aneurysm - a diverticulum the arterial wall due to its stretching
DESCRIPTION
Unsteady hemodynamic simulation of cerebral aneurysms А.А. Cherevko , А. P . Chupakhin , А.А. Yanchenko ( IGiL SB RAS , NSU ). Aneurysm - a diverticulum the arterial wall due to its stretching. - PowerPoint PPT PresentationTRANSCRIPT
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Unsteady hemodynamic simulation of cerebral aneurysms
А.А.Cherevko, А.P.Chupakhin, А.А.Yanchenko ( IGiL SB RAS, NSU)
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• Place the appearance of aneurysms: bifurcation of vessels, space anatomical changes structure of vessels, next to the arteriovenous malformation.
• The reasons of occurrence: structural changes in the arteries, hemodynamic factor, mechanical damage of the vessel wall.
• Found in 0.3-5% of the adult population, a rare occurrence in children.
• Aneurysmal wall material differs from the material of a healthy vessel wall.
Aneurysm - a diverticulum the arterial wall due to its stretching
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Endovascular treatment of aneurysms
Аневризма
treatment: embolization stenting
riskiness:rupturerecanalization
aneurysm
catheter
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Aneurysms hemodynamic modeling
• Preoperative simulation should be carried out quickly enough - 1-2 days
• The most simple and effective model, giving sufficient accuracy • Geometry of aneurysm - tomography data (NNIIPK)
• Flow parameters - intravascular pressure and velocity sensor (NNIIPK )
• CFD calculations – ANSYS (IGiL, NSU computer cluster)
What hemodynamic parameters determine the effectiveness of the operation?
What is the safe range of variation of these parameters?
Stages of work: • Reconstruction of the geometry from the CT scan• Numerical simulation of hemodynamics with fixed walls of the vessel • Simulation of the stress-strain state of the wall using the pressure distribution
obtained in the previous stage of the calculation
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Vessel geometry
before after controla year later
Progressive rectification of bifurcation
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Mathematical Statement of the Problem
Blood flow described by the Navier-Stokes equations for three-dimensional motion of an incompressible, viscous
Newtonian fluid
where v - velocity, p - pressure, ν - the kinematic viscosity, Ω - the internal volume of the computational domain, including the configuration of the vessels in the form of the tee and an aneurysm located at the bifurcation. γ = ∂ Ω - boundary wall of the vessel. Boundary conditions:
where vreal and preal - speed and pressure, taken from the sensor during operation.
Гin - cross section of the parent vessel tee; Г1out, Г2out - cross sections of child
vessels
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The computational domain (Before surgery)
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Clinical velocity and pressure data
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Hydrodynamics
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computational grid
Used computational grid of tetrahedra. When mesh refinement is 5 times - deviation of pressure is less than 1%, slightly larger deviations (up to 5%) observed in the values of the velocity modulus. Further refinement grid has almost no influence on the result.
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streamlines (up to stenting)
High speeds, vorticity within the aneurysm.
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Streamlines (after stenting)
Reducing the area of maximum speed. The appearance of "almost circular" vortex.
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Streamlines (control a year later)
Weak vorticity, velocity decreased.
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WSS (up to stenting)
Clearly visible zones of large WSS on bends (not on the cupola!).
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WSS (after stenting)
Zones of large WSS decreased.
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WSS (control a year later)
Zone of high stress is very small, almost all within the normal range (1.5-2 Pa).
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Energy flux (up to stenting)
Loss of energy flux is ~ 9%, which is quite a large value at longer tee is approximately equal to 2 cm
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Energy flux (after stenting)
After surgery, vascular geometry is restored almost to the health and loss constitute ~ 4%.
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Energy flux (control a year later)
Energy loss is ~ 1%.
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mechanics
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wall parameters
vessel aneurysm
Young's modulus 1 МPа 1.2 МPа
Poisson's ratio 0.49 0.49
wall thickness 4,e-4 m 1,e-4 m
Unsteady calculation. Aneurysm's zone has a different properties.
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Total deformation and von-Mises stress (up to stenting)
Maxima concentrated on the aneurysm's cupola.Compared with the stationary calculations: maximum deformations slightly
increased. Stress are increased (4.335e5 against 3.0894e5). Localization of maximums is not changed.
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Total deformation and von-Mises stress (after stenting)
Maximum values decreased slightly.Compared with the stationary calculations: Localization of maximums is not
changed.
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Total deformation and von-Mises stress (control a year later)
The maximum strain decreased by 2 times, the maximum stress at 1/3.
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Comparison of simulation results. (Maxima of displacement and von- Mises stress)
before after a year later
Steady 9.3551e-1 mm3.0894e5 Pа
8.2307e-1 mm3.1445e5 Pа
4.6604e-1 mm2.2557e5 Pа
Transient 1.3116 mm4.3346e5 Pa
1.0937 mm4.1624e5 Pa
6.1321e-1 mm2.9726e5 Pa
1 mm Hg = 133.322 Pа
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conclusions
• Maxima of stresses and displacements in the steady and unsteady calculations based differ in magnitude, but do not differ by location.
• To identify "dangerous places" stationary calculation with allocation of area of the aneurysm can be used.
• To find the magnitudes of stresses and displacements need to use unsteady calculations with allocation of area of the aneurysm.
• Unsteady calculation without separation zone of the aneurysm is not sufficiently accurate
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• Time costs: Steady calculation: a few minutes Transient calculation: 3 hours for 1 simulation
second
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Thank you for your attention!