Engineers at the Massachusetts Institute of Technology (MIT) and the California Institute of Technology (Caltech) have devised an ingestible sensor whose location can be monitored as it moves through the digestive tract.
This breakthrough
could help doctors more easily diagnose gastrointestinal motility disorders such as constipation, gastroesophageal reflux disease, and gastroparesis.
The tiny sensor works
by detecting a magnetic field produced by an electromagnetic coil located outside the body
.
The strength of the field varies with distance from the coil, so the position of the sensor can be calculated based on its measurement of the magnetic field.
In the new study, the results of which are published in
Nature Electronics
, the researchers showed they could use this technology to track the sensor as it moved through the digestive tracts of large animals.
Such a device
could offer an alternative to more invasive procedures, such as endoscopy,
which are currently used to diagnose motility disorders.
"Many people around the world suffer from GI dysmotility or poor motility, and having the
ability to monitor it without going to a hospital
is important to really understand what's happening to a patient," says Giovanni Traverso, Associate Professor of Engineering Mechanic Karl van Tassel from MIT and gastroenterologist at Brigham and Women's Hospital.
Traverso is one of the lead authors of the new study, along with Azita Emami, a professor of electrical engineering and medical engineering at Caltech, and Mikhail Shapiro, a professor of chemical engineering at Caltech and an investigator at the Howard Hughes Medical Institute.
Saransh Sharma, a graduate student at Caltech, and Khalil Ramadi, a former MIT graduate student and postdoc who is now an assistant professor of bioengineering at New York University, are the paper's lead authors.
Gastrointestinal motility disorders, which affect an estimated 35 million Americans, can occur anywhere in the digestive tract, resulting in food not moving through the tract.
They are usually diagnosed by nuclear imaging studies or X-rays, or by insertion of catheters
containing pressure transducers that detect contractions of the gastrointestinal tract.
The MIT and Caltech researchers
wanted to find an alternative that was less invasive and could be done in the patient's home
.
His idea was to develop a capsule that could be swallowed and then send out a signal that would reveal 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.
From home
To achieve this, the researchers took advantage of the fact that the field produced by an electromagnetic coil becomes weaker, predictably, as the distance from the coil increases.
The magnetic sensor they developed, which is small enough to fit in an ingestible capsule
, measures the surrounding magnetic field and uses that information to calculate its distance from a coil located outside the body.
"Because the magnetic field gradient uniquely encodes spatial positions, these small devices can be designed in a way that they can sense the magnetic field at their respective locations. After the device measures the field, we can back-calculate what the location is." of the device," says Sharma
To pinpoint a device's location inside the body, the system also includes a second sensor that remains outside the body and acts as a reference point.
This sensor could stick to the skin, and by comparing the position of this sensor to the position of the one inside the body, researchers
can accurately calculate where the
ingestible sensor is in the gastrointestinal tract.
The ingestible sensor also includes 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 every time it receives a wireless trigger from a smartphone, but it can also be programmed to take measurements at specific intervals.
"Our system can support
locating multiple devices at the same time without compromising accuracy
. It also has a large field of view, which is crucial for human and large animal studies," explains Emami.
The current version of the sensor can detect a magnetic field from electromagnetic coils within a distance of 60 centimeters or less.
The researchers envision that the coils could be attached to a patient's backpack or jacket, or even the back of a toilet, allowing the ingestible sensor to take measurements as long as it is within range of the coils.
location tracking
The article further notes that the researchers
tested their new system in a large animal model, placing the ingestible capsule in the stomach
and then monitoring its location as it moved through the digestive tract over several days.
In their first experiment, the researchers delivered two magnetic sensors linked together by a small rod, so they knew the exact distance between them.
They then compared their magnetic field measurements to this known distance and found that the
measurements were accurate to about 2 millimeters of resolution
, much higher than the resolution of previously developed magnetic field-based sensors.
Next, the researchers conducted tests using a single ingestible sensor along with an external sensor attached to the skin.
By measuring the distance from each sensor to the coils, the researchers demonstrated that they could track the ingested sensor as it moved from the stomach to the colon and then excreted.
The researchers compared the accuracy of their strategy with measurements taken by X-rays and found that they were accurate to within 5 to 10 millimeters.
"Using an external reference sensor helps to solve the problem that whenever an animal or human is next to the coils, there is a chance that they are not in exactly the same position as the previous time. In the absence of X-rays as a basis, it's hard to trace exactly where this pill is unless you have a consistent reference that is always in the same place," says Ramadi.
This kind of monitoring could make it much easier for doctors to determine which section of the GI tract
is causing slow digestion, the researchers say.
"I think the ability to characterize motility without the need for radiation or more invasive device placement will lower the barrier to testing people," Traverso says.
The researchers now hope to work with collaborators 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.
The research has been funded by the National Science Foundation, the Rothenberg Innovation Initiative, and the Heritage Medical Research Institute.
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