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

Abstract

Phase sensitive X-ray imaging methods can provide substantially increased contrast over conventional absorption-based imaging and therefore new and otherwise inaccessible information. The use of gratings as optical elements in hard X-ray phase imaging overcomes some of the problems that have impaired the wider use of phase contrast in X-ray radiography and tomography. So far, to separate the phase information from other contributions detected with a grating interferometer, a phase-stepping approach has been considered, which implies the acquisition of multiple radiographic projections. Here we present an innovative, highly sensitive X-ray tomographic phase-contrast imaging approach based on grating interferometry, which extracts the phase-contrast signal without the need of phase stepping. Compared to the existing phase-stepping approach, the main advantages of this new method dubbed "reverse projection" are not only the significantly reduced delivered dose, without the degradation of the image quality, but also the much higher efficiency. The new technique sets the prerequisites for future fast and low-dose phase-contrast imaging methods, fundamental for imaging biological specimens and in vivo studies.X-ray imaging | differential phase contrast | grating interferometer | tomography O ver the last few decades X-ray imaging has experienced a true revolution. The most striking advancement has been the production of coherent X-ray beams with their intrinsic capability of generating interference signals and, as a consequence, providing access to phase information within the investigated sample. This fact has been very stimulating for the X-ray-imaging community, which had been continually challenged by the frustrating question of how to increase the contrast in X-ray images without increasing the dose imparted to a specimen. It is well known that, different from conventional visible light, the refractive index in X-ray optics is very close to and smaller than unity. In first approximation, for a small and negligible anisotropy in the medium, the index of refraction characterizing the optical properties of a tissue can be expressed-including X-ray absorptionwith its complex form: n ¼ 1-δ-iβ where δ is the decrement of the real part of the refractive index, responsible for the phase shift, while the imaginary part β describes the absorption property of the tissue. In conventional absorption-based radiography, the X-ray phase shift information is usually not used for image reconstruction. However, at photon energies greater than 10 keV and for soft tissues (made up of low-Z elements), the phase shift term plays a more prominent role than the attenuation term because δ is typically three orders of magnitude larger than β (1). As a consequence, phase-contrast modalities can generate significantly greater image contrast compared to conventional, absorptionbased radiography. In fact, far from absorption edges, δ is inversely proportional to the square of the X-ray energy while β decreases as the fourth power of it. Conseq...

Image-based modelling of skeletal muscle oxygenation

“…Grating interferometry makes use of two further gratings placed in between sample and detector to extract phase-shift information. Using this technique it was possible to obtain images of rat brain [112], images of rat testicle at a comparable quality of histological images [113] and differential phase and dark field images of a cancerous mastectomy [114], showing the potential of grating-based interferometry for pre-clinical applications. All of the mentioned experiments have been carried out ex vivo.…”

Analysis of Absorption and Phase Difference Images from Differential Interference Contrast Microscopy

“…Here we present a simple, straightforward, non-iterative method capable of extracting the absorption and the phase difference images from two images collected at different phase shifts of the birefringent prisms (a Normaski or a modified Wollaston prism) in a DIC microscopy-a method less sensitive to mechanical instabilities of the optical system. The method is based on the physics and mathematics of diffraction enhanced imaging (DEI) and grating-based x-ray phase contrast imaging (GPI) [5][6][7]. Similar to information associated with absorption and refraction angle extraction obtained using the rocking curve in DEI and shifting curve in GPI, another kind of shifting curve is used here to extract the absorption and phase information from images in our DIC layout.…”

A dual weighted residual method applied to complex periodic gratings

“…This type of grating has been used recently in crystalline silicon solar cells [1], gas sensors [2] and medical X-ray imaging [3,4]. They are also used in acousto-optic devices to characterize the composition of drugs, and in spectroscopic sensing for detecting trace gases [5].…”