Wearable ultrasound patch images the heart in real time

A wearable ultrasound heart imager that’s about the size of a postage stamp, can be worn for up to 24 hours, and even works during exercise could one day help doctors detect heart problems that the Current medical technology could be lacking, according to a new study.

Heart disease is the leading cause of death in older people and is increasingly becoming a problem in younger people due to unhealthy diets and other factors. Signs of heart disease are often brief and unpredictable, so long-term cardiac imaging can help spot heart abnormalities that might otherwise escape detection.

For example, patients with heart failure can sometimes appear fine at rest, “because the heart sacrifices its efficiency to maintain the same cardiac output,” says the study’s co-lead author. Hongjie Hu, a nanoengineer at the University of California, San Diego. “Pushing the heart to its limits during exercise can make inefficiency apparent.”

Additionally, the heart can quickly recover from any problems it may encounter during exercise. That means doctors may miss these issues because cardiac imaging typically occurs after exercise, not during it, Hu says.

However, cardiac imaging techniques are often limited in when they can scan the heart, largely due to equipment clutter. For example, traditional cardiology ultrasound “Evaluates images of the heart just before and just after intensive exercise, since holding an ultrasound probe on the chest by hand and maintaining a stable position is impossible during this process,” Hu said. Previous wearable heart sensors could only pick up signals on the skin.

Today, scientists have developed a portableultrasound device that can enable safe, continuous, real-time, long-term, and highly detailed imaging of the heart. They detailed their findings online January 25 in the newspaper Nature.

“Potential applications include continuous monitoring of the heart in everyday life, during exercise, during surgery, and much more,” says the study co-author Ray Wu, a nanoengineer at the University of California, San Diego. “This will open up the possibility of detecting previously undetectable disease symptoms, identifying symptoms in their very early stages, and dramatically improving patient outcomes.”

The new device is a patch 1.9 cm long by 2.2 cm wide and only 0.9 millimeters thick. It uses an array of piezoelectric transducers to send and receive ultrasound waves to generate a constant stream of images of the structure and function of the heart. The researchers were able to obtain such images even during exercise on a stationary bicycle. No skin irritation or allergy was seen after 24 hours of continuous wear.

“The most exciting result is that our patch works well when an individual is moving,” Hu said. “Our patch allows us to assess cardiac performance throughout exercise, providing valuable information about the heart when under high stress.”

The new patch is about as flexible as human skin. It can also stretch up to 110% of its size, meaning it can survive far more stress than human skin typically experiences. These characteristics help it stick to the body, which is not possible with the rigid equipment often used for cardiac imaging.

“The wearable imager removes much of the bulk of traditional imagers and adheres to the body on its own,” says Wu. “It allows the heart to be imaged in ways and scenarios that were never possible before. while freeing the physician’s hands from the continued use of a traditional ultrasound probe.”

The wearable ultrasonic sensor is about the size of a postage stamp, can be worn for up to 24 hours, and works even during intense exercise.Xu Laboratory / UC San Diego Jacobs School of Engineering

In the new study, the researchers focused on imaging the left ventricle, the largest of the heart’s four chambers, “and strongly considered the most important in terms of cardiovascular health, as it is responsible for pumping oxygenated blood into whole body,” says Wu. Cardiac imaging typically focuses on the left ventricle, but the new device can image all four chambers of the heart simultaneously, “so it is possible that future research will focus on other or more cavities,” he adds. Additionally, “the imager can be applied to image various other organs, such as the stomach, kidney, or liver.”

Traditional cardiac ultrasound imaging constantly spins an ultrasound probe to scan the heart in multiple dimensions. To eliminate the need for this rotation, the new device’s array of ultrasonic sensors and emitters is shaped like a cross so that ultrasonic waves can travel at right angles to each other.

Scientists have developed a custom deep learning AI model that can analyze patch data and automatically and continuously estimate vital details, such as the percentage of blood pumped from the left ventricle with each beat and the volume of blood the heart pumps with each beat and minute . The root of most heart problems is the heart not pumping enough blood, problems that often only show up when the body is moving, the researchers note.

Scientists only began to study cardiac imaging after developing a portable ultrasound device.

“After learning in a casual conversation that one of our colleague’s relatives had died of a sudden heart attack, we realized that our technology could have a real impact on people’s lives,” says Hao Huang, study co-lead author and nano-engineer at the University of California. in San Diego. “We didn’t expect the image quality from the imager to be very good. However, it turned out that we could achieve quality comparable to commercial probes after careful engineering. We knew we were on to something big when we saw the images full of detail after many rounds of improvements, and we thought we should keep it that way so as not to waste the capabilities of the imager.

At first, “we always had trouble focusing the ultrasound beam,” Huang recalls. “Debugging involved extensive trial and error based on reads. After many failures, we used an automatic alignment strategy to make the transducer array with high uniformity and perfect alignment so that it guaranteed beam focus.

Another set of problems concerned noise in the signals. “We did a lot of trial and error to identify all sources of noise and isolate the imager from all of them, but we were still left with the most important one, the human body,” Huang explains. They eventually developed an expandable electromagnetic shield made of the same liquid metal used in the device’s electrodes “to eliminate human body noise while maintaining the imager’s flexibility and expandability.” It turned out that the optimized shielding layer worked very well and we could finally remove the noise from the images.

The researchers note that currently the device is connected by cables to a computer. They developed a wireless version of the patch, the details of which are in a study currently being reviewed, Hu says.

The lead author of the study, Sheng Xu, a professor at the University of California, San Diego, plans to commercialize the technology through Softsonics, a company co-founded with another of the study’s co-authors, Shu Xiang. Further work is needed to develop this device into a fully integrated portable system with an integrated power source, Hu said.