Research On Navigation Technology Of Robot Assisted Minimally Invasive Spinal Surgery Based On Intraoperative CT Images

Compared with the traditional open surgery,minimally invasive surgery can significantly reduce the surgical incision.However,the minimally invasive spine surgery has not been widely applied due to the small minimally invasive spine surgery wounds,which normally lead to the surgical vision is limited.Three of the outstanding problems are:fluoroscopic images and CT images can not reflect a perspective positional relationship directly;the second is that the quantitative mapping between patient space and medical imaging space intraoperatively cannot be achieved continuously,because the X-rays involved in the achieving process will cause serious injury to surgeons and patients;the last is the intraoperative lack of safety measures to prevent rupture of the pedicle.Robotic assisted surgical navigation is a combination of emerging technologies including span robotics,computer graphics,medical image processing and spatial registration as well as localization.It reflects the three-dimensional structure of the spine through medical images such as spinal three-dimensional models.By obtaining the position and posture of surgical instruments in the medical imaging space,the frequency of use of intraoperative fluoroscopy equipment is reduced.The safety of the operation can also be improved by controlling the movement of the robot in a safe range.Therefore,the problems mentioned above can be effectively solved,and the relative position and posture of the surgical instrument and the spine can be fed back in real time for the surgeon.This thesis aims at robot-assisted surgical navigation technology,researching CT data visualization modeling,automatic spatial registration,spatial positioning and trajectory planning methods.Specific content includes:Firstly,three-dimensional reconstruction algorithms and digital reconstruction radiological image algorithms based on CT data have been studied.In the three-dimensional reconstruction,the implementation process of the ray casting algorithm and the marching cubes algorithm is analyzed in detail.By comparing the rendering effect and efficiency between the maximum intensity projection algorithm and the isosurface algorithm,the marching cubes algorithm is selected to reconstruct the spine.Moreover,the problem of the lack of intra-spine information in reconstructed model has also been addressed in this thesis by using CT resection face images combined with 3D models.Digitally reconstructed radiographic algorithm yields images similar to X-ray fluoroscopy,which can not only obtain the fluoroscopic images that surgeons are accustomed to use,but also reduce the use of intraoperative X-ray imaging equipment.Secondly,the method of automatic spatial registration of CT images and patient space is studied.First of all,in the process of acquiring the spatial feature points of the CT image,the accuracy of feature extraction is improved by utilizing morphological filtering-based artifact correction algorithm.Based on the Hu moment,a three-dimensional feature point extraction algorithm based on improved invariant moments is proposed,and the precise position of the feature points is obtained.Then,according to the robot kinematics model and the mechanical dimension of the calibration model,the precise location of the spatial feature points of the patient is achieved.Finally,aiming at the non-orthogonality of ICP algorithm which is easy to fall into the local optimal solution and the least-squares method,a registration method based on first-order derivative of rotation and least squares is proposed.The error of the spatial registration is 0.49±0.18mm obtained through experiments,which verifies the feasibility of the registration method.Thirdly,the surgical instrument positioning and trajectory planning methods have also been studied.Using the "five-point method" to complete the calibration of the surgical instrument,the precise position of the end point of the surgical instrument in the robot base coordinate system is obtained.Based on the safety distance concept,a real-time intraoperative trajectory planning strategy based on velocity field is designed to ensure that surgical instruments move smoothly within the safety range.Finally,the surgical navigation system positioning accuracy experiment was completed.The positioning error is 1.28±0.41mm,which is lower than the allowable operation error of 1.9mm,and the feasibility of the navigation system was verified as well.As a result,the precise relative position and posture of the surgical instrument and the spine can be obtained in real time during the operation,and can be visually displayed in real time.