Monitoring the gastrointestinal tract in real-world settings, without interrupting the patient’s daily activities, has become possible with video capsule endoscopy and wireless motility capsules. However, the capsule’s location in the gastrointestinal (GI) tract has to be inferred from the acquired data, so only large-scale organ mapping is possible.

Researchers at Brigham and Women’s Hospital, MIT, and California Institute of Technology have devised a system for localizing and tracking wireless microdevices inside the GI tract in real-time and in non-clinical settings, with millimeter-scale spatial resolution and no need for X-ray radiation. Giovanni Traverso, MB, BChir, PhD, a gastroenterologist in the Division of Gastroenterology, Hepatology and Endoscopy at the Brigham and MIT; and Saransh Sharma and Azita Emami, PhD, of California Institute of Technology; and colleagues describe the system and its potential clinical applications in Nature Electronics.

System Concept

The team designed miniature devices called ingestible microdevices for the anatomical mapping of GI tract (iMAG). These generate a 3D magnetic field gradient that’s transmitted to an external receiver. The receiver maps the field data to the corresponding spatial location, allowing real-time position tracking of the iMAG devices as they move through the GI tract.

Other features of the system are:

• Wireless operation via Bluetooth
• Ultralow power for prolonged battery life (2–4 weeks)
• The small size of the ingestible device (20 mm length and 8 mm diameter)
• Biocompatibility
• Low cost (all components are off-the-shelf and inexpensive)

Large Animal Evaluation

The research team conducted three sets of experiments with iMAGs in pigs.

Limitation of a setting where an iMAG would be ingested and its position would be tracked:

The iMAG was endoscopically administered and evaluated throughout its passage about another iMAG, located externally on the animal’s skin. The researchers were able to locate the device in the stomach, colon, and rectum. The error in the decoded distance between the ingested and reference iMAG devices, compared with the distance obtained from X-ray scans, was <5 mm for the stomach and rectum and <10 mm for the colon. The ingested devices remained functional on excretion.

Utility for monitoring fecal incontinence:

An iMAG was placed 16 cm proximal to the anal sphincter in the colon, and two fixed reference iMAG devices were placed externally. The internal iMAG was pulled out in increments of 5 mm, with a measurement made at every step. When the iMAG was 10 cm inside, the error in the distance between the reference and moving iMAG was <3 mm, validating the system as an accurate (>97%) indicator of defecation.

Sensor of pre-labeled locations within the GI tract:

Highly magnetic barium beads were placed at a specific location in the colon, and the system was used to sense when the ingested iMAG passed that location. The beads interfered with the local magnetic field, affecting the magnetic field readings by the iMAG. The error in the decoded position was appreciable (>1 cm) when the iMAG was within 5 cm of the beads. Thus, the system was not only sensitive to magnetic labels but also immune to their presence when located sufficiently away (>5 cm in this case) from the iMAG being localized.

Clinical Outlook

Measuring GI transit time is vital to diagnosing and treating pathologies related to delayed or accelerated motility, such as gastroparesis, Crohn’s disease, functional dyspepsia, regurgitation, constipation, and fecal incontinence.

Other potential applications of the iMAG are anatomical targeting of drug delivery, medication adherence monitoring, and wireless electrical stimulation to specific regions of the GI tract.

The proven ability of the iMAG to detect the location of magnetic beads suggests it could be used to label injection sites, polyps, fistulas, stomas, or strictures requiring localized therapy.

The researchers have developed a prototype “smart toilet” with gradient coils attached to the seat for at-home measurements. They envision that the complete iMAG system could be incorporated into wearable jackets or portable backpacks.