Using the compound eyes of the humble 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.
The 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 (OSA) journal, Optics Letters.
Like 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 applications.
Now 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.
In 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.
One 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.
It 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.