High energy X-ray phase and dark-field imaging using a random absorption mask.

Hongchang Wang,Biao Cai,Kawal Sawhney,Yogesh Kashyap

doi:10.1038/srep30581

Abstract

High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science.

Highlights

IntroductionIt should be pointed out that the deflection angle induced by the sample is generally very small (a few microradians), and the corresponding displacement is only a few micrometres in the detector plane
For synchrotron radiation X-ray sources, the phase contrast speckle can be observed in the near field region if the average grain size is comparable the transverse coherence length
As highlighted in the rectangle region, the scorpion mouth is hardly noticeable in the absorption contrast image, while subtle structures can be distinctly observed in the phase contrast image

Summary

Introduction

It should be pointed out that the deflection angle induced by the sample is generally very small (a few microradians), and the corresponding displacement is only a few micrometres in the detector plane It requires only a single image for the speckle tracking mode[10,11], both the spatial and angular resolutions are compromised by selecting a surrounding subset area in order to perform the cross-correlation algorithm. These limitations can be overcome by raster scanning the speckle generator (such as, abrasive paper) along two orthogonal directions. According to the Fourier derivative theorem, and the wavefront phase shift Φinduced by the sample can be reconstructed by further applying inverse Fourier transform ( −1) of the term (g)[23], where −1 ( ) is the inverse (forward) Fourier operations

Methods

Results

Conclusion