Sharper X-rays Developed

Using novel x-ray optical components instead of sophisticated crystal optics has allowed dark-field images to be produced at wavelengths used in common medical and industrial imaging equipment. The dark-field images provide more detail than ordinary x-ray radiographs and could be used to diagnose the onset of osteoporosis, breast cancer or Alzheimer's disease, and to identify explosives in luggage.

Researchers at the Paul Scherrer Institute (PSI) and the EPFL (Ecole Polytechnique Fédérale de Lausanne) in Switzerland developed the method. Until now, dark-field x-ray imaging required sophisticated optics and could only be produced at facilities like the PSI’s 300-m diameter, $200 million synchrotron. With the new nanostructured gratings described in this research, published online January 20 in Nature Materials, dark-field images could soon be produced using ordinary x-ray equipment already in place in hospitals and airports around the world.

Left: Traditional absorption image of a chicken wing. Right: Dark-field image of a chicken wing.(Images courtesy Franz Pfeiffer, EPFL/PSI)

Unlike traditional x-ray images, which show a simple absorption contrast, dark-field images capture the scattering of the radiation within the material itself, exposing subtle inner changes in bone, soft tissue, or alloys.

The overall clarity of the images is striking. The improved sensitivity in measuring bone density and hairline fractures could help diagnose the onset of osteoporosis. Because cancer or plaque cells scatter radiation slightly differently than normal cells, dark-field x-ray images can also be used to explore soft tissue, providing safer early diagnosis of breast cancer or the plaques associated with Alzheimer’s disease.

Security screening equipment equipped with dark-field image capability could better identify explosives, whose microcrystalline structures strongly scatter x-ray radiation. And because x-rays penetrate a material without damaging it, dark-field images could help reveal scattering-producing microcracks and corrosion in structures such as airplane wings or the hulls of boats.

Left: Traditional x-ray radiograph of a fish. Right: Dark-field image of a fish.

“Researchers have been working on dark-field x-ray images for many years,” said Franz Pfeiffer, a professor at EPFL and researcher at the PSI. “Up until now these images have only been possible using sophisticated crystal optical elements.”

Crystal optics, however, only work for a single x-ray wavelength and are highly inefficient. “Our new technique uses novel x-ray optical components, in the form of nanostructured gratings, that permit the use of a broad energy spectrum, including the standard range of energies in traditional x-ray equipment used in hospitals or airports,” said Christian David, Pfeiffer’s colleague at PSI. “This opens up the possibility for adapting current imaging equipment to include dark-field imaging.”

Pfeiffer plans to collaborate with the Center for Biomedical Imaging (CIBM), a joint center with the universities of Lausanne and Geneva and their associated hospitals, to develop an adaptation for existing medical equipment.

“When combined with the phase contrast imaging technique that we developed in 2006, we now have the possibility of providing the same range of imaging techniques in broad-spectrum x-ray imaging that we do with visible light,” he said.

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