Ultrasound technology could soon be improved to produce high-quality, high-resolution images, thanks to the development of a new key material by a team of researchers in the Department of Biomedical Engineering at Texas A&M University, College Station.

Fig. 1 – An optical signal, represented by the red arrow, comes into contact with the metamaterial and interprets the ultrasound waves, resulting in an altered optical signal that is processed to produce a high-quality image.

The engineered material, known as a “metamaterial,” offers significant advantages over conventional ultrasound technology, which generates images by converting ultrasound waves into electrical signals. But ultrasound is still largely constrained by bandwidth and sensitivity limitations, which have been an obstacle in producing high-quality images as diagnostic tools.

The metamaterial is not subject to those limitations, primarily because it converts ultrasound waves into optical signals, rather than electrical ones. The optical processing of the signal does not limit the bandwidth or sensitivity of the transducer (converter), allowing greater detail.

“A high bandwidth allows you to sample the change of distance of the acoustic waves with a high precision,” said Professor Vladislav Yakovlev. “This translates into an image that shows greater detail. Greater sensitivity enables you to see deeper in tissue, suggesting we have the potential to generate images that might have previously not been possible with conventional ultrasound technology.”

The material consists of golden nanorods embedded in a polymer known as polypyrrole. An optical signal is sent into this material where it interacts with and is altered by incoming ultrasound waves before passing through the material. A detection device would then read the altered optical signal, analyzing the changes in its optical properties to process a higher resolution image, he explained. (See Figure 1)

The optical readout technology is already available. “We just recently discussed with Agilent opportunities for possible future collaboration on readout and digitization, Yakovlev stated.

“We developed a material that would enable optical signal processing of ultrasound,” Yakovlev said. “Nothing like this material exists in nature so we engineered a material that would provide the properties we needed. It has greater sensitivity and broader bandwidth. We can go from 0 to 150 MHz without sacrificing the sensitivity. Current technology typically experiences a substantial decline in sensitivity around 50 MHz.”

“Implementing this technology is actually feasible in a relatively near future,” he said, “since most of the components besides metamaterial are commercially available. Metamaterial itself needs some further optimization, since we haven't reached any fundamental limit yet, but it is inexpensive in prototyping and should be even less expensive in mass production,” he explained.

The material is the result of a collaborative effort by Yakovlev and those from King's College London, The Queen's University of Belfast, Ireland, and the University of Massachusetts Lowell. Their findings appear in the journal, Advanced Materials.