Research And Application Of High Precision Permanent Magnet Positioning Technology

At present,the most accepted treatment for cancer patients is radiation therapy,and a better dose distribution is an important prerequisite for successful treatment.However,the movement of the tumor caused by the respiratory movements of patients with lung tumors has greatly affected the accuracy of radiotherapy and prevented the patients from obtaining good treatment results.In the course of radiotherapy,the positioning and tracking of lung tumors can be achieved by means of a passive wireless positioning technology.Compared with the traditional radiotherapy positioning tracking method,magnetic positioning technology has the advantages of small tracking target,not limited by the sight line,millimeter-level positioning accuracy,and no radiation damage to the human body.In order to solve the above problems,this paper has conducted in-depth research on high-precision permanent magnet positioning technology and its application in lung tumor motion tracking.Due to the weakening of the magnetic field strength and the interference of the environment magnetic field,the tracking accuracy of the magnetic positioning technology deteriorates sharply with the increase of the distance between the magnet and the sensor array.In order to extend the tracking range,two novel methods are proposed.First of all,the advanced three-axis tunnel magnetoresistance(TMR)sensor is used to build the sensor array,which has significantly higher sensitivity and lower background noise than other types of magnetoresistance sensors.At the same time,a fusion method is proposed to extend the tracking range.The particle swarm optimization Levenberg Marquardt(PSO-LM)method based on the magnetic dipole model is applied to the near area(the magnet is closer to the sensor array),and the prior knowledge based back propagation neural network(PKBPNN)is applied to the far area(the magnet is farther from the sensor array).Finally,these two algorithms were fused by using an adaptive sigmoid function.Compared with using PSO-LM alone in the whole positioning space,it has higher tracking performance in the long-distance area.Experimental results show that within the tracking range of 216 to 296 mm,the tracking error is reduced from(18.24 ± 9.37 mm,12.45 ± 3.37 °)to(8.95 ± 1.74 mm,7.97 ± 2.08 °).In addition,the tracking distance is extended to 396 mm when the position error is less than 25 mm.It can be concluded that this method greatly expands the tracking range of the magnetic tracking system.For the problems of low positioning accuracy in multi-magnetic target positioning,this paper proposes a novel multi-magnetic target positioning method.The main positioning method is to use a small cylindrical magnet as a magnetic dipole,analyze the magnetic flux density model of multi-magnetic target,and use the combination of whale optimization algorithm and Levenberg-Marquardt to achieve multi-target real-time positioning.Through comparison experiments with the positioning methods in previous studies,the results show that the multimagnetic target positioning method proposed in this paper shows higher positioning accuracy when positioning and tracking multiple permanent magnets.Considering the urgent need of precise radiotherapy for lung cancer patients and the current research status of magnetic localization technology,this paper studies the real-time tracking of lung cancer based on magnetic localization technology.Multiple magnetic targets are placed around the tumor model,and the magnetic field information is obtained by the sensor array placed under the CIRS human lung model.The position and direction information of each magnet around the tumor is inversely deduced by the multi-magnetic target positioning algorithm,and the moving track of the magnet is obtained,so as to inversely deduce the moving track of the tumor.