Engineers from MIT and Caltech in the USA have presented a swallowable sensor whose position can be monitored as it passes through the digestive tract. Doctors could use it to more easily diagnose gastrointestinal motility disorders such as constipation, gastroesophageal reflux disease and gastroparesis.
The tiny sensor works by detecting a magnetic field generated by an electromagnetic coil outside the body. The strength of the field varies with the distance to the coil, so that the position of the sensor can be calculated based on the measurement of the magnetic field.
In the new study [2], the researchers showed that they can use this technology to track the sensor as it moves through the digestive tract of large animals. Such a device could provide an alternative to more invasive procedures such as endoscopy, which are currently used to diagnose motility disorders.
Many people around the world suffer from digestive tract dysmotility or poor motility, and the ability to monitor digestive tract motility without having to visit a hospital is important to truly understand what is happening to a patient.
GI motility disorders, which affect about 35 million Americans, can occur in any part of the digestive tract and cause food to not move through the tract. They are usually diagnosed using nuclear medicine scans or X-rays, or by inserting catheters with pressure transducers that measure contractions of the gastrointestinal tract. The researchers at MIT and Caltech wanted to develop an alternative that is less invasive and can be performed at the patient's home. Their idea was to develop a capsule that could be swallowed and then emit a signal showing where it was in the gastrointestinal tract, allowing doctors to determine which part of the tract was causing a slowdown and better determine how to treat the patient's condition (Fig. 1).
To accomplish this, the researchers took advantage of the fact that the field generated by an electromagnetic coil weakens in a predictable way as the distance to the coil increases. The magnetic sensor they developed, which is small enough to fit into an ingestible capsule, measures the surrounding magnetic field and uses this information to calculate the distance to a coil located outside the body. Since the magnetic field gradient uniquely encodes spatial positions, these small devices can be designed to detect the magnetic field at their respective locations. Once the device has measured the field, the location of the device can be calculated back.
Fig. 2: The sensor could be used to monitor GI motility disorders such as constipation or gastroesophageal reflux disease (courtesy of the researchers)To accurately determine the location of a device in the body, the system also includes a second sensor that remains outside the body and serves as a reference point. This sensor could be stuck to the skin. By comparing the position of this sensor with the position of the sensor inside the body, the researchers can calculate exactly where the ingestible sensor is located in the gastrointestinal tract.
The ingestible sensor also contains a wireless transmitter that sends the magnetic field measurement to a nearby computer or smartphone. The current version of the system is designed to take a measurement each time it receives a wireless trigger from a smartphone, but it can also be programmed to take measurements at specific intervals.
The system can locate multiple devices simultaneously without compromising accuracy. It also has a large field of view, which is crucial for studies on humans and large animals (Fig. 2).
The current version of the sensor can detect a magnetic field from electromagnetic coils at a distance of 60 centimeters or less. The researchers envision that the coils could be placed in the patient's backpack or jacket, or even on the back of a toilet, allowing the ingestible sensor to take measurements as soon as it is within range of the coils.
The researchers tested their new system in a large animal model by inserting the ingestible capsule into the stomach and then monitoring its position as it traveled through the digestive tract over several days.
In their first experiment, the researchers attached two magnetic sensors connected by a small rod so that they knew the exact distance between them. They then compared their magnetic field measurements with this known distance and found that the measurements were accurate to a resolution of about 2 millimeters - much more accurate than the resolution of previously developed magnetic field sensors.
Next, the researchers conducted tests using a single ingestible sensor and an external, skin-mounted sensor. By measuring the distance between each sensor and the coils, the researchers were able to show that they could track the ingested sensor as it traveled from the stomach to the colon and then to excretion. The researchers compared the accuracy of their strategy with X-ray measurements and found that they were able to get by with an accuracy of 5 to 10 millimeters.
Using an external reference sensor solves the problem that every time an animal or human is next to the coils, there is a chance that they are not in exactly the same position as the last time. If you don't have x-rays to base it on, it's difficult to determine exactly where the pill is unless you have a consistent reference that is always in the same place.
This type of monitoring could make it much easier for doctors to figure out which section of the gastrointestinal tract is causing a slowdown in digestion, the researchers say. The ability to characterize motility without the need for radiation or more invasive device placement will lower the barrier to studying people.
The researchers now hope to work with partners to develop manufacturing processes for the system and further characterize its performance in animals, with the hope of eventually testing it in human clinical trials.
Literature
[1] Source : https://news.mit.edu/2023/
[2] Sharma, S.; Ramadi, K.B.; Poole, N.H. et al: Location-aware ingestible microdevices for wireless monitoring of gastrointestinal dynamics, Nat Electron 6, 242-256 (2023). https://doi.org/10.1038/s41928-023-00916-0
