Degree

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Document Type

Dissertation

Abstract

Purpose: X-ray grating interferometry is a form of X-ray phase contrast imaging capable of simultaneously measuring attenuation, differential-phase, and dark-field images arising from X-ray absorption, refraction, and small-angle scattering, respectively. These additional contrast mechanisms have potential clinical and industrial applications, particularly for lung tissue characterization and disease identification. As grating interferometers approach clinical viability, key challenges include reducing X-ray dose, mitigating mechanical instability, and correcting spectral artifacts resulting from beam hardening.

Methods: The modulated phase grating interferometer (MPGI) is a potential solution for reducing X-ray dose by eliminating the analyzer grating used in alternative interferometer designs, including the Talbot-Lau interferometer (TLI). The theory of the MPGI is developed using realistic modeling of the two-dimensional grating structure, and predicted fringe visibility is compared with experimental measurements. Moiré artifacts caused by phase stepping inaccuracies and improper single-harmonic modeling are addressed using an iterative algorithm that estimates optimal phase stepping positions with a multi-harmonic model and total variation regularization. The proposed Moiré artifact correction algorithm is evaluated with a robust statistical analysis, imaging of a euthanized mouse with a TLI, and imaging of PMMA microspheres with an MPGI. Spectral artifacts in dark-field computed tomography (CT) are corrected by modeling the energy dependence of the dark-field signal using a power-law relationship and producing pseudo-monochromatic dark-field images. The model is validated with simulated polychromatic CT acquisitions of a computational thorax phantom.

Results: Experimental measurements confirm agreement between predicted and observed MPGI fringe visibility, and quantitative dark-field imaging agrees with independent porosimetry measurements. The multi-harmonic phase step correction algorithm produces attenuation, differential-phase, and dark-field images with significantly reduced Moiré artifacts. The spectral correction method reduces cupping artifacts and suppresses artificial dark-field signal arising from spectral effects, outperforming subtraction-based beam hardening correction approaches even under moderate model mismatch.

Conclusion: These contributions address major barriers to clinical translation of X-ray grating interferometers by providing solutions for reducing X-ray dose and improving algorithms for reduction of interferometry-specific artifacts, supporting future applications in lung imaging and dark-field CT.

Date

3-27-2026

Committee Chair

Joyoni Dey

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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