The Research On Key Algorithms Of Computer-assisted Oral Craniofacial Surgery And The System Development

Computer-assisted planning of oral-craniofacial surgery system has been widely applied in clinical use to improve the safety and accuracy of the surgery,as it provides detailed information of the patient for the surgeons and the important function of planning the surgery or designing the implant used during the surgery.Several key algorithms of medical image processing and computer graphics were studied in order to meet the clinical needs from the three most common surgeries of Oral craniofacial surgery including oral implant surgery,orthognathic surgery,and cranial defect restoration surgery.On this base,the system of computer-assisted preoperative planning and custom implant smart designing was developed and applied to clinical use.The algorithms can be elaborated as follow:1.In the aspect of designing custom implant,the algorithms for designing a better-shaped model including using the ruled surface and the multi-contours modeling method are presented.Through sampling and ordering the points from two cardinal carves into cells,the ruled surface can be generated for 3D panoramic view or forming the STL model.Multi-contours modeling can be divided into two key steps of using the key contours to sample the other contours and using the ruled surface to reconstruct the model based on the points from the contours.With the high efficiency,the STL model can be regenerated in real time when the key contours are changed.2.In the aspect of Boolean operation,the algorithm based on signed distance field was studied and can be described as follow: firstly,the actual intersection between the two models is detected using OBB algorithm,and the necessary cells are interpolated around the intersection to make the two models share the same lines.Then the signed distance between the two models are calculated and the result model can be generated by deleting or appending regarding cells based on the type of the Boolean operation.3.The algorithm of removing undercut is defined by several methods including cutting the model along the direction of assembling to generate the contours,sampling points inside the contours,appending the neighbor contour points to form the point cloud with the undercut feature,reconstructing the 3D model from the image data mapped from the point cloud,and using Boolean operation to removing the undercut.Based on the above algorithms,a computer-assisted oral-craniofacial surgery system with proprietary intellectual,user-friendly interface and clinical significance was developed under Microsoft Visual Studio 2015,using several open source kits including VTK7.1,ITK4.11 and Qt5.7.The system is consisted of the oral implant preoperative planning software DentalHelper,the implant design software ImplantDesign,dental splint design software EasySplint and cranial defect restoration software EasyCrania.Using these pieces of softwares,the surgeon only need a few operation via mouse and keyboard to achieve the automatic design of the custom medical implant.The phantom and clinical experiments have shown the great efficiency of the design process,the good reliability and repeatability of the software.The research result laid a solid base for computer-assisted preoperative planning for oral-craniofacial surgery even other surgery,which is significant to make the surgery more custom,accurate and minitrauma.