Eye imaging technology breaks through the skin by crossing rays


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Biomedical engineers at Duke University have demonstrated a method to increase the depth with which optical coherence tomography (OCT) can image structures under the skin.

The gold standard for imaging and diagnosing diseases of the retina, OCT has not yet found widespread use as an imaging technique for other parts of the body due to its inability to return clear images from more than a millimeter below the skin’s surface.

Duke researchers found that tilting the light source and detector used in the technique increases OCT’s image depth by almost 50%, putting skin diagnoses within reach. The “dual-axis” approach opens up new possibilities for OCT for use in applications such as spotting skin cancer, assessing burn injuries and healing progress, and guiding surgical procedures.

The results will be shown online on December 1 in the open access journal Biomedical Optics Express.

“It’s actually a pretty simple technique that sounds like something out of Ghostbusters – you get more power when you cross the bars,” said Adam Wax, professor of biomedical engineering at Duke. “Being able to use OCT even 2 or 3 millimeters into the skin is extremely helpful because there are a lot of biological processes going on at that depth, which can be a sign of diseases like skin cancer.”

Standard OCT is analogous to ultrasound, but uses light instead of sound. A ray of light shines down into an object, and by measuring how long it takes for it to bounce back, computers can deduce what the object’s internal structure looks like. It has become the go-to technology for imaging and diagnosing retinal diseases because the retina is so thin and easily accessible through the eye’s transparent cornea and lens.

However, most other biological tissues scatter and reflect light, making it difficult to penetrate with standard OCT approaches. The deeper the light goes, the more likely it is that it will be lost in the sample and miss the detection of the device.

In the new technique, scientists instead point the light at the object at a small angle and set up the detector at an equal and opposite angle, creating a double axis. This allows the detector to take advantage of the small scattering angle introduced by the physical nature of the object.

“By tilting the light source and detector, you increase your chances of collecting more of the light scattered at odd angles from the depths of a tissue,” said Evan Jelly, a doctoral student at Wax’s laboratory and first author of the paper. “And OCT is so sensitive that just a little bit more of the scattered light is all you need.”

According to Jelly, researchers have tried this dual-axis approach in other imaging modalities. But through his experiments, Jelly discovered how to apply this to OCT. His key discovery was that the depth of light focus in the tissue makes a big difference in how well the dual-axis approach works.

However, there is a catch: the larger the angle used to identify deeper signals, the smaller the field of view. To get around this problem, Jelly devised a method to scan the focus of the narrower window through different depths of the tissue and then use a computational algorithm to combine the data into a single image.

In the paper, Wax and Jelly tested this approach with fabricated tissue and hairless mice to benchmark its performance against standard OCT to see what information it could reveal in a live animal’s skin. The controlled experiments showed that the dual-axis OCT approach tends to exceed the standard setup. And in the living mice, the double-axis OCT was able to image the tip of a needle 2 millimeters below the surface of the skin, where 1.2 millimeters is traditionally landmark depth.

“The dual-axis OCT gave us images and information from the skin layers where blood and molecular exchanges take place, which is extremely valuable in detecting signs of disease,” Jelly said. “The technology is still in its infancy, but it is ready to be very successful for biosensing or indicative surgical procedures.”

3D polarization-sensitive OCT imaging of collagen organization in organ systems

More information:
Evan T. Jelly et al, Deep imaging with 13 dobbeltm double-axis optical coherence tomography and enhanced focal depth, Biomedical Optics Express (2021). DOI: 10.1364 / BOE.438621

Provided by Duke University

Citation: Eye Imaging Technology Breaks Through the Skin by Crossing Rays (2021, December 1) Retrieved December 2, 2021 from https://phys.org/news/2021-12-eye-imaging-technology-skin.html

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