Lens Converts Light Into Sound

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By Dexter Johnson, IEEE Spectrum

The researcher used sound waves to drill holes into a confetti-sized artificial kidney stone. Credit: Jay Gou, University of Michigan

Remember how Leonard McCoy performed surgery in Star Trek? He

would wave a device over the patient. The outer layers of the skin

didn't need not be cut, even when operating on internal organs, and the

precision of 23rd-century instrument reached down to the level of

individual cells.

Well, we already have a bit of that in the 21st.

Research at the University of Michigan, led by Jay Gou, has developed a

device that employs a carbon-nanotube-coated lens

capable of converting light into tightly focused sound waves. The new

ultrasound therapeutic tool that reaches new levels of precision — its

high-amplitude sound waves are able to target an object with dimensions

of 75 by 400 micrometers.

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"A major drawback of

current strongly focused ultrasound technology is a bulky focal spot,

which is on the order of several millimeters," says Hyoung Won Baac, who

worked on the project as a doctoral student and is now a research

fellow at Harvard Medical School, in a press release. "A few centimeters

is typical. Therefore, it can be difficult to treat tissue objects in a

high-precision manner, for targeting delicate vasculature, thin tissue

layer and cellular texture. We can enhance the focal accuracy 100-fold."

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The research, which was published in the journal Nature (“Carbon-Nanotube Optoacoustic Lens for Focused Ultrasound Generation and High-Precision Targeted Therapy”), coated a concave lens with a nano-composite film of carbon nanotubes (CNTs) and elastomeric polymer. A pulsed laser source is aimed at the lens. The CNTs absorb the light coming from the laser which generates heat. The

polymer expands from the heat being generated by the CNTs. This rapid

expansion of the polymer amplifies the signal.

The CNT-coated lens

when coupled with a pulsed laser is capable of extreme optoacoustic

pressures of >50 megapascals. This unprecedented level of pressure

results in both shock effects and cavitation without heat being used on

the target.

While recent research in sharpening sound waves — at least for imaging devices — has led to exotic acoustic hyperlenses made from metamaterials,

the underlying technique behind this device’s conversion of light to

sound goes back to at least Thomas Edison. But to date the sound

projected from devices employing these techniques was not strong enough

to prove useful in medical applications.

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"We believe this could

be used as an invisible knife for noninvasive surgery," Guo says in a

university press release. "Nothing pokes into your body, just the

ultrasound beam. And it is so tightly focused, you can disrupt

individual cells."

It may still be a while before your surgeon is able to wave a wand over

you and send you back to your hospital room without a scar — the

technology hasn't even been tested on animals yet — but we may get there

well before the 23rd century.

This article originally appeared on IEEE Spectrum as Nanoparticle Coated Lens Converts Light into Sound for Precise Non-invasive Surgery

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