The Key Technologies Research Of Preoperative Path Planning Assessment And Intraoperative Ultrasound Calibration In Spinal Navigation

Spinal surgery is a type of operation with great difficulty and high-risk,and will cause serious damage to patients once failed.Pedicle screw placement is a popular internal fixation treatment in spinal surgery.Computer assisted spinal navigation can improve the pedicle screw accuracy effectively.However,some patients with osteoporosis without misplacement still occuring screws loose or axial withdrawal and other issues after operation.The main reason is the lack of vertebral screws holding force.In preoperative planning,current technology lack screw placement postoperation effect prediction and evaluation.Due to the pedicle of individual differences,for each screw placement plan,surgeons need to adjust the screw path by manually which cost a lot of time and the effect depends on the surgeons’ naked eye standard.In addition,the current commercial spinal navigation systems are expensive,and most of the navigation systems combined with X-ray fluoroscopy imaging cause intraoperation radiation exposure to the surgical team and the patients.In order to solve the problems mentioned above that exist in the spinal surgery navigation technology,we did the related research.The detailed research work of this dissertation is as follows:For the lack of screw placement postoperation effect prediction and evaluation in preoperative planning,the dissertation proposed a bone mass assessment method specific to path planning,after comprehensive consideration of the impact of different depth and the threaded region bone mineral density.According to the given screw parameters,the method calculated the volume and bone mineral density of bone tissue which providing screw holding force,and the arithmetic product of the volume and bone mineral density is bone mass.In the aspect of bone mineral density measurement,the dissertation proposed a series of improved lumbar spine bone mineral density measurement methods without solid phantoms,including:QCT bone density measurement method by liquid phantoms instead of solid phantoms;based on the perspective of energy,dual-energy CT bone mineral density measurement method in dual-source CT scan,and bone mineral density measurement method based on fat calibration in single-energy CT scan.The bone mass results can provide surgeons quantitative analysis of screws fastness in preoperative planning,and surgeons can choose different surgical options based on the bone mass assessment,preventing postoperative screw loosening and axial withdrawal problems caused by insufficient bone mass.For the preoperative path planning problems,the dissertation proposed a set of highly automated path planning methods for lumbar pedicle screw placement.By analyzing lumbar pedicle morphology,the method can identify the area,and find the pedicle center line;get the pedicle center line as the initial path,and path bone mass as objective function,using the improved Nelder-Mead simplex method with limited boundary to achieve the optimal path planning.The methods greatly simplify the preoperative screw plan operation,save operative time for the surgeons and avoid the adverse subjective effects caused by manual planning,at the same time the methods taking the maximum bone mass as principle potentially improve the postoperative firmness of screws.For the radiation exposure and system costs problems,the dissertation set up and realized a set of intraoperative ultrasound calibration system based on the CT images guided spinal surgery navigation technology.The system collected spinal landmarks by tracked ultrasound images,and realized preoperative CT image spatial calibration by point set registration.The key technologies in the system include:sequence ultrasound data acquisition and image coordinates calibration;freehand three-dimensional ultrasound reconstruction;lumbar spinal landmarks collection and point set registration by singular value decomposition.The calibration system solves the radiation exposure problem by ultrasound imaging instead of X-ray fluoroscopy imaging,and realizes the minimally invasive surgery by percutaneous ultrasound scan.Currently intraoperative ultrasound calibration method is still in the research stage,and will reduce the cost of spinal surgerynavigation system significantly once applied to practical application.