Fig. 1

Principle of contrast formation in x-ray dark-field chest radiography. The grating interferometer generates a fine intensity modulation (perpendicular to the beam direction) on the propagating x-ray wave front. Penetrating regions with microscopic interfaces between materials of different refractive indices, this intensity pattern gets distorted as a result of multiple refractions. The dark-field signal intensity is encoded in the reduction of the pattern’s amplitude (fringe contrast). Composed of many inherent interfaces (air versus tissue), healthy lung parenchyma induces strong small angle scattering yielding a distinct dark-field signal. On the contrary, emphysematous regions where the respiratory surface is reduced or has already been fully vanished, represent less or no scatter activity resulting in a reduced or zero dark-field signal