MIT engineers develop ultrasound stickers that can see inside the body

New stamp-sized ultrasound adhesives provide clear images of the heart, lungs and other internal organs.

When clinicians need live images of a patient’s internal organs, they often turn to ultrasound imaging for a safe and non-invasive view of the body’s workings. To take these insightful images, trained professionals manipulate ultrasound wands and probes to direct sound waves into the body. These waves are reflected back and used to produce high-resolution images of the patient’s heart, lungs, and other deep organs.

Ultrasound imaging currently requires bulky and specialized equipment available only in hospitals and doctors’ offices. However, a new design developed by[{” attribute=””>MIT engineers might make the technology as wearable and accessible as buying Band-Aids at the drugstore.

The engineers presented the design for the new ultrasound sticker in a paper published on July 28 in the journal Science. The stamp-sized device sticks to skin and can provide continuous ultrasound imaging of internal organs for 48 hours.

To demonstrate the invention, the researchers applied the stickers to volunteers. They showed the devices produced live, high-resolution images of major blood vessels and deeper organs such as the heart, lungs, and stomach. As the volunteers performed various activities, including sitting, standing, jogging, and biking, the stickers maintained a strong adhesion and continued to capture changes in underlying organs.

In the current design, the stickers must be connected 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 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.

Making the devices work wirelessly is a goal the team is currently working toward. If they are successful, 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.

Sticky problem

To detect with ultrasound, the technician first applies a liquid gel that allows ultrasound waves to pass through the patient’s skin. A probe or transducer is then pressed against the gel, sending sound waves into the body that bounce off internal structures and return to the probe, where the echo signals are converted into visual images.

For patients who require extended periods of imaging, some hospitals offer probes attached to robotic arms that can hold the transducer in place without tiring, but the liquid ultrasound gel eventually leaks and dries, interrupting long-term imaging.

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 tiny ultrasound sensors, the idea being that such a device would stretch and conform to the patient’s body.

But these experimental designs produce low-resolution images, in part because of their stretching: As they move with the body, the transducers shift their location relative to each other, distorting the resulting image.

“The ultrasound imaging device will have enormous potential in the future of clinical diagnostics. However, the resolution and imaging duration of existing ultrasound patches are relatively low, and they cannot detect deep organs,” says Jeonghe Wang, a graduate student at MIT.

View from the inside

By combining a flexible adhesive layer with a solid array of sensors, the MIT team’s new ultrasound sticker produces higher-resolution images over longer periods of time. “This combination allows the device to conform to the skin while maintaining the relative positioning of the sensors for sharper and more accurate images.” Wang says.

The adhesive layer of the device consists of two thin layers of elastomer that enclose a middle layer of hard hydrogel, a mostly water-based material that easily transmits sound waves. Unlike traditional ultrasound gels, the MIT team’s hydrogel is flexible and elastic.

“The elastomer prevents the hydrogel from dehydrating,” says Chen, an MIT postdoc. “Only when the hydrogel is highly hydrated can sound waves effectively penetrate and provide high-resolution images of internal organs.”

The bottom layer of elastomer is designed to adhere to the skin, while the top layer adheres to a solid array of transducers that the team also designed and manufactured. The entire ultrasonic sticker is about 2 square centimeters across and 3 millimeters thick—about the size of a postage stamp.

The researchers put the ultrasound sticker through a series of tests with healthy volunteers who wore the stickers on different parts of the body, including the neck, chest, abdomen and arms. The stickers remained attached to their skin and produced clear images of the underlying structures for 48 hours. During this time, the volunteers performed various activities in the laboratory, from sitting and standing to jogging, cycling and lifting weights.

From the images of the stickers, the team was able to observe the change in the diameter of the main blood vessels in the sitting and standing position. The stickers also capture details of deeper organs, such as how the heart changes shape under stress during exercise. The researchers were also able to watch the stomach expand and then contract as the volunteers drank and then expelled the juice from their system. And when some volunteers lifted weights, the team was able to detect bright patterns in the underlying muscles, signaling temporary micro-damage.

“With imaging, we could capture the moment of exercise before overexertion and stop before the muscles hurt,” says Chen. “We don’t yet know when that moment might come, but now we can provide imaging data that experts can interpret.”

A team of engineers is working on making the stickers work wirelessly. They are also developing AI-based software algorithms that can better interpret and diagnose sticker images. Zhao then envisions that patients and consumers can package and purchase ultrasound stickers and use them not only to monitor various internal organs, but also the progression of tumors, as well as fetal development in the womb.

“We envision that we could have a box of stickers, each designed to represent different areas of the body,” Zhao says. “We believe this represents a breakthrough in wearables and medical imaging.”

Reference: “Bioadhesive ultrasound for long-term continuous imaging of various organs” by Zhonghe Wang, Xiaoyu Chen, Liu Wang, Mitsutoshi Makihata, Xiao-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 Military Nanotechnology Institute.