Design of an asymmetric window function in single grid-based dark-field X-ray imaging for ensuring improved image quality

Single grid-based dark-field X-ray imaging (SG-DFXI) is a single-exposure, non-interferometric technique used to obtain dark-field images using a microfocus X-ray source and a common X-ray grid. It requires minimal exposure and minimal system setup for potential medical and industrial applications. However, dark-field images are often distorted by the image artifacts caused by spectral overlap of adjacent harmonic peaks in the Fourier spectrum when an X-ray grid is used. This can degrade the SG-DFXI quality. In this study, we designed a new type of rectangular window function that was applied asymmetrically to the first-order harmonic peak to extract its corresponding harmonic image, avoiding spectral-overlap artifacts and improving image resolution. An experiment was conducted on test samples of a cookie (attached to a piece of wooden chopstick) and a resolution pattern using a tabletop setup to demonstrate the efficacy of the proposed asymmetric window function. Our experimental results indicate that the asymmetric window function effectively eliminated spectral-overlap artifacts and improved the spatial resolution of dark-field images. The contrast-to-noise ratio of the dark-field image obtained using the asymmetric window function with a partial Fourier factor of PF = 0.55 was approximately 12.0, which represents a 4.3-fold improvement over the image using the symmetric window function, demonstrating the efficacy of the proposed window function.