Biologically inspired integrated nanostructures that increase scintillator light absorption efficiency in x-ray imaging

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When an x-ray image is taken, a device known as a scintillator is used to process the light. A scintillator is a luminescent material that when struck by an incoming particle absorbs its energy and reemits the energy in the form of light. "The use of microphotonics and nanophotonics can help us to explore new structural flashing material, such as artificial micro–nano structures, photonic crystals, optical microcavity, and surface plasmon materials" (Yashi et al. 2012: 2808). Applying an artificial micro-nano structure can improve extraction efficiency of light emitting materials, particularily a scintillator. By studying different materials that excel at light extraction, such as Lu2SiO5:Ce in this case, one can unveil what films/materials will function most efficiently and thus harness the most light energy. Moth eyes provide great insight into materials that may be better at absorbing light; materials that mimic the structure of moth eyes are favored for their broadband antireflection. Nanostructures that utilize an array of circular protrubances (similar to those found in the eyes of moths) may also be applied to light extraction from a scintillator (as opposed to simply being used as an antireflective). Extracting more light allows for clearer, more defined x-ray images because the amount of reflected light is greatly reduced.

Key Differentiators

Most scinitillators have a small total reflection critical angle due to their high refractive index. This small angle causes much of the light to become trapped inside the crystal of the scintillator, rather than released to the air. "[O]nly between 10 and 30% of the light from the scintillator can enter into the photo-detector, the majority of light couldn’t be effectively extracted" (Yashi et al. 2012: 2080). By enlarging the mimicked moth eye and adding roughness to the sides of the original pyramidal design, Yashi and his team managed to effectively reduce the amount of reflection from the scintillator, thus enhancing their x-ray images greatly from existing imaging techniques.

Biomimicry Story

"'The moth eye has been considered one of the most exciting bio structures because of its unique nano-optical properties," said Yi, "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 the patient would not be aware of it at all'" (Science Daily 2012: p10).   Yasha Yi is a professor at the City University of New York as well as an affiliate of Massachusetts Institute of Technology. The moth eye, as he stated above, is useful structure to study in many fields of science. Having worked on many medical innovations, Yi wanted to expand the eloquence of this bio structure to application in his field. While the idea is young, Yi estimates that within three to five years the reflective properties of this new scintillator material that mimics the moth eye will be under full development and bettering the image capturing of x-rays for radiologists across the world.

Challenges Solved

Using materials that closely mimic moth eyes (i.e., reduce reflection of light, absorb more energy) can provide clearer, higher resolution x-ray images. More light absorbance also means that patients would need lower doses of radiation (because materials like Lu2SiO5:Ce thin film would be more effectively absorbing the light energy). Thus, patient health may be better preserved and medical imaging may even be able to move to a smaller scale.

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Giant light extraction enhancement of medical imaging scintillation materials using biologically inspired integrated nanostructuresOptics LettersJuly 5, 2012
P. Pignalosa, Bo Liu, Hong Chen, H. Smith, Yasha Yi

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