August 18, 2022 | Ultrasound is a standard diagnostic tool that uses sound waves and electrical signals to produce internal images. Unlike X-rays and CT scans, ultrasound machines do not use ionizing radiation, making them safe for most patients. Aside from the occasional administration of cold hydrogel—a water-based gel applied to the patient’s skin to prevent sound wave disruption—the procedure is free of any discomfort.
Though ultrasound offers many advantages, traditional machines require bulky equipment and trained sonographers to produce reliable results. Clinical staff must stabilize the machine’s probes for the entirety of an exam, leading to muscle fatigue during lengthy and complex cases.
In response to these obstacles, a Massachusetts Institute of Technology (MIT) engineering team invented a new ultrasound sticker that generates continuous high-resolution images. The self-adhesive wearable patch is the size of a postage stamp and operates without technical supervision for up to two days.
Like traditional ultrasound machines, these stickers connect to a computer for imaging. However, their low profile and self-adhesive backing eliminate the issues associated with conventional devices. Without depending on a sonographer or the continuous reapplication of hydrogel, they become vital diagnostic tools for patients needing round-the-clock monitoring.
“We believe we’ve opened a new era of wearable imaging: With a few patches on your body, you could see your internal organs,” said Xuanhe Zhao, senior author and MIT Mechanical Engineering and Civil and Environmental Engineering professor, in a press release.
Published in Science (DOI: 10.1126/science.abo2542), the team produced internal images for various healthy volunteers. The stickers were applied to multiple locations on the body, including the neck, chest, arms, and abdomen. They captured the body’s physiological response to daily activities such as sitting, standing, and exercising for 48 hours.
Not only did the patches display distinct details like the dilation and constriction of major blood vessels or the peristaltic movement of the digestive tract, but they also produced high-resolution images of deep organs such as the heart, lungs, and stomach—an impossible feat for previous models.
“Wearable ultrasound imaging tools would have huge 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,” said Chonghe Wang, lead author and MIT graduate student.
A combination of elastomers, elastic self-adhesive material, and a rigid piezoelectric transducer array facilitates exceptionally high resolution. Piezoelectric materials convert mechanical energy, like vibrational sound waves, into electric signals.
Combining these specialized materials gives the patch sufficient flexibility to sustain manipulative forces with enough stability to prevent the transducers from shifting. “This combination enables the device to conform to the skin while maintaining the relative location of transducers to generate clearer and more precise images,” Wang said.
The stickers also have built-in capabilities to extend the hydrogel’s viability. Even ultrasound machines employing robotic arms require regular replenishment of gel for continuous use. The team’s stickers comprise two acoustically transparent elastomer layers surrounding a single hydrogel slab, an elastomer-hydrogel hybrid, that attaches to the transducer for a complete and encapsulated ultrasound unit.
“The elastomer prevents dehydration of hydrogel,” said lead author Xiaoyu Chen, an MIT postdoctoral researcher. “Only when hydrogel is highly hydrated can acoustic waves penetrate effectively and give high-resolution imaging of internal organs.”
Moving forward, the team plans to add wireless capabilities to the stickers’ functionality. “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,” said Zhao. When the wireless version is released, patients will have the option of remote monitoring without major interruptions to their daily lives.
On-demand AI analysis also permits diagnostic interpretation of a patient’s daily routine. For example, the study detected temporary muscular microdamage during specific exercises. AI analysis could help patients pinpoint their safe zone when participating in physical activities.
“With imaging, we might be able to capture the moment in a workout before overuse and stop before muscles become sore,” Chen said. “We do not know when that moment might be yet, but now we can provide imaging data that experts can interpret.”
Wireless capabilities also support the packaging and selling of patches at drug stores and pharmacies. “We imagine we could have a box of stickers, each designed to image a different location of the body,” Zhao said. “We believe this represents a breakthrough in wearable devices and medical imaging.”
Continuous, mobile, and high-resolution imaging unlocks an abundance of human health and disease information. Soon, the stickers could monitor tumor growth and other complex conditions in real-time. Pregnant patients on bed rest could have fetal development supervised remotely. Whatever the application, it may be safe to assume that it will only scratch the surface of this technology’s full potential.