Tracking Technology For Capsule Endoscope Based On Magnetic Sensor

Endoscopy is the gold standard for screening early gastric cancer.However,the traditional endoscope brought great pain to the examinee due to the mechanical insertion.With the advantages of non-invasive,painless etc.,capsule endoscope has greatly improved the attitude of the patients to endoscopy,which is an important direction for the development of endoscope.Nevertheless,it is difficult for capsule endoscope to locate the diseased parts and the doctor cannot control the capsule endoscope.The tracking technology is necessary for solving these problems.The tracking technology based on magnetic sensing has the advantages of high positioning accuracy,fast positioning speed,high real-time performance etc.In this article,the tracking technology of capsule endoscope based on magnetic sensing was studied.Because of the human body has no shielding against the magnetic signal,we fixed a permanent magnet in the capsule endoscope.By means of the periodically detection of the magnetic field by external magnetic sensors,the position and orientation of the endoscope were obtained by using the location algorithm.The main research work involves:First of all,a new multi-magnetic-dipole model is proposed for overcoming the problems of the reduction of positioning range and positioning accuracy in the magnetic tracking system,which are caused by inaccurate model of the single magnetic dipole of cylindrical permanent magnet.In this model,the cylindrical magnet is equivalent to a set of multiple magnetic dipoles arranged along the axis of the magnet.Compared with the traditional single magnetic dipole model,the multi-magnetic-dipole model can guarantee the effectiveness in the near field region of magnet,and expand the positioning range of the magnetic positioning system.Next,aiming at the problems of low dynamic precision and easy to fail in tracking under magnetic interference,we proposed a magnetic localization algorithm based on Particle Filter(PF),which add the estimation of the target motion and magnetic interference.The former is used to compensate the non-real-time magnetic field measurement under sequential sampling,and the latter is used to compensate the magnetic interference.Compared with the traditional positioning algorithm,the PF algorithm can keep the positioning accuracy of the capsule in the process of moving.Besides,the PF algorithm can overcome the influence of ferromagnetic material or energized coil on the magnetic field environment.Finally,we built a capsule endoscope tracking system based on magnetic sensing.The front end of the system is an array which composed of 16 three-axis magnetic sensors HMC5983.The outputs of the sensors are collected serially through IIC by a STM32 micro controller,and are sent to the computer through a serial port.The computer can locate the target through a variety of tracking algorithms by using the magnetic positioning software.And the software can display the three-dimensional trajectory of the target based on OpenGL.The static positioning experiments and dynamic tracking experiments without or with magnetic interference were carried out by utilizing this magnetic tracking system.The experimental results show that,in magnetic interference,the proposed PF algorithm based on multi-magnetic-dipole model can reach a static positioning accuracy of 3.17 mm,an orientation accuracy of 2.77 degrees.Furthermore,when the speed of the moving object is less than 8 mm/s,the dynamic positioning accuracy is below 6 mm.