Dark x-rays provide sharper images

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Researchers at the Paul Scherrer Institute (PSI) and the EPFL in Switzerland have developed a way of producing extremely detailed x-ray images, or ‘dark field’ images, using conventional imaging equipment, which could be of use in a number of applications, including medical imaging and security screening. Results were published online in advance in the January 2008 issue of Nature Materials.

Scientists used nanostructured gratings fitted to conventional x-ray sources to produce dark-field images, which they said provide more detail than ordinary x-ray radiographs by capturing the scattering of the x-rays within the material itself, showing subtle changes in bone, soft tissues and other materials. This technique could be used to diagnose the onset of osteoporosis, breast cancer or Alzheimer's disease, to identify explosives in hand luggage, or to pinpoint hairline cracks or corrosion in functional structures.

According to researchers, dark-field x-ray imaging previously required sophisticated optics and could only be produced at facilities like the PSI's 300m-diameter, $200 million synchrotron. With the new nanostructured gratings described in the research, dark-field images could soon be produced using ordinary x-ray equipment already in place in hospitals and airports around the world.

"Researchers have been working on dark-field x-ray images for many years," explains 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 thus are highly inefficient, he added.

"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," adds 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, 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,” Pfeiffer said.