Angular resolution in magnification radiography and the observation of x-ray wave interaction signatures

High resolution x-ray imaging studies have demonstrated significant radiographic contrast enhancements that are attributed to wave interactions within the sample. This paper reviews diffraction and refraction in the context of medical radiography, describing signatures produced by each process and the necessary experimental conditions for observing them. The concept of angular resolution is introduced and applied to current x-ray source and detector configurations, testing their ability to record these features. It is difficult to record interference patterns arising from refractive phase shifts because their formation requires a mono-energetic beam. The refraction of x-rays across boundaries, as described by Snell's law, produces strong contrast enhancements when they are struck at close to the glancing incidence. Deflections are proportional to the change in electron density (at energies above the K-edge) and square root of the wavelength, so they can be observed with a poly-energetic beam. Diffraction can also be observed with white radiation, but produce fringes with far narrower separation under the same irradiation conditions. In both cases, the observation of wave interaction signatures requires a propagation distance between the sample and detector, and selection of an appropriate geometric magnification, which can be estimated using a simple model presented here.