Wearable Permanent Magnet Tracking System for Wireless Capsule Endoscope

Abstract

Permanent magnet tracking technology is a reliable solution used to localize the wireless capsule endoscope (WCE) with an embedded permanent magnet. However, in wearable permanent magnet tracking systems, compensation for the geomagnetic field plays a key role in the localization accuracy. The geomagnetic field superimposed on the sensor measurement will change in accordance with human body posture changes, thus causing a reduction in localization accuracy. In this study, a wearable permanent magnet tracking system and a corresponding calibration method are proposed to compensate for the geomagnetic field interference dynamically. The proposed system overcomes the shortcomings of existing systems that prevent patients from freely changing posture. In addition, a nine-axis inertial measurement unit is adopted to obtain a robust posture estimation that contributes to the compensation of the geomagnetic field. This innovation allows the localization accuracy to be maintained over a longer period of time than with current technology. The experiments show the effectiveness and stability of the wearable permanent magnet tracking system for realizing the geomagnetic field compensation. Within a tracking region of 46 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times34$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times28$ </tex-math></inline-formula> cm, the proposed method achieves a 15-Hz update rate. Furthermore, the average position error caused by postural changes is reduced from 9.9 mm to 1.8 mm, and the average orientation error is reduced from 25.4° to 5.1°.