A Compensation Method for Relative Movement Between a Sensor Array and the Abdomen for Magnetic Localization of Capsule Endoscopes

Abstract

Magnetic localization is an excellent candidate for localization of capsule endoscopes. A small magnet is embedded into the capsule, and its magnetic field is measured at a sensor array around the patient’s abdomen. However, relative movement between the abdomen and the array causes high localization errors. In this study, an innovative movement compensation method is proposed. A rigid array comprising 12 sensors was used to localize a permanent magnet. Furthermore, two orthogonal reference coils fed with a low-frequency signal were assumed to be fixed at the abdomen. The coils were alternately switched on and off, and thus, all three magnetic objects were separately localized since their magnetic fields can be distinguished in the time and frequency domains. A reference coordinate system was set up with the coils, in which the magnet was localized. The proposed compensation method was evaluated for relative rotations and displacements between the sensors and the three magnetic objects. Moreover, the compensation method was evaluated for two reference magnets and compared with the coil-based approach. The mean position error was reduced by approximately a factor of 10 from 41.5 ± 15.5 to 3.8 ± 1.1 mm, respectively, and the orientation error did not exceed 3° for the coil-based compensation method. In contrast, with two reference magnets, the mean position and orientation errors were higher than 30 mm and 20°, respectively. Consequently, it was shown that the coil-based method is the next step toward a wearable magnetic localization system to compensate for relative movement.