Abstract
Phase-contrast imaging with x-rays is a developing field for imaging weakly absorbing materials. In this work, two phase-contrast imaging methods, grating- and speckle-based imaging, that measure the derivative of the phase shift, have been implemented with a laboratory source and compared experimentally. It was found that for the same dose conditions, the speckle-tracking differential phase-contrast images have considerably higher contrast-to-noise ratio than the grating-based images, but at the cost of lower resolution. Grating-based imaging performs better in terms of resolution, but would require longer exposure times, mainly due to absorption in the grating interferometer.
Highlights
To overcome the limitations of low resolution and poor contrast when imaging weakly absorbing objects with x-rays, different phase-sensitive imaging techniques are being developed
Published under licence by IOP Publishing Ltd interferometer used in grating-based imaging (GBI) was designed with grating periods p1 = 4.08 μm of the π-shifting phase grating G1 and p2 = 2.4 μm of the absorption grating G2
For a plastic wedge with a small angle, a LEGO R sword (Fig. 2), the contrast-to-noise ratios (CNR) of the Differential phase contrast (DPC) images were evaluated as CNR = |IA − IB|/σ
Summary
To overcome the limitations of low resolution and poor contrast when imaging weakly absorbing objects with x-rays, different phase-sensitive imaging techniques are being developed. The well-established propagation-based imaging method (PBI) measures the second-order derivative of the phase, while grating-based imaging (GBI) [1] and the relatively new speckle-based imaging (SBI) [2, 3] measure the refraction angle. By tracking the shift of a known intensity pattern, a map of the refraction angle, which is proportional to the derivative of the phase shift, can be constructed. GBI and SBI use a Talbot pattern [4] and a near-field speckle pattern, respectively. These two methods have been implemented with a laboratory micro-focus x-ray source, and have been used to image different samples under the same dose conditions, with the goal of comparing the quality of the obtained images
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