Computational design of Intracranial Stent p gusing 3D visualization system

Institute of Fluid Science, Tohoku UniversityMakoto OHTA

Graduate school of EngineeringHitomi Anzai

Graduate school of Biomedical EngineeringToshio Nakayama

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Background

Cause-specific death rate in Japan (H19) Endovascular treatment

Causes of death Stent placement

(Population Survey Report )

Minimal invasivenessGood prognosis of pationts

Endovascular treatment

Malignantneoplasm35 8%P i

otherSole stenting

Reduction of flow in aneurysm35.8%Pneumonia

11.7%M. Aenis et al. (1997)

aneurysm

Heart disease18.7%

Cerebral vasculardisease13.5%

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Cardiovascular disease32.3%

stent strut

Integration of realistic stent data to realistic patient data

Our team firstly succeeded to develop this method in the world

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y pAnd provided this techniques to VISC (2006).

MethodAne r sm and stent geometr as reconstr cted merging geometriesAneurysm and stent geometry was reconstructedusing Digital Subtraction Angiography and Micro CT

merging geometriesusing 3D CAD technique

Inlet

OutletInlet・Velocity : 0.162 [m/s]・Density : 1050 [kg/m3]

Numerical simulation・Finite Volume Method・Incompressible-Newtonian

Boundary condition on the wall・Non-Slip

Outlet

Density : 1050 [kg/m ]・Viscosity : 0.0035 [Pa・s]・Reynolds number : about 200

(assuming Basilar Artery)O

pfluid

・Equation of continuity・Navier-Stokes equations・Steady flow

Mesh・The number : about 1,200,000

(in all cases)T T h d

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Outlet・Pressure : 0 [Pa]

・Steady flow・Fluent 6.3 (Fluent, Inc.)

・Type : Tetrahedron・Using Size Function

Figure: Stent image

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Silk stent

Still tStill rupture...Risk of embolizationStill underfinished..Less materials is better

We need to reduce the material volume

Look for the most effective (reduce-able) point

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Realization Workspace (CAVE) in IFS3D realization may help a lot for understanding the flow3D realization may help a lot for understanding the flow

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Specification of inflow zone

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Purpose

Background and Purpose

To verify the validity of 3D visualization to understand the flowon stent as a new way of stent development

Purpose

Flowchart

G d t t ?

Numerical Simulation

Good stent ?Good knowledge about

effective stenting ?

3D Visualization

Discussions

Improvement of stent

Numerical simulation

Specification of inflow zonecc

Numerical simulation(before strut addition)

& Inflow zone

Inflow from Inlet

3D visualization

Addition of strutto cover inflow zone

Outflow to Outlet

Flow

“Inflow zone”Add a strut at this position

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Addition of strut

• Strut diameter : 0.15 [mm]

• Curvature : 667 [1/m]

• Change strut position

x=0.50[mm] x=1.30[mm] x=2.00[mm]12

The role of stent strut on the flow

FlowAddition of strut

x=1.00[mm]x=0.50[mm] x=1.30[mm]Velocity

SSWSS

x=1.65 [mm] x=2.00[mm]15

The most effective stenting position ・・・？

Flow is very complex around aneurysm!We cannot understand what factor can reduce the flow without visual information!

To verify the validity of 3D visualization to understand the flowPurpose

We cannot understand what factor can reduce the flow without visual information!

To verify the validity of 3D visualization to understand the flowon stent as a new way of stent development

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Models We used 3types of real arterial geometry

MethodModels

Flowchart

We used 3types of real arterial geometry

Numerical Simulation

3D VisualizationConditions

Inlet・uniform velocity profile

Outlet・Pressure: 0 [Pa]

Discussions

・uniform velocity profile ・steady flow・rate: 2.36×10-6 [m3/s]

・Pressure: 0 [Pa]Viscosity: 4.0×10-3 [Pa⊕s]Density: 1.0×103 [kg/m3]

Improvement of stent

3D visualization

We visualized numerical results in Realization

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Workspace (AFI-IFS)Software : EnSight Gold 8.2 (CEI)

Results1 Specification of inflow zone

2 inlets & 1 outlet 1 inlet & 3 outlets1 inlet & 1 outlet

Inflow zone Inflow zoneInflow zone

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Proceedings of ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting and 8th International Conference on Nanochannels, Microchannels, and Minichannels FEDSM2010-ICNMM2010 August 1-5, 2010, Montreal, Canada

FEDSM-ICNMM2010-30591THE EFFECT OF 3D VISUALIZATION ON OPTIMAL DESIGN FOR STRUT POSITION OF INTRACRANIAL STENT

Hitomi Anzai, Toshio Nakayama, Yuriko Takeshima, Makoto Ohta

Results2 Strut placement1 inlet & 1 outletStrut position 1 inlet & 1 outlet

■Strut position was decided to disturb inflow from parent artery

Strut position

from parent artery.■Strut was placed using 3D CAD techniques.

Strut

Without strut With one strut2 inlet s& 1 outlet

After placement Strut

■The flow direction is changed.■WSS di trib ti i

p

Strut

1 inlet & 3 outlets■WSS distribution is changed.

18Without strut With one strut

Parameter Study of HemodynamicsParameter Study of Hemodynamics Simulation at Internal

Carotid StenosisCarotid Stenosis

○ Toshio Nakayama Institute of Fluid Science, Tohoku University

Hitoshi Hayase Neurological Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, y

Koji Tokunaga Neurological Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences

Makoto Ohta Institute of Fluid Science, Tohoku UniversityMakoto Ohta Institute of Fluid Science, Tohoku University

Nakayama, Hayase, Tokunaga, Ohta, J. Flu. Sci. Tech. 3, 544, 08The effect of outlet pressure on the flow distribution

0P 280P 420P0Pa 280Pa 420Pa

Simulation ResultsSimulation Results

• Flow rate proportion & maximum flow• Flow rate proportion & maximum flow velocity of ICA ECA

Pressure to internal carotid artery [Pa]

0 70 140 210 280 350 420

Max.Velocity (ICA) [m/s] 1.3200 1.2903 1.2608 1.2324 1.2017 1.1723 1.1867

Max.Velocity(ECA) [m/s] 1.0532 1.0770 1.1000 1.1220 1.1467 1.1701 1.1932

Flow rate proportion 1.2533 1.1980 1.1461 1.0983 1.0479 1.0018 0.9945

• Output of ultrasound – ICA： 1 124[m/s] ECA: 1 094 [m/s]ICA： 1.124[m/s], ECA: 1.094 [m/s]– Flow rate proportion: 102.74

The proper flow rateThe proper flow rate

•• The proper of flow rate:Flow rate of simulation

= Flow rate of ultrasound

I t ti i t liporti

on

Intersection in two lines

Form figure,I t l tid t 310 922[P ]at

e to

pro

•Internal carotid artery: 310.922[Pa]

Flow

ra

[Pa]Pressure:Flow rate of ultrasound

:Flow rate of simulation

ResultsResults

• The Proper Case ResultsThe Proper Case Results• Outlet Condition

– ICA:310.922 [Pa]ICA:310.922 [Pa]– ECA:0 [Pa]

• Velocity (Measurement Position))– Internal carotid artery:

1.1888[m/s]– External carotid artery:

1.1585[m/s]

Optimisation of StentsOptimisation of Stents

Makoto OHTA, K SrinivasInstitute of Flow Science, Tohoku Universityy

Sydney University

OptimisationOptimisationOptimisationOptimisation

Latin HypercubeLatin Hypercubesample Variables

FLUENTE l t FitEvaluate Fitness

KriggingThe best candidate

60 samples

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Two-dimensional optimisation of a stent for cerebral aneurysm

K. Srinivas, M. Ohta, T. Nakayama, S. Obayashi, T. Yamaguchi

Journal of Medical Devices (accepted)

Objective FunctionObjective FunctionObjective FunctionObjective Function

MaximiseMaximiseMaximise Maximise Velocity

Reduction Shear StressReduction in

C iinCavity

Cavity

VorticityyReduction in

Cavity

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Computational DetailsComputational Details5mm

5mm

5mm

10mm4mm

40mm

10mm

• 2D Computation with 75,000 nodes• Reynolds Number 300 Inlet velocity 0 3 m/sReynolds Number 300, Inlet velocity 0.3 m/s. • Standard Boundary Conditions• Each calculation about 2 mins on Super ComputerEach calculation about 2 mins on Super Computer

Non Dominated SolutionsNon Dominated Solutions(Aneurysm)(Aneurysm)

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Optimal StrutOptimal Strut--Gap ArrangementsGap ArrangementsOptimal StrutOptimal Strut Gap ArrangementsGap Arrangements

⊗ V -max

-max⊗

V ma⊗

compromise

V -max⊗

-max⊗

compromise

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Proceedings of ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting and 8th International Conference on Nanochannels Microchannels and Minichannels

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International Conference on Nanochannels, Microchannels, and Minichannels

FEDSM2010-ICNMM2010 August 2-4, 2010, Montreal, Canada FEDSM-ICNMM2010-30592

DEVELOPMENT OF STENT STRUT PATTERN FOR CEREBRAL ANEURYSM

Toshio Nakayama, Shinkyu Jeong, Srinivas karkenahalli, Makoto Ohta

Conclusion

・WSS distribution and flow pattern were changed by one strut.・3D visualization system may be useful to observe flow pattern around strut.・These 3D information may be helpful to design stent strut pattern.

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Thank you for your attention

www.ics-meeting.net

AcknowledgementAcknowledgement

Global COE in IFS, Tohoku University, JSPSCore to core in IFS, Tohoku University, JSPSG t i id JNIHGrant-in-aid, JNIHGrant-in-aid, JSPS

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