the compound eyes of the lowly moth as their inspiration, an
international team of physicists has developed new nanoscale materials
that could someday reduce the radiation dosages received by patients
getting X-rayed, while improving the resolution of the resulting images.
work, led by Yasha Yi—a professor of the City University of New York,
who is also affiliated with Massachusetts Institute of Technology and
New York University—was published today in the Optical Society’s
journal, Optics Letters.
their Lepidopteran cousins the butterflies, moths have large compound
eyes, made up of many thousands of ommatidia—structures made up of a
primitive cornea and lens, connected to photoreceptor cells. But moth
eyes, unlike those of butterflies, are remarkably anti-reflective,
bouncing back very little of the light that strikes them. The adaptation
helps the insects be stealthier and less visible to predators during
their nocturnal flights. Because of this feature, engineers have looked
to the moth eye to help design more efficient coatings for solar panels
and antireflective surfaces for military devices, among other
Yi and his colleagues have gone a step further, using the moth eye as a
model for a new class of materials that improve the light-capturing
efficiency of X-ray machines and similar medical imaging devices.
particular, the researchers focused on so-called “scintillation”
materials: compounds that, when struck by incoming particles (say, X-ray
photons), absorb the energy of the particles and then reemit that
absorbed energy in the form of light. In radiographic imaging devices,
such scintillators are used to convert the X-rays exiting the body into
the visible light signals picked up by a detector to form an image.
way to improve the output (the intensity of light signals read by the
detector, and thus the resolution of the resulting images) is to
increase the input—that is, to use a higher x-ray dosage. But that’s not
healthy for patients because of the increased levels of radiation. An
alternative, Yi and colleagues figured, is to improve the efficiency
with which the scintillator converts X-rays to light. Their new material
does just that.
consists of a thin film, just 500 nanometers thick, made of a special
type of crystal known as cerium-doped lutetium oxyorthosilicate. These
crystals were encrusted with tiny pyramid-shaped bumps or protuberances
made of the ceramic material silicon nitride. Each protuberance, or
“corneal nipple,” is modeled after the structures in a moth’s eye and is
designed to extract more light from the film.
100,000 to 200,000 of the protuberances fit within a 100 x 100
micrometer square, or about the same density as in an actual moth eye.
The researchers then made the sidewalls of the device rougher,
improving its ability to scatter light and thus enhancing the efficiency
of the scintillator.
lab experiments, Yi and colleagues found that adding the thin film to
the scintillator of an X-ray mammographic unit increased the intensity
of the emitted light by as much as 175 percent compared to that produced
using a traditional scintillator.
current work, Yi says, represents a proof-of-concept evaluation of the
use of the moth-eye-based nanostructures in medical imaging materials.
“The moth eye has been considered one of the most exciting bio
structures because of its unique nano-optical properties,” he says, “and
our work further improved upon this fascinating structure and
demonstrated its use in medical imaging materials, where it promises to
achieve lower patient radiation doses, higher-resolution imaging of
human organs, and even smaller-scale medical imaging. And because the
film is on the scintillator,” he adds, “the patient would not be aware
of it at all.”
estimates that it will take at least another three to five years to
evaluate and perfect the film, and test it in imaging devices. “We will
need to work with medical imaging experts and radiologists for this to
be actually used in clinical practice,” he says.
The work was done in collaboration with Professors Bo Liu and Hong Chen of Tongji University in Shanghai.