Ultrasound imaging is a safe, non-invasive window into how the body functions, providing clinicians with live images of a patient’s internal organs. To capture these images, trained technicians manipulate wands and ultrasound probes to direct sound waves into the body. These waves reflect to produce high resolution images of a patient’s heart, lungs and other deep organs.
Currently, ultrasound imaging requires large, specialized equipment available only in hospitals and medical practices. But a new design from MIT engineers could make the technology as portable and accessible as buying band-aids at the pharmacy.
In an article published today in Scienceengineers present the design of a new ultrasound sticker – a tampon-sized device that sticks to the skin and can provide continuous ultrasound imaging of internal organs for 48 hours.
The researchers applied the stickers to volunteers and showed that the devices produced high-resolution live images of major blood vessels and deeper organs such as the heart, lungs and stomach. The stickers maintained a strong bond and picked up changes in the underlying organs as the volunteers performed various activities, including sitting, standing, jogging, and bicycling.
The current design requires connecting the stickers to instruments that translate reflected sound waves into images. The researchers point out that even in their current form, the stickers could have immediate applications: for example, the devices could be applied to patients in the hospital, like heart monitoring ECG stickers, and could continuously image internal organs without require a technician. hold a catheter in place for long periods of time.
If the devices can be made to work wirelessly – a goal the team is currently working towards – the ultrasound stickers could be turned 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 stuck to different places on the body, and the patches would communicate with your mobile phone, where AI algorithms would analyze the images on demand,” says lead study author Xuanhe Zhao, a professor of mechanical and civil engineering and environmental engineering at MIT. “We think we’ve ushered in a new era of wearable imaging: with a few patches on your body, you can 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, as well as Hsiao-Chuan Liu of the Mayo Clinic in Rochester, Minnesota.
A sticky question
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 through the body that echo internal structures and return to the probe, where the returned signals are translated into visual images.
For patients who require long periods of imaging, some hospitals offer probes attached to robotic arms that can hold a transducer in place without fatigue, but the liquid ultrasound gel will leak out and dry out over time, interrupting long-term imaging.
In recent years, researchers have explored expandable ultrasound probe designs that would provide portable, unobtrusive imaging of internal organs. These designs yielded a flexible array of tiny ultrasound transducers, the idea being that such a device would stretch and conform to a patient’s body.
But these experimental designs produced low-resolution images, in part because of their stretch: as they move with the body, the transducers move relative to each other, distorting the resulting image.
“A portable ultrasound imaging tool would have enormous potential in the future of clinical diagnostics. However, the resolution and imaging time of existing ultrasound patches are relatively low, and they cannot image deep organs,” says Chonghe Wang, who is a graduate student at MIT.
An inside look
The MIT team’s new ultrasonic sticker produces higher-resolution images over a longer period of time by combining a stretchy adhesive layer with a rigid array of transducers. “This combination allows the device to conform to the skin while maintaining the relative location of the transducers to generate clearer, more accurate images.” Wang said.
The device’s adhesive layer consists of two thin layers of elastomer that encapsulate an intermediate layer of solid hydrogel, a primarily 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 the hydrogel,” says Chen, a postdoctoral fellow at MIT. “Only when the hydrogel is highly hydrated can acoustic waves effectively penetrate and provide high-resolution imaging of internal organs.”
The bottom elastomer layer is designed to stick to the skin, while the top layer adheres to a rigid array of transducers that the team also designed and manufactured. The whole ultrasonic sticker is about 2 square centimeters in diameter and 3 millimeters thick, about the area of a postage stamp.
The researchers subjected the sticker to ultrasound 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, the volunteers performed a variety of activities in the lab, ranging from sitting and standing to jogging, cycling and lifting weights.
From the sticker images, the team was able to observe the change in diameter of major blood vessels when seated compared to when standing. The stickers also captured deeper organ details, such as how the heart changes shape as it moves during exercise. The researchers were also able to observe the stomach expand and then retract as the volunteers drank and then expelled juice from their system. And as some volunteers lifted weights, the team could detect light patterns in underlying muscles, signaling temporary microdamage.
“With imagery, we might be able to capture the timing of a workout before overuse and stop before muscles become sore,” says Chen. “We don’t yet know when that time might be, but now we can provide imaging data that experts can interpret.”
The team is working to make the stickers work wirelessly. They are also developing AI-based software algorithms that can better interpret and diagnose sticker images. Next, Zhao envisions that ultrasound stickers can 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 represent a different location on the body,” Zhao explains. “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 US Army Research Office through the Institute for Soldier Nanotechnologies at MIT.