Locating Intra-Body Capsule Object by Three-Magnet Sensing System

Abstract

Magnetic localization is an appropriate method for tracing an intra-body capsule object because of its satisfactory accuracy and efficiency. In this method, the capsule is enclosed in a ring magnet, which establishes a magnetic field around the human body. By using a sensor array system with a number of triaxial magnetic sensors, the magnetic flux densities can be measured, and the magnet can be localized by an appropriate algorithm. However, a problem for such a system is that the movements of the human body have interferences on the localization. Therefore, in order to compensate the interferences, we propose a three-magnet localization method. Here, in addition to the capsule object magnet, two other magnets are fixed on the surface of the human body to serve as reference objects. The position and orientation parameters of all the three magnets are determined by applying the optimal algorithm on the sensing data from the sensor array. Then, a reference coordinate system is built based on the two reference objects, and the capsule magnet is relatively tracked with respect to this reference system in human body. The experimental results show that the average localization error caused by the body movement interference is reduced from 30.1 mm (in the original coordinate system) to 3.82 mm (in reference coordinate system) and the average direction error reduced from 17.7°to 2.2°.

Localization and Tracking of Implantable Biomedical Sensors

“…In [40], a three-magnet positioning method is introduced to eliminate the interference caused by the complicated structure of the human body during the localization process using a magnetic flux density-based algorithm and a sensor array with tri-axial magnetic sensors. The study in [44] proposed an original approach where the magnetic field sensors are placed in a biomedical sensor for positioning by considering a pre-computed magnetic field model together with the sensed data.…”

A Novel Relative Position Estimation Method for Capsule Robot Moving in Gastrointestinal Tract

“…Its position and orientation information is related to the movement of the body, the vibration of the belly, and the motility of the GI tract. For the positioning problem when the human body moves, a positioning method based on the human body coordinate system was proposed in our previous work [27]. However, the problem of evaluating the distance of a capsule robot relative to a marker point based on the absolute position of the space with squirming of the GI is necessary for medial surgery, but has not been well-solved.…”

“…Therefore, under the conditions of GI tract peristalsis and fluttering of the belly, the absolute tracking results may fail to provide the correct tissue position, and thus affect the correctness of the diagnosis. Some researchers proposed relative positioning methods based on the human body coordinate system [26,27]. By using additional tracking objects mounted on the human body to serve as tracking references, these methods can easily transform the capsule position results into the body coordinates.…”

Magnetically guided capsule endoscopy

“…163,164 Recent developments include algorithms for 6-DOF localization, 165 multiobject tracking, 166 and the use of body attached permanent magnets as field references to compensate for unpredictable patient movements. 167 Motilis Medica SA (Switzerland) offers a commercial localization system, which employs an array of external field sensors to detect the position and orientation of a magnetic capsule. Their first nonambulatory system, the MTS-1, consists of a 4 9 4 array of 16 sensors placed 5 cm apart.…”

“…The localization algorithm generally consists of minimizing the error between a point dipole field approximation and the measurements . Recent developments include algorithms for 6‐DOF localization, multiobject tracking, and the use of body attached permanent magnets as field references to compensate for unpredictable patient movements …”