Biomedical Engineering Reference
In-Depth Information
ample the letter 'G' in place of the 'X' gives VGL which is the geometry library
files and the letter 'I' gives VIL which is an image processing library.
3.3.6
Surface and Volume Reconstruction
After segmentation a 3D output file can be saved under different CAD formats
which need to have certain conditions to be mesh-able for further computational
fluid dynamics analysis. For example the outputted model may only contain a wire-
frame model which lacks geometric topological relationships such as vertex, lines,
faces, and the topology of the face perimeters or volume shells. A generic work
flow is shown as a flowchart in Fig. 3.11 . After segmentation the output file can
be directly read into a CFD meshing software or additional topological data can be
included into the model. An advantage of including the topological data is that the
file becomes compatible with CFD software. During the addition of topological
View/Organise Images
Software should be able to
display coronal, sagittal, and
axial views.
Image Acquisition
CT/MRI scanned images from patient.
Data are typically stored as DICOM files
Automatic Segmentation
A threshold limit is commonly used to create a
first definition of the segmentation. Other
automatic algorithms can then be applied e.g.
region growing, active contours
ManualSegmentation
Manual clean up including internal gap fills,
boolean operations on segmented regions etc.
Is the segmented
region satisfactory?
NO
NO
YES
CAD/Reverse Engineering
Segmented model can be exported
with or without additional CAD data
Is the segmented
region satisfactory?
YES
Point Cloud Data
New surface creation,
triangulation, decimation and
surface refinements needed.
Direct Convert
Can be saved into standard CAD
format (IGES, STEP, STL) with no
additional data included into the model
CFD
Mesh
Software
Additional Topological Data
Geometry refinement, creation of a watertight
NURBS surface for exporting to CFD mesh
applications.
Final Output Model
Conversion to standard CAD formats
(IGES, STEP, STL) with additional data
Fig. 3.11  Flow chart showing the segmentation process to extract and export a region of interest
into a 3D computer model commonly referred to as a Computer-Aided-Drawing (CAD) model
 
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