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AN ULTRA-CHEAP
optical system based on a fly's eye is being developed to
allow weak laser light to be used for medical imaging.
A team led by
Joseph Rosen and David Abookasis of the Ben-Gurion University
of the Negev in Beersheba, Israel, has tested the system on
harder objects such as bones, and hopes eventually to use it
to scan the body's soft tissues for tumours. If successful,
the technique could be an alternative to expensive procedures
such as MRI or potentially damaging X-ray mammography,
allowing investigations to be carried out more often.
Attempts to
use light for medical imaging have to overcome the problem of
detecting the few photons that pass directly from the object
being imaged through the intervening tissue. Until now, this
has meant using costly cameras with special shutters that
block "noise", the light scattered by the intervening tissue.
Rosen and his team have taken a different approach. Adapting
the way a fly's eye sees, they collect several images and
combine them in a way that allows the scattered light to be
subtracted, leaving a clearer picture of the tissue.
A fly's
compound eye has many optical units, each with its own lens,
producing multiple images of the same picture. The neural
circuits leading from each unit average out the images to pick
out a clearer single picture from a "noisy" background. This
enables the fly to escape from predators, especially in poor
light.
To test the
idea, the researchers took two chicken breasts and hid a wing
bone between them. They then illuminated one side of the meat
with a low-power optical laser and placed a fly's-eye
arrangement of 132 tiny lenses, called a microlens array, on
the other. A conventional lens focused these images onto the
sensor of a digital camera, whose output was captured by
image-processing software. This subtracted most of the noise
produced by the scattered light, leaving a clearer image of
the hidden bone.
With more
microlenses and other refinements, it should be possible to
boost the resolution, Rosen says. "With investment to develop
it further, our system could in a year be seeing the bones in
the palm of the hand or the root of a tooth."
Because the
infrared system penetrates only soft tissues, it will never
replace whole-body CT or MRI scans. But simple, cheap optical
mammography might be one application, as might a non-invasive
way to scan the gut - which at present requires uncomfortable
endoscopes or "pill cameras" that patients swallow.
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