Eye imaging technology breaks through skin by crossing beams
New approach to optical coherence tomography increases its depth of view
in biological tissues

Date:
December 1, 2021
Source:
Duke University
Summary:
Biomedical engineers have demonstrated a method for increasing
the depth at which optical coherence tomography (OCT) can image
structures beneath skin. The new 'dual-axis' approach opens new
possibilities for OCT to be used in applications such as spotting
skin cancer, assessing burn damage and healing progress, and
guiding surgical procedures.



FULL STORY ========================================================================== Biomedical engineers at Duke University have demonstrated a method
for increasing the depth at which optical coherence tomography (OCT)
can image structures beneath skin.


==========================================================================
The gold standard for imaging and diagnosing diseases within the retina,
OCT has yet to find 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 beneath the skin's surface.

Duke researchers found that tilting the light source and detector used in
the technique increases OCT's imaging depth by almost 50%, putting skin diagnoses within reach. The "dual-axis" approach opens new possibilities
for OCT to be used in applications such as spotting skin cancer, assessing
burn damage and healing progress, and guiding surgical procedures.

The results appear online on December 1 in the open access journal
Biomedical Optics Express.

"It's actually a fairly simple technique that sounds like something
out of Ghostbusters -- you get more power when you cross the beams,"
said Adam Wax, professor of biomedical engineering at Duke. "Being able
to use OCT even 2 or 3 millimeters into the skin is extremely useful
because there are a lot of biological processes happening at that depth
that can be indicative of diseases like skin cancer." Standard OCT is analogous to ultrasound but uses light instead of sound. A beam of light
is shined down into an object, and by measuring how long it takes for
it to bounce back, computers can deduce what the internal structure of
the object 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.



==========================================================================
Most other biological tissues, however, scatter and reflect light, making
it difficult to penetrate with standard OCT approaches. The deeper the
light goes, the more likely it is to get lost in the sample and miss
the device's detection.

In the new technique, researchers instead point the light at the object
at a slight angle and set up the detector at an equal and opposite angle, creating a dual-axis. This allows the detector to benefit from the slight scattering angle introduced by the object's physical nature.

"By tilting the light source and detector, you increase your chances
of collecting more of the light that's scattering off at odd angles
from a tissue's depths," said Evan Jelly, a doctoral student in Wax's laboratory and first author of the paper. "And OCT is so sensitive
that just a little bit more of that 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 the
focal point of light within the tissue makes a large difference in how
well the dual-axis approach works.

However, there is a catch: The greater the angle used to identify deeper signal, the smaller the field of view becomes. To get around this issue,
Jelly devised a method of scanning the focus of the narrower window
through various depths of the tissue and then using a computational
algorithm to combine the data into a single image.

In the paper, Wax and Jelly tested this approach with fabricated tissues
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 does tend
to outperform the standard setup. And in the live mice, the dual-axis
OCT was able to image the tip of a needle 2 millimeters beneath the
skin's surface, where 1.2 millimeters is traditionally the landmark depth.

"The dual-axis OCT gave us images and information from the layers of skin
where blood and molecular exchanges are occurring, which is extremely
valuable for detecting signs of diseases," said Jelly. "The technology
is still in its infancy, but it is primed to be highly successful for biosensing or guiding surgical procedures." This research was funded
by the National Science Foundation (CBET-2009841, IIP- 1827560).

========================================================================== Story Source: Materials provided by Duke_University. Original written
by Ken Kingery. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Evan T. Jelly, Yang Zhao, Kengyeh K. Chu, Hillel Price, Michael
Crose,
Zachary A. Steelman, Adam Wax. Deep imaging with 13 mym
dual-axis optical coherence tomography and an enhanced depth
of focus. Biomedical Optics Express, 2021; 12 (12): 7689 DOI:
10.1364/BOE.438621 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211201162033.htm

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