## 1 Introduction  
Phase-contrast imaging methods have attracted a lot of attention in the scientific community due to their ability to offer enhanced information on the inner structure of the various objects, in additionto conventional attenuation contrast [1; 2]. These methods enable the detection of X-ray refraction and scattering while passing through the object under investigation. Following increasing interest, the application of phase-contrast imaging was made available not only at synchrotron facilities with highly coherent and monochromatic radiation, but also with conventional X-ray tubes [1]. X-ray refraction and scattering within laboratory setups are usually detected with the help of the intended optical components, so-called gratings, introduced into the beam path. Several interferometric [2; 3; 4] and non-interferometric [5; 6; 7] techniques utilizing grating structures have been proposed. Despite the remarkable results in imaging achieved by these techniques, there is still an open question as to whether it is possible to further optimize the stability of the setup, acquisition time, and flux efficiency [8]. From this perspective, one of the most promising approaches is the utilization of a single optical element in a single-shot configuration. The implementation of only one optical component in the beam path relaxes the alignment requirements, increases the mechanical stability and versatility of the setup, and significantly reduces the attenuation introduced by the grating. Single-shot acquisition of imaging information, in turn, substantially shortens the total exposure time, simplifies the experimental procedure and reduces the total amount of data to be processed. All those advantages can be exploited by non-interferometric single-exposure imaging methods [9; 10; 11], in which all three contrast modalities are retrieved from a single projection image. In this approach, the incident beam is periodically modulated by the absorption grating, which can be placed before or after the object. The projected grating pattern distortion introduced by the object is recorded with a single exposure and then analyzed [6; 9; 10; 11; 12; 13; 14; 15]. To respond to the growing interest in the single-shot phase-contrast imaging, one should pay special attention to the optical components in use. Gratings for X-ray imaging are represented by a matrix with periodically-alternating opaque and transparent structures. When X-ray radiation is incident on the grating, it is partially transmitted by the low-absorbing substrate, while radiation incident on the gold structures' array is predominantly absorbed. Diffraction on the multiple apertures occurs, but its effect is feeble due to the short wavelength of X-rays. The grating converts X-ray tube radiation into multiple coherent sources; the wavefront is sampled to create a pattern inverse to the grating design. One-dimensional line gratings conventionally used in phase-contrast imaging allow only orientation-dependent analysis of structures, because only sensitivity in the direction, perpendicular to the grating lamellae, is possible [16]. Providing enhanced information on the material structure in several directions of two-dimensional gratings has been introduced [9; 12; 13; 14; 16]. As in the single-shot phase-contrast imaging, the information is retrieved from the overlapped grating-object image, it is of great importance to ensure high quality and efficient performance of the grating. The sensitivity of the discussed single-shot imaging method scales with the period of the grating [9]. In order to sufficiently resolve the grating pattern, the camera pixel size should be equal to, or less than, one-third of the projected grating period [17]. This means that the detector's resolution sets the lower limit for the grating period. To achieve the highest possible resolution within a specific setup, the use of customized gratings is superior to the off-the-shelf grids.