Physical optics basis for the X-ray phase imaging of low contrast samples: a primer.

X-ray imaging of biological materials has, in the past, relied on the difference in absorption between the two of the main constituents of living matter (water and carbon) at certain energies. In recent years, phase techniques relying on the X-ray refractive index difference of materials have been developed that have allowed biological and other low-contrast materials to be imaged. In this primer, we aim to cover some of the terminology and methods involved in X-ray phase imaging and provide a framework for understanding phase-imaging and phase-retrieval methods. We conclude with a discussion on some of the most recent advances in this field where far-field diffraction patterns of samples can be inverted to provide very high-resolution structure leading, possibly, to the prospect of single-molecule imaging. [ABSTRACT FROM AUTHOR]