MIT engineers designed an adhesive patch that produces ultrasound images of the body. The stamp-sized device sticks to the skin and can provide continuous ultrasound images of internal organs for 48 hours. Credit: Felice Frankel
New stamp-sized ultrasound stickers provide clear images of the heart, lungs and other internal organs.
When doctors need live images of a patient’s internal organs, they often turn to ultrasound for a safe, non-invasive window into the workings of the body. To capture these insightful images, trained technicians manipulate ultrasound wands and probes to direct sound waves into the body. These waves are reflected and used to produce high-resolution images of a patient’s heart, lungs, and other deep organs.
Currently, ultrasound requires bulky and specialized equipment available only in hospitals and doctor’s offices. However, a new design developed by MIT engineers could make the technology as portable and accessible as buying cures at the pharmacy.
The engineers presented the design of the new ultrasound sticker in a paper published July 28 in the journal Science. The stamp-sized device sticks to the skin and can provide continuous ultrasound images of internal organs for 48 hours.
To demonstrate the invention, the researchers applied the stickers to volunteers. They showed that the devices produced high-resolution live images of major blood vessels and deeper organs such as the heart, lungs and stomach. As the volunteers performed various activities, including sitting, standing, running and cycling, the stickers maintained a strong grip and continued to capture changes in the underlying organs.
In the current design, the stickers must be attached to instruments that translate the reflected sound waves into images. According to the researchers, the stickers could have immediate applications even in their current form. For example, the devices could be applied to hospital patients, similar to heart-monitoring EKG stickers, and could continuously image internal organs without a technician holding a probe in place for long periods of time.
Making the devices work wirelessly is a goal the team is currently working towards. If successful, the ultrasound stickers could become portable imaging products that patients could take home from a doctor’s office or even buy at a pharmacy.
“We envision a few patches attached to different locations on the body, and the patches will communicate with your mobile phone, where AI algorithms would analyze the images on demand,” says lead study author Xuanhe Zhao, a professor in 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 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 of MIT, along with Hsiao-Chuan Liu of the Mayo Clinic in Rochester, Minnesota.
A sticky topic
For ultrasound imaging, 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 ice, sending sound waves into the body that echo off internal structures and back to the probe, where the resonant signals are translated into visual images.
For patients requiring long imaging periods, some hospitals offer probes attached to robotic arms that can hold a transducer in place without tiring, but the liquid ultrasound gel flows and dries over time, disrupting the long-term picture.
In recent years, scientists have explored designs for stretchable ultrasound probes that would provide portable, low-profile images of internal organs. These designs yielded a flexible array of small ultrasound transducers, the idea being that this device would stretch and conform to a patient’s body.
But these experimental designs have produced low-resolution images, in part because of their stretching: As they move with the body, the transducers shift locations relative to each other, distorting the resulting image.
“The portable ultrasound imaging tool would have great 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,” he says. Chonghe Wang, who is a graduate student at MIT.
An inside look
By combining an elastic adhesive layer with a rigid array of transducers, the MIT team’s new ultrasound adhesive produces higher-resolution images for a longer duration. “This combination allows the device to conform to the skin while maintaining the relative location of the transducers to generate clearer and more accurate images.” says Wang.
The adhesive layer of the device is made of 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 springy and elastic.
“The elastomer prevents dehydration of the hydrogel,” says Chen, an MIT postdoc. “Only when the hydrogel is highly hydrated can the acoustic waves penetrate effectively and give high-resolution images of the internal organs.”
The elastomer bottom 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 entire ultrasound sticker measures about 2 square centimeters in diameter and 3 millimeters thick, about the area of a postage stamp.
The researchers used the ultrasound sticker in 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 stuck to their skin and produced clear images of the underlying structures for up to 48 hours. During this time, the volunteers performed various activities in the lab, from sitting and standing, to running, cycling and lifting weights.
From the images of the stickers, the team was able to observe the changing diameter of major blood vessels when sitting and standing. The stickers also captured deeper organ details, such as how the heart changes shape as it contracts during exercise. The researchers were also able to watch the stomach expand, then shrink as the volunteers drank and then got juice out of their system. And as some volunteers lifted weights, the team could detect bright patterns in the underlying muscles, indicating temporary microdamage.
“With imaging, we could capture the moment of a workout before overuse and stop before the muscles hurt,” says Chen. “We don’t yet know when that moment might come, but we can now provide imaging data that experts can interpret.”
The engineering team is working on making the stickers work wirelessly. They are also developing artificial intelligence-based software algorithms that can better interpret and diagnose sticker images. Zhao envisions that patients and consumers will then be able to package and purchase ultrasound stickers and use them not only to monitor various internal organs, but also to monitor the progression of tumors as well as the development of fetuses in the womb.
“We imagine we could have a box of stickers, each one designed to represent a different location on the body,” says Zhao. “We believe this represents a breakthrough in wearable devices and medical imaging.”
Citation: “Bioadhesive ultrasound for long-term continuous imaging of various organs” by Chonghe Wang, Xiaoyu Chen, Liu Wang, Mitsutoshi Makihata, Hsiao-Chuan Liu, Tao Zhou, and Xuanhe Zhao, 28 July 2022, Science.DOI : 10.1126/science .abo2542
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 MIT Soldier Nanotechnologies Institute.