Ultrasound sticker detects changing stiffness of internal organs, could help identify early signs of acute liver failure

MIT engineers have developed a small ultrasound sticker that can monitor the stiffness of deep organs in the body. The sticker, the size of a postage stamp, can be worn on the skin and is designed to detect signs of disease, such as liver and kidney failure and the progression of solid tumors.

In an open access study published in Scientists progress, the team reports that the sensor can send sound waves through the skin and into the body, where the waves reflect off internal organs and return to the sticker. The pattern of reflected waves can be read as a signature of organ stiffness, which the sticker can measure and track.

“When certain organs suffer from disease, they can stiffen over time,” says the paper’s lead author, Xuanhe Zhao, a professor of mechanical engineering at MIT. “With this wearable sticker, we can continuously monitor changes in stiffness over long periods of time, which is of critical importance for the early diagnosis of internal organ failure.”

The team demonstrated that the sticker can continuously monitor organ stiffness for 48 hours and detect subtle changes that could signal disease progression. In preliminary experiments, the researchers found that the sticky sensor could detect early signs of acute liver failure in rats.

Engineers are working to adapt the design for use in humans. They envision that the sticker could be used in intensive care units (ICUs), where discrete sensors could continuously monitor patients recovering from organ transplants.

“We imagine that, right after a liver or kidney transplant, we can stick this sticker on a patient and observe how the stiffness of the organ changes over the days,” says lead author Hsiao-Chuan Liu. “If acute liver failure is diagnosed early, doctors can act immediately instead of waiting for the disease to worsen.”

Liu was a visiting scientist at MIT at the time of the study and is currently an assistant professor at the University of Southern California. Co-authors of the study at MIT include Xiaoyu Chen and Chonghe Wang, as well as collaborators at USC.

Detect oscillations

Just like our muscles, the tissues and organs in our body stiffen as we age. In some diseases, organ stiffening may become more pronounced, signaling a potentially precipitous decline in health.

Clinicians currently have ways to measure the stiffness of organs such as the kidneys and liver using ultrasound elastography, a technique similar to ultrasound imaging, in which a technician manipulates a hand-held probe or a magic wand on the skin. The probe sends sound waves through the body, which causes internal organs to vibrate slightly and send waves back. The probe detects vibrations induced by an organ, and the pattern of vibrations can translate into how wobbly or stiff the organ should be.

Ultrasound elastography is typically used in intensive care to monitor patients who have recently undergone organ transplantation. Technicians periodically check a patient shortly after surgery to quickly probe the new organ and look for signs of stiffening and potential failure or acute rejection.

“After an organ transplant, the first 72 hours are the most crucial in intensive care,” says another lead author, Qifa Zhou, a professor at USC. “With traditional ultrasound, you have to place a probe on the body. But you can’t do that continuously and over the long term. Doctors risk missing a crucial moment and realizing too late that the organ is failing.”

The team realized they might be able to offer a more continuous wearable alternative. Their solution extends to an ultrasound sticker they previously developed to image deep tissues and organs.

“Our imaging sticker captured longitudinal waves, whereas this time we wanted to capture shear waves, which would tell you how stiff the organ is,” says Zhao.

Existing ultrasound eastrography probes measure shear waves or vibrations of an organ in response to sound pulses. The faster a shear wave travels through the organ, the stiffer the organ is interpreted to be. (Think about the bounce of a water balloon versus a soccer ball.)

The team sought to miniaturize ultrasound elastography to fit on a sticker the size of a tampon. They also aimed to maintain the same sensitivity as commercial handheld probes, which typically incorporate around 128 piezoelectric transducers, each of which transforms an incoming electric field into outgoing sound waves.

“We used advanced manufacturing techniques to cut small transducers from high-quality piezoelectric materials, which allowed us to design miniaturized ultrasonic stickers,” says Zhou.

The researchers precisely fabricated 128 miniature transducers that they embedded on a 25-millimeter square chip. They covered the underside of the chip with a hydrogel-based adhesive, a sticky, stretchy material that is a mixture of water and polymer, which allows sound waves to enter and exit the device almost without loss.

In preliminary experiments, the team tested the rigidity-detecting sticker in rats. They found that the stickers were able to continuously measure liver stiffness for 48 hours. From the data collected on the sticker, the researchers observed clear and early signs of acute liver failure, which they then confirmed with tissue samples.

“Once the liver fails, the rigidity of the organ increases several times,” notes Liu.

“You can go from a healthy liver that’s as wonky as a boiled egg to a diseased liver that’s more like a hard-boiled egg,” Zhao adds. “And this sticker can detect these differences deep inside the body and provide an alert if an organ fails.”

The team is working with clinicians to adapt the sticker for use in patients recovering from organ transplants in intensive care. In this scenario, they don’t anticipate much change in the current design of the sticker, because it can be stuck to a patient’s skin and any sound waves it sends and receives can be delivered and collected by electronic components connected to the sticker, in the same way. electrodes and ECG machines in a doctor’s office.

The researchers also hope to turn the sticker into a more portable, self-contained version, where all of the accompanying electronics and processing are miniaturized to fit into a slightly larger patch. Next, they envision that the sticker could be worn by patients at home, to continuously monitor conditions over longer periods of time, such as the progression of solid tumors, known to harden with gravity.

“We believe this is a life-saving technology platform,” says Zhao. “In the future, we believe people will be able to stick a few stickers on their bodies to measure many vital signals, as well as visualize and track the health of major organs in the body.”

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and education.