Moire Artifact Reduction in Grating Interferometry Using Multiple Harmonics and Total Variation Regularization

X-ray interferometry is an emerging imaging modality with a wide range of potential clinical applications, including lung and breast imaging, as well as non destructive testing in fields such as additive manufacturing and porosimetry. A grating interferometer uses a diffraction grating to produce a periodic interference pattern and measures how a patient or sample perturbs the pattern, producing three unique images that highlight X-ray absorption, refraction, and small angle scattering, known as the attenuation, differential phase, and dark-field images. Image artifacts unique to X-ray interferometry are introduced when assuming the fringe pattern is perfectly sinusoidal and the phase steps are evenly spaced. Inaccuracies in grating position, coupled with multi-harmonic fringes, lead to Moire artifacts. We have developed an image recovery algorithm that estimates the true phase stepping positions using multiple harmonics and total variation regularization, removing the Moire artifacts present in the attenuation, differential phase, and dark-field images. We demonstrate the algorithm's utility for the Talbot-Lau and Modulated Phase Grating interferometers by imaging multiple samples, including PMMA microspheres and a euthanized mouse.