Transcript FE-Mesh-Development_Upload

Towards Automating PatientSpecific 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 Design
The University of Iowa, Iowa City, IA
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
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
FE Model Development
Acquire
Medical
Imaging
Data
Segment Regions
of Interest
Surface
Generation
Apply Boundary/Load
Conditions
and Material Properties
Finite Element
Analysis
Generate
FE Mesh
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
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
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
Objective
• Automate the generation of high quality
hexahedral meshes
– Projection method
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
Bones of Interest
Extend to irregular
bones such as the
vertebrae
Image Analysis
• Cadaveric specimens were imaged with
CT scans
– Hand: Cadaveric specimen amputated above
the elbow
– Spine: Visible male dataset
Regions of Interest
Projection Method
Carpal Bone
Initial Bounding
Box
Bounding Box
with Assigned
Mesh Seeding
Projected
Mesh
Projection Method Example –
Proximal Phalanx Bone
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
Projection Method Multiple Boxes
Projection Method Movie
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
Results of Mesh Smoothing
Unsmoothed
Unsmoothed
Smoothed
Smoothed
Multiple Bounding Boxes
Spine
Acknowledgements
• Grant funding
– R21 (EB001501)
– R01 (EB005973)
• Nicole Kallemeyn, Nicole DeVries, Esther
Gassman