| Complex maxillofacial malformations continue to present challenges in analysis and correction using conventional methods, which is based on two-dimensional analysis, diagnosis and simulation. Fortunately, the development of computed tomography and three-dimensional reconstruction and visualization technique have brought a revolution in medicine. Three-dimensional visualization with proper computer software and environment can be used for diagnosis and surgical planning and simulation of operation. Based on this, a three-dimensional Orthognathic planning and simulation system is developed to raise the level of clinical diagnosis and treatment, and promote the communication and cooperation between patients and doctors.Our system was established on the basis of Windows 98 and the VisualC++6.0.The design of the whole system abides by idea of OO(Object Oriented), which guarantees modularization and maintainability. The well interfaces between modules guarantee the incessancy of the system .This paper included four parts as follows:1. 3-D facial model reconstruction:All the raw data of CT scans were digitally transferred from the CT scanner to our PC with FTP through Internet based TCP/IP protocol without losing any signal. After 2-D and 3-D image preprocessing, Marching Cubes algorithm was used to generate the 3-D skeletal and soft tissue model. OpenGL was used for developing interactive two-dimensional and three dimensional visualization, and VTK was used programming surface rendering and decimation computation. The reconstructed image can be seen from an arbitrary viewing point.2. 3-D measurementIn our system a 3-D spatial coordinate system should be defined for visualization and further process, so five landmarks were selected to generate the 3-D coordinates(nasion,right- and left-hand side porion and right- and left-hand-side orbitale). According to previous study, we pick up 62 feature points on the 3-D bone model interactively and compute 82 characteristic values including linear and spatial measurement. Based on the 3-D measurement and clinical experience, surgical planning can be made before surgical simulation.3. 3-D osteotomy simulationIn order to achieve the virtual osteotomy simulation, this stage requires cutting through the 3-D bone dataset with a surface and then displaying interpolated data values on the surfaces. One bone can be separated into several parts by using cutting planes. After osteotomies, each bone segment with its own ID could be manipulated separately, including translation, rotation, elevation, changing rotation center, displaying movement parameter. The classic orthognathic osteotomies were performed in our system interactively, such as Lefort I osteotomy, Lefort II osteotomy, SSRO, and Genioplasty. The osteotomy simulation can be repeated until the results were satisfactory.4. 3-D soft tissue simulation and predictionAfter the bone segment was moved to a new position, the soft tissue model was correspondingly deformed. Because of the nonlinear and complicated feature of the soft tissue deformation, we use some simple rules derived from studies of changes in midline produced by facial surgery and during follow-up analyses. In the area of bone displacement, the soft tissues are modified with the same displacement as those for the underlying bone (1: 1) . Along the midline, away from the area where bone displacement has occurred, the movement of the soft tissue is decreased in a linear fashion to the point at which no underlying bone displacement has occurred. At the same time Ray Projection-based Model Deformation algorithm was used to compute the soft tissue deformation. The soft tissue changes were also predicted interactively and repeatedly before the result is satisfactory. The predicted soft tissue model can be rotated freely and visualized from arbitrary observing angle.All of the functions provided above, however, are based on individual computer modules, programs and schemes, and complicated parameters need to be inputted during surgical p...
|
PDF Full Text Request