X-Ray Efficiency Boosted with Nanomaterials

Gypsy moth (NCAGR.gov)

Physicists in the U.S. and China have developed nanoscale materials using a design based on the eye of a moth to increase the efficiency of X-ray devices, which can lead to higher resolution images with lower doses of radiation. The research team led by Yasha Yi at City University of New York published its findings today in the journal Optics Letters (paid subscription required).

Yi, whose lab is affiliated with Massachusetts Institute of Technology, with colleagues from MIT, New York University, and Tongji University in Shanghai, used the moth as a model. Moths have large compound eyes comprised of thousands of structures made up of a primitive cornea and lens, connected to photoreceptor cells. Moth eyes also do not reflect much light, making them less visible to predators.

This ability to absorb rather than reflect light led Yi’s team to devise a new type of material that improves the light-capturing efficiency of X-ray and other medical imaging devices. The researchers focused on materials in X-ray devices that absorb the energy of the particles and then re-emit that absorbed energy in the form of light. In radiographic imaging these scintillators, as the materials are called, convert the X-rays exiting the body into the visible light signals picked up by a detector to form an image.

Yi and colleagues devised a new type of material aimed at boosting the efficiency of the process, by which the scintillator converts X-rays to light. The material consists of a film, only 500 nanometers thick, made of a cerium-doped lutetium oxyorthosilicate crystal. The researchers added to the crystals a series of tiny pyramid-shaped bumps or protuberances made of the ceramic material silicon nitride. [sponsored link] Each protuberance is modeled on the structure of a moth’s eye and designed to extract more light from the film.

From 100,000 to 200,000 of the protuberances fit on a 100 micrometer square, about the same density as the corneal structures in an actual moth eye.  The researchers then made the sidewalls of the device rougher, improving the device’s ability to scatter light and thus enhancing the efficiency of the scintillator.

Yi and colleagues added the material-enhanced film to the scintillator of an X-ray mammography unit. The team found the film added to the scintillator increased the intensity of the emitted light by as much as 175 percent compared to the light produced using a traditional scintillator alone.

Yi says this proof-of-concept test of the film with an everyday X-ray unit “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.” Yi estimates that it will take at least another three to five years to evaluate and perfect the film, and test it in imaging devices, before is can be used in clinical practice.

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