Wireless Capsule Endoscope Precisely Positioning Technology Based On Magnetic Sensors Array

The wireless capsule endoscope reduced the pain of gastrointestinal disease patients greatly when they take the traditional cable type endoscope inspect, it can inspect the whole gastrointestinal tract comprehensively and clearly. Accurately obtaining the position and direction of the capsule in the human body is very important for doctors to diagnose the location and size of the patient's lesions. Meanwhile, it is the key technology to control the capsule moving and attitude in the future. However, the existing technology cannot position the capsule accurately, rapidly and conveniently.Magnetic localization method and magnetic field distribution of magnet are studied in this paper. We modified the problem that the magnetic dipole model is not applicable in the near field, then proposed correction model. In this paper, we designed a magnetic sensor array which is suitable for human body by using the HMC1043 magnetic sensor. Detected the magnetic of the magnet, and put out voltage signal which characterization the magnetic field strength. Using AD623 amplifier to amplify the voltage signals in differential mode, then we send them to the ARM K60 through DG406 selection chips. K60 A/D converter sampled the analog voltage signals in 16 bit accuracy, and treatment these signals, then sent the digital voltage signals to the computer through the serial port. The position and direction information of the capsule are calculated by the C++ positioning software on the computer. Finally, the position, direction information, and the track of the capsule are displayed on the monitor.This paper proposed two methods to compensate the interference which caused by the relative movement between human body and magnetic sensor array. We placed two reference targets on the surface of human body, used multiple targets location method to position the targets at same time. Set up coordinate system at the reference targets(human body). According to the proposed algorithm, the position and orientation of the capsule ware convent to the human body coordinate system, then interference compensate be realized.We researched the influence of magnetic sensor quantity and distribution to positioning results. The experimental data shows that the positioning errors of the capsule will decrease with the number of magnetic sensors increase, but when the number of sensors is enough, the positioning error will no longer reduced significantly. When the magnetic sensors distribution uniform, the positioning error is smaller than they distribution at single side. Finally, the positioning results are reasonable when the positioning system with 24 to 32 magnetic sensors. Here, the positioning error is about 1.2mm, and the directional error at about 1.1°.