Key Technology For Articular Cartilage Distribution Measurement And Automatic Segmentation Of Bones Based On Medical Image

The medical imaging technology has been closely integrated with the computer technology,which enables the assistive technology of computer and medical imaging to exert a huge role in diagnosis and treatment of the diseases like osteoarthritis.There is a large quantity of image-related information contained in the high-resolution and high-SNR MR as well as CT medical images of bones and joints,including the complicated bone structures,the changeable bone shapes as well as the positions and thickness of lesions etc.However,the large quantity of information on bone and joint images is far less capable for doctors to process manually.As it is very difficult for doctors to conceive the positions of lesions,variation in thickness of cartilages and state of adjacent tissues from the medical images,so the contemporary clinical diagnosis has brought forward the technical requirements of high speed and high precision on the structures of bones and joints.Nevertheless,the existing detection algorithm on bone structures has been unable to achieve the practical clinical application.In particular,it will be even more difficult to detect the bone structures in close vicinity or with severe osteoarthritis(OA).Aiming at the abovementioned problems,the paper,by taking knee joints,hip joints and carpus as research objects,has realized the accurate automatic segmentation and thickness measurement of articular cartilages speaking of MR images,and realized the accurate automatic segmentation of articular cartilages speaking of CT images,which have greatly improved doctors’ diagnosis accuracy and treatment effect.The paper has put forward a multilevel automatic segmentation method of threedimensional images based on B-spline DGVF snake model,which has solved the segmentation problem of knee and hip articular cartilages;it has brought forward a theoretical simulation method of cartilage model,which has verified that the zero-crossing method is unsuitable to measure the cartilage structures with narrow gaps and that it will cause a considerably big deviation;it has come up with a new method based on boundary detection and thickness measurement of hip articular cartilages within the plane of the deviation model,which has solved the thickness measurement problem of extremely adjacent bone structures(femoral cartilages and acetabular cartilages);and eventually,it has proposed a multistage automatic segmentation method based on the combination of surface tracking correction and Gaussian standard deviation SD σ,which has solved the segmentation problem of extremely adjacent bone structures(hip joint and carpus).The primary research work and achievements of the paper are as follows:(1)As for the segmentation of hip articular cartilages(femoral cartilages and acetabular cartilages),namely,solving the problem of extremely adjacent and edge-blurred cartilages,the paper has put forward a multilevel automatic segmentation algorithm of three-dimensional images based on B-spline DGVF(Directional Gradient Vector Flow)snake model.This segmentation method is primarily comprised of image preprocessing,rough segmentation and accurate segmentation of articular cartilages.In the first phase,the non-linear filtering method and the sinc interpolation algorithm have been utilized to solve the problems of image noises and isotropy;in the second phase,the three eigenvalues of Hessian matrix and the method of optimal threshold have been adopted to solve the problems of strengthening articular cartilages,confirming cartilage positions and acquiring the initial contour of closely adjoined articular cartilage edge;in the third phase,a segmentation algorithm of three-dimensional images based on B-spline DGVF snake model has been taken advantage of to extract the edge contour of articular cartilages.This automatic segmentation algorithm has less calculated amount,which can conduct effective segmentation on articular cartilages.(2)With regards to the problems arising from the most frequently used zero-crossing method measuring the thickness of hip articular cartilages,the theoretical simulation method of cartilage model proposed in this paper has verified that the zero-crossing method is not suitable for measuring cartilage structures with narrow gaps and that it will cause a considerably big deviation.The theoretical simulation method of cartilage model has also pointed out the reasons why the zero-crossing method will cause a big deviation in thickness measurement.The theoretical simulation analysis method of cartilage model proposed in this paper is the first proposed new method.(3)As for the problem of deviation existing in the commonly used zero-crossing method at present measuring the thickness of hip articular cartilages and acetabular cartilages,the paper has put forward a new method based on boundary detection and thickness measurement of hip articular cartilages within the two-dimensional plane of the model,which is called the deviation method based on the model for short.This deviation method has translated the problem of cartilage thickness measurement into the problem of the deviation between the prediction curve and the actual curve observed in NMR data.When there is the smallest deviation between the analog signal of an arbitrary edge point on the cartilage surface along the normal direction and the signal of the actual cartilage edge point along the normal direction,the accurate cartilage edge position and thickness within the plane can be obtained.Based on the fact that the thickness measurement method of deviation model can overcome the limitations of the excessively short distance between mutually adjoined thin structures and the system’s inherent spatial resolution to thickness measurement.Meanwhile,the paper has proposed a new three-dimensional cartilage thickness correction method,which rectifies the excessively estimated plane thickness of images caused by inclined sections.Those based on deviation model method and threedimensional cartilage thickness correction method put forward in this paper are the first proposed new methods.(4)In terms of the difficulty while segmenting the hip joint and the carpus due to their internal closely-integrated bone structures,the paper has put forward a multistage automatic segmentation method based on the combination of surface tracking correction and Gaussian standard deviation,which has solved the problem of segmenting this type of closely integrated bone structures(hip joint and carpus)and is able to provide important information for the plan formulation of total articular replacement arthroplasty,the navigation during operation and post-operation assessment.In the process of surface tracking correction,the paper has utilized the estimation method of geometrical information of the current point improving the normal direction of the follow-up point,which enables the three-dimensional surface tracking calculation to continue to acquire information of the follow-up points until the previously discovered points are re-visited or certain conditions are no longer satisfied.As the value of Gaussian standard deviation has been optimized at the same time of correcting normal direction,so the methods in this paper have robustness on the segmentation of joint space narrowing caused by noise images and severe degeneration of joints.Comparing the experiment with the current most advanced method,the methods in this paper have obtained higher segmentation accuracy.The method of combining surface tracking correction and Gaussian standard deviation,and the method of acquiring the optimum scale of surface points in the correction process of normal directions have been proposed for the first time.