New Ultrasound Technology Penetrates Bone and Metal

Researchers have developed a technique that allows ultrasound to penetrate bone or metal using customized structures that offset the distortion typically caused by these so-called “aberrating layers.”

“We’ve designed complementary metamaterials that will make it easier for medical professionals to use ultrasound for diagnostic or therapeutic applications, such as monitoring blood flow in the brain or to treat brain tumors,” commented Tarry Chen Shen, a PhD student at North Carolina (NC) State University (Raleigh, USA), and lead author of an article on the study, which was published November 18, 2014, in the journal Physical Review Letters. “This has been difficult in the past because the skull distorts the ultrasound’s acoustic field.”

“Using the new technology, it’s as if the aberrating layer isn’t even there. These metamaterials could also be used in industrial settings,” stated Dr. Yun Jing, an assistant professor of mechanical and aerospace engineering at NC State, and senior author of the paper. “For example, it would allow you to use ultrasound to detect cracks in airplane wings under the wing’s metal ‘skin.’”

Ultrasound imaging works by emitting high frequency acoustic waves. When those waves bounce off an object, they return to the ultrasound unit, which then converts the waves into an image. However, some substances, such as metal or bone, have physical characteristics that block or distort ultrasound’s acoustic waves. These materials are called aberrating layers. The researchers addressed this hurdle by designing customized metamaterial structures that take into account the acoustic characteristics of the aberrating layer and counterbalancing them. The metamaterial structure uses a series of membranes and small tubes to achieve the desired acoustic characteristics.

The researchers have assessed the technique using computer simulations and are in the process of developing and testing a physical prototype. In simulations, only 28% of ultrasound wave energy makes it past an aberrating layer of bone when the metamaterial structure is not in place. But with the metamaterial structure, the simulation shows that 88% of ultrasound wave energy passes through the aberrating layer. “In effect, it’s as if the aberrating layer isn’t even there,” Dr. Jing said.

The technique can be used for ultrasound imaging, as well as therapeutically, such as using ultrasound to apply energy to brain tumors in order to burn them.

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