Suture Odometry: A Novel Hardware-Independent Method for Precise Medical Capsule Localization in the Gastrointestinal Tract

Precise localization of ingestible medical capsules within the gastrointestinal (GI) tract is crucial for optimal diagnosis and treatment of GI diseases, yet current methods struggle with accuracy and reliability due to signal interference through tissue, shifting anatomical reference frames, and dependency on external hardware. While existing approaches like electromagnetic tracking, magnetic sensing, and optical methods can approximate general capsule position, they cannot provide continuous, precise distance measurements through the tortuous GI environment. This paper presents a novel suture odometry system that enables accurate, hardware-independent capsule localization by measuring the unwinding of a dissolvable suture thread from an internal spool as the capsule traverses the GI tract, with the suture anchored in the stomach serving as a fixed reference point. The system was extensively validated in both simulated environments and freshly excised porcine intestines, demonstrating an average localization accuracy of 7.78 cm and precision of 8.24 cm over 9 meters of intestine—performance that notably exceeds existing methods while remaining robust through intestinal bends, retrograde flow, and varying tissue conditions. The device maintains Food and Drug Administration (FDA)-approved capsule dimensions and can be integrated into various therapeutic and diagnostic capsule designs, operating independent of external hardware or complex signal processing. This technology represents a significant advance in medical capsule localization, enabling more precise targeted therapy and diagnostic capabilities throughout the GI tract while offering a simple, reliable solution that could be readily incorporated into existing capsule designs.