Study On Key Technologies Of Modeling For Rehabilitation Of Femoral Head

To meet the need of modeling for rehabilitation of femoral head necrosis and manufacture of artificial joint,modeling from CT images of hip joint is systematically studied in this dissertation.Some key technologies related to the research of this dissertation,such as medical image denoising,image enhancement,bone segmentation,the methods of modeling for rehabilitation of collapsing bone and the theory of modeling in reverse engineering etc.are studied and some novel methods have been presented too.The main contents and contributions are as follows:(1) A novel multi-scale denoising-enhancing mehod for CT image based on the Contourlet transform is presented.Contourlet is a new "true" two-dimensional representation for images that can capture the intrinsic geometrical structure of image information. Contourlet transform has better performance in representing edges than wavelets for its anisotropy and directionality,and is therefore well-suited for multi-scale edge enhancement. By analyzing the drawbacks of conventional method of contourlet transform,we present a new method named Enhancing Edge Contourlet Transform(EECT) denoising,which improves the denoising ability of ordinary contourlet transform method in automatic selecting thresholding value,eliminating the effects of moving,enhancing the detail information of image contour and improving resolution,etc.Compared with other denoising methods based on the Wavelet transform and conventional contourlet transform,experiment results show that the proposed algorithm has more prominent effects of denoising and enhancing the weak edges than above methods.The application of the algorithm on CT images of patients' hip joint shows that images have an encouraging improvement,and might be helpful for segmentation.(2) Accurate segmentation is necessary for followed modeling and diagnosing,ect proceeddings.However,it is very difficult to automatically segment bone precisely, especially at joints,due to injuries,bone's inhomogeneous structure,and the limitation and resolution of CT images.Under this circumstance,we present a new method that well-suited for bone segmentation based on ASM,which have already incorporated the statistic attributes of femur bone.In this dissertation,a complete solving scheme for building ASM is described in detail.The problem of automatic selecting landmarks is solved by curve simplification.The problem of point correspondence is solved by shape comparability.Then,in order to further upgrade the the segmentation quality,a neighbor gray statistical feature of landmark and Snake model are introduced and a new searching scheme is presented,which can improve the performance of both ASM and Snake.(3) Accurate model of femoral head is the key to surgical simulating,pre-operative planning and surgical navigation of osteonecrosis of femoral head.In order to reconstruct complete model from partial information extracted from hip joint CT images,a modeling for rehabilitation approach based on 3D segmentation and shape prediction using a 3D statistical shape model is presented.The method is the 3D extension of 2D ASM described in the chapter 4.Under the guidance of prior knowledge model,the patient-specific femur bone with the complete femoral head can be constructed from the patient's own hip joint CT images.(4) The theory and methods of reconstruction of surface based on point cloud data is also studied in this dissertation.On the one hand,the point cloud data usually contains large numbers of noise and redundancy,which affects the calculating precision of triangulation, surfacing fitting,and calculating speed ect.On the other hand,the point in point cloud data has no obvious topology relationship,which will affect the searching efficiency in followed reconstruction.Therefore,a new octree coding method is introduced and applied to express and compress the point cloud data and a curvaturer rule based reduction scheme is put to use then.The proposed method not only reduces the amount of point,but also regularizes the point cloud data,which makes it easy to traversing and searching for point data.(5) The accurate model of femoral head plays an important role in a total hip replacement. An innovative 3D modeling method for the hip joint and modeling for rehabilitation of femoral head based on point cloud data is proposed.After being reduced,the part point data of femoral head and acetabulum were extracted respectively and fitted by the way of the least square.Experiments show that the new method can reconstruct hip joint model and femoral head of patients perfectly.It can be applied to other joints or bone tissues too.The method affords theoretical model for accurate operation position fixing in orthopedics clinic and biomechanics analyses,and it also provides more effective ways for the individually manufacturing of artificial hip joint.