MIT engineers designed an adhesive patch that produces ultrasound images of the body.
The stamp-sized device sticks to skin and can provide continuous ultrasound imaging
of internal organs for 48 hours.
Ultrasound imaging is a safe and noninvasive window into the body’s workings, providing
clinicians with live images of a patient’s internal organs.
To capture these images, trained technicians manipulate ultrasound wands and probes to
direct sound waves into the body.
These waves reflect back 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 the journal 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.
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.
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.
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.
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.
Only when hydrogel is highly hydrated acoustic waves can 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.
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.