Analysis and correction of bias induced by phase stepping jitter in grating-based X-ray phase-contrast imaging

Abstract

Grating-based X-ray phase-contrast (gbPC) is an X-ray phase-contrast imaging method involving optical gratings that typically employs the Talbot self-imaging effect. X-ray phase contrast is known to provide significant benefits for biomedical imaging. To investigate these benefits for gbPC, a high-sensitivity gbPC micro-CT setup for small biological samples has been constructed. A gbPC projection measurement simultaneously retrieves the transmittance, differential-phase and dark-field modalities of a sample. Phase stepping, the most common gbPC acquisition technique, involves several acquisitions at different lateral positions of one of the gratings. The three modalities can then be retrieved by least-squares- or FFT-based methods. Unfortunately, increasing differential-phase sensitivity also leads to an increased magnitude of artifacts introduced during retrieval of the modalities from the phase-stepping data, which limits image quality. Most importantly, processing of phase-stepping data with incorrect stepping positions (i.e., spatial sampling jitter) can introduce artifacts to the modalities. Using data from the high-sensitivity gbPC setup, as well as simulations, we show that an artifact is introduced by the jitter which is correlated with the phase of the stepping curve. We present a theoretical explanation for this correlation by introducing small deviations to an equidistant sampling of a stepping curve and approximating the effect on the calculation of the three gbPC modalities with a first-order Taylor approximation. Finally, we present an algorithm for the detection and removal of these artifacts that exploits these correlations. We show that this algorithm is able to eliminate these artifacts without degrading true image information.

Talbot-Lau x-ray phase-contrast setup for fast scanning of large samples

“…For phase stepping reconstruction, several approaches to estimate such a correction factor have been proposed 44,45,59–61 . These approaches have one shared assumption, namely that the grating motion occurs only perpendicular to the direction of the gratings bars.…”

Quantitative X-ray phase contrast computed tomography with grating interferometry

“…Advanced signal extraction methods to reduce jitter manifested in the stepping curve can be applied for homogeneous artifact-free DPC projections [90][91][92][93][94]. Additional phase ramp correction of the raw DPC signal is often needed to retrieve homogeneous DPC projections [95].…”

A novel method to inspect coating thickness of tristructural isotropic fuel particles

“…The X‐ray PCI technique can image the particles with better layer discrimination than the conventional X‐ray method because these samples are composed of light elements, such as silicon and carbon, with small variations in the density and thickness of coating layers . Currently, several PCI methods such as the crystal interferometer, in‐line method, diffraction‐enhanced imaging, and grating‐based method have been developed. Among these methods, the in‐line method promises to be a prominent technique in many applications such as medical diagnosis and nondestructive testing due to its simplicity and reliability.…”