Imaging improved by scrambling X-rays

X-ray phase-contrast imaging can provide high-quality images of objects with lower radiation doses. But until now these images have been hard to obtain and required special X-ray sources whose properties are typically only found at large particle accelerator facilities.

Using a laboratory source with unprecedented brightness, scientists from the Technische Universität München (TUM) and the Royal Institute of Technology in Stockholm (KTH), as well as Dr Pierre Thibault (UCL Physics & Astronomy), have demonstrated a new approach to get reliable phase contrast with an extremely simple setup.

X-ray phase-contrast imaging is a method that uses the refraction (bending) of X-rays as they pass through a specimen instead of their attenuation (dimming), which often produces images of much higher quality.

In their new study, the scientists have now developed an extremely simple setup to produce X-ray phase-contrast images. The solution to many of their difficulties may seem counter-intuitive: scramble the X-rays to give them a random structure. These so-called 'speckles' encode a wealth of information about the sample as they travel through it. The scrambled X-rays are collected with a high-resolution X-ray camera, and the information is then extracted afterwards.

Using their new technique, the researchers have demonstrated the efficiency and versatility of their approach. "From a single measurement, we obtain an attenuation image, the phase image, but also a dark-field image," explains Dr Irene Zanette (TUM), lead author of the publication. "The phase image can be used to measure accurately the specimen's projected thickness. The dark-field image can be just as important because it maps structures in the specimen too small to be resolved, such as cracks or fibers in materials," she adds.

The source's high brightness is also key to these results. "In the source we used a liquid metal jet as the X-ray-producing target instead of the solid targets normally used in laboratory X-ray sources," says Tunhe Zhou from KTH Stockholm, project partner of the TUM. "This makes it possible to gain the high intensity needed for phase-contrast imaging without damaging the X-ray-producing target."

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The intensity "landscape" of the scrambled X-rays has a multitude of random bright and dark spots called speckles. These speckles are here rendered as the height of a surface. A sample placed in the beam changes slightly the position, height and depth of the hills and valleys of this landscape. These changes are analyzed to form the images of the sample

Credit: I. Zanette (TUM)

To obtain all images at once, an algorithm scans the speckles and analyzes the minute changes in their shape and position caused by the specimen. "Our refined speckle-tracking approach is quite robust" says Dr Pierre Thibault, from UCL. "We have also introduced a phase integration step that converts the deflection angles into accurate quantitative phase images."

Notes

• The research is published in the journal Physical Review Letters in an article entitled 'Speckle-based X-ray Phase-contrast and dark-field imaging with a laboratory source'

Related links

• Paper in Physical Review Letters
  
• UCL Physics & Astronomy
• TUM press release

High-resolution images

Attenuation, phase-contrast and dark-field images

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• View image on Flickr

Intensity landscape of X-ray speckles

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• View image on Flickr

These images can be reproduced freely for the purposes of news reporting and discussion. For other queries, please contact Dr Irene Zanette (Technical University of Munich, Germany), on irene.zanette@tum.de or by phone on +49 89 289 10802.

Science contact

Dr Pierre Thibault
UCL Physics & Astronomy
020 7679 1558
p.thibault@ucl.ac.uk

Media contact

Oli Usher
UCL Faculty of Mathematical & Physical Sciences
020 7679 7964
o.usher@ucl.ac.uk