Teschke, M. and Sinzinger, S.
Phase contrast imaging: A generalized perspective.  Journal of the Optical Society of America 26A: 1015-1021 (2009).

We present a novel mathematical approach to describe phase contrast imaging. The approach is applied to analyze the interferometric phase contrast technique and phase contrast methods, which are based on spatial filtering of the undiffracted or diffracted light. Our new approach makes it possible to analyze phase contrast imaging achieved by phase perturbation of the diffracted light. We show that phase retarding of the diffracted light is an important advantage in the fabrication of the Fourier filter for spatial filtering.