Gastrointestinal (GI) motility disorders such as constipation, gastro esophageal reflux disease, and gastroparesis affect millions of people globally and can occur in any part of the digestive tract, stopping the movement of food through the tract. Doctors generally diagnose the condition by using nuclear imaging studies or X-rays, or inserting catheters with pressure transducers that can sense contractions of the GI tract. Now, a team of engineers has demonstrated an ingestible sensor that allows its location to be monitored as it moves through the digestive tract and could help doctors diagnose GI motility disorders more easily.

The tiny sensor developed by engineers at MIT (Cambridge, MA, USA) and Caltech (Pasadena, CA, USA) detects a magnetic field created by an electromagnetic coil located outside the body. The strength of the field varies depending upon the distance from the coil, as a result of which the sensor’s position is calculated based on its measurement of the magnetic field. In the new study, the researchers showed that they could use the technology to track the sensor as it moved through the digestive tract of large animals. The device could offer an alternative to more invasive procedures, such as endoscopy, that are presently being used to diagnose GI motility disorders.

The MIT and Caltech researchers set out to develop an alternative for diagnosing GI motility disorders that was less invasive and could be done at the patient’s home. They worked on developing a capsule that could be swallowed and would transmit a signal to reveal its position in the GI tract. This would enable doctors to identify the precise part of the tract that was causing a slowdown and decide the appropriate treatment needed for the patient’s condition. They achieved this by taking advantage of the fact that the field produced by an electromagnetic coil becomes predictably weaker with the increase in the distance from the coil. The magnetic sensor developed by the researchers is tiny enough to fit inside an ingestible capsule and measures the surrounding magnetic field. It then uses that information to calculate its distance from a coil located outside the body.

In order to accurately pinpoint the location of a device inside the body, the system has another sensor that remains outside the body and acts as a reference point. Researchers can compare the position of this sensor that can be taped to the skin with the position of the sensor inside the body to precisely calculate where the ingestible sensor lies in the GI tract. The ingestible sensor also features a wireless transmitter that transmits the magnetic field measurement to a nearby computer or smartphone. The system’s current version can take a measurement any time it receives a wireless trigger from a smartphone and can also be programmed to take measurements at specific intervals. It can detect a magnetic field from electromagnetic coils within a distance of 60 centimeters or less. The coils could be placed in the patient’s backpack or jacket, or even the back of a toilet, according to the researchers, thus enabling the ingestible sensor to take measurements whenever it comes within range of the coils.

The researchers used a large animal model to test their new system by placing the ingestible capsule in the stomach and then tracking its location as it moved through the digestive tract over a period of several days. In the first experiment, the team delivered two magnetic sensors attached to each other by a small rod that allowed them to know the exact distance between them. They then compared their magnetic field measurements to this known distance and found the measurements to be accurate to a resolution of about two millimeters which was far higher than the resolution of the magnetic-field-based sensors developed earlier. The team then went on to perform tests using a single ingestible sensor accompanied by an external sensor attached to the skin.

By measuring the distance from each sensor to the coils, the research team demonstrated that it was possible to track the ingested sensor as it moved from the stomach to the colon and was finally excreted. Upon comparing the accuracy of their strategy with the measurements taken by X-ray, the researchers found them to be accurate within 5 to 10 millimeters. Such level of monitoring can allow doctors to more easily identify the section of the GI tract causing a slowdown in digestion. The researchers now plan to develop manufacturing processes for the system in collaboration with others and further characterize its performance in animals, ultimately paving the way to its testing in human clinical trials.

“Many people around the world suffer from GI dysmotility or poor motility, and having the ability to monitor GI motility without having to go into a hospital is important to really understand what is happening to a patient,” said Giovanni Traverso, an associate professor of mechanical engineering at MIT and a gastroenterologist at Brigham and Women’s Hospital. “The ability to characterize motility without the need for radiation, or more invasive placement of devices, I think will lower the barrier for people to be evaluated.” 

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