title: The projection approximation and edge contrast for x-ray propagation-based phase contrast imaging of a cylindrical edge.
abstract: We examine the projection approximation in the context of propagation-based phase contrast imaging using hard x-rays. Specifically, we consider the case of a cylinder or a rounded edge, as a simple model for the edges of many biological samples. The Argand-plane signature of a propagation-based phase contrast fringe from the edge of a cylinder is studied, and the evolution of this signature with propagation. This, along with experimental images obtained using a synchrotron source, reveals how propagation within the scattering volume is not fully described in the projection approximation's ray-based approach. This means that phase contrast fringes are underestimated by the projection approximation at a short object-to-detector propagation distance, namely a distance comparable to the free-space propagation within the volume. This failure of the projection approximation may become non-negligible in the detailed study of small anatomical features deep within a large body. Nevertheless, the projection approximation matches the exact solution for a larger propagation distance typical of those used in biomedical phase contrast imaging.
authors.affiliation: School of Physics, Monash University, Victoria 3800, Australia. Kaye.Morgan@sci.monash.edu.au
authors.forename: K S
authors.initials: KS
authors.lastname: Morgan
authors.forename: K K W
authors.initials: KK
authors.lastname: Siu
authors.forename: D M
authors.initials: DM
authors.lastname: Paganin
mesh_terms: D003198:Computer Simulation; D008858:Microscopy, Phase-Contrast / Q000379:methods*; D008954:Models, Biological; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011859:Radiography / Q000379:methods*; D012542:Scattering, Radiation