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

Abstract

X-ray interferometry is an emerging imaging modality with a wide variety of potential clinical applications, including lung imaging. 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, respectively. Inaccuracies in grating position and multi-harmonic fringes produce Moiré artifacts when assuming the fringe pattern is perfectly sinusoidal and the phase steps are evenly spaced. We have developed an image recovery algorithm that estimates the true phase stepping positions using multiple harmonics and total variation regularization, removing the Moiré 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.

Figures (14)

• Figure 1: Schematics of the (a) Talbot-Lau and (b) Modulated Phase Grating Interferometers. In this study, the Talbot-Lau Interferometer used curved gratings. For the MPGI, a RectMPG was used and no G0 grating was used.
• Figure 2: (a) Attenuation, (b) differential-phase, and (c) dark-field images taken with a TLI with no object (comparing two reference scans), calculated using the nominal phase steps. The amplitude of the Moiré artifact was calculated for the line of interest shown and statistically compared between the images calculated with the nominal phase steps and corrected phase steps.
• Figure 3: (a) Attenuation, (b) differential-phase, and (c) dark-field images taken with a TLI with no object (comparing two reference scans), calculated using the iterative method with 1 harmonic. The variance of the images calculated using the nominal phase steps was statistically compared with the images calculated using the corrected phase steps. Additionally, the amplitude of the Moiré artifact was calculated for the line of interest shown and statistically compared between the images calculated with the nominal phase steps and corrected phase steps. Results are summarized in Table \ref{['tab:statistical_analysis_results']}.
• Figure 4: (a) Attenuation, (b) differential-phase, and (c) dark-field images taken with a TLI of a euthanized mouse, calculated using the nominal phase steps. A $3 \: mm$ scalebar is shown.
• Figure 5: (a) Attenuation, (b) differential-phase, and (c) dark-field images taken with a TLI of a euthanized mouse, calculated using the iterative method with 1 harmonic. A $3 \: mm$ scalebar is shown.