Measurement and simulative proof concerning the visibility loss in x-ray Talbot-Lau Moiré imaging

Abstract

X-ray grating-based phase-contrast imaging is a very promising imaging technique for medical imaging and non-destructive testing. Simultaneously to the attenuation properties additional information about the phase-shift and the scattering properties of an object can be gained. Nevertheless, to obtain this information multiple shots per image have to be taken in the so-called phase-stepping process. Thus, it often is a time consuming imaging procedure. In contrast, Moiré imaging with a Talbot-Lau interferometer is a very fast single-shot imaging method. To obtain the Moiré pattern which encodes the object information the interferometer has to be slightly detuned. This leads to a loss in visibility and therefore to a loss in image quality compared to the more time consuming phase-stepping method. Thus, it is important for the Moiré imaging method to evaluate the mechanisms of visibility loss. In this publication we present measurements and simulations investigating the visibility loss due to detuning the Talbot-Lau interferometer. Thus, a deeper understanding of Moiré imaging can be gained.

A fast alignment method for grating-based X-ray phase-contrast imaging systems

“…The envisaged single-shot imaging approach, Fourier imaging, depends on the quality and structure of the moiré stripes which encode the object's phase shift. To ensure high quality and resolution of the phase retrieval via Fourier imaging, a fine moiré fringe pattern is favorable which period is still large enough to be adequately resolved by the detection system [39,40]. Such sought-after moiré patterns are depicted in the outer fields of figure 3 and motivate the performed z-scan of G2.…”

“…the inter-grating distances and angles, can easily be read off from the moiré map look-up table. This is in particular relevant for single-shot phase retrieval techniques that benefit from a specific arrangement of the moiré fringes like Fourier imaging where fine moiré stripes are needed [39,40].…”

A phase-sampling method for an X-ray Talbot-Lau scanner with continuous grating movement

“…For other methods like the standard scanning method or moiré imaging, moiré stripes are needed which show a specific shape and frequency. Thus, the interferometer has to be detuned slightly [32,43]. In contrary, for the continuous phase-sampling scanning method an overall better adjusted interferometer is usable enabling a higher reference visibility.…”

“…Another idea would be to use moiré imaging [50,51] to get the projections by single-shot imaging. However, here it is necessary that moiré stripes of appropriate frequency [43] are available over the whole grating area. As single grating tiles are stitched together in our interferometer, an appropriate moiré pattern cannot be ensured in all regions at the same time.…”

“…To the best of our knowledge, the continuous back and forth movement of the G0 grating for phase-sampling during a projective scan procedure has not been published before. The main advantage of our scanning method compared to other scanning acquisition schemes [32,43] is its independence from the occurring moiré pattern shape. This independence allows for an optimal alignment of the grating interferometer.…”