New stamp-sized ultrasound adhesives produce clear images of heart, lungs, and other internal organs
Massachusetts Institute of Technology
To capture these images, trained technicians manipulate ultrasound wands and probes to direct sound waves into the body.
These waves reflect back out to produce
high-resolution images of a patient's heart, lungs, and other deep organs.
Currently,
ultrasound imaging requires bulky and specialized equipment available only in
hospitals and doctor's offices. But a new design by MIT engineers might make
the technology as wearable and accessible as buying Band-Aids at the pharmacy.
In
a paper appearing in Science, the engineers present the
design for a new ultrasound sticker -- a stamp-sized device that sticks to skin
and can provide continuous ultrasound imaging of internal organs for 48 hours.
The
researchers applied the stickers to volunteers and showed the devices produced
live, high-resolution images of major blood vessels and deeper organs such as
the heart, lungs, and stomach. The stickers maintained a strong adhesion and
captured changes in underlying organs as volunteers performed various
activities, including sitting, standing, jogging, and biking.
Video: https://youtu.be/Kn2J8W4csNc
The current design requires connecting the stickers to instruments that translate the reflected sound waves into images. The researchers point out that even in their current form, the stickers could have immediate applications: For instance, the devices could be applied to patients in the hospital, similar to heart-monitoring EKG stickers, and could continuously image internal organs without requiring a technician to hold a probe in place for long periods of time.
If
the devices can be made to operate wirelessly -- a goal the team is currently
working toward -- the ultrasound stickers could be made into wearable imaging
products that patients could take home from a doctor's office or even buy at a
pharmacy.
"We
envision a few patches adhered to different locations on the body, and the
patches would communicate with your cellphone, where AI algorithms would
analyze the images on demand," says the study's senior author, Xuanhe
Zhao, professor of mechanical engineering and civil and environmental
engineering at MIT. "We believe we've opened a new era of wearable
imaging: With a few patches on your body, you could see your internal
organs."
The
study also includes lead authors Chonghe Wang and Xiaoyu Chen, and co-authors
Liu Wang, Mitsutoshi Makihata, and Tao Zhao at MIT, along with Hsiao-Chuan Liu
of the Mayo Clinic in Rochester, Minnesota.
A
sticky issue
To
image with ultrasound, a technician first applies a liquid gel to a patient's
skin, which acts to transmit ultrasound waves. A probe, or transducer, is then
pressed against the gel, sending sound waves into the body that echo off
internal structures and back to the probe, where the echoed signals are
translated into visual images.
For
patients who require long periods of imaging, some hospitals offer probes
affixed to robotic arms that can hold a transducer in place without tiring, but
the liquid ultrasound gel flows away and dries out over time, interrupting
long-term imaging.
In
recent years, researchers have explored designs for stretchable ultrasound
probes that would provide portable, low-profile imaging of internal organs.
These designs gave a flexible array of tiny ultrasound transducers, the idea
being that such a device would stretch and conform with a patient's body.
But
these experimental designs have produced low-resolution images, in part due to
their stretch: In moving with the body, transducers shift location relative to
each other, distorting the resulting image.
"Wearable
ultrasound imaging tool would have huge potential in the future of clinical
diagnosis. However, the resolution and imaging duration of existing ultrasound
patches is relatively low, and they cannot image deep organs," says
Chonghe Wang, who is an MIT graduate student.
An
inside look
The
MIT team's new ultrasound sticker produces higher resolution images over a
longer duration by pairing a stretchy adhesive layer with a rigid array of
transducers. "This combination enables the device to conform to the skin
while maintaining the relative location of transducers to generate clearer and
more precise images." Wang says.
The
device's adhesive layer is made from two thin layers of elastomer that
encapsulate a middle layer of solid hydrogel, a mostly water-based material
that easily transmits sound waves. Unlike traditional ultrasound gels, the MIT
team's hydrogel is elastic and stretchy.
"The
elastomer prevents dehydration of hydrogel," says Chen, an MIT postdoc.
"Only when hydrogel is highly hydrated can acoustic waves penetrate
effectively and give high-resolution imaging of internal organs."
The
bottom elastomer layer is designed to stick to skin, while the top layer
adheres to a rigid array of transducers that the team also designed and
fabricated. The entire ultrasound sticker measures about 2 square centimeters
across, and 3 millimeters thick -- about the area of a postage stamp.
The
researchers ran the ultrasound sticker through a battery of tests with healthy
volunteers, who wore the stickers on various parts of their bodies, including
the neck, chest, abdomen, and arms. The stickers stayed attached to their skin,
and produced clear images of underlying structures for up to 48 hours. During
this time, volunteers performed a variety of activities in the lab, from
sitting and standing, to jogging, biking, and lifting weights.
From
the stickers' images, the team was able to observe the changing diameter of
major blood vessels when seated versus standing. The stickers also captured
details of deeper organs, such as how the heart changes shape as it exerts
during exercise. The researchers were also able to watch the stomach distend,
then shrink back as volunteers drank then later passed juice out of their
system. And as some volunteers lifted weights, the team could detect bright
patterns in underlying muscles, signaling temporary microdamage.
"With
imaging, we might be able to capture the moment in a workout before overuse,
and stop before muscles become sore," says Chen. "We do not know when
that moment might be yet, but now we can provide imaging data that experts can
interpret."
The
team is working to make the stickers function wirelessly. They are also
developing software algorithms based on artificial intelligence that can better
interpret and diagnose the stickers' images. Then, Zhao envisions ultrasound
stickers could be packaged and purchased by patients and consumers, and used
not only to monitor various internal organs, but also the progression of
tumors, as well as the development of fetuses in the womb.
"We
imagine we could have a box of stickers, each designed to image a different
location of the body," Zhao says. "We believe this represents a
breakthrough in wearable devices and medical imaging."
This research was funded, in part, by MIT, the Defense Advanced Research Projects Agency, the National Science Foundation, the National Institutes of Health, and the U.S. Army Research Office through the Institute for Soldier Nanotechnologies at MIT.
