Plaque builds up in arteries as we age. Some types of plaque are deemed 'vulnerable', meaning that they are more likely to detach from the artery wall and cause heart attack or stroke, said researchers from North Carolina State University and the University of North Carolina at Chapel Hill.
"Existing state-of-the-art technologies are capable of determining if plaque is present in the arteries, but can't tell whether it's vulnerable. And that makes it difficult to assess a patient's risk," said Dr Paul Dayton, co-author of a paper on the new device and professor in the joint biomedical engineering department at NC State and Chapel Hill.
"Our goal was to develop something that could effectively identify which plaques are vulnerable," Dayton said.
"There are two ultrasound techniques that can help identify vulnerable plaques, but both depend on the use of contrast agents called 'microbubbles'," he said.
The first technique is to identify 'vasa vasorum' in arteries. These are clusters of small blood vessels that often infiltrate arterial plaque, and which are considered indicators that a plaque is vulnerable.
When microbubbles are injected into an artery, they follow the flow of the blood. If vasa vasorum are present, the microbubbles will flow through these blood vessels as well, effectively highlighting them on ultrasound images.
The second technique is called molecular imaging, and relies on the use of 'targeted' microbubbles.
These microbubbles attach themselves to specific molecules that are more likely to be found in vulnerable plaques, making the plaques stand out on ultrasound images.
"The problem is that existing intravascular ultrasound technology does not do a very good job in detecting contrast agents," said Dr Xiaoning Jiang, an NC State associate professor of mechanical and aerospace engineering, an adjunct professor of biomedical engineering and co-author of the paper.
"So we've developed a dual-frequency intravascular ultrasound transducer which transmits and receives acoustic signals," Jiang said.
"Operating on two frequencies allows us to do everything the existing intravascular ultrasound devices can do, but also makes it much easier for us to detect the contrast agents - or microbubbles - used for molecular imaging and vasa vasorum detection," Jiang added.
The prototype device has performed well in laboratory testing, but the researchers said they are continuing to optimise the technology. They hope to launch pre-clinical studies in the near future.