Towards Automating Patient- Specific Finite Element Model Development Kiran H. Shivanna 1,4, Brian...
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![Page 1: Towards Automating Patient- Specific Finite Element Model Development Kiran H. Shivanna 1,4, Brian D. Adams 2,1, Vincent A. Magnotta 3,1,4, Nicole M. Grosland.](https://reader035.fdocuments.in/reader035/viewer/2022062417/5514ed00550346a80c8b4b87/html5/thumbnails/1.jpg)
Towards Automating Patient-Specific Finite Element Model Development
Kiran H. Shivanna1,4, Brian D. Adams2,1,Vincent A. Magnotta3,1,4, Nicole M. Grosland1,2,4
1Department of Biomedical Engineering,
2Department of Orthopaedics and Rehabilitation, 3Department of Radiology,
4Center for Computer-Aided DesignThe University of Iowa, Iowa City, IA
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Finite Element Method
• Invaluable tool in musculoskeletal research
• Demands associated with modeling the geometrically complex structures of the human body often limit its utility – restricting analyses to baseline models
• Conventional meshing techniques often prove inadequate
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Patient Specific Models
• In order to bring FE to the “bedside” for guiding surgical procedures the technique must be unencumbered from the image segmentation and mesh generation process
• Overcome the limitations associated with individualized, or patient-specific models
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FE Model Development
AcquireMedicalImaging
Data
Segment Regions of Interest
Generate FE Mesh
Apply Boundary/Load Conditions
and Material Properties
Finite ElementAnalysis
SurfaceGeneration
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Tetrahedral Meshes
• Most commonly used solid meshing technique
• Several automated techniques for filling a surface based definition of a region of interest– Paving, advancing front,
others– Advantages: well
developed algorithms, straight forward to implement
– Disadvantages: overly stiff elements
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Voxel Based Meshing Techniques
• Direct conversion of CT data to hexahedral elements– Keyak et al. 1990– Advantages: easy to
implement, voxel-wise material properties, fast
– Disadvantages: stair step artifacts in mesh, not appropriate for contact analysis
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Hexahedral Meshes
• Most commonly used meshing technique for surface contact analysis
• Few methods to generate the meshes– Shelling, whisker weaving,
mapped mesh– Advantages: More
appropriate for surface contact analysis
– Disadvantages: Less well developed algorithms, prone to element shape problems, regional control of mesh density difficult
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Objective
• Automate the generation of high quality hexahedral meshes– Projection method
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Bones of Interest
Why initiate with the bones of the hand?
• Long bones and cuboidal bones
• Number of bones per cadaveric specimen
• Readily extended to the other long bones of the body
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Bones of Interest
Extend to irregular bones such as the vertebrae
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Image Analysis
• Cadaveric specimens were imaged with CT scans– Hand: Cadaveric specimen amputated above
the elbow– Spine: Visible male dataset
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Regions of Interest
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Projection Method Carpal Bone
Initial Bounding Box
Bounding Boxwith AssignedMesh Seeding
ProjectedMesh
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Projection Method Example – Proximal Phalanx Bone
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Extending Projection Method
• A single bounding box coupled with the projection technique may not always prove sufficient
• Method has been extended to add multiple boxes and/or subdivide existing boxes
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Projection Method Multiple Boxes
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Projection Method Movie
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Solid Mesh Smoothing
• Projection of initial mesh onto the surface oftentimes yields distorted elements
• Need to smooth resulting mesh – Iterative Laplacian smoothing for solid mesh
• Method– Apply Laplacian smoothing to surface nodes holding
interior nodes fixed– Project nodes back onto the original surface– Smooth interior nodes with surface nodes held fixed– Iterate for specified number of iterations or until
convergence threshold is reached
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Results of Mesh Smoothing
Unsmoothed Smoothed
Unsmoothed
Smoothed
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Multiple Bounding Boxes Spine
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Acknowledgements
• Grant funding– R21 (EB001501)– R01 (EB005973)
• Nicole Kallemeyn, Nicole DeVries, Esther Gassman
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