Localization Of Key Points And Line Of Hip Prosthesis In CT Images

Some patients who have undergone total hip arthroplasty have pathological conditions that require a second revision.Before revision,it is necessary to obtain the parameter information of key anatomical points and anatomical axes from patients’ CT images to assist doctors in preoperative planning and improve surgical accuracy.According to the clinical needs,the task was determined,which was to locate the bulb and the center of the socket of the hip prosthesis,and to fit the axis of the stem and the axis of the neck of the prosthesis.In view of the fact that the points and lines to be located are not significant points on the anatomical structure and there are few case images,a localization scheme based on traditional image processing was developed by making full use of the features of the hip prosthesis.The algorithm can be divided into three steps: data preprocessing;fitting the center of the bulb and the acetabular fossa based on the surface points of the bulb and the acetabular fossa;fitting the axis of the stem and the axis of the journal based on the center points of the stem and the cervical shaft.In the pre-processing stage,in view of the problems of metal artifacts in the data,the resolution is not uniform,and the distribution of the prosthesis is varied,the data are corrected by metal artifacts,resampling by equal square,and segmented by left and right sides.Threshold segmentation method was used to segment the prosthesis,and connected region markers were used to obtain the ROI range of the socket and femoral prosthesis and remove the small connected domain.When locating the center of the ball head,the upper and lower bounds of the hemisphere on the Z-axis were determined according to the morphological characteristics of the prosthesis,and the boundary tracking algorithm was used to extract the boundary of the half section of each hemisphere.When locating the center of the acetabulum,the relative position relationship between the acetabulum fossa and the prosthesis was made full use of,and parallel lines were sent out from the center of the ball head to find the internal surface points of the acetabulum fossa.Finally,the spherical surface points obtained were fitted by the least square method.The centroid of the normal plane perpendicular to the target axis in the prosthesis mask was calculated as the observation point of straight line fitting during the fitting of the stem axis and the neck axis.For the axis of the stem,its normal plane in the prosthesis is reflected by each Z-axis section of the lower part of the femoral stem,and the centroid of these sections is calculated as the sample point for the axis fitting of the stem.For the cervical axis,the ball head center was taken as the midpoint of the edges in the original image,and the small rectangle was cut out.In the small rectangle,the ball head center was taken as the center of the ball to generate hollow spheres of different radii.The intersection planes between these spheres and the femoral neck were taken as the normal plane and the centroid points were calculated.Finally,the line sample points are fitted by the random sampling consistency algorithm.The existing data sets are used to test the location algorithm,and the experimental results show that the center location results with small errors and the axis fitting results with small deviations can be obtained.