Hemodynamics in growing and stable cerebral aneurysms

ObjectiveThe detailed mechanisms of cerebral aneurysm evolution are poorly understood but are important for objective aneurysm evaluation and improved patient management. The purpose of this study was to identify hemodynamic conditions that may predispose aneurysms to growth.MethodsA total of 33 intracranial unruptured aneurysms longitudinally followed with three-dimensional imaging were studied. Patient-specific computational fluid dynamics models were constructed and used to quantitatively characterize the hemodynamic environments of these aneurysms. Hemodynamic characteristics of growing (n=16) and stable (n=17) aneurysms were compared. Logistic regression statistical models were constructed to test the predictability of aneurysm growth by hemodynamic features.ResultsGrowing aneurysms had significantly smaller shear rate ratios (p=0.01), higher concentration of wall shear stress (p=0.03), smaller vorticity ratios (p=0.01), and smaller viscous dissipation ratios (p=0.01) than stable aneurysms. They also tended to have larger areas under low wall shear stress (p=0.06) and larger aspect ratios (p=0.18), but these trends were not significant. Mean wall shear stress was not significantly different between growing and stable aneurysms. Logistic regression models based on hemodynamic variables were able to discriminate between growing and stable aneurysms with a high degree of accuracy (94–100%).ConclusionsGrowing aneurysms tend to have complex intrasaccular flow patterns that induce non-uniform wall shear stress distributions with areas of concentrated high wall shear stress and large areas of low wall shear stress. Statistical models based on hemodynamic features seem capable of discriminating between growing and stable aneurysms.

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Exploring High Frequency Temporal Fluctuations in the Terminal Aneurysm of the Basilar Bifurcation

Journal of Biomechanical Engineering ◽

10.1115/1.4007279 ◽

2012 ◽

Vol 134 (9) ◽

Cited By ~ 15

Author(s):

Matthew D. Ford ◽

Ugo Piomelli

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

High Frequency ◽

Cerebral Aneurysms ◽

Patient Specific ◽

Disturbed Flow ◽

Frequency Fluctuations ◽

Wall Shear ◽

Inflow Jet

Cerebral aneurysms are a common cause of death and disability. Of all the cardiovascular diseases, aneurysms are perhaps the most strongly linked with the local fluid mechanic environment. Aside from early in vivo clinical work that hinted at the possibility of high-frequency intra-aneurysmal velocity oscillations, flow in cerebral aneurysms is most often assumed to be laminar. This work investigates, through the use of numerical simulations, the potential for disturbed flow to exist in the terminal aneurysm of the basilar bifurcation. The nature of the disturbed flow is explored using a series of four idealized basilar tip models, and the results supported by four patient specific terminal basilar tip aneurysms. All four idealized models demonstrated instability in the inflow jet through high frequency fluctuations in the velocity and the pressure at approximately 120 Hz. The instability arises through a breakdown of the inflow jet, which begins to oscillate upon entering the aneurysm. The wall shear stress undergoes similar high-frequency oscillations in both magnitude and direction. The neck and dome regions of the aneurysm present 180 deg changes in the direction of the wall shear stress, due to the formation of small recirculation zones near the shear layer of the jet (at the frequency of the inflow jet oscillation) and the oscillation of the impingement zone on the dome of the aneurysm, respectively. Similar results were observed in the patient-specific models, which showed high frequency fluctuations at approximately 112 Hz in two of the four models and oscillations in the magnitude and direction of the wall shear stress. These results demonstrate that there is potential for disturbed laminar unsteady flow in the terminal aneurysm of the basilar bifurcation. The instabilities appear similar to the first instability mode of a free round jet.

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Computational Fluid Dynamics Characterization of Two Patient-Specific Systemic-to-Pulmonary Shunts before and after Operation

Computational and Mathematical Methods in Medicine ◽

10.1155/2019/1502318 ◽

2019 ◽

Vol 2019 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Neichuan Zhang ◽

Haiyun Yuan ◽

Xiangyu Chen ◽

Jiawei Liu ◽

Qifei Jian ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Pulmonary Artery ◽

Energy Loss ◽

Three Dimensional ◽

Left Pulmonary Artery ◽

Postoperative Recovery ◽

Patient Specific ◽

Wall Shear ◽

Ct Data

Studying the haemodynamics of the central shunt (CS) and modified Blalock–Taussig shunt (MBTS) benefits the improvement of postoperative recovery for patients with an aorta-pulmonary shunt. Shunt configurations, including CS and MBTS, are virtually reconstructed for infants A and B based on preoperative CT data, and three-dimensional models of A, 11 months after CS, and B, 8 months after MBTS, are reconstructed based on postoperative CT data. A series of parameters including energy loss, wall shear stress, and shunt ratio are computed from simulation to analyse the haemodynamics of CS and MBTS. Our results showed that the shunt ratio of the CS is approximately 30% higher than the MBTS and velocity distribution in the left pulmonary artery (LPA) and right pulmonary artery (RPA) was closer to a natural development in the CS than the MBTS. However, energy loss of the MBTS is lower, and the MBTS can provide more symmetric pulmonary artery (PA) flow than the CS. With the growth of infants A and B, the shunt ratio of infants was decreased, but maximum wall shear stress and the distribution region of high wall shear stress (WSS) were increased, which raises the probability of thrombosis. For infant A, the preoperative abnormal PA structure directly resulted in asymmetric growth of PA after operation, and the LPA/RPA ratio decreased from 0.49 to 0.25. Insufficient reserved length of the MBTS led to traction phenomena with the growth of infant B; on the one hand, it increased the eddy current, and on the other hand, it increased the flow resistance of anastomosis, promoting asymmetric PA flow.

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STUDY ON THE RELATIONSHIP BETWEEN WALL SHEAR STRESS AND ASPECT RATIO OF CEREBRAL ANEURYSMS WITH DIFFERENT PRESSURE DIFFERENCES USING CFD SIMULATIONS

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519418500550 ◽

2018 ◽

Vol 18 (05) ◽

pp. 1850055

Author(s):

ALFREDO ARANDA ◽

ALVARO VALENCIA

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Cerebral Aneurysms ◽

Cfd Simulations ◽

Unruptured Aneurysms ◽

Ruptured Aneurysms ◽

Sphericity Index ◽

Wall Shear ◽

The Relationship

CFD simulations were performed for 60 human cerebral aneurysms (30 previously ruptured and 30 previously unruptured) to study the behavior of the time-averaged wall shear stress (TAWSS) with respect to the aspect ratio (AR), implementing a set of low, normal, and high-pressure differences between the inlet and the outlets of each artery. It is well known that there exists a direct relationship between TAWSS and the rupture. In this investigation, we presented an important result because the condition of the pressure among the branches and the AR may be measured in any patient, then a slope may be associated, and finally a TAWSS may be estimated. We found that when the pressure difference increased, the absolute slopes between TAWSS and AR increased as well. Also, the magnitude of the slope in the previously unruptured aneurysms was 4.7 times the slope in the previously ruptured aneurysms. On the other hand, TAWSS was higher in the previously unruptured aneurysm than previously ruptured aneurysms due to the unruptured aneurysms that have a smaller surface area. Furthermore, we analyzed the relationship between TAWSS and other geometric parameters of the aneurysm, such as bottleneck and non-sphericity index; however, no correlation was found for either cases.

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Hemodynamic differences between unstable and stable unruptured aneurysms independent of size and location: a pilot study

Journal of NeuroInterventional Surgery ◽

10.1136/neurintsurg-2016-012327 ◽

2016 ◽

Vol 9 (4) ◽

pp. 376-380 ◽

Cited By ~ 23

Author(s):

Waleed Brinjikji ◽

Bong Jae Chung ◽

Carlos Jimenez ◽

Christopher Putman ◽

David F Kallmes ◽

...

Keyword(s):

Shear Stress ◽

Pilot Study ◽

Wall Shear Stress ◽

Intracranial Aneurysms ◽

Wilcoxon Test ◽

Patient Specific ◽

Unruptured Aneurysms ◽

Unruptured Intracranial Aneurysms ◽

Wall Shear ◽

Geometric Variables

BackgroundWhile clinical and angiographic risk factors for intracranial aneurysm instability are well established, it is reasonable to postulate that intra-aneurysmal hemodynamics also have a role in aneurysm instability.ObjectiveTo identify hemodynamic characteristics that differ between radiologically unstable and stable unruptured intracranial aneurysms.Materials and methods12 pairs of unruptured intracranial aneurysms with a 3D rotational angiographic set of images and followed up longitudinally without treatment were studied. Each pair consisted of one stable aneurysm (no change on serial imaging) and one unstable aneurysm (demonstrated growth of at least 1 mm diameter or ruptured during follow-up) of matching size (within 10%) and locations. Patient-specific computational fluid dynamics models were created and run under pulsatile flow conditions. Relevant hemodynamic and geometric variables were calculated and compared between groups using the paired Wilcoxon test.ResultsThe area of the aneurysm under low wall shear stress (low shear stress area (LSA)) was 2.26 times larger in unstable aneurysms than in stable aneurysms (p=0.0499). The mean aneurysm vorticity was smaller by a factor of 0.57 in unstable aneurysms compared with stable aneurysms (p=0.0499). No statistically significant differences in geometric variables or shape indices were found.ConclusionsThis pilot study suggests there may be hemodynamic differences between unstable and stable unruptured cerebral aneurysms. In particular, the area under low wall shear stress was larger in unstable aneurysms. These findings should be considered tentative until confirmed by future larger studies.

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Cerebral aneurysm rupture status classification using statistical and machine learning methods

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1177/09544119211000477 ◽

2021 ◽

pp. 095441192110004

Author(s):

Nicolás Amigo ◽

Alvaro Valencia ◽

Wei Wu ◽

Sourav Patnaik ◽

Ender Finol

Keyword(s):

Machine Learning ◽

Shear Stress ◽

Random Forest ◽

Wall Shear Stress ◽

Confusion Matrix ◽

Cerebral Aneurysms ◽

Machine Learning Algorithms ◽

Size Ratio ◽

Patient Specific ◽

Wall Shear

Morphological characterization and fluid dynamics simulations were carried out to classify the rupture status of 71 (36 unruptured, 35 ruptured) patient specific cerebral aneurysms using a machine learning approach together with statistical techniques. Eleven morphological and six hemodynamic parameters were evaluated individually and collectively for significance as rupture status predictors. The performance of each parameter was inspected using hypothesis testing, accuracy, confusion matrix, and the area under the receiver operating characteristic curve. Overall, the size ratio exhibited the best performance, followed by the diastolic wall shear stress, and systolic wall shear stress. The prediction capability of all 17 parameters together was evaluated using eight different machine learning algorithms. The logistic regression achieved the highest accuracy (0.75), whereas the random forest had the highest area under curve value among all the classifiers (0.82), surpassing the performance exhibited by the size ratio. Hence, we propose the random forest model as a tool that can help improve the rupture status prediction of cerebral aneurysms.

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Decreased wall shear stress at high-pressure areas predicts the rupture point in ruptured intracranial aneurysms

Journal of Neurosurgery ◽

10.3171/2018.12.jns182897 ◽

2020 ◽

Vol 132 (4) ◽

pp. 1116-1122 ◽

Cited By ~ 1

Author(s):

Tomoaki Suzuki ◽

Christopher J. Stapleton ◽

Matthew J. Koch ◽

Kazutoshi Tanaka ◽

Soichiro Fujimura ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Dynamic Pressure ◽

Cerebral Aneurysms ◽

Aneurysm Rupture ◽

Maximum Pressure ◽

Parent Artery ◽

Hemodynamic Parameters ◽

Unruptured Aneurysms ◽

Wall Shear

OBJECTIVEDegenerative cerebral aneurysm walls are associated with aneurysm rupture and subarachnoid hemorrhage. Thin-walled regions (TWRs) represent fragile areas that may eventually lead to aneurysm rupture. Previous computational fluid dynamics (CFD) studies reported the correlation of maximum pressure (Pmax) areas and TWRs; however, the correlation with aneurysm rupture has not been established. This study aims to investigate this hemodynamic correlation.METHODSThe aneurysmal wall surface at the Pmax areas was intraoperatively evaluated using a fluid flow formula under pulsatile blood flow conditions in 23 patients with 23 saccular middle cerebral artery (MCA) bifurcation aneurysms (16 unruptured and 7 ruptured). The pressure difference (Pd) at the Pmax areas was calculated by subtracting the average pressure (Pave) from the Pmax and normalized by dividing this by the dynamic pressure at the aneurysm inlet side. The wall shear stress (WSS) was also calculated at the Pmax areas, aneurysm dome, and parent artery. These hemodynamic parameters were used to validate the correlation with TWRs in unruptured MCA aneurysms. The characteristic hemodynamic parameters at the rupture points in ruptured MCA aneurysms were then determined.RESULTSIn 13 of 16 unruptured aneurysms (81.2%), Pmax areas were identified that corresponded to TWRs. In 5 of the 7 ruptured cerebral aneurysms, the Pmax areas coincided with the rupture point. At these areas, the Pd values were not higher than those of the TWRs in unruptured cerebral aneurysms; however, minimum WSS, time-averaged WSS, and normalized WSS at the rupture point were significantly lower than those of the TWRs in unruptured aneurysms (p < 0.01).CONCLUSIONSAt the Pmax area of TWRs, decreased WSS appears to be the crucial hemodynamic parameter that indicates the risk of aneurysm rupture.

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Near-Wall Flow in Cerebral Aneurysms

Fluids ◽

10.3390/fluids4020089 ◽

2019 ◽

Vol 4 (2) ◽

pp. 89 ◽

Cited By ~ 3

Author(s):

Vahid Goodarzi Ardakani ◽

Xin Tu ◽

Alberto M. Gambaruto ◽

Iolanda Velho ◽

Jorge Tiago ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Flow Field ◽

Cardiovascular System ◽

Cerebral Aneurysms ◽

Patient Specific ◽

Normal Velocity ◽

Wall Flow ◽

Wall Shear ◽

Near Wall

The region where the vascular lumen meets the surrounding endothelium cell layer, hence the interface region between haemodynamics and cell tissue, is of primary importance in the physiological functions of the cardiovascular system. The functions include mass transport to/from the blood and tissue, and signalling via mechanotransduction, which are primary functions of the cardiovascular system and abnormalities in these functions are known to affect disease formation and vascular remodelling. This region is denoted by the near-wall region in the present work, and we outline simple yet effective numerical recipes to analyse the near-wall flow field. Computational haemodynamics solutions are presented for six patient specific cerebral aneurysms, at three instances in the cardiac cycle: peak systole, end systole (taken as dicrotic notch) and end diastole. A sensitivity study, based on Newtonian and non-Newtonian rheological models, and different flow rate profiles, is effected for a selection of aneurysm cases. The near-wall flow field is described by the wall shear stress (WSS) and the divergence of wall shear stress (WSSdiv), as descriptors of tangential and normal velocity components, respectively, as well as the wall shear stress critical points. Relations between near-wall and free-stream flow fields are discussed.

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In-Vitro Blood Flow and Wall Shear Stress Measurements in Idealised and Patient Specific Models of the Carotid Artery Bifurcation

ASME 2008 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2008-193263 ◽

2008 ◽

Cited By ~ 1

Author(s):

Nicolas A. Buchmann ◽

Mark C. Jermy

Keyword(s):

Shear Stress ◽

Carotid Artery ◽

Wall Shear Stress ◽

Three Dimensional ◽

Patient Specific ◽

Specific Geometry ◽

Wall Shear ◽

Magnetic Resonance Imaging Mri ◽

Vitro Model

This work presents Particle Image Velocimetry (PIV) measurements in idealised and patient specific human carotid artery bifurcations (CAB) under steady and pulsatile flow. The geometry and corresponding boundary conditions were obtained by Magnetic Resonance Imaging (MRI) and replicated in an in-vitro model. A complex three-dimensional flow structure exists inside the CAB and vorticity and wall shear stress data are used to quantify the differences between the idealised and patient specific geometry.

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Wall shear stress gradient is independently associated with middle cerebral artery aneurysm development: a case-control CFD patient-specific study based on 77 patients

BMC Neurology ◽

10.1186/s12883-021-02251-3 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Mikołaj Zimny ◽

Edyta Kawlewska ◽

Anna Hebda ◽

Wojciech Wolański ◽

Piotr Ładziński ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Middle Cerebral Artery ◽

Cerebral Artery ◽

Case Control ◽

Independent Effect ◽

Patient Specific ◽

Aneurysm Formation ◽

Wall Shear ◽

Mca Aneurysm

Abstract Background Previously published computational fluid dynamics (CFD) studies regarding intracranial aneurysm (IA) formation present conflicting results. Our study analysed the involvement of the combination of high wall shear stress (WSS) and a positive WSS gradient (WSSG) in IA formation. Methods We designed a case-control study with a selection of 38 patients with an unruptured middle cerebral artery (MCA) aneurysm and 39 non-aneurysmal controls to determine the involvement of WSS, oscillatory shear index (OSI), the WSSG and its absolute value (absWSSG) in aneurysm formation based on patient-specific CFD simulations using velocity profiles obtained from transcranial colour-coded sonography. Results Among the analysed parameters, only the WSSG had significantly higher values compared to the controls (11.05 vs − 14.76 [Pa/mm], P = 0.020). The WSS, absWSSG and OSI values were not significantly different between the analysed groups. Logistic regression analysis identified WSS and WSSG as significant co-predictors for MCA aneurysm formation, but only the WSSG turned out to be a significant independent prognosticator (OR: 1.009; 95% CI: 1.001–1.017; P = 0.025). Significantly more patients (23/38) in the case group had haemodynamic regions of high WSS combined with a positive WSSG near the bifurcation apex, while in the control group, high WSS was usually accompanied by a negative WSSG (14/39). From the analysis of the ROC curve for WSSG, the area under the curve (AUC) was 0.654, with the optimal cut-off value −0.37 Pa/mm. The largest AUC was recognised for combined WSS and WSSG (AUC = 0.671). Our data confirmed that aneurysms tend to form near the bifurcation apices in regions of high WSS values accompanied by positive WSSG. Conclusions The development of IAs is determined by an independent effect of haemodynamic factors. High WSS impacts MCA aneurysm formation, while a positive WSSG mainly promotes this process.

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