Characterization of a Laboratory-Based X-Ray Computed Nanotomography System for Propagation-Based Method of Phase Contrast Imaging

Phase contrast imaging (PCI) is used to extend X-ray computed nanotomography (nCT) technique for analyzing samples with a low X-ray contrast, such as polymeric structures or soft tissues. Although this technique is used in many variations at synchrotrons, along with the development of X-ray tubes and X-ray detectors, a PCI becomes available also for laboratory systems. This paper is focused on determining the conditions for propagation-based PCI in laboratory nCT systems based on three criteria. It is mostly employed in near-field imaging regime, which is quantified via the Fresnel number. X-rays must reach a certain degree of coherence to form edge enhancement. Finally, the setup of every computed tomography (CT) measurement has to avoid geometrical unsharpness due to the finite focal spot size. These conditions are evaluated and discussed in terms of different properties and settings of the CT machine. Propagation-based PCI is tested on a sample of carbon fibers reinforced polyethylene and the implementation of the Paganin phase retrieval algorithm on the CT data is shown.