| Surgical navigation is a technology which takes use of the rapid processing capacity of computer for digital medical images.By providing the surgeons with a virtual operation environment,it assists them to complete the surgery,making the surgery in a safe,accurate,minimally invasive development.Registration is one of the core techniques of surgical navigation.The common clinical registration methods,such as preoperative implant markers registration,are not suitable for pelvic fractures and other orthopedic surgery,thus limiting the promotion and application of surgical navigation for pelvis.Therefore,in this paper,we focused on the problem of registration in pelvic surgical navigation.The pelvic surgical navigation system based on the noninvasive percutaneous ultrasound registration method was studied and implemented.Specific contents of this paper include the following four aspects:(1)The ultrasound calibration methods were analyzed synthetically,which provide the basis for the selection of subsequent ultrasound calibration methods.Based on the basic principle of ultrasound calibration,the advantages and disadvantages of various calibration methods were analyzed in detail,including the point phantom,the line phantom,the plane phantom and non-phantom methods.At the same time,the iterative and closed-form methods for solving ultrasound calibration methods were analyzed,and the methods to evaluate the precision and accuracy of ultrasound calibration were introduced here.Finally,a comprehensive evaluation of various calibration methods was carried out from the aspects of accuracy,time,number of required images and reliability of calibration,which provided the reference for the selection of subsequent calibration method and the design of phantom.(2)Based on the above analysis of various calibration methods,a novel calibration method based on N-wedge phantom was proposed in this paper.The phantom not only used the unique parallel line geometry of Nwire phantom,but also took advantage of the plane phantom which was imaged as a straight line in the ultrasound image.The calibration principle and the algorithm for ultrasound automatic image processing based on Nwedge phantom were discussed in detail.The calibration precision,accuracy and so on were also analyzed here.In addition,the N-wedge phantom was compared with the N-wire phantom and three-points phantom from some aspects as accuracy,the image processing time,the required image number,operation difficulty and so on.We concluded that N-wedge phantom had more advantages in accuracy,actual operation,calibration time and phantom manufacture.(3)The noninvasive registration algorithm for percutaneous ultrasound images was realized and the accuracy of registration was verified by experiments.Firstly,the source surface data points in the patient space were collected by using the ultrasound probe.At the same time,the surface data point set in the computer 3D model space was collected in the software.Then,the surface registration algorithm was implemented on the ICP algorithm.At last,a pelvic prosthesis model experiment in uniform medium and a swine hip experiment in inhomogeneous medium were carried out.The results showed that TRE of the pelvic prosthesis model experiment was 1.21 mm and TRE of the swine hip bone experiment was 1.48 mm.The feasibility of the experimental scheme and the reliability of the registration accuracy were verified.(4)Based on the pelvic prosthesis model experiment and swine hip experiment,a cadaver experiment of screw implantation in pelvis with image-guided system was carried out with the surgical navigation system based on the noninvasive registration method of ultrasound.The hardware and software of the system were introduced in detail.The experimental results showed that the distance error could be controlled within 1.95 mm and the angle error could be controlled within 4.58°.The system initially could meet the requirements of the clinical application. |
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