From Treadmill to 3D Imaging: 2 UToledo Scientists Rethink Ultrasound

From Treadmill to 3D Imaging: 2 UToledo Scientists Rethink Ultrasound

The idea for Dr. Jian-yu Lu's latest invention began not in a laboratory but on a treadmill.

Lu, a professor of bioengineering at The University of Toledo and a physicist and engineer who has spent nearly four decades studying how sound waves travel, was undergoing a treadmill stress echocardiogram - a common test used to evaluate how the heart performs under exertion.

He ran. His heart rate climbed.

Then he stepped off the treadmill, walked to an exam bed and waited while an ultrasound technologist positioned a probe on his chest, moving it from angle to angle to capture images.

By the time the imaging began, Lu's heart rate was already coming down.

"That had me thinking: Wouldn't it be better to have an ultrasound device attached directly to the body and capture any problems while I'm still exercising?" Lu recalled.

For most patients, that delay between peak exertion and imaging is simply part of how a traditional stress echocardiogram works. For Lu, however, it looked like an engineering problem waiting to be solved.

His solution is a patent-pending concept for a lightweight, potentially wearable ultrasound device designed to capture real-time 3D images of the heart and other organs while a patient is moving or even while exercising.

_{A New Way to Make an Ultrasound Beam}

To understand Lu's idea, it helps to understand the problem he had been working on for much of his career.

In the late 1980s, researchers in optics developed what are known as Bessel beams -waves that can remain tightly focused over a longer distance than conventional beams. That property can be useful for imaging because it allows an imaging system to remain in focus over a larger depth.

Lu was among the first researchers to bring that concept into ultrasound. In the early 1990s, he developed an ultrasound transducer using 10 concentric annular rings to generate a Bessel-like beam.

But there was a practical problem. Each ring required its own high-voltage, high-frequency power amplifier. A working system therefore required about 10 amplifiers - manageable in a research laboratory, but far too bulky and power-hungry for a small device worn on a patient's body.

So Lu asked a different question: could the same type of ultrasound beam be generated using just one power amplifier instead of 10?

He demonstrated that it could.

That advance became the foundation for a new device concept: a potentially wearable, battery-powered ultrasound probe that could capture 3D images using a small number of ultrasound elements and a mechanically moving reflector, rather than the hundreds or even thousands of electronically controlled elements that can be required for conventional 3D ultrasound imaging.

"We have a tilting reflector that is reflecting the ultrasound and creating the 3D volumetric images," said Dr. Samer Khouri, director of cardiac imaging at the University of Toledo Medical Center, who has collaborated with Lu on the technology. "We are replacing what can require a very large number of imaging elements with only seven elements and a moving reflector. That could create a very light, low-power and high-speed ultrasound probe."

_{Seeing the Whole Heart, Not Just a Slice}

Most point-of-care ultrasound systems produce two-dimensional images: a single slice through the body, similar to one slice cut from a watermelon. To build a more complete picture of an organ such as the heart, a trained technologist may need to manually reposition and angle the probe to capture multiple views.

Lu and Khouri's approach is designed to do something different.

Instead of collecting one slice at a time, the proposed device would capture a three-dimensional volume of data. Once the entire volume is acquired, physicians could use computer software to display the particular slices or views they need.

"If you acquire the entire 3D ultrasound volume, then your data is all there," Lu said. "Later, you can use computer manipulation to display whichever slice you want to see."

The design could also reduce the size, weight and power requirements of a 3D imaging system. By using a small number of ultrasound elements together with a moving reflector, the researchers hope to create a device that is lighter, runs cooler and can operate longer on battery power than conventional systems. The concept is also intended to be compatible with wireless communication and smartphones or computers.

Although wearable ultrasound is an active area of development, creating a device that combines high-quality imaging, long battery life, low heat generation and real-time 3D imaging remains a significant engineering challenge.

_{A Collaboration Three Decades in the Making}

Lu and Khouri's partnership dates back nearly three decades.

Lu joined UToledo in 1997 with a $1.5 million, five-year National Institutes of Health grant to develop high-frame-rate ultrasound imaging. The work required access to patients and clinical expertise that Lu, as an engineer and physicist, did not have on his own. A colleague introduced him to Khouri, beginning a collaboration that has continued.

Together, their work contributed to the development and application of high-frame-rate, or ultrafast, ultrasound imaging, an approach now used in areas including echocardiography, shear-wave elastography, tissue motion and strain imaging, ultrasound localization microscopy, contrast-enhanced ultrasound, functional brain imaging, ultrafast Doppler imaging, and high-speed B-mode imaging.

So when Lu's own stress test sparked a new idea, he knew exactly whom to call.

"I wanted to use this device for treadmill echocardiography, and I approached Dr. Khouri again to see whether we could work together," Lu said.

Khouri's role has focused on expanding the technology's potential clinical applications.

"This gives us the potential to capture nearly the whole heart in one or a few beats," Khouri said. "One acquisition could provide heart motion, while additional beats could provide other types of mechanical information. Instead of spending 20 minutes collecting data sequentially, we may be able to capture much more information much faster."

Khouri said that kind of speed and simplicity could eventually make advanced cardiac imaging more portable, accessible and affordable. It could also allow physicians to observe changes that might be missed when imaging begins only after a patient has stopped exercising.

_{From the Clinic to the Battlefield and Beyond}

The researchers see potential applications far beyond a traditional cardiology exam.

Khouri has proposed that the technology could eventually be used for continuous or repeated heart monitoring in demanding environments, including astronauts during spaceflight, military personnel in the field and fighter pilots.

The same basic idea that began with Lu asking why ultrasound imaging could not happen during a treadmill stress test could ultimately make it possible to bring advanced imaging to places where conventional ultrasound systems are impractical.

_{The Path to a Prototype}

On June 30, The University of Toledo Technology Transfer Office filed a Patent Cooperation Treaty patent application covering the invention, titled "Imaging systems, beam generators, and beam steering modules," preserving the option to pursue international patent protection.

Lu and Khouri are now pursuing grant funding to build and test a working prototype, which is the next major step in determining how the concept performs outside the laboratory and whether it can be translated into a practical medical device.

"This is the intersection of ultrasound, materials science, mechanical engineering and medicine," Khouri said. "It has four or five fields that need to come together to create this technology. It's a complex concept, even though on paper it may look simple."

Khouri said the potential payoff for patients and the healthcare system makes the challenge worthwhile.

"The more we can make our devices accessible for our patients, the more people will benefit," Khouri said. "And if we can reduce the cost of obtaining important medical information, the entire healthcare system could benefit."

Somewhere down the road, another patient may step off a treadmill to find the images already captured - because this time, the ultrasound device was watching the heart all along.