Magnetic Localization of Wireless Ingestible Capsules Using a Belt-Shaped Array Transmitter

In the last 20 years, research into and clinical use of wireless ingestible capsules (WIC) has increased, with capsule endoscopy being the most common application in clinical practice. Additionally, there has been an increased research interest in sensing capsules. To maximize the usefulness of the information provided by these devices, it is crucial to know their location within the gastrointestinal tract. The main WIC localization methods in research include radio frequency approaches, video-based methods, and magnetic-based methods. Of these methods, the magnetic-based methods show the most potential in terms of localization accuracy. However, the need for an external transmitting (or sensing) array poses an important limitation, as evidenced by most of the reported methods involving a rigid structure. This poses a challenge to its wearability and performance in daily life environments. This paper provides an overview of the state of the art on magnetic-based localization for WIC, followed by a proof of concept of a system that aims to solve the wearability challenges. Comparative performance simulations of different transmitter arrays are presented. The effect of including one or two receiver coils in the WIC is also evaluated in the simulation. Experimental localization results for a planar transmitter array and for a more wearable belt-shaped transmitter are presented and compared. A localization mean absolute error (MAE) as low as 6.5 mm was achieved for the planar array in a volume of 15 cm x 15 cm x 15 cm, starting at a 5 cm distance from the transmitter. Evaluating the belt array in a similar volume of interest (15 cm x 15 cm x 15 cm starting at 7.5 cm distance from the transmitter) resulted in an MAE of 13.1 mm across the volume and a plane-specific MAE as low as 9.5 mm when evaluated at a 12.5 cm distance. These initial results demonstrate comparable performances between these two transmitters, while the belt array has the potential to enable measurements in daily-life environments. Despite these promising results, it was identified that an improvement in the model for the magnetic field when using transmitter coils with ferrite cores is necessary and is likely to result in better localization accuracy. This belt-array approach, together with compensation techniques for body motion, as recently reported for rigid arrays, has the potential to enable WIC localization in uncontrolled environments with minimal impact on the user's daily life.