MIT engineers have developed ultrasound stickers that can see inside the body

MIT engineers have developed an adhesive patch that produces ultrasound images of the body. The stamp-sized device is attached to the skin and can continuously scan 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 clinicians need live images of a patient’s internal organs, they often turn to ultrasound for a safe and noninvasive window into the body’s workings. To capture these insightful images, trained technicians manipulate ultrasound wands and probes to direct sound waves into the body. These waves are reflected back and used to obtain high-resolution images of the patient’s heart, lungs, and other deep organs.

Currently, ultrasound imaging requires bulky and specialized equipment available only in hospitals and doctors’ offices. However, the new design was 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.

A sticky issue

To take an ultrasound image, the technician first applies a liquid gel to the patient’s skin, which conducts the ultrasound waves. A probe or transducer is then pressed onto the gel, sending sound waves into the body, which travel through internal structures and back to the probe, where the updated signals are translated into visual images.

For patients requiring long-term imaging, some hospitals offer probes mounted on robotic arms that can hold the transducer without tiring, but the liquid ultrasound gel leaks and dries over time, disrupting long-term imaging.

In recent years, scientists have explored low-profile designs of stretchable ultrasound probes that can provide portable, profile-based imaging of internal organs. These designs yielded flexible arrays of tiny ultrasound transducers, the idea being that the device would stretch and conform to the patient’s body.

But these experimental designs produced images of lower resolution, in part because of their stretch: when moving with the body, the transducers moved relative to each other, distorting the resulting image.

“A wearable ultrasound device would have great potential in clinical diagnostics in the future. However, current ultrasound patches have relatively low resolution and imaging duration, and they cannot image deep organs,” said MIT graduate student Chonghe Wang.

Interior view

By pairing a long adhesive layer with solid array transducers, the MIT team’s new ultrasound sticker produces high-resolution images over a long period of time. “This combination allows the device to conform to the skin while maintaining the relative location of the transducers to produce clear and precise images.” Van says.

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

“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 provide high-resolution imaging of internal organs.”

The bottom elastomeric layer is designed to adhere to the skin, while the top layer adheres to a rigid matrix array designed and manufactured by the team. All ultrasound stickers are approximately 2 square centimeters wide and 3 millimeters thick – about the size of a postage stamp.

The researchers put the ultrasound patch through a battery of tests on healthy volunteers who wore it on different parts of their body, including the neck, chest, abdomen and arms. The stickers stuck to their skin, creating precise images of the underlying structures for up to 48 hours. During this time, the volunteers performed a variety of activities in the lab, including sitting and standing, running, cycling, and lifting weights.

From the images of the stickers, the team was able to observe changes in the diameter of major blood vessels while sitting and standing. The stickers also showed deeper organ details, such as how the heart changed shape during exercise. The researchers were also able to observe that the stomachs of the volunteers who drank it would expand, then shrink again, and then expel the juice from their system. And when some volunteers lifted weights, the team observed bright patterns in the underlying muscles, indicating temporary microdamage.

“By taking pictures, we can capture the moment during exercise before we overuse it and stop before the muscles hurt,” says Chen. “We don’t know when that moment will be, but now we can provide imaging data that experts can interpret.”

The engineering team is working on making the stickers work wirelessly. They are also developing software algorithms that better interpret and diagnose sticker images based on artificial intelligence. After that, Zhao thinks that ultrasound stickers can be packaged and bought by patients and consumers, and can be used not only to monitor various internal organs, but also to monitor the progression of tumors, as well as the development of the fetus inside the uterus.

“We think we could have a box of stickers, each designed to represent a different location on the body,” says Zhao. “We believe this is a breakthrough in wearables and medical imaging.”

Reference: “Bioadhesive Contrasted Ultrasound for Long-Term Continuous Imaging of Organs” by Chonghe 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 the U.S. Army Research Office through MIT, the Defense Advanced Research Projects Agency, the National Science Foundation, the National Institutes of Health, and the Warrior Nanotechnology Institute at MIT.

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