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

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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Statistical wall shear stress maps of ruptured and unruptured middle cerebral artery aneurysms

Journal of The Royal Society Interface ◽

10.1098/rsif.2011.0490 ◽

2011 ◽

Vol 9 (69) ◽

pp. 677-688 ◽

Cited By ~ 37

Author(s):

L. Goubergrits ◽

J. Schaller ◽

U. Kertzscher ◽

N. van den Bruck ◽

K. Poethkow ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Middle Cerebral Artery ◽

Cerebral Artery ◽

Dimensional Space ◽

Neck Region ◽

Spherical Shape ◽

Unruptured Aneurysms ◽

Ruptured Aneurysms ◽

Wall Shear

Haemodynamics and morphology play an important role in the genesis, growth and rupture of cerebral aneurysms. The goal of this study was to generate and analyse statistical wall shear stress (WSS) distributions and shapes in middle cerebral artery (MCA) saccular aneurysms. Unsteady flow was simulated in seven ruptured and 15 unruptured MCA aneurysms. In order to compare these results, all geometries must be brought in a uniform coordinate system. For this, aneurysms with corresponding WSS data were transformed into a uniform spherical shape; then, all geometries were uniformly aligned in three-dimensional space. Subsequently, we compared statistical WSS maps and surfaces of ruptured and unruptured aneurysms. No significant ( p > 0.05) differences exist between ruptured and unruptured aneurysms regarding radius and mean WSS. In unruptured aneurysms, statistical WSS map relates regions with high (greater than 3 Pa) WSS to the neck region. In ruptured aneurysms, additional areas with high WSS contiguous to regions of low (less than 1 Pa) WSS are found in the dome region. In ruptured aneurysms, we found significantly lower WSS. The averaged aneurysm surface of unruptured aneurysms is round shaped, whereas the averaged surface of ruptured cases is multi-lobular. Our results confirm the hypothesis of low WSS and irregular shape as the essential rupture risk parameters.

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Quantification of hemodynamic irregularity using oscillatory velocity index in the associations with the rupture status of cerebral aneurysms

Journal of NeuroInterventional Surgery ◽

10.1136/neurintsurg-2018-014489 ◽

2019 ◽

Vol 11 (6) ◽

pp. 614-617 ◽

Cited By ~ 2

Author(s):

Satoru Tanioka ◽

Fujimaro Ishida ◽

Tomoyuki Kishimoto ◽

Masanori Tsuji ◽

Katsuhiro Tanaka ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Cerebral Aneurysms ◽

Flow Patterns ◽

Hemodynamic Parameter ◽

Hemodynamic Parameters ◽

Unstable Flow ◽

Ruptured Aneurysms ◽

Oscillatory Velocity ◽

Wall Shear

BackgroundComplex and unstable flow patterns are reported to be associated with the rupture status of cerebral aneurysms, while their evaluation depends on qualitative analysis of streamlines of bloodflow. Oscillatory velocity index (OVI) is a hemodynamic parameter to quantify flow patterns. The aim of this study is to elucidate the associations between OVI and the rupture status of cerebral aneurysms.MethodsOne hundred and twenty-nine ruptured and unruptured cerebral aneurysms were analyzed with computational fluid dynamics under pulsatile flow conditions. With the use of median value of OVI, all aneurysms were divided into high and low OVI groups. Statistical analysis was performed to compare rupture status, and morphological and hemodynamic parameters between the two groups.ResultsThe median value of OVI was 0.006. High OVI was more likely observed in ruptured aneurysms (P=0.028) and associated with irregular shape, complex flow patterns, and unstable flow patterns (P<0.001, respectively). In morphological parameters, maximum size, aspect, projection, size, and volume-to-ostium area ratios were significantly higher in the high OVI group (P<0.001, respectively). In hemodynamic parameters, wall shear stress and wall shear stress gradient were significantly lower, and oscillatory shear index and gradient oscillatory number were significantly higher in the high OVI group (P<0.001, respectively).ConclusionHigh OVI was associated with rupture status, and morphological and hemodynamic characteristics of ruptured aneurysms. These results indicate that OVI may serve as a valuable hemodynamic parameter for diagnosing rupture status and risks of aneurysms.

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Hemodynamics in growing and stable cerebral aneurysms

Journal of NeuroInterventional Surgery ◽

10.1136/neurintsurg-2014-011339 ◽

2015 ◽

Vol 8 (4) ◽

pp. 407-412 ◽

Cited By ~ 29

Author(s):

Daniel M Sforza ◽

Kenichi Kono ◽

Satoshi Tateshima ◽

Fernando Viñuela ◽

Christopher Putman ◽

...

Keyword(s):

Shear Stress ◽

Logistic Regression ◽

Wall Shear Stress ◽

Statistical Models ◽

Three Dimensional ◽

Cerebral Aneurysms ◽

Patient Specific ◽

Unruptured Aneurysms ◽

Aspect Ratios ◽

Wall Shear

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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Analysis of Morphological-Hemodynamic Risk Factors for Aneurysm Rupture Including a Newly Introduced Total Volume Ratio

Journal of Personalized Medicine ◽

10.3390/jpm11080744 ◽

2021 ◽

Vol 11 (8) ◽

pp. 744

Author(s):

Ui Yun Lee ◽

Hyo Sung Kwak

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Volume Ratio ◽

Wall Stress ◽

Aneurysm Rupture ◽

Oscillatory Shear Index ◽

Unstable Flow ◽

Ruptured Aneurysms ◽

Wall Shear

The purpose of this study was to evaluate morphological and hemodynamic factors, including the newly developed total volume ratio (TVR), in evaluating rupture risk of cerebral aneurysms using ≥7 mm sized aneurysms. Twenty-three aneurysms (11 unruptured and 12 ruptured) ≥ 7 mm were analyzed from 3-dimensional rotational cerebral angiography and computational fluid dynamics (CFD). Ten morphological and eleven hemodynamic factors of the aneurysms were qualitatively and quantitatively compared. Correlation analysis between morphological and hemodynamic factors was performed, and the relationship among the hemodynamic factors was analyzed. Morphological factors (ostium diameter, ostium area, aspect ratio, and bottleneck ratio) and hemodynamic factors (TVR, minimal wall shear stress of aneurysms, time-averaged wall shear stress of aneurysms, oscillatory shear index, relative residence time, low wall shear stress area, and ratio of low wall stress area) were statistically different between ruptured and unruptured aneurysms (p < 0.05). By simple regression analysis, the morphological factor aspect ratio and the hemodynamic factor TVR were significantly correlated (r2 = 0.602, p = 0.001). Ruptured aneurysms had complex and unstable flow. In ≥7 mm ruptured aneurysms, high aspect ratio, bottleneck ratio, complex flow, unstable flow, low TVR, wall shear stress at aneurysm, high oscillatory shear index, relative resistance time, low wall shear stress area, and ratio of low wall stress area were significant in determining the risk of aneurysm rupture.

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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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Role of pressure and wall shear stress in initiation and development of cerebral aneurysms

2011 2nd International Conference on Instrumentation, Communications, Information Technology, and Biomedical Engineering ◽

10.1109/icici-bme.2011.6108629 ◽

2011 ◽

Cited By ~ 2

Author(s):

Nedya Utami ◽

Hasballah Zakaria ◽

Tati L. R. Mengko ◽

Oerip S. Santoso

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Cerebral Aneurysms ◽

Wall Shear

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An Effect of Aspect Ratio and Roughness on the Wall Shear Stress of Open Channel

PROCEEDINGS OF THE JAPANESE CONFERENCE ON HYDRAULICS ◽

10.2208/prohe1975.29.821 ◽

1985 ◽

Vol 29 ◽

pp. 821-826

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Open Channel ◽

Wall Shear

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Assessing Bioinspired Topographies for their Antifouling Potential Control Using Computational Fluid Dynamics (CFD)

MATEC Web of Conferences ◽

10.1051/matecconf/201815202004 ◽

2018 ◽

Vol 152 ◽

pp. 02004 ◽

Cited By ~ 1

Author(s):

Jacky Ling ◽

Felicia Wong Yen Myan

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Extended Period ◽

Slip Boundary Condition ◽

Shear Stresses ◽

Cfd Simulations ◽

Potential Control ◽

Slip Boundary ◽

Computational Fluid Dynamics Cfd ◽

Wall Shear

Biofouling is the accumulation of unwanted material on surfaces submerged or semi submerged over an extended period. This study investigates the antifouling performance of a new bioinspired topography design. A shark riblets inspired topography was designed with Solidworks and CFD simulations were antifouling performance. The study focuses on the fluid flow velocity, the wall shear stress and the appearance of vortices are to be noted to determine the possible locations biofouling would most probably occur. The inlet mass flow rate is 0.01 kgs-1 and a no-slip boundary condition was applied to the walls of the fluid domain. Simulations indicate that Velocity around the topography averaged at 7.213 x 10-3 ms-1. However, vortices were observed between the gaps. High wall shear stress is observed at the peak of each topography. In contrast, wall shear stress is significantly low at the bed of the topography. This suggests the potential location for the accumulation of biofouling. Results show that bioinspired antifouling topography can be improved by reducing the frequency of gaps between features. Linear surfaces on the topography should also be minimized. This increases the avenues of flow for the fluid, thus potentially increasing shear stresses with surrounding fluid leading to better antifouling performance.

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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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