A wearable ultrasound sticker roughly the size of a postage stamp could help enable continuous medical imaging of internal organs for patients on the move, a new study finds.

Ultrasound imaging is one of the most common medical tools for scanning inside the body in a safe, noninvasive manner. Currently, to image with ultrasound, first a liquid gel is applied to a patient’s skin that helps transmit ultrasound waves. Then an ultrasound probe, or transducer, is pressed against the gel.

Continuous long-term ultrasound imaging could help shed light on potentially vital changes in a patient’s health over days or even months. However, ultrasound imaging currently requires bulky, rigid equipment, making long-term monitoring difficult.

In addition, capturing ultrasound images demands highly trained sonographers to properly apply and orient the ultrasound probes onto a patient’s body. Practically speaking, and even just to avoid repetitive motion injuries, these practical restrictions often limit the length of ultrasound sessions. For patients who need long periods of imaging, some hospitals offer probes on robotic arms that can hold a transducer in place without tiring. However, the liquid ultrasound gel flows away and dries out over time, interrupting the sessions and producing less-than-ideal results.Recently scientists have explored stretchable ultrasound probes that can better conform to a patient’s body for potential wearable applications. However, such designs have suffered from low resolution and poor image quality during body movements, among other problems.

Now scientists have developed an ultrasound sticker they say can overcome many of these challenges. They detailed their findings in the 29 July issue of the journal Science.

The new device consists of a thin, rigid scanner array possessing 400 ultrasound transducers per square centimeter. This array is coupled to a soft, durable, sticky layer that can bond onto skin. The entire sticker measures 3 millimeters thick and 2 square centimeters in size.

The device’s adhesive layer contains a soft hydrogel, a material similar to the absorbent stuffing inside disposable diapers. This hydrogel easily transmits sound waves, and unlike traditional ultrasound gels, is stretchy and elastic. The hydrogel is encapsulated between two thin rubbery layers that help keep the hydrogel wet so acoustic waves can pass through it.

In tests, the researchers had healthy volunteers wear the devices on various parts of their body, including the neck, chest, abdomen and arms. They also had the participants perform a variety of activities in the lab, such as sitting, standing, jogging, biking, weightlifting and drinking juice.

The devices stuck onto the skin of the volunteers and produced clear images of underlying structures for up to 48 hours. They could watch how the jugular vein widened after volunteers went from sitting or standing to a supine position; how the heart swelled after a half hour of exercise; how the lungs behaved during jogging and cycling; how the stomach distended and shrank as the volunteers drank juice that later flowed out; and how biceps became flooded with blood after lifting weights.

The image resolution of the bioadhesive ultrasound (BAUS) device “is on a similar level to point-of-care ultrasound,” says study senior author Xuanhe Zhao, a mechanical engineer at MIT. More work is needed to reach the performance of mature conventional ultrasound machines, he adds.

Although the stickers do continuously image the body with ultrasound waves, “the imaging frequency is low, such as one image per 30 minutes or 1 hour,” Zhao says. “Therefore, BAUS is safe for the body.” [READ MORE]