Small ultrasound stickers allow you to monitor the hardness of internal organs

MIT engineers have developed a tiny ultrasound sticker that can monitor the stiffness of organs deep in the body. The stickers are about the size of a postage stamp and can be applied to the skin and are designed to catch signs of diseases such as liver and kidney failure and the progression of solid tumors.

In an open access study published in scientific progressThe researchers report that the sensor sends sound waves through the skin and into the body, where they can bounce off internal organs and return to the sticker. The pattern of reflected waves can be read as a sign of organ hardness, which the sticker can measure and track.

When some organs become diseased, they can become stiff over time. This wearable sticker allows continuous monitoring of changes in stiffness over time. This is very important for early diagnosis of visceral failure. ”

Xuanhe Zhao, senior author of the paper and MIT professor of mechanical engineering

The researchers demonstrated that the sticker could continuously monitor organ stiffness over a 48-hour period, detecting subtle changes that could signal disease progression. In preliminary experiments, researchers found that adhesive sensors could detect early signs of acute liver failure in rats.

Engineers are working to adapt this design for human use. They believe the stickers could be used in intensive care units (ICUs), where the thin sensors could continuously monitor patients recovering from organ transplants.

“We think this sticker could be placed on a patient immediately after a liver or kidney transplant and we could observe how the organ’s stiffness changes over a few days,” said lead author Xiaochuan Liu. says. “Early diagnosis of acute liver failure allows doctors to take action immediately rather than waiting until symptoms become severe,” said Liu, who was a visiting scholar at MIT at the time of the study. He is currently an assistant professor at the University of Southern California.

Co-authors of the study include Xiaoyu Chen and Chonghe Wang of MIT and collaborators at USC.

Wobble detection

Like muscles, our body’s tissues and organs become stiffer as we age. In certain diseases, the hardening of organs becomes more pronounced, indicating that the state of health can deteriorate rapidly. Clinicians now have a way 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 wand over the skin. When the rover sends sound waves into the body, the internal organs vibrate slightly and send sound waves in return. The probe senses the vibrations induced in the organ, and the pattern of the vibrations can be used to determine how shaky or stiff the organ is.

Ultrasound elastography is typically used in the ICU to monitor patients who have recently undergone an organ transplant. Technicians regularly check on patients immediately after surgery to quickly examine the new organ and look for signs of hardening or potential acute failure or rejection.

“The first 72 hours after organ transplantation are the most critical in the ICU,” says USC professor Qifa Zhou, another senior author. “Traditional ultrasound examinations require a probe to be applied to the body, but this cannot be done continuously over a long period of time. It may be too late.”

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

“Our imaging sticker captured longitudinal waves, but this time we wanted to capture transverse waves, so we can see the stiffness of the organ,” Zhao explains.

Existing ultrasound elastography probes measure the vibrations of organs in response to shear waves, or sound wave impulses. The faster the shear waves travel through an organ, the stiffer the organ is interpreted to be. (Think of the bounce of a water balloon compared to a soccer ball.)

The research team looked at miniaturizing ultrasound elastography to fit on a postage stamp-sized sticker. We also aimed to maintain the same sensitivity as commercially available handheld probes. Commercially available handheld probes typically incorporate approximately 128 piezoelectric transducers, each of which converts an incoming electric field into an outgoing sound wave.

“We used advanced manufacturing techniques to cut small transducers from high-quality piezoelectric material. This allowed us to design miniature ultrasonic stickers,” Zhou said.

The researchers precisely manufactured 128 miniature transducers and integrated them onto a 25-millimeter square chip. They lined the underside of the chip with an adhesive made from hydrogel. A sticky, stretchy material that is a mixture of water and polymers that allows sound waves to enter and leave the device with little loss.

As a preliminary experiment, the researchers tested the hardness-sensing stickers on rats. They found that the stickers could continuously measure liver stiffness over a 48-hour period. The researchers observed clear early signs of acute liver failure from data collected from the stickers, which they later confirmed with tissue samples.

“When the liver malfunctions, the stiffness of the organ increases many times,” Liu points out.

“You can go from a healthy liver that looks wobbly like a soft-boiled egg to a diseased liver that looks like a hard-boiled egg,” Zhao added. “And this sticker can sense those differences deep within the body and alert you when organ failure occurs.”

The team is working with clinicians to adapt the stickers for use on patients recovering from organ transplants in the ICU. In that scenario, no major changes are expected to the sticker’s current design, as the sticker can be applied to the patient’s skin and the transmitted and received sound waves can be delivered and collected by electronics connected to the sticker. . For electrodes and electrocardiogram devices in clinics.

The researchers also hope to engineer the sticker into a more portable, self-enclosed version, with all the accompanying electronics and processing miniaturized to fit into a slightly larger patch. They envision that the stickers could be worn by patients at home to continuously monitor conditions over time, such as the progression of solid tumors, which are known to become harder in severe cases. There is.

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

This research was supported in part by the National Institutes of Health.