Optical images of the devices when twisted and stretched, showing its mechanical compliance and robustness, and conforming to the lateral shoulder joint and neck for tissue stiffness monitoring. (Image: UC San Diego Jacobs School of Engineering)

A team of engineers at the University of California San Diego has developed a stretchable ultrasonic array capable of serial, non-invasive, three-dimensional imaging of tissues as deep as four centimeters below the surface of human skin, at a spatial resolution of 0.5 mm. This new method provides a non-invasive, longer-term alternative to current methods, with improved penetration depth.

The research emerges from the lab of Sheng Xu, a Professor of Nanoengineering at UC San Diego Jacobs School of Engineering and corresponding author of the study. “We invented a wearable device that can frequently evaluate the stiffness of human tissue,” said Hongjie Hu, a Postdoctoral Researcher in the Xu group and study coauthor. “In particular, we integrated an array of ultrasound elements into a soft elastomer matrix and used wavy serpentine stretchable electrodes to connect these elements, enabling the device to conform to human skin for serial assessment of tissue stiffness.”

The elastography monitoring system can provide serial, non-invasive and three-dimensional mapping of mechanical properties for deep tissues. This has several key applications including in medical research, serial data on pathological tissues can provide crucial information on the progression of diseases such as cancer, which normally causes cells to stiffen as well as monitoring muscles, tendons, and ligaments can help diagnose and treat sports injuries.

In addition to monitoring cancerous tissues, this technology can also be applied in other scenarios such as monitoring of fibrosis and cirrhosis of the liver. By using this technology to evaluate the severity of liver fibrosis, medical professionals can accurately track the progression of the disease and determine the most appropriate course of treatment. It can also be used for assessing musculoskeletal disorders such as tendonitis, tennis elbow and carpal tunnel syndrome. By monitoring changes in tissue stiffness, this technology can provide valuable insight into the progression of these conditions, allowing doctors to develop individualized treatment plans for their patients.

Wearable ultrasound patches accomplish the detection function of traditional ultrasound and also break through the limitations of traditional ultrasound technology, such as onetime testing, testing only within hospitals and the need for staff operation. “This allows patients to continuously monitor their health status anytime, anywhere,” said Hu.

This could help reduce misdiagnoses and fatalities, as well as significantly cutting costs by providing a non-invasive and low-cost alternative to traditional diagnostic procedures.

The array conforms to human skin and acoustically couples with it, allowing for accurate elastographic imaging validated with magnetic resonance elastography.

In testing, the device was used to map three-dimensional distributions of the Young’s modulus of tissues ex vivo, to detect microstructural damage in the muscles of volunteers prior to the onset of soreness and monitor the dynamic recovery process of muscle injuries during physiotherapy.

The device consists of a 16 by 16 array. Each element is composed of a 1-3 composite element and a backing layer made from a silver-epoxy composite designed to absorb excessive vibration, broadening the bandwidth, and improving axial resolution.

Professor Xu is now commercializing this technology via Softsonics LLC.

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