Study On Rapid Prototyping Of Cranial Prosthesis Based On Reverse Engineering

1.IntroductionMuch more attentions have been brought to medical rehabilitation following the civilization and progress of society, development of economy and improvement of living standard. Many people want the damaged bone to be repaired more perfectly. To fabricate prostheses is the key step for rehabilitation of damaged bone. Conventional methods to design prostheses depend on the evaluation and experience of doctor, so prostheses have bad individual matching and low precision, and it is hard to meet the expected requirements of high degree harmonious, comfort and simulation degree. The method to accomplish 3-D reconstruction with the theory of Bionic design and Bio-manufacturing, the technology of rapid prototyping(RP) and Reverse Engineering(RE), can efficiently fabricate prostheses that have the higher shape and dimensional accuracy and can reduce the complication, so this method has a certain actual meaning and value.2.Cranial cross-sectional image acquisitionBoth exterior and interior contour information can be obtained by cross-sectional scanning. Therefore the basic theory of CT must be known and the actual requirement must be considered, So the cross-sectional images of the cranium are obtained with Germany Sensation 16 spiral CT machine of the second affiliated hospital of Jilin University from x-ray radiotherapy department. There contain many detailed information in images, so these images are needed to be divided into small images which contain simple information with Matlab software.3.CT image processingImage processing correctly is an important assurance for the cranial 3-D reconstruction. Median filter can not only reduce the noise pixels but also strengthen the edge information, and it's suitable for CT image process, so it is selected for image filter. Image segmentation of region and edge are presented in this paper. The images are divided into binary image which consist of background and cranium information, then the edge segmentation is used for representing the edge information clearly, at last the coordinates are transformed that obtained from images after contour extraction with the method of 8-chain trace rule, then the real space coordinates data of cranium are exported, and the Z coordinates are decided during the scanning process, so the data is input and it must be assured that it is in accordance with practical case. At the same time, CT image processing software on the basis of Imgcx software is developed with Visual C++ language, and the software have the functions of image filter, image segment, and contour extraction and so on, how to realize these functions of the software are illustrated in Fig 1. 4.Image interpolation and 3-D reconstructionDuring scanning, the interval between arbitrary adjacent two layers which restrict the accuracy of prostheses is usually 1～10mm because of the factors such as scanning methods, equipment accuracy, cost and so on, so two methods of cross-sectional images interpolation are introduced in this paper and linear interpolation is selected. Under the aid of Matlab software, interpolation is realized for the images whose interval is 1.2mm, and then point cloud is put into the facet feature of RE module of Pro/E software, cranial 3-D reconstruction is done, and the STL format model data is output, the whole process is illustrated in Fig 2. 5.Cranial RP fabricationBecause of the practical technics, FDM has advantage on the field of cranial prostheses fabrication compared with other conventional technics, during the whole fabrication, there is solid-liquid transition only and the chemical change dose not happen, so this method is suitable for fabricating artificial organ, especially cranial prostheses. In this paper, ABS cranial prostheses about small cross-sectional interval, big cross-sectional interval and interpolated for big interval are obtained with the method of FDM (Fig 3), meanwhile the basic operations and attentions about fabricating process are introduced simply, and the breaks can be avoided during fabrication because of operation mistakes.6.ConclusionThis paper mainly discuss RP technology for fabrication of cranial prostheses under the background of project"Study on bioactivity material of cranial prosthesis and RP technology"that Jilin province science and technology development plan project(NO.20061114). And the processes of fabricating contain cranial images acquisition, CT image filter, segmentation, contour extraction and so on, at the same time, interpolation calculations are explored too, and 3-D reconstruction of cranial prostheses are accomplished with the help of CAD, and at last the prostheses are obtained that are fabricated with RP machine, and the following conclusions are summarized:(1) Spiral CT scanning is selected for cranial image acquisition, and the images which have detailed information are divided into many small and simple images with the image processing module of Matlab software.(2) A CT image processing software with Visual C++ language is developed, and the software has the functions of image filter, image segment, contour extraction and so on, it also can realize coordinates transform and output from screen coordinates to actual space coordinates.(3) Linear interpolation is selected to realize interpolation for CT image of 1.2mm interval, then put the point cloud data into Pro/E software to accomplish 3-D reconstruction and STL format document is output.(4) MEM-300-II FDM RP machine is used to fabricate cranial prostheses. The results show that the technology of image process and RP fabrication can accomplish fabricating of cranial prostheses from CT image data to solid model.