COOL TECH
If at First You Don’t Succeed, You May be onto Something New technology illuminates tumour development By Mifi Purvis
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t was a bit of a coup, getting published in Nature’s Light: Science & Applications, a top-ranked journal about optics, and for Parsin Hajireza and Roger Zemp, it almost didn’t happen. But by investigating a puzzling anomaly, these Faculty of Engineering researchers have devised new non-contact medical imaging technology that will be able to deliver razorsharp pictures to health-care practitioners. Three years ago, Hajireza was more than a year into his PhD in biomedical engineering under the supervision of Zemp, investigating a technique called photoacoustic imaging. He was at his lab bench aiming a couple of laser beams set to different wavelengths through an ultrasound transducer at some carbon fibres. To his surprise, he saw a signal on his monitor after he had backed the transducer away from his target. It must be some kind of environmental noise, he thought. He repeated the steps and came up with the same signal. He kept coming back to one idea: the signal represented a non-contact detection of photoacoustic signals. He took the idea to Zemp. “That doesn’t make sense,” his supervisor told him, for good reason. In 1888, Alexander Graham Bell discovered the photoacoustic effect, in which laser light is absorbed and converted to ultrasound waves. Anything that
LIGHT LABOUR: Paying attention to an unusual finding led Parsin Hajireza, left, and his supervisor Roger Zemp, right, to a photoacoustic discovery.
absorbs light, such as blood or even DNA for example, generates an ultrasound wave. Photoacoustic imaging generates high-resolution contrast but, like the more familiar ultrasound, it requires the imaging device to be in contact with the subject. Hajireza was seeing signals that were generated photoacoustically from centimetres away, through the air. Zemp and Hajireza devised experiments to explain the mechanism behind the mysterious signals, developed a model to describe it, and built a system around it. They called the technique Photoacoustic Remote Sensing (PARS) microscopy. The system trains two laser beams at a target: one a visible pulsed beam to generate reflectivity, the other a near-infrared beam to detect it. “It’s like double-bouncing a friend on a trampoline,” says Zemp. “Our pulsed beam creates a change in the reflectivity of a sample, which creates a large bounce. Our near-infrared beam detects it. The effect is much larger than we anticipated.” The new system allows them to see stunning images. They can follow a single red blood cell through a capillary in real time. It lets them see structures that absorb light,
rather than scatter or emit light, providing them previously unavailable information. Zemp and Hajireza, with co-authors Wei Shi, Kevan Bell and Robert Paproski, published the work in Light: Science & Applications earlier this year. The technique, which Zemp and Hajireza are commercializing in a company called illumiSonics, will be useful in clinical applications where traditional imaging isn’t possible, in cases such as wounds, burns, tissues during surgery, brain imaging, dental cavity imaging and early cancer detection, when small tumours are building their network of blood vessels. And new developments are enabling them to see deeper into tissues, letting them measure the oxygen in blood and allowing them to glimpse gene expression. “Sometimes scientists focus on what they expect to see and don't consider other possibilities,” Hajireza says. “I think we were successful because we took what I saw seriously and with open minds. Then we spent two years building a system around it.” U OF A ENGINEER SPRING 2017
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