From synchrotron radiation to lab source: advanced speckle-based X-ray imaging using abrasive paper

Abstract

X-ray phase and dark-field imaging techniques provide complementary and inaccessible information compared to conventional X-ray absorption or visible light imaging. However, such methods typically require sophisticated experimental apparatus or X-ray beams with specific properties. Recently, an X-ray speckle-based technique has shown great potential for X-ray phase and dark-field imaging using a simple experimental arrangement. However, it still suffers from either poor resolution or the time consuming process of collecting a large number of images. To overcome these limitations, in this report we demonstrate that absorption, dark-field, phase contrast, and two orthogonal differential phase contrast images can simultaneously be generated by scanning a piece of abrasive paper in only one direction. We propose a novel theoretical approach to quantitatively extract the above five images by utilising the remarkable properties of speckles. Importantly, the technique has been extended from a synchrotron light source to utilise a lab-based microfocus X-ray source and flat panel detector. Removing the need to raster the optics in two directions significantly reduces the acquisition time and absorbed dose, which can be of vital importance for many biological samples. This new imaging method could potentially provide a breakthrough for numerous practical imaging applications in biomedical research and materials science.

State of the Art of X-ray Speckle-Based Phase-Contrast and Dark-Field Imaging

“…However, the concepts discussed here can easily be applied to diverging sources, as mostly encountered in the laboratory [85,87] or for microscopy applications with a magnifying geometry implemented, e.g., with a Fresnel zone plate [139]. The concepts and reconstruction approaches presented here still hold in these cases, but one needs to take into account the magnification of the speckle pattern and sample.…”

“…This was simplified further by taking only one single 1D scan to obtain the 2D refraction information [87]. In this mode, here called 1D XSS, the diffuser is stepped only in one direction-horizontally or vertically-in equidistant steps that are much smaller than the average speckle size and in the order of the pixel size.…”

“…As the speckles have an irregular, random shape and a distribution of sizes, only an average speckle size can be estimated. This is done for example by determining the spatial frequency at the maximum of the power spectrum [86,87,123,129] or from a 2D auto-correlation of the speckle pattern [88,128,[130][131][132][133][134]. Generally, well-defined, small speckles that can be resolved easily and cover a few pixels in the detector plane are desired.…”

“…where σ I andĪ are the standard deviation and the mean intensity value, respectively, of the speckle pattern in a small region of interest (typically around 150 × 150 pixels), as, e.g., used in [87,88,133,135,136], or:…”

Applications of Laboratory-Based Phase-Contrast Imaging Using Speckle Tracking Technique towards High Energy X-Rays

“…[33]. The spatial resolution for speckle tracking technique here is largely limited by the correlation window size but can be largely improved by using extra stages to scan the wavefront modulator, e.g., in 1D, 2D raster or a non-gird scheme [26,39,40]. The speckle size and visibility also affect the spatial resolution and noise level [24,25], which can be adjusted by changing to different diffusers for other applications.…”