montpellier, France
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Lampropoulos DS, Boutopoulos ID, Bourantas GC, Miller K, Zampakis PE, Loukopoulos VC. Hemodynamics of anterior circulation intracranial aneurysms with daughter blebs: investigating the multidirectionality of blood flow fields. Comput Methods Biomech Biomed Engin 2023; 26:113-125. [PMID: 35297711 DOI: 10.1080/10255842.2022.2048374] [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: 12/24/2022]
Abstract
Recent advances in diagnostic neuroradiological imaging, allowed the detection of unruptured intracranial aneurysms (IAs). The shape - irregular or multilobular - of the aneurysmal dome, is considered as a possible rupture risk factor, independently of the size, the location and patient medical background. Disturbed blood flow fields in particular is thought to play a key role in IAs progression. However, there is an absence of widely-used hemodynamic indices to quantify the extent of a multi-directional disturbed flow. We simulated blood flow in twelve patient-specific anterior circulation unruptured intracranial aneurysms with daughter blebs utilizing the spectral/hp element framework Nektar++. We simulated three cardiac cycles using a volumetric flow rate waveform while we considered blood as a Newtonian fluid. To investigate the multidirectionality of the blood flow fields, besides the time-averaged wall shear stress (TAWSS), we calculated the oscillatory shear index (OSI), the relative residence time (RRT) and the time-averaged cross flow index (TACFI). Our CFD simulations suggest that in the majority of our vascular models there is a formation of complex intrasaccular flow patterns, resulting to low and highly oscillating WSS, especially in the area of the daughter blebs. The existence of disturbed multi-directional blood flow fields is also evident by the distributions of the RRT and the TACFI. These findings further support the theory that IAs with daughter blebs are linked to a potentially increased rupture risk.
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Affiliation(s)
| | | | - George C Bourantas
- Intelligent Systems for Medicine Laboratory, The University of Western Australia, Perth, Western Australia, Australia
| | - Karol Miller
- Intelligent Systems for Medicine Laboratory, The University of Western Australia, Perth, Western Australia, Australia.,Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Petros E Zampakis
- Department of Diagnostic and Interventional Neuroradiology, University of Patras, Patras, Greece
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High-fidelity fluid structure interaction simulations of turbulent-like aneurysm flows reveals high-frequency narrowband wall vibrations: A stimulus of mechanobiological relevance? J Biomech 2022; 145:111369. [PMID: 36375263 DOI: 10.1016/j.jbiomech.2022.111369] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 10/19/2022] [Accepted: 10/30/2022] [Indexed: 11/06/2022]
Abstract
Recent high-fidelity/resolution computational fluid dynamics simulations of intracranial aneurysm hemodynamics have revealed turbulent-like flows. We hypothesized that the associated high-frequency pressure fluctuations could promote aneurysm wall vibrations. We performed fully coupled high-fidelity transient fluid structure interaction simulations between the blood flow and compliant aneurysm sac wall taking 5,000 time steps per second using a 3D patient-specific model previously shown to harbour turbulent-like flow. Our results show that the flow velocity contained fluctuations with a smooth and continuously decaying energy up to ∼160Hz, and fluctuating pressures with characteristic frequency peaks at approximately 30, 130 and 210Hz. There was a strong two-way coupling between the pressure and the wall deformation, for which the frequency spectrum showed similar characteristics, but with a narrow band peak at ∼120Hz with large regional differences in amplitude up to 80μm. The physics of the flow is broadly consistent with clinical reports of turbulent-like flows, while the physics of the wall is consistent with reports of spectral peaks in aneurysm patients. As many aneurysms are known to harbour turbulent-like flows, wall vibrations could be a widespread phenomenon. Finally, since aneurysms are vascular pathologies by definition and many/most aneurysms do not have endothelial cells but still display a focal remodeling, we hypothesize that vibrations and stresses within the wall itself might play a role in the mechanobiological processes of vessel wall pathology.
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Effects of Pulsatile Flow Rate and Shunt Ratio in Bifurcated Distal Arteries on Hemodynamic Characteristics Involved in Two Patient-Specific Internal Carotid Artery Sidewall Aneurysms: A Numerical Study. Bioengineering (Basel) 2022; 9:bioengineering9070326. [PMID: 35877376 PMCID: PMC9311626 DOI: 10.3390/bioengineering9070326] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 07/05/2022] [Accepted: 07/15/2022] [Indexed: 01/08/2023] Open
Abstract
The pulsatile flow rate (PFR) in the cerebral artery system and shunt ratios in bifurcated arteries are two patient-specific parameters that may affect the hemodynamic characteristics in the pathobiology of cerebral aneurysms, which needs to be identified comprehensively. Accordingly, a systematic study was employed to study the effects of pulsatile flow rate (i.e., PFR−I, PFR−II, and PFR−III) and shunt ratio (i.e., 75:25 and 64:36) in bifurcated distal arteries, and transient cardiac pulsatile waveform on hemodynamic patterns in two internal carotid artery sidewall aneurysm models using computational fluid dynamics (CFD) modeling. Numerical results indicate that larger PFRs can cause higher wall shear stress (WSS) in some local regions of the aneurysmal dome that may increase the probability of small/secondary aneurysm generation than under smaller PFRs. The low WSS and relatively high oscillatory shear index (OSI) could appear under a smaller PFR, increasing the potential risk of aneurysmal sac growth and rupture. However, the variances in PFRs and bifurcated shunt ratios have rare impacts on the time-average pressure (TAP) distributions on the aneurysmal sac, although a higher PFR can contribute more to the pressure increase in the ICASA−1 dome due to the relatively stronger impingement by the redirected bloodstream than in ICASA−2. CFD simulations also show that the variances of shunt ratios in bifurcated distal arteries have rare impacts on the hemodynamic characteristics in the sacs, mainly because the bifurcated location is not close enough to the sac in present models. Furthermore, it has been found that the vortex location plays a major role in the temporal and spatial distribution of the WSS on the luminal wall, varying significantly with the cardiac period.
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Zhang M, Hou X, Qian Y, Chong W, Zhang X, Duan CZ, Ou C. Evaluation of aneurysm rupture risk based upon flowrate-independent hemodynamic parameters: a multi-center pilot study. J Neurointerv Surg 2022:neurintsurg-2022-018691. [PMID: 35688619 DOI: 10.1136/neurintsurg-2022-018691] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 05/21/2022] [Indexed: 01/07/2023]
Abstract
BACKGROUND Specifying generic flow boundary conditions in aneurysm hemodynamic simulations yields a great degree of uncertainty for the evaluation of aneurysm rupture risk. Herein, we proposed the use of flowrate-independent parameters in discriminating unstable aneurysms and compared their prognostic performance against that of conventional absolute parameters. METHODS This retrospective study included 186 aneurysms collected from three international centers, with the stable aneurysms having a minimum follow-up period of 24 months. The flowrate-independent aneurysmal wall shear stress (WSS) and energy loss (EL) were defined as the coefficients of the second-order polynomials characterizing the relationships between the respective parameters and the parent-artery flows. Performance of the flowrate-independent parameters in discriminating unstable aneurysms with the logistic regression, Adaboost, and support-vector machine (SVM) methods was quantified and compared against that of the conventional parameters, in terms of sensitivity, specificity, and area under the curve (AUC). RESULTS In discriminating unstable aneurysms, the proposed flowrate-independent EL achieved the highest sensitivity (0.833, 95% CI 0.586 to 0.964) and specificity (0.833, 95% CI 0.672 to 0.936) on the SVM, with the AUC outperforming the conventional EL by 0.133 (95% CI 0.039 to 0.226, p=0.006). Likewise, the flowrate-independent WSS outperformed the conventional WSS in terms of the AUC (difference: 0.137, 95% CI 0.033 to 0.241, p=0.010). CONCLUSION The flowrate-independent hemodynamic parameters surpassed their conventional counterparts in predicting the stability of aneurysms, which may serve as a promising set of hemodynamic metrics to be used for the prediction of aneurysm rupture risk when physiologically real vascular boundary conditions are unavailable.
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Affiliation(s)
- Mingzi Zhang
- Macquarie Medical School, Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Xiaoxi Hou
- Macquarie Medical School, Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, New South Wales, Australia
| | - Yi Qian
- Neurosurgery Center, Department of Cerebrovascular Surgery, The National Key Clinical Specialty, The Engineering Technology Research Center of Education Ministry of China on Diagnosis and Treatment of Cerebrovascular Disease, Guangdong Provincial Key Laboratory on Brain Function Repair and Regeneration, The Neurosurgery Institute of Guangdong Province, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Winston Chong
- Neuroradiology Department, Monash Medical Centre, Melbourne, Victoria, Australia
| | - Xin Zhang
- Neurosurgery Center, Department of Cerebrovascular Surgery, The National Key Clinical Specialty, The Engineering Technology Research Center of Education Ministry of China on Diagnosis and Treatment of Cerebrovascular Disease, Guangdong Provincial Key Laboratory on Brain Function Repair and Regeneration, The Neurosurgery Institute of Guangdong Province, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Chuan-Zhi Duan
- Neurosurgery Center, Department of Cerebrovascular Surgery, The National Key Clinical Specialty, The Engineering Technology Research Center of Education Ministry of China on Diagnosis and Treatment of Cerebrovascular Disease, Guangdong Provincial Key Laboratory on Brain Function Repair and Regeneration, The Neurosurgery Institute of Guangdong Province, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China
| | - Chubin Ou
- Macquarie Medical School, Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, New South Wales, Australia .,Neurosurgery Center, Department of Cerebrovascular Surgery, The National Key Clinical Specialty, The Engineering Technology Research Center of Education Ministry of China on Diagnosis and Treatment of Cerebrovascular Disease, Guangdong Provincial Key Laboratory on Brain Function Repair and Regeneration, The Neurosurgery Institute of Guangdong Province, Zhujiang Hospital, Southern Medical University, Guangzhou, Guangdong, China
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11
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Berod A, Chnafa C, Mendez S, Nicoud F. A heterogeneous model of endovascular devices for the treatment of intracranial aneurysms. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2022; 38:e3552. [PMID: 34806847 DOI: 10.1002/cnm.3552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 03/25/2021] [Accepted: 07/31/2021] [Indexed: 06/13/2023]
Abstract
Numerical computations of hemodynamics inside intracranial aneurysms treated by endovascular braided devices such as flow-diverters contribute to understanding and improving such treatment procedures. Nevertheless, these simulations yield high computational and meshing costs due to the heterogeneity of length scales between the dense weave of the fine struts of the device and the arterial volume. Homogeneous strategies developed over the last decade to circumvent this issue substitute local dissipations due to the wires with a global effect in the form of a pressure-drop across the device surface. However, these methods cannot accurately reproduce the flow-patterns encountered near the struts, the latter strongly dictating the intra-saccular flow environment. In this work, a versatile theoretical framework which aims at correctly reproducing the local flow heterogeneities due to the wires while keeping memory consumption, meshing and computational times as low as possible is introduced. This model reproduces the drag forces exerted by the device struts onto the fluid, thus producing local and heterogeneous effects on the flow. Extensive validation for various flow and geometric configurations using an idealized device is performed. To further illustrate the method capabilities, a real patient-specific aneurysm endovascularly treated with a flow-diverter is used, enabling quantitative comparisons with classical approaches for both intra-saccular velocities and computational costs reduction. The proposed heterogeneous model endeavors to bridge the gap between computational fluid dynamics and clinical applications and ushers in a new era of numerical treatment planning with minimally costing computational tools.
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Affiliation(s)
- Alain Berod
- IMAG, Univ Montpellier, CNRS, Montpellier, France
- Sim&Cure, Montpellier, France
| | | | - Simon Mendez
- IMAG, Univ Montpellier, CNRS, Montpellier, France
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12
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Kjeldsberg HA, Bergersen AW, Valen-Sendstad K. Automated landmarking of bends in vascular structures: a comparative study with application to the internal carotid artery. Biomed Eng Online 2021; 20:120. [PMID: 34838018 PMCID: PMC8626959 DOI: 10.1186/s12938-021-00957-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 11/15/2021] [Indexed: 11/16/2022] Open
Abstract
Automated tools for landmarking the internal carotid artery (ICA) bends have the potential for efficient and objective medical image-based morphometric analysis. The two existing algorithms rely on numerical approximations of curvature and torsion of the centerline. However, input parameters, original source code, comparability, and robustness of the algorithms remain unknown. To address the former two, we have re-implemented the algorithms, followed by sensitivity analyses. Of the input parameters, the centerline smoothing had the least impact resulting in 6-7 bends, which is anatomically realistic. In contrast, centerline resolution showed to completely over- and underestimated the number of bends varying from 3 to 33. Applying the algorithms to the same cohort revealed a variability that makes comparison of results between previous studies questionable. Assessment of robustness revealed how one algorithm is vulnerable to model smoothness and noise, but conceptually independent of application. In contrast, the other algorithm is robust and consistent, but with limited general applicability. In conclusion, both algorithms are equally valid albeit they produce vastly different results. We have provided a well-documented open-source implementation of the algorithms. Finally, we have successfully performed this study on the ICA, but application to other vascular regions should be performed with caution.
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Affiliation(s)
- Henrik A Kjeldsberg
- Department of Computational Physiology, Simula Research Laboratory AS, Kristian Augusts gate 23, 0164 Oslo, Norway
| | - Aslak W Bergersen
- Department of Computational Physiology, Simula Research Laboratory AS, Kristian Augusts gate 23, 0164 Oslo, Norway
| | - Kristian Valen-Sendstad
- Department of Computational Physiology, Simula Research Laboratory AS, Kristian Augusts gate 23, 0164 Oslo, Norway
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13
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Veeturi SS, Rajabzadeh-Oghaz H, Pintér NK, Waqas M, Hasan DM, Snyder KV, Siddiqui AH, Tutino VM. Aneurysm risk metrics and hemodynamics are associated with greater vessel wall enhancement in intracranial aneurysms. ROYAL SOCIETY OPEN SCIENCE 2021; 8:211119. [PMID: 34804573 PMCID: PMC8580418 DOI: 10.1098/rsos.211119] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Accepted: 09/27/2021] [Indexed: 06/13/2023]
Abstract
Vessel wall enhancement (VWE) in contrast-enhanced magnetic resonance imaging (MRI) is a potential biomarker for intracranial aneurysm (IA) risk stratification. In this study, we investigated the relationship between VWE features, risk metrics, morphology and hemodynamics in 41 unruptured aneurysms. We reconstructed the IA geometries from MR angiography and mapped pituitary stalk-normalized MRI intensity on the aneurysm surface using an in-house tool. For each case, we calculated the maximum intensity (CRstalk) and IA risk (via size and the rupture resemblance score (RRS)). We performed correlation analysis to assess relationships between CRstalk and IA risk metrics (size and RRS), as well as each parameter encompassed in RRS, i.e. aneurysmal size ratio (SR), normalized wall shear stress (WSS) and oscillatory shear index. We found that CRstalk had a strong correlation (Pearson correlation coefficient, PCC = 0.630) with size and a moderate correlation (PCC = 0.472) with RRS, indicating an association between VWE and IA risk. Furthermore, CRstalk had a weak negative correlation with normalized WSS (PCC = -0.320) and a weak positive correlation with SR (PCC = 0.390). Local voxel-based analysis showed only a weak negative correlation between normalized WSS and contrast-enhanced MRI signal intensity (PCC = -0.240), suggesting that if low-normalized WSS induces enhancement-associated pathobiology, the effect is not localized.
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Affiliation(s)
- Sricharan S. Veeturi
- Canon Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY, USA
- Department of Mechanical and Aerospace Engineering, University at Buffalo, Buffalo, NY, USA
| | - Hamidreza Rajabzadeh-Oghaz
- Canon Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY, USA
- Department of Neurosurgery, University at Buffalo, Buffalo, NY, USA
| | | | - Muhammad Waqas
- Canon Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY, USA
- Department of Neurosurgery, University at Buffalo, Buffalo, NY, USA
| | - David M. Hasan
- Department of Neurosurgery, University of Iowa Health Care, Iowa City, IA, USA
| | - Kenneth V. Snyder
- Canon Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY, USA
- Department of Neurosurgery, University at Buffalo, Buffalo, NY, USA
| | - Adnan H. Siddiqui
- Canon Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY, USA
- Department of Neurosurgery, University at Buffalo, Buffalo, NY, USA
| | - Vincent M. Tutino
- Canon Stroke and Vascular Research Center, University at Buffalo, Buffalo, NY, USA
- Department of Mechanical and Aerospace Engineering, University at Buffalo, Buffalo, NY, USA
- Department of Pathology and Anatomical Sciences, University at Buffalo, Buffalo, NY, USA
- DENT Neurologic Institute, Buffalo, NY, USA
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14
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Integrating multi-fidelity blood flow data with reduced-order data assimilation. Comput Biol Med 2021; 135:104566. [PMID: 34157468 DOI: 10.1016/j.compbiomed.2021.104566] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2021] [Revised: 05/30/2021] [Accepted: 06/08/2021] [Indexed: 11/20/2022]
Abstract
High-fidelity patient-specific modeling of cardiovascular flows and hemodynamics is challenging. Direct blood flow measurement inside the body with in-vivo measurement modalities such as 4D flow magnetic resonance imaging (4D flow MRI) suffer from low resolution and acquisition noise. In-vitro experimental modeling and patient-specific computational fluid dynamics (CFD) models are subject to uncertainty in patient-specific boundary conditions and model parameters. Furthermore, collecting blood flow data in the near-wall region (e.g., wall shear stress) with experimental measurement modalities poses additional challenges. In this study, a computationally efficient data assimilation method called reduced-order modeling Kalman filter (ROM-KF) was proposed, which combined a sequential Kalman filter with reduced-order modeling using a linear model provided by dynamic mode decomposition (DMD). The goal of ROM-KF was to overcome low resolution and noise in experimental and uncertainty in CFD modeling of cardiovascular flows. The accuracy of the method was assessed with 1D Womersley flow, 2D idealized aneurysm, and 3D patient-specific cerebral aneurysm models. Synthetic experimental data were used to enable direct quantification of errors using benchmark datasets. The accuracy of ROM-KF in reconstructing near-wall hemodynamics was assessed by applying the method to problems where near-wall blood flow data were missing in the experimental dataset. The ROM-KF method provided blood flow data that were more accurate than the computational and synthetic experimental datasets and improved near-wall hemodynamics quantification.
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15
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Xu H, Baroli D, Veneziani A. Global Sensitivity Analysis for Patient-Specific Aortic Simulations: The Role of Geometry, Boundary Condition and Large Eddy Simulation Modeling Parameters. J Biomech Eng 2021; 143:1086637. [PMID: 32879943 DOI: 10.1115/1.4048336] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Indexed: 11/08/2022]
Abstract
Numerical simulations for computational hemodynamics in clinical settings require a combination of many ingredients, mathematical models, solvers and patient-specific data. The sensitivity of the solutions to these factors may be critical, particularly when we have a partial or noisy knowledge of data. Uncertainty quantification is crucial to assess the reliability of the results. We present here an extensive sensitivity analysis in aortic flow simulations, to quantify the dependence of clinically relevant quantities to the patient-specific geometry and the inflow boundary conditions. Geometry and inflow conditions are generally believed to have a major impact on numerical simulations. We resort to a global sensitivity analysis, (i.e., not restricted to a linearization around a working point), based on polynomial chaos expansion (PCE) and the associated Sobol' indices. We regard the geometry and the inflow conditions as the realization of a parametric stochastic process. To construct a physically consistent stochastic process for the geometry, we use a set of longitudinal-in-time images of a patient with an abdominal aortic aneurysm (AAA) to parametrize geometrical variations. Aortic flow is highly disturbed during systole. This leads to high computational costs, even amplified in a sensitivity analysis -when many simulations are needed. To mitigate this, we consider here a large Eddy simulation (LES) model. Our model depends in particular on a user-defined parameter called filter radius. We borrowed the tools of the global sensitivity analysis to assess the sensitivity of the solution to this parameter too. The targeted quantities of interest (QoI) include: the total kinetic energy (TKE), the time-average wall shear stress (TAWSS), and the oscillatory shear index (OSI). The results show that these indexes are mostly sensitive to the geometry. Also, we find that the sensitivity may be different during different instants of the heartbeat and in different regions of the domain of interest. This analysis helps to assess the reliability of in silico tools for clinical applications.
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Affiliation(s)
- Huijuan Xu
- School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332; Siemens Coporate Technology, Princeton, NJ 08540
| | - Davide Baroli
- Aachen Institute for Advanced Study in Computational Engineering Science, Aachen 52062, Germany
| | - Alessandro Veneziani
- Department of Mathematics, Emory University, Atlanta, GA 30322; Department of Computer Science, Emory University, Atlanta, GA 30322
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16
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Numerical investigation of patient-specific thoracic aortic aneurysms and comparison with normal subject via computational fluid dynamics (CFD). Med Biol Eng Comput 2020; 59:71-84. [PMID: 33225424 DOI: 10.1007/s11517-020-02287-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2020] [Accepted: 11/05/2020] [Indexed: 10/22/2022]
Abstract
Vascular hemodynamics play an important role in cardiovascular diseases. This work aimed to investigate the effects of an increase in ascending aortic diameter (AAD) on hemodynamics throughout a cardiac cycle for real patients. In this study, two scans of thoracic aortic aneurysm (TAA) subject with different AADs (42.94 mm and 48.01 mm) and a scan of a normal subject (19.81 mm) were analyzed to assess the effects of hemodynamics on the progression of TAA with the same flow rate. Real-patient aortic geometries were scanned by computed tomography angiography (CTA), and steady and pulsatile flow conditions were used to simulate real patient aortic geometries. Aortic arches were obtained from routine clinical scans. Computational fluid dynamics (CFD) simulations were performed with in vivo boundary conditions, and 3D Navier-Stokes equations were solved by a UDF (user-defined function) code defining a real cardiac cycle of one patient using Fourier series (FS). Wall shear stress (WSS) and pressure distributions were presented from normal subject to TAA cases. The results show that during the peak systolic phase pressure load increased by 18.56% from normal subject to TAA case 1 and by 23.8% from normal subject to TAA case 2 in the aneurysm region. It is concluded that although overall WSS increased in aneurysm cases but was low in dilatation areas. As a result, abnormal changes in WSS and higher pressure load may lead to rupture and risk of further dilatation. CFD simulations were highly effective to guide clinical predictions and assess the progress of aneurysm regions in case of early surgical intervention. Graphical abstract.
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17
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Steinman DA, Pereira VM. How patient specific are patient-specific computational models of cerebral aneurysms? An overview of sources of error and variability. Neurosurg Focus 2020; 47:E14. [PMID: 31261118 DOI: 10.3171/2019.4.focus19123] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 04/12/2019] [Indexed: 01/20/2023]
Abstract
Computational modeling of cerebral aneurysms, derived from clinical 3D angiography, has become widespread over the past 15 years. While such "image-based" or "patient-specific" models have shown promise for the assessment of rupture risk, much debate remains about their reliability in light of necessary modeling assumptions and incomplete or uncertain model input parameters derived from the clinic. The aims of this review were to walk through the various steps of this so-called patient-specific modeling pipeline and to highlight evidence supporting those steps that we can or cannot rely on. The relative importance of the different sources of error and variability on hemodynamic predictions is summarized, with recommendations to standardize for those that can be avoided and to pay closer attention those to that cannot.
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Affiliation(s)
- David A Steinman
- 1Department of Mechanical and Industrial Engineering and Institute of Biomaterials and Biomedical Engineering, University of Toronto; and
| | - Vitor M Pereira
- 2Divisions of Neuroradiology and Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada
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18
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Berg P, Saalfeld S, Voß S, Beuing O, Janiga G. A review on the reliability of hemodynamic modeling in intracranial aneurysms: why computational fluid dynamics alone cannot solve the equation. Neurosurg Focus 2020; 47:E15. [PMID: 31261119 DOI: 10.3171/2019.4.focus19181] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 04/09/2019] [Indexed: 12/23/2022]
Abstract
Computational blood flow modeling in intracranial aneurysms (IAs) has enormous potential for the assessment of highly resolved hemodynamics and derived wall stresses. This results in an improved knowledge in important research fields, such as rupture risk assessment and treatment optimization. However, due to the requirement of assumptions and simplifications, its applicability in a clinical context remains limited.This review article focuses on the main aspects along the interdisciplinary modeling chain and highlights the circumstance that computational fluid dynamics (CFD) simulations are embedded in a multiprocess workflow. These aspects include imaging-related steps, the setup of realistic hemodynamic simulations, and the analysis of multidimensional computational results. To condense the broad knowledge, specific recommendations are provided at the end of each subsection.Overall, various individual substudies exist in the literature that have evaluated relevant technical aspects. In this regard, the importance of precise vessel segmentations for the simulation outcome is emphasized. Furthermore, the accuracy of the computational model strongly depends on the specific research question. Additionally, standardization in the context of flow analysis is required to enable an objective comparison of research findings and to avoid confusion within the medical community. Finally, uncertainty quantification and validation studies should always accompany numerical investigations.In conclusion, this review aims for an improved awareness among physicians regarding potential sources of error in hemodynamic modeling for IAs. Although CFD is a powerful methodology, it cannot provide reliable information, if pre- and postsimulation steps are inaccurately carried out. From this, future studies can be critically evaluated and real benefits can be differentiated from results that have been acquired based on technically inaccurate procedures.
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Affiliation(s)
- Philipp Berg
- 1Department of Fluid Dynamics and Technical Flows.,2Research CampusSTIMULATE, and
| | - Sylvia Saalfeld
- 2Research CampusSTIMULATE, and.,3Department of Simulation and Graphics, University of Magdeburg; and
| | - Samuel Voß
- 1Department of Fluid Dynamics and Technical Flows.,2Research CampusSTIMULATE, and
| | - Oliver Beuing
- 2Research CampusSTIMULATE, and.,4Department of Neuroradiology, University Hospital Magdeburg, Magdeburg, Germany
| | - Gábor Janiga
- 1Department of Fluid Dynamics and Technical Flows.,2Research CampusSTIMULATE, and
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19
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Najafi M, Cancelliere NM, Brina O, Bouillot P, Vargas MI, Delattre BM, Pereira VM, Steinman DA. How patient-specific do internal carotid artery inflow rates need to be for computational fluid dynamics of cerebral aneurysms? J Neurointerv Surg 2020; 13:459-464. [PMID: 32732256 DOI: 10.1136/neurintsurg-2020-015993] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 07/01/2020] [Accepted: 07/02/2020] [Indexed: 11/03/2022]
Abstract
BACKGROUND Computational fluid dynamics (CFD) has become a popular tool for studying 'patient-specific' blood flow dynamics in cerebral aneurysms; however, rarely are the inflow boundary conditions patient-specific. We aimed to test the impact of widespread reliance on generalized inflow rates. METHODS Internal carotid artery (ICA) flow rates were measured via 2D cine phase-contrast MRI for 24 patients scheduled for endovascular therapy of an ICA aneurysm. CFD models were constructed from 3D rotational angiography, and pulsatile inflow rates imposed as measured by MRI or estimated using an average older-adult ICA flow waveform shape scaled by a cycle-average flow rate (Qavg) derived from the patient's ICA cross-sectional area via an assumed inlet velocity. RESULTS There was good overall qualitative agreement in the magnitudes and spatial distributions of time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and spectral power index (SPI) using generalized versus patient-specific inflows. Sac-averaged quantities showed moderate to good correlations: R2=0.54 (TAWSS), 0.80 (OSI), and 0.68 (SPI). Using patient-specific Qavg to scale the generalized waveform shape resulted in near-perfect agreement for TAWSS, and reduced bias, but not scatter, for SPI. Patient-specific waveform had an impact only on OSI correlations, which improved to R2=0.93. CONCLUSIONS Aneurysm CFD demonstrates the ability to stratify cases by nominal hemodynamic 'risk' factors when employing an age- and vascular-territory-specific recipe for generalized inflow rates. Qavg has a greater influence than waveform shape, suggesting some improvement could be achieved by including measurement of patient-specific Qavg into aneurysm imaging protocols.
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Affiliation(s)
- Mehdi Najafi
- Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
| | - Nicole M Cancelliere
- Joint Department of Medical Imaging, Toronto Western Hospital, Toronto, Ontario, Canada
| | - Olivier Brina
- Department for Diagnostic and Interventional Neuroradiology, Hôpitaux Universitaires de Geneve, Geneva, Switzerland
| | - Pierre Bouillot
- Department for Diagnostic and Interventional Neuroradiology, Hôpitaux Universitaires de Geneve, Geneva, Switzerland
| | - Maria I Vargas
- Department for Diagnostic and Interventional Neuroradiology, Hôpitaux Universitaires de Geneve, Geneva, Switzerland
| | - Benedicte Ma Delattre
- Department for Diagnostic and Interventional Neuroradiology, Hôpitaux Universitaires de Geneve, Geneva, Switzerland
| | - Vitor M Pereira
- Joint Department of Medical Imaging, Toronto Western Hospital, Toronto, Ontario, Canada
- Department of Neurosurgery, Toronto Western Hospital, Toronto, Ontario, Canada
| | - David A Steinman
- Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
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Abstract
Dynamic mode decomposition (DMD) is a purely data-driven and equation-free technique for reduced-order modeling of dynamical systems and fluid flow. DMD finds a best fit linear reduced-order model that represents any given spatiotemporal data. In DMD, each mode evolves with a fixed frequency and therefore DMD modes represent physically meaningful structures that are ranked based on their dynamics. The application of DMD to patient-specific cardiovascular flow data is challenging. First, the input flow rate is unsteady and pulsatile. Second, the flow topology can change significantly in different phases of the cardiac cycle. Finally, blood flow in patient-specific diseased arteries is complex and often chaotic. The objective of this study was to overcome these challenges using our proposed multistage dynamic mode decomposition with control (mDMDc) method and use this technique to study patient-specific blood flow physics. The inlet flow rate was considered as the controller input to the systems. Blood flow data were divided into different stages based on the inlet flow waveform and DMD with control was applied to each stage. The system was augmented to consider both velocity and wall shear stress (WSS) vector data, and therefore study the interaction between the coherent structures in velocity and near-wall coherent structures in WSS. First, it was shown that DMD modes can exactly represent the analytical Womersley solution for incompressible pulsatile flow in tubes. Next, our method was applied to image-based coronary artery stenosis and cerebral aneurysm models where complex blood flow patterns are anticipated. The flow patterns were studied using the mDMDc modes and the reconstruction errors were reported. Our augmented mDMDc framework could capture coherent structures in velocity and WSS with a fewer number of modes compared to the traditional DMD approach and demonstrated a close connection between the velocity and WSS modes.
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21
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Bergersen AW, Kjeldsberg HA, Valen-Sendstad K. A framework for automated and objective modification of tubular structures: Application to the internal carotid artery. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2020; 36:e3330. [PMID: 32125768 DOI: 10.1002/cnm.3330] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Revised: 02/26/2020] [Accepted: 02/27/2020] [Indexed: 06/10/2023]
Abstract
Patient-specific medical image-based computational fluid dynamics has been widely used to reveal fundamental insight into mechanisms of cardiovascular disease, for instance, correlating morphology to adverse vascular remodeling. However, segmentation of medical images is laborious, error-prone, and a bottleneck in the development of large databases that are needed to capture the natural variability in morphology. Instead, idealized models, where morphological features are parameterized, have been used to investigate the correlation with flow features, but at the cost of limited understanding of the complexity of cardiovascular flows. To combine the advantages of both approaches, we developed a tool that preserves the patient-specificness inherent in medical images while allowing for parametric alteration of the morphology. In our open-source framework morphMan we convert the segmented surface to a Voronoi diagram, modify the diagram to change the morphological features of interest, and then convert back to a new surface. In this paper, we present algorithms for modifying bifurcation angles, location of branches, cross-sectional area, vessel curvature, shape of bends, and surface roughness. We show qualitative and quantitative validation of the algorithms, performing with an accuracy exceeding 97% in general, and proof-of-concept on combining the tool with computational fluid dynamics. By combining morphMan with appropriate clinical measurements, one could explore the morphological parameter space and resulting hemodynamic response using only a handful of segmented surfaces, effectively minimizing the main bottleneck in image-based computational fluid dynamics.
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Affiliation(s)
- Aslak W Bergersen
- Department of Computational Physiology, Simula Research Laboratory, Fornebu, Akershus, Norway
| | - Henrik A Kjeldsberg
- Department of Computational Physiology, Simula Research Laboratory, Fornebu, Akershus, Norway
| | - Kristian Valen-Sendstad
- Department of Computational Physiology, Simula Research Laboratory, Fornebu, Akershus, Norway
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22
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Damiano RJ, Tutino VM, Paliwal N, Patel TR, Waqas M, Levy EI, Davies JM, Siddiqui AH, Meng H. Aneurysm characteristics, coil packing, and post-coiling hemodynamics affect long-term treatment outcome. J Neurointerv Surg 2019; 12:706-713. [PMID: 31848217 DOI: 10.1136/neurintsurg-2019-015422] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 11/20/2019] [Accepted: 11/25/2019] [Indexed: 12/26/2022]
Abstract
BACKGROUND Recurrence of intracranial aneurysms after endovascular coiling is a serious clinical concern. OBJECTIVE We hypothesized that recurrence is associated with aneurysm morphology and flow, as well as the coil intervention and the induced flow modifications. METHODS We collected 52 primary-coiling aneurysm cases that were either occluded (n=34) or recurrent (n=18) at >1 year follow-up. We created aneurysm models from pre-coiling digital subtraction angiographic images, calculated aneurysm morphology, simulated pre-coiling hemodynamics, modeled coil deployment, and obtained post-coiling hemodynamics for each case. We performed univariable analysis on 26 morphologic, treatment-specific, and hemodynamic parameters to distinguish between recurrent and occluded groups, and multivariable analysis to identify independently significant parameters associated with recurrence. Univariable analysis was also performed on ruptured and unruptured aneurysm subcohorts separately to investigate if they shared specific significant parameters. RESULTS Recurrence was associated with pre-coiling aneurysm morphologic and flow parameters including larger size (maximum dimension and volume), larger neck (diameter, area, and neck-to-parent-artery ratio), and higher flow momentum and kinetic energy. Recurrence was also associated with lower coil packing (packing density and uncoiled volume), higher post-treatment flow (velocity, momentum, and kinetic energy), lower post-treatment washout time, and higher post-treatment impingement force at the neck. Multivariable analysis identified two aneurysmal characteristics (neck diameter and pre-coiling flow kinetic energy), one coil packing parameter (uncoiled volume), and one post-treatment hemodynamic parameter (flow momentum) that were independently associated with recurrence. In ruptured aneurysms, recurrence was associated with larger neck (diameter and area), whereas in unruptured aneurysms, recurrence was associated with larger size (maximum dimension and volume). In both subcohorts, recurrence was associated with higher post-coiling flow momentum and kinetic energy. CONCLUSION Recurrence at >1 year after coil treatment is associated with intrinsic aneurysm characteristics, coiling itself, and flow changes induced by coiling. Larger aneurysm size and neck, less coil packing, and higher intra-aneurysmal flow before and after coiling predict recurrence.
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Affiliation(s)
- Robert J Damiano
- Mechanical and Aerospace Engineering, Canon Stroke & Vascular Research Center, University at Buffalo, State University of New York, Buffalo, New York, USA
| | - Vincent M Tutino
- Canon Stroke & Vascular Research Center, Neurosurgery, Biomedical Engineering, Pathology and Anatomical Sciences, University at Buffalo, State University of New York, Buffalo, New York, USA
| | - Nikhil Paliwal
- Mechanical and Aerospace Engineering, Canon Stroke & Vascular Research Center, University at Buffalo, State University of New York, Buffalo, New York, USA
| | - Tatsat R Patel
- Mechanical and Aerospace Engineering, Canon Stroke & Vascular Research Center, University at Buffalo - The State University of New York, Buffalo, New York, USA
| | - Muhammad Waqas
- Neurosurgery, University at Buffalo - The State University of New York, Buffalo, New York, USA
| | - Elad I Levy
- Neurosurgery, University at Buffalo - The State University of New York, Buffalo, New York, USA
| | - Jason M Davies
- Neurosurgery, University at Buffalo - The State University of New York, Buffalo, New York, USA
| | - Adnan H Siddiqui
- Canon Stroke & Vascular Research Center, Neurosurgery, University at Buffalo, State University of New York, Buffalo, New York, USA
| | - Hui Meng
- Mechanical and Aerospace Engineering, Canon Stroke & Vascular Research Center, Neurosurgery, Biomedical Engineering, University at Buffalo - The State University of New York, Buffalo, New York, USA
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Cancelliere NM, Najafi M, Brina O, Bouillot P, Vargas MI, Lovblad KO, Krings T, Pereira VM, Steinman DA. 4D-CT angiography versus 3D-rotational angiography as the imaging modality for computational fluid dynamics of cerebral aneurysms. J Neurointerv Surg 2019; 12:626-630. [DOI: 10.1136/neurintsurg-2019-015389] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 11/06/2019] [Accepted: 11/07/2019] [Indexed: 11/03/2022]
Abstract
Background and purposeComputational fluid dynamics (CFD) can provide valuable information regarding intracranial hemodynamics. Patient-specific models can be segmented from various imaging modalities, which may influence the geometric output and thus hemodynamic results. This study aims to compare CFD results from aneurysm models segmented from three-dimensional rotational angiography (3D-RA) versus novel four-dimensional CT angiography (4D-CTA).MethodsFourteen patients with 16 cerebral aneurysms underwent novel 4D-CTA followed by 3D-RA. Endoluminal geometries were segmented from each modality using an identical workflow, blinded to the other modality, to produce 28 'original' models. Each was then minimally edited a second time to match length of branches, producing 28 additional 'matched' models. CFD simulations were performed using estimated flow rates for 'original' models (representing real-world experience) and patient-specific flow rates from 4D-CTA for 'matched' models (to control for influence of modality alone).ResultsOverall, geometric and hemodynamic results were consistent between models segmented from 3D-RA and 4D-CTA, with correlations improving after matching to control for operator-introduced variability. Despite smaller 4D-CTA parent artery diameters (3.49±0.97 mm vs 3.78±0.92 mm for 3D-RA; p=0.005) and sac volumes (157 (37–750 mm3) vs 173 (53–770 mm3) for 3D-RA; p=0.0002), sac averages of time-averaged wall shear stress (TAWSS), oscillatory shear (OSI), and high frequency fluctuations (measured by spectral power index, SPI) were well correlated between 3D-RA and 4D-CTA 'matched' control models (TAWSS, R2=0.91; OSI, R2=0.79; SPI, R2=0.90).ConclusionsOur study shows that CFD performed using 4D-CTA models produces reliable geometric and hemodynamic information in the intracranial circulation. 4D-CTA may be considered as a follow-up imaging tool for hemodynamic assessment of cerebral aneurysms.
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Bergersen AW, Chnafa C, Gallo D, Piccinelli M, Steinman DA, Valen-Sendstad K. Automated and objective removal of bifurcation aneurysms: Incremental improvements, and validation against healthy controls. J Biomech 2019; 96:109342. [PMID: 31630772 DOI: 10.1016/j.jbiomech.2019.109342] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Revised: 09/09/2019] [Accepted: 09/11/2019] [Indexed: 12/01/2022]
Abstract
Abnormal hemodynamic stresses are thought to correlate with aneurysm initiation, growth, and rupture. We have previously investigated the role of wall shear stress (WSS) and WSS gradients (WSSG) in search for a mechanistic link to formation of sidewall aneurysms using an automated and objective tool for aneurysm removal and arterial reconstruction in combination with computational fluid dynamics (CFD). However, we warned against the use of the tool for bifurcation type aneurysms because of a potential unrealistic reconstruction of the apex. We hypothesized that inclusion of additional morphological features from the surrounding vasculature could overcome these constraints. We extended the previously published method for removal and reconstruction of the bifurcation vasculature based on diverging and converging points of the parent and daughter artery centerlines, to also include two new centerlines between the daughter vessels, one of them passed through the bifurcation center. Validation was performed by comparing the efficacy of the two algorithms, using ten healthy models of the internal carotid artery terminus as ground truth. Qualitative results showed that the bifurcation apexes became smoother relative to the original algorithm; more consistent with the reference models. This was reflected quantitatively by a reduced maximum distance between the reference and reconstructed surfaces, although not statistically significant. Furthermore, the modified algorithm also quantitatively improved CFD derived WSS and WSSG, especially the latter. In conclusion, the modified algorithm does not perfectly reconstruct the bifurcation apex, but provides an incremental improvement, especially important for the derived hemodynamic metrics of interest in vascular pathobiology.
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Affiliation(s)
- Aslak W Bergersen
- Department of Computational Physiology, Simula Research Laboratory, Lysaker, Norway
| | - Christophe Chnafa
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, Canada
| | - Diego Gallo
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Torino, Italy
| | - Marina Piccinelli
- Department of Radiology and Imaging Sciences, Emory University, GA, USA
| | - David A Steinman
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, Canada
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Voß S, Beuing O, Janiga G, Berg P. Stent-induced vessel deformation after intracranial aneurysm treatment – A hemodynamic pilot study. Comput Biol Med 2019; 111:103338. [DOI: 10.1016/j.compbiomed.2019.103338] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 06/18/2019] [Accepted: 06/18/2019] [Indexed: 12/13/2022]
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Flow-splitting-based computation of outlet boundary conditions for improved cerebrovascular simulation in multiple intracranial aneurysms. Int J Comput Assist Radiol Surg 2019; 14:1805-1813. [PMID: 31363984 DOI: 10.1007/s11548-019-02036-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 07/18/2019] [Indexed: 01/20/2023]
Abstract
PURPOSE Image-based hemodynamic simulations have great potential for precise blood flow predictions in intracranial aneurysms. Due to model assumptions and simplifications with respect to boundary conditions, clinical acceptance remains limited. METHODS Within this study, we analyzed the influence of outflow-splitting approaches on multiple aneurysm studies and present a new outflow-splitting approach that takes the precise morphological vessel cross sections into account. We provide a detailed comparison of five outflow strategies considering eight intracranial aneurysms: zero-pressure configuration (1), a flow splitting inspired by Murray's law with a square (2) and a cubic (3) vessel diameter, a flow splitting incorporating vessel bifurcations based on circular vessel cross sections (4) and our novel flow splitting including vessel bifurcations and anatomical vessel cross sections (5). Other boundary conditions remain constant. For each simulation and each aneurysm, we conducted an evaluation based on common hemodynamic parameters, e.g., normalized wall shear stress and inflow concentration index. RESULTS The comparison of five outflow strategies for image-based simulations shows a large variability regarding the parameters of interest. Qualitatively, our strategy based on anatomical cross sections yields a more uniform flow rate distribution with increased aneurysm inflow rates. The commonly used zero-pressure approach shows the largest variations, especially for more distal aneurysms. A rank ordering of multiple aneurysms in one patient might still be possible, since the ordering appeared to be independent of the outflow strategy. CONCLUSIONS The results reveal that outlet boundary conditions have a crucial impact on image-based blood flow simulations, especially for multiple aneurysm studies. We could confirm the advantages of the more complex outflow-splitting model (4) including an incremental improvement (5) compared to strategies (1), (2) and (3) for this application scenario. Furthermore, we discourage from using zero-pressure configurations that lack a physiological basis.
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Voß S, Beuing O, Janiga G, Berg P. Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH)-Phase Ib: Effect of morphology on hemodynamics. PLoS One 2019; 14:e0216813. [PMID: 31100101 PMCID: PMC6524809 DOI: 10.1371/journal.pone.0216813] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 04/29/2019] [Indexed: 12/16/2022] Open
Abstract
Background Image-based blood flow simulations have been increasingly applied to investigate intracranial aneurysm (IA) hemodynamics. However, the acceptance among physicians remains limited due to the high variability in the underlying assumptions and quality of results. Methods To evaluate the vessel segmentation as one of the most important sources of error, the international Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH) was announced. 26 research groups from 13 different countries segmented three datasets, which contained five IAs in total. Based on these segmentations, 73 time-dependent blood flow simulations under consistent conditions were carried out. Afterwards, relevant flow and shear parameters (e.g., neck inflow rate, parent vessel flow rate, spatial mean velocity, and wall shear stress) were analyzed both qualitatively and quantitatively. Results Regarding the entire vasculature, the variability of the segmented vessel radius is 0.13 mm, consistent and independent of the local vessel radius. However, the centerline velocity shows increased variability in more distal vessels. Focusing on the aneurysms, clear differences in morphological and hemodynamic parameters were observed. The quantification of the segmentation-induced variability showed approximately a 14% difference among the groups for the parent vessel flow rate. Regarding the mean aneurysmal velocity and the neck inflow rate, a variation of 30% and 46% was observed, respectively. Finally, time-averaged wall shear stresses varied between 28% and 51%, depending on the aneurysm in question. Conclusions MATCH reveals the effect of state-of-the-art segmentation algorithms on subsequent hemodynamic simulations for IA research. The observed variations may lead to an inappropriate interpretation of the simulation results and thus, can lead to inappropriate conclusions by physicians. Therefore, accurate segmentation of the region of interest is necessary to obtain reliable and clinically helpful flow information.
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Affiliation(s)
- Samuel Voß
- Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany
- Forschungscampus STIMULATE, Magdeburg, Germany
- * E-mail:
| | - Oliver Beuing
- Forschungscampus STIMULATE, Magdeburg, Germany
- Institute of Neuroradiology, University Hospital Magdeburg, Magdeburg, Germany
| | - Gábor Janiga
- Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany
- Forschungscampus STIMULATE, Magdeburg, Germany
| | - Philipp Berg
- Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany
- Forschungscampus STIMULATE, Magdeburg, Germany
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Reza MMS, Arzani A. A critical comparison of different residence time measures in aneurysms. J Biomech 2019; 88:122-129. [DOI: 10.1016/j.jbiomech.2019.03.028] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2018] [Revised: 03/16/2019] [Accepted: 03/20/2019] [Indexed: 12/13/2022]
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Shimano K, Serigano S, Ikeda N, Yuchi T, Shiratori S, Nagano H. Understanding of boundary conditions imposed at multiple outlets in computational haemodynamic analysis of cerebral aneurysm. ACTA ACUST UNITED AC 2019. [DOI: 10.17106/jbr.33.32] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Kenjiro Shimano
- Department of Mechanical Systems Engineering, Faculty of Engineering, Tokyo City University
| | - Shota Serigano
- Graduate School of Integrative Science and Engineering, Tokyo City University
| | - Naoki Ikeda
- Department of Mechanical Systems Engineering, Faculty of Engineering, Tokyo City University
| | - Tomoki Yuchi
- Department of Mechanical Systems Engineering, Faculty of Engineering, Tokyo City University
| | - Suguru Shiratori
- Department of Mechanical Systems Engineering, Faculty of Engineering, Tokyo City University
| | - Hideaki Nagano
- Department of Mechanical Systems Engineering, Faculty of Engineering, Tokyo City University
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Berg P, Radtke L, Vos S, Serowy S, Janiga G, Preim B, Beuing O, Saalfeld S. 3DRA Reconstruction of Intracranial Aneurysms - How does Voxel Size Influences Morphologic and Hemodynamic Parameters. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2018; 2018:1327-1330. [PMID: 30440636 DOI: 10.1109/embc.2018.8512524] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Three-dimensional shape analysis and imagebased hemodynamic simulations are widely used to assess the individual rupture risk of intracranial aneurysms. However, the quality of those results highly depends on pre-simulative working steps including image reconstruction and segmentation. Within this study, three patient-specific aneurysms were reconstructed using three different voxel sizes (0.1 mm, 0.3 mm, 0.5 mm). Afterwards, 3D segmentations and time-dependent blood flow simulations were carried out to evaluate the impact of the reconstruction size. The results indicate that overall all voxel sizes lead to a qualitatively good agreement with respect to the aneurysm surfaces. However, deviations occur regarding the neck representation as well as the consideration of perforating arteries. Further, morphological differences lead to clear hemodynamic variations, especially for shear force predictions. The findings indicate that depending on the desired analysis, careful reconstruction parameter selection is required. Particularly, for quantitative morphology and blood flow studies, the early step of reconstruction can have a crucial effect on subsequent results.
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Chnafa C, Bouillot P, Brina O, Najafi M, Delattre B, Vargas M, Pereira V, Steinman D. Errors in power-law estimations of inflow rates for intracranial aneurysm CFD. J Biomech 2018; 80:159-165. [DOI: 10.1016/j.jbiomech.2018.09.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Revised: 08/02/2018] [Accepted: 09/04/2018] [Indexed: 11/28/2022]
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Arzani A. Accounting for residence-time in blood rheology models: do we really need non-Newtonian blood flow modelling in large arteries? J R Soc Interface 2018; 15:rsif.2018.0486. [PMID: 30257924 DOI: 10.1098/rsif.2018.0486] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 09/03/2018] [Indexed: 12/27/2022] Open
Abstract
Patient-specific computational fluid dynamics (CFD) is a promising tool that provides highly resolved haemodynamics information. The choice of blood rheology is an assumption in CFD models that has been subject to extensive debate. Blood is known to exhibit shear-thinning behaviour, and non-Newtonian modelling has been recommended for aneurysmal flows. Current non-Newtonian models ignore rouleaux formation, which is the key player in blood's shear-thinning behaviour. Experimental data suggest that red blood cell aggregation and rouleaux formation require notable red blood cell residence-time (RT) in a low shear rate regime. This study proposes a novel hybrid Newtonian and non-Newtonian rheology model where the shear-thinning behaviour is activated in high RT regions based on experimental data. Image-based abdominal aortic and cerebral aneurysm models are considered and highly resolved CFD simulations are performed using a minimally dissipative solver. Lagrangian particle tracking is used to define a backward particle RT measure and detect stagnant regions with increased rouleaux formation likelihood. Our novel RT-based non-Newtonian model shows a significant reduction in shear-thinning effects and provides haemodynamic results qualitatively identical and quantitatively close to the Newtonian model. Our results have important implications in patient-specific CFD modelling and suggest that non-Newtonian models should be revisited in large artery flows.
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Affiliation(s)
- Amirhossein Arzani
- Department of Mechanical Engineering, Northern Arizona University, Flagstaff, AZ, USA
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33
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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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Berg P, Saalfeld S, Janiga G, Brina O, Cancelliere NM, Machi P, Pereira VM. Virtual stenting of intracranial aneurysms: A pilot study for the prediction of treatment success based on hemodynamic simulations. Int J Artif Organs 2018; 41:698-705. [PMID: 29783867 DOI: 10.1177/0391398818775521] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Endovascular treatment of intracranial aneurysms using flow-diverting devices has revolutionized the treatment of large and complex lesions due to its minimally invasive nature and potential clinical outcomes. However, incomplete or delayed occlusion and persistent intracranial aneurysm growth are still an issue for up to one-third of the patients. We evaluated two patients with intracranial aneurysm located at the internal carotid artery who were treated with flow-diverting devices and had opposite outcomes. Both patients presented with similar aneurysms and were treated with the same device, but after a 1-year follow-up, one case presented with complete occlusion (Case 1) and the other required further treatment (Case 2). To reproduce the interventions, virtual stents were deployed and blood flow simulations were carried out using the respective patient-specific geometries. Afterward, hemodynamic metrics such as aneurysmal inflow reduction, wall shear stresses, oscillatory shear, and inflow concentration indices were quantified. The hemodynamic simulations reveal that for both cases, the neck inflow was clearly reduced due to the therapy (Case 1: 19%, Case 2: 35%). In addition, relevant hemodynamic parameters such as time-averaged wall shear stress (Case 1: 35.6%, Case 2: 57%) and oscillatory shear (Case 1: 33.1%, Case 2: 26.7%) were decreased considerably. However, although stronger relative reductions occurred in the unsuccessful case, the absolute flow values in the successful case were approximately halved. The findings demonstrate that a high relative effect of endovascular devices is not necessarily associated with the desired treatment outcome. Instead, it appears that a successful intracranial aneurysm therapy requires a certain patient-specific inflow threshold.
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Affiliation(s)
- Philipp Berg
- 1 Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany.,2 Forschungscampus STIMULATE, Magdeburg, Germany
| | - Sylvia Saalfeld
- 2 Forschungscampus STIMULATE, Magdeburg, Germany.,3 Department of Simulation and Graphics, University of Magdeburg, Magdeburg, Germany
| | - Gábor Janiga
- 1 Department of Fluid Dynamics and Technical Flows, University of Magdeburg, Magdeburg, Germany.,2 Forschungscampus STIMULATE, Magdeburg, Germany
| | - Olivier Brina
- 4 Interventional Neuroradiology Unit, University Hospital of Geneva, Geneva, Switzerland
| | - Nicole M Cancelliere
- 5 Joint Department of Medical Imaging, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
| | - Paolo Machi
- 4 Interventional Neuroradiology Unit, University Hospital of Geneva, Geneva, Switzerland
| | - Vitor M Pereira
- 5 Joint Department of Medical Imaging, Toronto Western Hospital, University Health Network, Toronto, ON, Canada.,6 Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University Health Network, Toronto, ON, Canada
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Chnafa C, Brina O, Pereira VM, Steinman DA. Better Than Nothing: A Rational Approach for Minimizing the Impact of Outflow Strategy on Cerebrovascular Simulations. AJNR Am J Neuroradiol 2018; 39:337-343. [PMID: 29269407 DOI: 10.3174/ajnr.a5484] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 10/13/2017] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND PURPOSE Computational fluid dynamics simulations of neurovascular diseases are impacted by various modeling assumptions and uncertainties, including outlet boundary conditions. Many studies of intracranial aneurysms, for example, assume zero pressure at all outlets, often the default ("do-nothing") strategy, with no physiological basis. Others divide outflow according to the outlet diameters cubed, nominally based on the more physiological Murray's law but still susceptible to subjective choices about the segmented model extent. Here we demonstrate the limitations and impact of these outflow strategies, against a novel "splitting" method introduced here. MATERIALS AND METHODS With our method, the segmented lumen is split into its constituent bifurcations, where flow divisions are estimated locally using a power law. Together these provide the global outflow rate boundary conditions. The impact of outflow strategy on flow rates was tested for 70 cases of MCA aneurysm with 0D simulations. The impact on hemodynamic indices used for rupture status assessment was tested for 10 cases with 3D simulations. RESULTS Differences in flow rates among the various strategies were up to 70%, with a non-negligible impact on average and oscillatory wall shear stresses in some cases. Murray-law and splitting methods gave flow rates closest to physiological values reported in the literature; however, only the splitting method was insensitive to arbitrary truncation of the model extent. CONCLUSIONS Cerebrovascular simulations can depend strongly on the outflow strategy. The default zero-pressure method should be avoided in favor of Murray-law or splitting methods, the latter being released as an open-source tool to encourage the standardization of outflow strategies.
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Affiliation(s)
- C Chnafa
- From the Biomedical Simulation Laboratory (C.C., D.A.S.), Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
| | - O Brina
- Joint Division of Medical Imaging (O.B., V.M.P.), Department of Medical Imaging and Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University Health Network, and University of Toronto, Toronto, Ontario, Canada
| | - V M Pereira
- Joint Division of Medical Imaging (O.B., V.M.P.), Department of Medical Imaging and Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University Health Network, and University of Toronto, Toronto, Ontario, Canada
| | - D A Steinman
- From the Biomedical Simulation Laboratory (C.C., D.A.S.), Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
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Chnafa C, Bouillot P, Brina O, Delattre BMA, Vargas MI, Lovblad KO, Pereira VM, Steinman DA. Vessel calibre and flow splitting relationships at the internal carotid artery terminal bifurcation. Physiol Meas 2017; 38:2044-2057. [DOI: 10.1088/1361-6579/aa92bf] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Khan MO, Steinman DA, Valen-Sendstad K. Non-Newtonian versus numerical rheology: Practical impact of shear-thinning on the prediction of stable and unstable flows in intracranial aneurysms. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2017; 33:e2836. [PMID: 27696717 DOI: 10.1002/cnm.2836] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2016] [Accepted: 09/28/2016] [Indexed: 06/06/2023]
Abstract
Computational fluid dynamics (CFD) shows promise for informing treatment planning and rupture risk assessment for intracranial aneurysms. Much attention has been paid to the impact on predicted hemodynamics of various modelling assumptions and uncertainties, including the need for modelling the non-Newtonian, shear-thinning rheology of blood, with equivocal results. Our study clarifies this issue by contextualizing the impact of rheology model against the recently demonstrated impact of CFD solution strategy on the prediction of aneurysm flow instabilities. Three aneurysm cases were considered, spanning a range of stable to unstable flows. Simulations were performed using a high-resolution/accuracy solution strategy with Newtonian and modified-Cross rheology models and compared against results from a so-called normal-resolution strategy. Time-averaged and instantaneous wall shear stress (WSS) distributions, as well as frequency content of flow instabilities and dome-averaged WSS metrics, were minimally affected by the rheology model, whereas numerical solution strategy had a demonstrably more marked impact when the rheology model was fixed. We show that point-wise normalization of non-Newtonian by Newtonian WSS values tended to artificially amplify small differences in WSS of questionable physiological relevance in already-low WSS regions, which might help to explain the disparity of opinions in the aneurysm CFD literature regarding the impact of non-Newtonian rheology. Toward the goal of more patient-specific aneurysm CFD, we conclude that attention seems better spent on solution strategy and other likely "first-order" effects (eg, lumen segmentation and choice of flow rates), as opposed to "second-order" effects such as rheology.
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Affiliation(s)
- M O Khan
- Mechanical & Industrial Engineering, University of Toronto, Toronto, ON, Canada
- Simula Research Laboratory AS, Fornebu, Lysaker, Norway
| | - D A Steinman
- Mechanical & Industrial Engineering, University of Toronto, Toronto, ON, Canada
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Robustness of common hemodynamic indicators with respect to numerical resolution in 38 middle cerebral artery aneurysms. PLoS One 2017; 12:e0177566. [PMID: 28609457 PMCID: PMC5469453 DOI: 10.1371/journal.pone.0177566] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 04/28/2017] [Indexed: 11/19/2022] Open
Abstract
Background Using computational fluid dynamics (CFD) to compute the hemodynamics in cerebral aneurysms has received much attention in the last decade. The usability of these methods depends on the quality of the computations, highlighted in recent discussions. The purpose of this study is to investigate the convergence of common hemodynamic indicators with respect to numerical resolution. Methods 38 middle cerebral artery bifurcation aneurysms were studied at two different resolutions (one comparable to most studies, and one finer). Relevant hemodynamic indicators were collected from two of the most cited studies, and were compared at the two refinements. In addition, correlation to rupture was investigated. Results Most of the hemodynamic indicators were very well resolved at the coarser resolutions, correlating with the finest resolution with a correlation coefficient >0.95. The oscillatory shear index (OSI) had the lowest correlation coefficient of 0.83. A logarithmic Bland-Altman plot revealed noticeable variations in the proportion of the aneurysm under low shear, as well as in spatial and temporal gradients not captured by the correlation alone. Conclusion Statistically, hemodynamic indicators agree well across the different resolutions studied here. However, there are clear outliers visible in several of the hemodynamic indicators, which suggests that special care should be taken when considering individual assessment.
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Bozzi S, Morbiducci U, Gallo D, Ponzini R, Rizzo G, Bignardi C, Passoni G. Uncertainty propagation of phase contrast-MRI derived inlet boundary conditions in computational hemodynamics models of thoracic aorta. Comput Methods Biomech Biomed Engin 2017; 20:1104-1112. [DOI: 10.1080/10255842.2017.1334770] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Silvia Bozzi
- Department of Electronics, Information Science, and Bioengineering, Politecnico di Milano, Milan, Italy
| | - Umberto Morbiducci
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy
| | - Diego Gallo
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy
| | | | | | - Cristina Bignardi
- Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy
| | - Giuseppe Passoni
- Department of Electronics, Information Science, and Bioengineering, Politecnico di Milano, Milan, Italy
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Sarrami-Foroushani A, Lassila T, Frangi AF. Virtual endovascular treatment of intracranial aneurysms: models and uncertainty. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2017; 9. [PMID: 28488754 DOI: 10.1002/wsbm.1385] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 01/09/2017] [Accepted: 02/07/2017] [Indexed: 01/11/2023]
Abstract
Virtual endovascular treatment models (VETMs) have been developed with the view to aid interventional neuroradiologists and neurosurgeons to pre-operatively analyze the comparative efficacy and safety of endovascular treatments for intracranial aneurysms. Based on the current state of VETMs in aneurysm rupture risk stratification and in patient-specific prediction of treatment outcomes, we argue there is a need to go beyond personalized biomechanical flow modeling assuming deterministic parameters and error-free measurements. The mechanobiological effects associated with blood clot formation are important factors in therapeutic decision making and models of post-treatment intra-aneurysmal biology and biochemistry should be linked to the purely hemodynamic models to improve the predictive power of current VETMs. The influence of model and parameter uncertainties associated to each component of a VETM is, where feasible, quantified via a random-effects meta-analysis of the literature. This allows estimating the pooled effect size of these uncertainties on aneurysmal wall shear stress. From such meta-analyses, two main sources of uncertainty emerge where research efforts have so far been limited: (1) vascular wall distensibility, and (2) intra/intersubject systemic flow variations. In the future, we suggest that current deterministic computational simulations need to be extended with strategies for uncertainty mitigation, uncertainty exploration, and sensitivity reduction techniques. WIREs Syst Biol Med 2017, 9:e1385. doi: 10.1002/wsbm.1385 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Ali Sarrami-Foroushani
- Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), The University of Sheffield, Sheffield, UK
| | - Toni Lassila
- Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), The University of Sheffield, Sheffield, UK
| | - Alejandro F Frangi
- Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), The University of Sheffield, Sheffield, UK
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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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Daughter Sac Formation Related to Blood Inflow Jet in an Intracranial Aneurysm. World Neurosurg 2016; 96:396-402. [DOI: 10.1016/j.wneu.2016.09.040] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2016] [Revised: 09/08/2016] [Accepted: 09/08/2016] [Indexed: 10/21/2022]
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Sarrami-Foroushani A, Lassila T, Gooya A, Geers AJ, Frangi AF. Uncertainty quantification of wall shear stress in intracranial aneurysms using a data-driven statistical model of systemic blood flow variability. J Biomech 2016; 49:3815-3823. [PMID: 28573970 DOI: 10.1016/j.jbiomech.2016.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 09/06/2016] [Accepted: 10/09/2016] [Indexed: 01/17/2023]
Abstract
Adverse wall shear stress (WSS) patterns are known to play a key role in the localisation, formation, and progression of intracranial aneurysms (IAs). Complex region-specific and time-varying aneurysmal WSS patterns depend both on vascular morphology as well as on variable systemic flow conditions. Computational fluid dynamics (CFD) has been proposed for characterising WSS patterns in IAs; however, CFD simulations often rely on deterministic boundary conditions that are not representative of the actual variations in blood flow. We develop a data-driven statistical model of internal carotid artery (ICA) flow, which is used to generate a virtual population of waveforms used as inlet boundary conditions in CFD simulations. This allows the statistics of the resulting aneurysmal WSS distributions to be computed. It is observed that ICA waveform variations have limited influence on the time-averaged WSS (TAWSS) on the IA surface. In contrast, in regions where the flow is locally highly multidirectional, WSS directionality and harmonic content are strongly affected by the ICA flow waveform. As a consequence, we argue that the effect of blood flow variability should be explicitly considered in CFD-based IA rupture assessment to prevent confounding the conclusions.
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Affiliation(s)
- Ali Sarrami-Foroushani
- Centre for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), Department of Electronic and Electrical Engineering, The University of Sheffield, Pam Liversidge Building, Mappin Street, Sheffield S1 3JD, UK
| | - Toni Lassila
- Centre for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), Department of Electronic and Electrical Engineering, The University of Sheffield, Pam Liversidge Building, Mappin Street, Sheffield S1 3JD, UK
| | - Ali Gooya
- Centre for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), Department of Electronic and Electrical Engineering, The University of Sheffield, Pam Liversidge Building, Mappin Street, Sheffield S1 3JD, UK
| | - Arjan J Geers
- Centre for Cardiovascular Science, University of Edinburgh, UK
| | - Alejandro F Frangi
- Centre for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), Department of Electronic and Electrical Engineering, The University of Sheffield, Pam Liversidge Building, Mappin Street, Sheffield S1 3JD, UK.
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Fluid-Structure Simulations of a Ruptured Intracranial Aneurysm: Constant versus Patient-Specific Wall Thickness. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2016; 2016:9854539. [PMID: 27721898 PMCID: PMC5045998 DOI: 10.1155/2016/9854539] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 07/31/2016] [Indexed: 11/17/2022]
Abstract
Computational Fluid Dynamics is intensively used to deepen the understanding of aneurysm growth and rupture in order to support physicians during therapy planning. However, numerous studies considering only the hemodynamics within the vessel lumen found no satisfactory criteria for rupture risk assessment. To improve available simulation models, the rigid vessel wall assumption has been discarded in this work and patient-specific wall thickness is considered within the simulation. For this purpose, a ruptured intracranial aneurysm was prepared ex vivo, followed by the acquisition of local wall thickness using μCT. The segmented inner and outer vessel surfaces served as solid domain for the fluid-structure interaction (FSI) simulation. To compare wall stress distributions within the aneurysm wall and at the rupture site, FSI computations are repeated in a virtual model using a constant wall thickness approach. Although the wall stresses obtained by the two approaches—when averaged over the complete aneurysm sac—are in very good agreement, strong differences occur in their distribution. Accounting for the real wall thickness distribution, the rupture site exhibits much higher stress values compared to the configuration with constant wall thickness. The study reveals the importance of geometry reconstruction and accurate description of wall thickness in FSI simulations.
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Schrauwen JTC, Schwarz JCV, Wentzel JJ, van der Steen AFW, Siebes M, Gijsen FJH. The impact of scaled boundary conditions on wall shear stress computations in atherosclerotic human coronary bifurcations. Am J Physiol Heart Circ Physiol 2016; 310:H1304-12. [PMID: 26945083 DOI: 10.1152/ajpheart.00896.2015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Accepted: 02/26/2016] [Indexed: 01/06/2023]
Abstract
The aim of this study was to determine if reliable patient-specific wall shear stress (WSS) can be computed when diameter-based scaling laws are used to impose the boundary conditions for computational fluid dynamics. This study focused on mildly diseased human coronary bifurcations since they are predilection sites for atherosclerosis. Eight patients scheduled for percutaneous coronary intervention were imaged with angiography. The velocity proximal and distal of a bifurcation was acquired with intravascular Doppler measurements. These measurements were used for inflow and outflow boundary conditions for the first set of WSS computations. For the second set of computations, absolute inflow and outflow ratios were derived from geometry-based scaling laws based on angiography data. Normalized WSS maps per segment were obtained by dividing the absolute WSS by the mean WSS value. Absolute and normalized WSS maps from the measured-approach and the scaled-approach were compared. A reasonable agreement was found between the measured and scaled inflows, with a median difference of 0.08 ml/s [-0.01; 0.20]. The measured and the scaled outflow ratios showed a good agreement: 1.5 percentage points [-19.0; 4.5]. Absolute WSS maps were sensitive to the inflow and outflow variations, and relatively large differences between the two approaches were observed. For normalized WSS maps, the results for the two approaches were equivalent. This study showed that normalized WSS can be obtained from angiography data alone by applying diameter-based scaling laws to define the boundary conditions. Caution should be taken when absolute WSS is assessed from computations using scaled boundary conditions.
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Affiliation(s)
- Jelle T C Schrauwen
- Department of Biomedical Engineering, Thorax Center, Erasmus Medical Center, Rotterdam, The Netherlands
| | - Janina C V Schwarz
- Department of Biomedical Engineering and Physics, Academic Medical Center, Amsterdam, The Netherlands; and
| | - Jolanda J Wentzel
- Department of Biomedical Engineering, Thorax Center, Erasmus Medical Center, Rotterdam, The Netherlands
| | - Antonius F W van der Steen
- Department of Biomedical Engineering, Thorax Center, Erasmus Medical Center, Rotterdam, The Netherlands; Department of Imaging Physics, Delft University of Technology, Delft, The Netherlands
| | - Maria Siebes
- Department of Biomedical Engineering and Physics, Academic Medical Center, Amsterdam, The Netherlands; and
| | - Frank J H Gijsen
- Department of Biomedical Engineering, Thorax Center, Erasmus Medical Center, Rotterdam, The Netherlands;
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