Influence of the Processes Parameters on the Properties of The ...

Chapter 4.
Experimental Procedures and Protocols for Analyses
Figure 4.29: Set up <strong>of</strong> CT and flow chart <strong>of</strong> CT measurement process.
4.4.1 Acquisition
The sample is rotated through 360 degrees on a precision turntable and a set <strong>of</strong> high resolution
digital radiographs are acquired at regular (typically 0.5 degree) increments. The accuracy <strong>of</strong> this data set
determines <strong>the</strong> ultimate quality <strong>of</strong> <strong>the</strong> final 3D data.
4.4.2 Corrections
Each projected image from <strong>the</strong> data set undergoes geometric and shading correction, to remove
spatial and intensity non linearities introduced by <strong>the</strong> imaging device.
4.4.3 Reconstruction
By combining all <strong>of</strong> <strong>the</strong> individually corrected images and using a cone beam back projection
technique, a geometrically correct, three dimensional data cloud is computed. The patented s<strong>of</strong>tware has a
real-time viewer that shows <strong>the</strong> reconstruction progressing in parallel with <strong>the</strong> x-ray images being captured.
4.4.4 Viewing Results
The CT data collection, reconstruction and display are presented to <strong>the</strong> operator via <strong>the</strong> X-Tek
graphical user interface. This has been developed to provide ease <strong>of</strong> use with <strong>the</strong> highest performance for
systems to fit users’ budgets without compromise. The data cloud can be sliced open in any direction to
reveal internal detail, surface rendering s<strong>of</strong>tware similar to that used in 3D CAD systems is used to visualise
<strong>the</strong> exposed features.
4.4.5 Wide Variety <strong>of</strong> Post Processing
The data cloud can be output as a stereo lithography file, a format accepted by most CAD
packages. Once imported into a CAD system, <strong>the</strong> radiographic information can be compared directly with
<strong>the</strong> original design file to highlight differences when checking first <strong>of</strong>f manufactured parts, or if <strong>the</strong> original
design is not available, <strong>the</strong>n <strong>the</strong> radiographic data is used to create a new CAD file for rapid prototyping and
reverse engineering.
Micro CT <strong>of</strong> different scaffolds was taken from different angles and views. Slices were taken to
observe <strong>the</strong> interconnectivity and porosity <strong>of</strong> <strong>the</strong> scaffold structure. An example <strong>of</strong> a polymer skeletal
structure along <strong>the</strong> top, front and right views are taken (cf. Figure 4.30). These images can be fur<strong>the</strong>r used
for porosity and pore size distribution analysis. CT can directly provide <strong>the</strong> porosity and interconnectivity
in tested foam. The results obtained from CT are real results compared to <strong>the</strong> results obtained from
calculations and o<strong>the</strong>r derived analysis such as images analysis.
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