12. 4.12 Maxilla Cranio Facial – Medical

This case study again shows the necessity of rapid prototyping in medicine.
 
 

4.12.1 Background
 
 

The patient, a three-year-old boy, was scanned at the Pretoria East Hospital clinic with the aid of their Toshiba Spiral X-Vision/GX CAT scanner. The CAT scanner at Pretoria East Hospital based in Pretoria. The 2D CAT slices were again stored on ¼" data cartridge magnetic tape. 2D CAT images of various positions were stored on film for record. The patient required maxilla cranio facial surgery.

Maxilla-Facial specialists from the University of Pretoria requested a prototype of the patient’s skull. The skull was required for pre-surgical planning.

Permission was granted so that this patient’s data may be retrieved from the CAT scanner. Please refer to section (3.7) for the data retrieval procedures. Pretoria East Hospital prepared a 3D visualization of the scanned area. The spiral data was prepared in one set. The radiology team prepared one set of 3mm thick slices and 3mm intervals or spacing. The finest possible slice thickness and slice spacing were again requested to obtain the best results. In this case it would be better to sample more data than required. The CAT scanner parameters were restricted to scanning distance and slice thickness. The surgeon was particularly interested in the frontal or facial area of the skull. For a successful facial reconstruction, the facial geometry had to be known.

The data was then processed and a meeting was arranged with the surgeons, to verify the results on the computer screen. They were please with the results and requested that we continue with the next phase of the project.

The next stage was to create a prototype of the skull. The 3dd file was used with the Materialise, CTM software to generate a STL format file. The STL file was then used with the Stratasys QuickSlice software. Horizontal slices were created. The software performed support generation, automatically. The SML file was created. The FDM machines require this data to build a prototype. The prototype was grown with the red ICW06 wax material and finished by removing the support structure generated by the FDM process. The skull was grown in two section to simplify the prototyping process. This also made the removal of the support structure easier.

The prototype of the skull was supplied to the maxilla-facial surgeons. This prototype could only be used for visual inspection. Wax prototypes are very fragile and can break easily when handled. It also does not machine easily. A bronze casting was made from this wax skull with the aid of the investment casting process.

A second skull prototype was produced by a group in Holland. The South African Selective Laser Sintering (SLS) rapid prototyping system was not operational at that stage. The skull was produced in the glass filled nylon material.
 
 

4.12.2 Conclusion
 
 

The SLS system proved to be the best system to use with this technology. It is of great use to produce prototypes without the generation of a support structure. The support structure always need to be removed and very often causes problems to the extent of damaging the prototype.

The surgeons worked with ease with the glass filled nylon material prototype. The skull prototype was marked and cut in sections as the surgeons planned the operation. A brace was also fitted to reposition the eye socket section.

2D CAT images were checked during scanning. . CAT scanned film was also provided with 2D slice information as well as 3D rendering to be used for verification. The window settings were optimized on the CT computer. Measurements were checked. Window and threshold settings were set to the ideal conditions.

Both the maxilla cranio- facial- and neuro-surgeons frequently referred to the skull prototype during the eight-hour operation.

The Bronze casting proved to be useful for preserving the wax prototype but unfortunately warped slightly. Other casting imperfections such as pit holes were evident.

This skull data was supplied to the CSIR Virtual Reality Centre. Initially they battled to retrieve the data due to a lack of computer power. This skull is now used to demonstrate the virtual reality surgery concept to be used by medical students.
 
 

4.12.2.1 Images
 

Figure 4.12.2.1 2D CAT scan slice at the 1100 position	Figure 4.12.2.2 2D CAT scan slice at the 1080 position
Figure 4.12.2.3 SLS skull prototype in GF nylon	Figure 4.12.2.4 Bronze casting of the skull
Figure 4.12.2.5 FDM skull prototype in ICW06 wax.	Figure 4.12.2.6 Surgical Reconstructed SLS prototype.
Figure 4.12.2.7 3D Image of skull, combines soft and hard tissue.	Figure 4.12.2.8 3D Image of skull, bone structure only.

 

4.12.3 Maxilla Cranio Facial Data Sheet:
 
 
 

	Description	Options (Default)	Data
1	CT Image Names		seun.00
2	Patient/Project Name		seun.pat
3	Number of First Input Image		1.6912.2
4	Number of Last Input Image		1.6912.319
5	Number of First Output Image		seun.00
6	CT or MRI	CT, MRI	CT
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	Toshiba
11	Pixel Type	B,UB,S,US,L,UL,F	-
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)	-1021.5
17	Distance Between Slices	(mm)	3 recon to 1
18	Slice thickness	(mm)	3 recon to 1
19	Pixel Size SQ.	F.O.R./Nr. Hor. Pixels (mm)	0.39
20	Gantry Tilt Angle	Degrees	0
21	Field of Reconstruction/View	(mm)	200
22	Number of Images		154
23	File Size of CAT Image	kb	521
24	File Size of Converted Image	kb	76-131
25	.3dd file size	Mb	6*.srf
26	.STL file size	Mb	96, 17.9 with filter
27	RP Method	(SLA,FDM,OTHER)	FDM, SLS
28	.IGS file size	Mb	-
29	RP Slice file size	Mb	28.9+19.4
30	RP Download File size	Mb	12.1+13.9
31	Grow Time	Hour	132.9
32	Tip size	(T12, T25)	T12
33	Slice Thickness	(0.01", 0.014")	0.01"
34	Finishing Time	Hour	8
35	Processing Time	Hour	16
36	Data Retrieval Time	Hour	3
37	Total Cost	Rand	=27*250+7500=14250