In grating-based x-ray phase sensitive imaging, dark-field contrast refers to the extinction of the interference fringes due to small-angle scattering. For configurations where the sample is placed before the beamsplitter grating, the dark-field contrast has been quantified with theoretical wave propagation models. Yet when the grating is placed before the sample, the dark-field contrast has only been modeled in the geometric optics regime. Here we attempt to quantify the dark-field effect in the grating-before-sample geometry with first-principle wave calculations and understand the associated particle-size selectivity. We obtain an expression for the dark-field effect in terms of the sample material’s complex refractive index, which can be verified experimentally without fitting parameters. A dark-field computed tomography experiment shows that the particle-size selectivity can be used to differentiate materials of identical x-ray absorption.
Original Manuscript: April 18, 2011
Revised Manuscript: June 2, 2011
Manuscript Accepted: June 2, 2011
Published: July 22, 2011
Vol. 6, Iss. 9 Virtual Journal for Biomedical Optics
Susanna K. Lynch, Vinay Pai, Julie Auxier, Ashley F. Stein, Eric E. Bennett, Camille K. Kemble, Xianghui Xiao, Wah-Keat Lee, Nicole Y. Morgan, and Han Harold Wen, "Interpretation of dark-field contrast and particle-size selectivity in grating interferometers," Appl. Opt. 50, 4310-4319 (2011)