Image based meshing
Image-based meshing refers to the automated process of creating simplified surface descriptions from three-dimensional image files without having to reconstruct the surface beforehand. Image files that have been created, for example, by magnetic resonance imaging (MRI), computed tomography (CT) or microtomography , can be converted into a computer model using this method, which can be further processed, for example, in numerical fluid mechanics or finite element analysis .
Mesh creation from a 3D image file
The creation of polygon meshes from a three-dimensional image file poses a multitude of challenges, but also unique possibilities for making more realistic and precise geometric descriptions of the domains of definition. There are generally two methods of meshing a 3D image file:
Surface-based method
The majority of the methods used so far traditionally work with CAD applications by incorporating an intermediate step in which a surface reconstruction is carried out, which is followed by traditional CAD-based meshing algorithms. CAD-based methods use the scan data to define the surface of the work area and create elements within these self-defined boundaries. Although robust algorithms are available for this, these techniques are often very time-consuming and sometimes it is also not possible to represent the complex structures of image data. Sometimes it is also not possible to create a mesh of more than one domain, since multiple surfaces can create gaps and overlaps at interfaces when several structures meet.
Image-based method
This is a more direct method of meshing, as the geometric detection and meshing phases are combined in one process, which leads to more robust and accurate results than meshing surface data. The most frequently used meshing method is the voxel conversion technique, which generates meshes with brick elements, and the Marching Cubes algorithm, which generates meshes with tetrahedral elements. A new, improved volumetric marching cubes method generates four- or six-surface 3D elements through the volume of the definition area and thereby directly creates the mesh with multi-part surfaces. If complex structures with possibly hundreds of unconnected domains are to be modeled, this procedure is much simpler, more effective, more robust and more precise.
Creation of a model
The following steps are necessary to create a 3D image-based model:
Scan and image processing
A variety of image processing programs can be used to obtain very accurate 3D image-based models, e.g. B. MRI, CT, MicroCT, (XMT) and Ultrasound. Of particular interest can be:
- Segmentation (e.g. threshold value method, level set methods ...)
- Filter and smoothing (e.g. volume and structure preserving smoothing)
Volume and surface mesh creation
Image-based meshing enables the direct creation of meshes from segmented 3D data. Of particular interest can be:
- Multi-part meshing (mesh of any structure at the same time)
- Images to depict material properties based on signal strength (e.g. Young's modulus or Hounsfield scale )
- Smoothing meshes (e.g. preserving the structure of data to maintain connectivity and volume-neutral smoothing to avoid the shrinkage of convex cladding)
- Export of FEA and CFD codes for analyzes (e.g. nodes, elements, material properties, contact surfaces)
Areas of application
- Biomechanics and the design of medical and dental implants
- nutritional science
- forensic science
- Materials science (composites and foams)
- Material testing
- Paleontology and morphology
- Reverse engineering
- Soil Science and Petrology
Individual evidence
- ↑ Viceconti et al., 1998. TRI2SOLID: an application of reverse engineering methods to the creation of CAD models of bone segments. Computer Methods and Programs in Biomedicine, 56, 211-220.
- ↑ a b Young et al., 2008. An efficient approach to converting 3D image data into highly accurate computational models. Philosophical Transactions of the Royal Society A , 366, 3155-3173.
- ↑ Fyhrie et al., 1993. The probability distribution of trabecular level strains for vertebral cancellous bone. Transactions of the 39th Annual Meeting of the Orthopedic Research Society, San Francisco.
- ↑ Frey et al., 1994. Fully automatic mesh generation for 3-D domains based upon voxel sets. International Journal of Methods in Engineering , 37, 2735-2753.