Helical X-ray phase-contrast computed tomography without phase stepping.

M Marschner,J Herzen,G Potdevin,P B Noël,A Fehringer,F Pfeiffer,M Willner

doi:10.1038/srep23953

M Marschner, J Herzen + Show 5 more

Open Access

https://doi.org/10.1038/srep23953

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Abstract

X-ray phase-contrast computed tomography (PCCT) using grating interferometry provides enhanced soft-tissue contrast. The possibility to use standard polychromatic laboratory sources enables an implementation into a clinical setting. Thus, PCCT has gained significant attention in recent years. However, phase-contrast CT scans still require significantly increased measurement times in comparison to conventional attenuation-based CT imaging. This is mainly due to a time-consuming stepping of a grating, which is necessary for an accurate retrieval of the phase information. In this paper, we demonstrate a novel scan technique, which directly allows the determination of the phase signal without a phase-stepping procedure. The presented work is based on moiré fringe scanning, which allows fast data acquisition in radiographic applications such as mammography or in-line product analysis. Here, we demonstrate its extension to tomography enabling a continuous helical sample rotation as routinely performed in clinical CT systems. Compared to standard phase-stepping techniques, the proposed helical fringe-scanning procedure enables faster measurements, an extended field of view and relaxes the stability requirements of the system, since the gratings remain stationary. Finally, our approach exceeds previously introduced methods by not relying on spatial interpolation to acquire the phase-contrast signal.

Highlights

X-ray phase-contrast computed tomography (PCCT) using grating interferometry provides enhanced soft-tissue contrast
With the recent introduction of grating interferometry, which relies on transmission gratings with μm-size periods, high-sensitivity phase measurements are possible with laboratory sources[2,3]
The potential benefit arising from using grating interferometry for biomedical imaging has been verified by several investigators[4,5]

Summary

Introduction

X-ray phase-contrast computed tomography (PCCT) using grating interferometry provides enhanced soft-tissue contrast. Phase-contrast CT scans still require significantly increased measurement times in comparison to conventional attenuation-based CT imaging. This is mainly due to a time-consuming stepping of a grating, which is necessary for an accurate retrieval of the phase information. The sample is recorded multiple times with different relative positions of the gratings These images can be combined to phase-stepping curves for each pixel[3,6]. The information related to absorption, refraction and scattering strength can be extracted by Fourier analysis or a least-squares fit of these curves This so-called phase-stepping procedure is a limiting factor in the reduction of the overall acquisition time, because it limits the rotation speed of the sample or the gantry. The major shortcoming of these single-shot approaches is a decrease in spatial resolution, due to the fact that multiple pixels are merged to extract the phase information

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