Computational design of Intracranial Stent using 3D visualization system Institute of Fluid Science, Tohoku University Makoto OHTA Graduate school of Engineering Hitomi Anzai Graduate school of Biomedical Engineering Toshio Nakayama 1
Background Causes of death Cause-specific death rate in Japan (H19) (Population Survey Report ) other Malignant neoplasm Pneumonia 35.8% 11.7% Stent placement Endovascular treatment Sole stenting Minimal invasiveness Good prognosis of pationts Reduction of flow in aneurysm aneurysm M. Aenis et al. (1997) Cerebral vascular disease Heart disease 13.5% 18.7% Cardiovascular disease 32.3% stent strut 2
Integration of realistic stent data to realistic patient data Our team firstly succeeded to develop this method in the world And provided this techniques to VISC (2006). 3
Method Aneurysm and stent geometry was reconstructedcted merging geometries using Digital Subtraction Angiography and Micro CT using 3D CAD technique Inlet Numerical simulation Inlet Finite Volume Method Velocity : 0.162 [m/s] Incompressible-Newtonian Density : 1050 [kg/m 3 ] fluid Viscosity : 0.0035 [Pa s] Equation of continuity Reynolds number : about 200 Navier-Stokes equations (assuming Basilar Artery) Steady flow Outlet Fluent 6.3 (Fluent, Inc.) Pressure : 0 [Pa] Outlet Boundary condition on the wall Non-Slip Mesh The number : about 1,200,000 (in all cases) Type : Tetrahedron Using Size Function 6
Figure: Stent image 5
Silk stent Still rupture... Risk of embolization Still underfinished.. Less materials is better
We need to reduce the material volume Look for the most effective (reduce-able) point 7
Realization Workspace (CAVE) in IFS 3D realization may help a lot for understanding the flow 8
Specification of inflow zone 9
Background and Purpose Purpose To verify the validity of 3D visualization to understand the flow on stent as a new way of stent development Flowchart Numerical Simulation 3D Visualization Good stent t? Good knowledge about effective stenting? Discussions Improvement of stent
Specification of inflow zone cc Numerical simulation (before strut addition) & 3D visualization Inflow from Inlet Inflow zone Addition of strut to cover inflow zone Outflow to Outlet Flow Inflow zone Add a strut at this position 10
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
Addition of strut Flow Velocity WSS x=0.50[mm] x=1.00[mm] x=1.30[mm] 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! Purpose To verify the validity of 3D visualization to understand the flow on stent as a new way of stent development 15
Method Models We used 3types of real arterial geometry Flowchart Numerical Simulation Conditions Inlet uniform velocity profile steady flow rate: 2.36 10-6 [m 3 /s] 3D visualization Outlet Pressure: 0 [Pa] Viscosity: 4.0 10-3 [Pa s] Density: 1.0 10 3 [kg/m 3 ] 3D Visualization Discussions We visualized numerical results in Realization Workspace (AFI-IFS) Software : EnSight Gold 8.2 (CEI) Improvement of stent 16
Results1 Specification of inflow zone 1 inlet & 1 outlet 2 inlets & 1 outlet 1 inlet & 3 outlets Inflow zone Inflow zone Inflow zone 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-ICNMM2010-30591 THE EFFECT OF 3D VISUALIZATION ON OPTIMAL DESIGN FOR STRUT POSITION OF INTRACRANIAL STENT Hitomi Anzai, Toshio Nakayama, Yuriko Takeshima, Makoto Ohta 17
Results2 Strut placement Strut position Strut position was decided to disturb inflow from parent artery. Strut was placed using 3D CAD techniques. 1 inlet & 1 outlet 2 inlet s& 1 outlet Without strut With one strut After placement The flow direction is changed. WSS distribution ti is changed. Strut 1 inlet & 3 outlets Strut Without strut With one strut 18
Parameter Study of Hemodynamics Simulation at Internal Carotid Stenosis Toshio Nakayama Hitoshi Hayase Koji Tokunaga Makoto Ohta Institute of Fluid Science, Tohoku University Neurological Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Neurological Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences Institute of Fluid Science, Tohoku University
Nakayama, Hayase, Tokunaga, Ohta, J. Flu. Sci. Tech. 3, 544, 08 The effect of outlet pressure on the flow distribution 0Pa 280Pa 420Pa
Simulation Results 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], 124[m/s] ECA: 1.094 [m/s] Flow rate proportion: 102.74
The proper flow rate portion Flow ra ate to pro The proper of flow rate: Flow rate of simulation = Flow rate of ultrasound Intersection ti in two lines Form figure, Internal carotid artery: 310.922[Pa] Pressure [Pa] :Flow rate of ultrasound :Flow rate of simulation
Results The Proper Case Results Outlet Condition 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 Stents Makoto OHTA, K Srinivas Institute of Flow Science, Tohoku University Sydney University
Optimisation Latin Hypercube sample Variables FLUENT Evaluate Fitness 60 samples Krigging The best candidate Two-dimensional optimisation of a stent for cerebral aneurysm K. Srinivas, M. Ohta, T. Nakayama, S. Obayashi, T. Yamaguchi Journal of Medical Devices (accepted) 25
Objective Function Maximise Velocity Reduction in Cavity Shear Stress Reduction in Cavity Vorticity Reduction in Cavity 26
Computational Details 5mm 5mm 4mm 10mm 40mm 2D Computation with 75,000 nodes Reynolds Number 300, Inlet velocity 0.3 m/s. Standard Boundary Conditions Each calculation about 2 mins on Super Computer
Non Dominated Solutions (Aneurysm) 29
Optimal Strut-Gap Arrangements V -max -max compromise V -max -max compromise 30
Proceedings of ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting and 8th 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 31 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. 32
Thank you for your attention www.ics-meeting.net Acknowledgement Global COE in IFS, Tohoku University, JSPS Core to core in IFS, Tohoku University, JSPS Grant-in-aid, id JNIH Grant-in-aid, JSPS 33