Study Of Real-time Optical Positioning Technology With High Synchronization

Minimally invasive surgical navigation technology with high accuracy has been more andmore widely used in medical application. It helps physicians make the plan of operation bygiving the image of the nidus in preoperation. In addition, Physicians can perform a virtualoperation which can effectively improve the success rate of surgery. In intraoperation thesurgical navigation system tracks the surgical tools in real-time and shows the relativeposition between the tools and the target. In this way, physicians can get the information ofinternal organs without incision which highly reduces the trauma of patient. In postoperationit accesses the rehabilitation of the patients which facilitates physicians to analyze thetherapeutic effect. Positioning system plays an important role of surgical navigationtechnology. Binocular vision-based optical positioning system(OPS) has been widely usedbecause it has the advantages of high accuracy, easy operation and so on. In China the studyof optical positioning system falls behind that in foreign countries a lot. In order to design anoptical positioning system with independent property rights there are some key problems needto be solved: design of binocular vision system, synchronization of binocular vision cameras,the real-time transmission, visualization of image data and sub-pixel extraction, the softwareof OPS etc. In order to further improve the accuracy of this OPS, an algorithm for analyzingaccuracy and an error distribution need to be studied. According to the aforementioned keyproblems, the main work of this paper is as follow:An FPGA-based OPS has been built. In this system, a binocular vision circuit and ahigh-speed Universal Serial Bus(USB) transmission circuit have been designed. The twocameras of the binocular vision system work synchronously. The USB transmission systemcan transmit data with high speed which meets the requirement of real-time of OPS. Field－Programmable Gate Array（FPGA）has been used to control the two camera capture images atthe same time with its parallel processing ability and flexible arithmetic. Imagepre-processing and sub-pixel extraction are performed in FPGA, and then these datum aresent to computer via USB transmission system. The following procedures such as image andsub-pixel process, registration of tool, images saving are carried out in the software.A fast and precise sub-pixel extraction method which totally based on the hardware of FPGA is designed. The speed of OPS will increase a lot because only sub-pixel data need tobe sent to the computer.A method for analyzing synchronous error has been designed which can be used toanalyze the error made by the desynchrony cameras. It is used to prove the synchronization ofour system. The experimental result illustrates that the FPGA-based OPS can worksynchronously. Moreover, the error distribution of the field of view of OPS has been analyzedwhich can guide physicians to operate in high precision position.This paper has designed an FPGA-base OPS which consist of the hardware and software.Experimental results show that this OPS meets the real-time requirement. It avoid the errormade by the desynchrony of cameras. This OPS has the characters of high precision,high-speed and robustness.