A phase contrast X-ray imaging system includes: an illumination source adapted to illuminate a region of interest; a diffraction grating adapted to receive illumination from the illuminated region of interest, the diffraction grating comprising a spatial structure having a first periodicity superimposed with a second periodicity that is different from the first periodicity; and a detector adapted to detect illumination passing through the diffraction grating, wherein the spatial structure is defined by varying height and/or pitch, and wherein the spatial structure imparts a first phase dependence based on the first periodicity and an additional phase dependence based on the second periodicity on the illumination passing through the diffraction grating.