Advanced phase-contrast imaging using a grating interferometer

Abstract

Phase-sensitive X-ray imaging methods can provide substantially increased contrast over conventional absorption-based imaging, and therefore new and otherwise inaccessible information. Differential phase-contrast (DPC) imaging, which uses a grating interferometer and a phase-stepping technique, has been integrated into TOMCAT, a beamline dedicated to tomographic microscopy and coherent radiology experiments at the Swiss Light Source. Developments have been made focusing on the fast acquisition and post-processing of data to enable a high-throughput of samples, with obvious advantages, also through increasing the efficiency of the detecting system, of helping to reduce radiation dose imparted to the sample. A novel aquarium design allows a vertical rotation axis below the sample with measurements performed in aqueous environment. Optimization of the data acquisition procedure enables a full phase volume (1024 x 1024 pixels x 1000 projections x 9 phase steps, i.e. 9000 projections in total) to be acquired in 20 min (with a pixel size of 7.4 microm), and the subsequent post-processing has been integrated into the beamline pipeline for sinogram generation. Local DPC tomography allows one to focus with higher magnification on a particular region of interest of a sample without the presence of local tomography reconstruction artifacts. Furthermore, 'widefield' imaging is shown for DPC scans for the first time, enabling the field of view of the imaging system to be doubled for samples that are larger than the magnification allows. A case study is illustrated focusing on the visualization of soft tissue features, and particularly the substantia nigra of a rat brain. Darkfield images, based on local X-ray scattering, can also be extracted from a grating-based DPC scan: an example of the advantages of darkfield contrast is shown and the potential of darkfield X-ray tomography is discussed.

Low-dose, simple, and fast grating-based X-ray phase-contrast imaging

“…We have operated the interferometer described in ref. 24 at 25 keV and in the third Talbot distance. In this configuration, the visibility of the interferometer has been measured to be 30%.…”

Tomographic Hard X-ray Phase Contrast Micro- and Nano-imaging at TOMCAT

“…For moderate spatial resolution requirements (5 to 10 microns) TOMCAT operates a two-gratings interferometer, as described in McDonald et al [1]. In this instrument, a silicon phase grating divides the incident X-ray beam into the first two diffraction orders, which, through the Talbot effect, form a periodic interference pattern in the plane of the a second (absorption) grating, usually dubbed analyzer.…”

Combining Monte Carlo methods with coherent wave optics for the simulation of phase-sensitive X-ray imaging

“…1081 projections over 180 with five phase steps and a pixel size of 7.4 mm were acquired at an energy of 25 keV and with the absorption grating placed at the second Lohmann distance, which is close to optimal imaging conditions (Modregger et al, 2011a). Further details about the experimental arrangement can be found by McDonald et al (2009). For the simulation, the same parameters as for the measurement were chosen.…”

“…A phase-sensitive imaging technique which exploits absorption, phase and dark-field contrast is grating-based hard X-ray interferometry (GI) (Momose et al, 2003;David et al, 2002). GI has been shown to have a particularly high sensitivity to electron density variations, making it well suited for biological imaging (McDonald et al, 2009;). An additional advantage of GI is the comparatively low coherence requirement, which allows not only the use of synchrotron sources but, utilizing a third grating, also of standard laboratory X-ray tubes (Pfeiffer et al, 2006).…”