4.10 Meerkat Skull - Industrial/Medical

4.10.1 Background

The scull of a Meerkat was glued to an aluminum fixture. The fixture was designed to be used by both CAT scanner and CMM and manufactured by a precision toolmaker. The fixture has three cylindrical pins to be used to register the two data sets.

The case study was used to evaluate the accuracy of the CAT scanner. A certain area of the scull was selected to perform the dimensional tests. The area needed to be easily accessed by the CMM touch probe. The curvature of the selected area also needed to be constant to simplify the probe compensation.

The fixed scull was placed in the CAT scanner and a series of images was taken. The fixture needed to be lifted by about 10mm to fit in the vertical workspace.

The data was retrieved and converted. The next step was to sample 3D point data of the scull, at the area of interest. ASCII data of the 3D coordinate points was then transferred to the HP computer with the aid of FTP. Surfacer software package was used import the data and to place splines through the selected points. A series of axial sections was produced.

Both CAT and CMM data sets were exported to IGES format. Intergraph EMS software was used to import the data sets into one file. The CMM data set was rotated by 90 degrees and moved to match the CAT scanned data set. A surface was placed through the CAT scanned spline data set. A parametric point language program was used to determine the deviation. Software such as STRIM, AVS and Surfacer were also used to check the deviation. Another method was used to compare the STL format of the surface and to compare it with the ASCII data. A 3D-deviation map and rendering were generated to display the area of deviation.

4.10.2 Conclusion

Better planning will reduce the time to manipulate the two data sets that will place the sets in the same coordinate system. The correct software to compare the data sets still needs to be explored properly. The average deviation was less than 0.2 mm. The pixel size was 0.13 mm. Images
Figure 4.10.2 

Meerkat Skull with fixture



4.10.3 Meerkat Skull Data Sheet:
  Description Options (Default) Data


1 CT Image Names   fos.00
2 Patient/Project Name   fos.pat
3 Number of First Input Image   27/01
4 Number of Last Input Image   157/99
5 Number of First Output Image   000
7 Horisontal Nr. Of Image Pixels 0 to 65535 (265,512,1024) 512
8 Vertical Nr. Of Image Pixels 0 to 65535 (265,512,1024) 512
9 Number of Images per File (1) 1
10 File Swap Format (0,3) 0,3 0
11 Pixel Type B,UB,S,US,L,UL,F US
12 Header Size *see formula below -
13 Inter Image Header Size 0 -
14 Add Value 0 to 4095 -
15 Scale Value 0 to 4095 -
16 Table Position (mm) 0
17 Distance Between Slices (mm) 1
18 Slice thickness (mm) 0.2
19 Pixel Size SQ. F.O.R./Nr. Hor. Pixels (mm) 0.13
20 Gantry Tilt Angle Degrees 0
21 Field of Reconstruction/View (mm) 69
22 Number of Images   99
23 File Size of CAT Image kb 265
24 File Size of Converted Image kb 215
25 .3dd file size Mb 4
26 .STL file size Mb 17
28 .IGS file size Mb 4
29 RP Slice file size Mb 12
30 RP Download File size Mb 14
31 Grow Time Hour 4
32 Tip size (T12, T25) T12
33 Slice Thickness (0.01", 0.014") 0.01"
34 Finishing Time Hour 2
35 Processing Time Hour 5
36 Data Retrieval Time Hour 4
37 Total Cost Rand =11*100=1100


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