R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Working with medical scan data 55
4.21 The effect of STL resolution settings on medical data showing
(left) low resolution and (right) the highest possible resolution.
in a more effi cient manner to make them suitable for transfer over the
Internet.
4.6.4 Finite element meshes
Finite element analysis packages rely on breaking down three-dimensional
objects into a large number of small discrete elements. These elements may
make up only the surface of the object; for example, the STL fi le described
above may be considered a triangular surface mesh. However, some meshes
may break the whole object into discrete three-dimensional elements.
These may be tetrahedral, cuboids or other three-dimensionally tessellating
polyhedra.
Depending on the software package used, the voxel data of a CT or MR
scan may be exported or translated into a solid or surface mesh suitable for
use in FEA. There are usually variables to set when conducting the translation
that affect the quality of the mesh and the resulting fi le size. This is
similar to specifying the quality versus fi le size compromise for STL fi les
described previously.
Many FEA packages have their own formats for meshing, and some
medical software packages can produce and export the correct format for
a given analysis package. However, this may require the purchase of specifi c
translators or additional modules for the software package.
4.6.5 Mathematical curve-based surfaces
Unlike faceted polygon surfaces, curve-based surfaces use complex mathematical
routines to produce smooth curves in three-dimensional space.