Dark-field X-rays shed new light on structure

Characterization

February 20, 2008

Conventional transmission image (left) and new dark-field image (right) of a chicken wing using the same radiation dose. The X-ray scattering from the porous microstructure of the bones and the reflection at internal or external interfaces produces a strong signal in the dark-field image. (© 2008 Nature Publishing Group.)

High-quality dark-field scatter images have been obtained using conventional X-ray tubes, an advance that could pave the way to revealing microcracks and corrosion in aeroplane wings and boat hulls or identifying explosives [Pfeiffer et al., Nat. Mater. (2008) 7, 134].

Until now, dark-field X-ray scattering-based information for energies in the multi-keV range has been limited to systems with a brilliant synchrotron X-ray source because standard optics are restricted to very narrow energy bandwidths.

However, a team from Switzerland and Denmark has incorporated a grating interferometer into an X-ray setup that allows these restrictions to be overcome.

Nanostructured gratings permit the use of a broad energy spectrum, including the standard range of energies that are used in traditional X-ray equipment. Current imaging equipment can be adapted to include dark-field imaging data obtained from small-angle scattering, revealing information on the microporous or microcrystalline structure of the material.

Potential applications include security screening at airports where explosives with microcrystalline structures can be identified because of their ability to scatter X-ray radiation significantly.

The image shown demonstrates the potential of dark-field imaging for improved contrast in medical applications. When compared with images obtained by traditional X-rays, the boundaries are visibly sharper and there is also a noticeable difference between grayscale values for bone and tissue.

“In cases of complicated bone fractures, where small splinters can intrude into the surrounding tissue, dark-field contrast could provide the necessary specificity to visualize subtle details,” says lead author Franz Pfeiffer of the Paul Scherrer Institut, Switzerland.

Katerina Busuttil