/pdf/high-resolution-x-ray-computed-tomography-in-geosciences-a-3sj7249knj.pdf

High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications

Imaging with visible light today uses numerous contrast mechanisms, including bright- and dark-field contrast, phase-contrast schemes and confocal and fluorescence-based methods. X-ray imaging, on the other hand, has only recently seen the development of an analogous variety of contrast modalities. Although X-ray phase-contrast imaging could successfully be implemented at a relatively early stage with several techniques, dark-field imaging, or more generally scattering-based imaging, with hard X-rays and good signal-to-noise ratio, in practice still remains a challenging task even at highly brilliant synchrotron sources. In this letter, we report a new approach on the basis of a grating interferometer that can efficiently yield dark-field scatter images of high quality, even with conventional X-ray tube sources. Because the image contrast is formed through the mechanism of small-angle scattering, it provides complementary and otherwise inaccessible structural information about the specimen at the micrometre and submicrometre length scale. Our approach is fully compatible with conventional transmission radiography and a recently developed hard-X-ray phase-contrast imaging scheme. Applications to X-ray medical imaging, industrial non-destructive testing and security screening are discussed.

Hard-X-ray dark-field imaging using a grating interferometer

We study the problem of recovering the phase from magnitude measurements; specifically, we wish to reconstruct a complex-valued signal $ \boldsymbol {x}\in \mathbb {C}^{n}$ about which we have phaseless samples of the form $y_{r} = \left |{\langle \boldsymbol {a}_{r}, \boldsymbol {x} \rangle }\right |^{2}$ , $r = 1,\ldots , m$ (knowledge of the phase of these samples would yield a linear system). This paper develops a nonconvex formulation of the phase retrieval problem as well as a concrete solution algorithm. In a nutshell, this algorithm starts with a careful initialization obtained by means of a spectral method, and then refines this initial estimate by iteratively applying novel update rules, which have low computational complexity, much like in a gradient descent scheme. The main contribution is that this algorithm is shown to rigorously allow the exact retrieval of phase information from a nearly minimal number of random measurements. Indeed, the sequence of successive iterates provably converges to the solution at a geometric rate so that the proposed scheme is efficient both in terms of computational and data resources. In theory, a variation on this scheme leads to a near-linear time algorithm for a physically realizable model based on coded diffraction patterns. We illustrate the effectiveness of our methods with various experiments on image data. Underlying our analysis are insights for the analysis of nonconvex optimization schemes that may have implications for computational problems beyond phase retrieval.

Phase Retrieval via Wirtinger Flow: Theory and Algorithms

Phase-contrast x-ray imaging (PCI) is an innovative method that is sensitive to the refraction of the x-rays in matter. PCI is particularly adapted to visualize weakly absorbing details like those often encountered in biology and medicine. In past years, PCI has become one of the most used imaging methods in laboratory and preclinical studies: its unique characteristics allow high contrast 3D visualization of thick and complex samples even at high spatial resolution. Applications have covered a wide range of pathologies and organs, and are more and more often performed in vivo. Several techniques are now available to exploit and visualize the phase-contrast: propagation- and analyzer-based, crystal and grating interferometry and non-interferometric methods like the coded aperture. In this review, covering the last five years, we will give an overview of the main theoretical and experimental developments and of the important steps performed towards the clinical implementation of PCI.

http://iopscience.iop.org/article/10.1088/0031-9155/58/1/R1/pdf

X-ray phase-contrast imaging: from pre-clinical applications towards clinics

The understanding and management of strain is of fundamental importance in the design and implementation of materials. The strain properties of nanocrystalline materials are different from those of the bulk because of the strong influence of their surfaces and interfaces, which can be used to augment their function and introduce desirable characteristics. Here we explain how new X-ray diffraction techniques, which take advantage of the latest synchrotron radiation sources, can be used to obtain quantitative three-dimensional images of strain. These methods will lead, in the near future, to new knowledge of how nanomaterials behave within active devices and on unprecedented timescales.

Coherent X-ray diffraction imaging of strain at the nanoscale.

A dynamical theory for diffractive x-ray imaging of one-dimensional periodic objects is derived by solving the Helmholtz equation in the parabolic approximation using the coupled-wave theory A method to account for volume-diffraction effects, based on propagating backwards the eigenmodes of the microfluidic array, is demonstrated for a colloidal suspension in confinement

/pdf/dynamical-theory-for-diffractive-x-ray-imaging-of-one-hxeg8bsmng.pdf

Dynamical theory for diffractive x-ray imaging of one-dimensional periodic objects

Facing the challenges of X-ray diffraction from tiny samples subjected to multimegabar pressures, instrumentation developments are presented that enable, among other studies, single-crystal data collection from micrometer- to sub-micrometer-sized grains. The developments are based on a sub-micrometer beam capability employing compound refractive lenses operating with a phase correcting plate and a precise motorization solution.

Sub-micrometer focusing setup for high-pressure crystallography at the Extreme Conditions beamline at PETRA III

Die Erfindung betrifft eine Anordnung und Verfahren zur projektiven und/oder tomographischen Phasenkontrastbildgebung mit Rontgenstrahlung, wobei ein oder mehrere Phasengitter (G1) im Strahlengang derart angeordnet ist/sind, dass wahrend einer Umdrehung der mindestens einen Rontgenquelle (B) das Untersuchungsobjekt (P) mit unterschiedlichen raumlichen Orientierungen der Gitterlinien relativ zum Untersuchungsobjekt (P) gescannt wird, so dass aus den beiden Scans mit unterschiedlich orientierten Phasengittern (G1) je Rontgenstrahl der vollstandige Refraktionswinkel und damit der vollstandige Phasenschubgradient bestimmt werden kann, um den Phasenschub eines Untersuchungsobjektes (P) projektionsweise oder in tomographischer Darstellung zeigen zu konnen.

Anordnung und Verfahren zur projektiven und/oder tomographischen Phasenkontrastbildgebung mit Röntgenstrahlung

Rontgen-CT-System (1) mit mindestens einem Quellen/Detektor-System (F, D) zur Erzeugung tomographischer Phasenkontrast- oder Dunkelfeldaufnahmen, welches auf einer, um eine Systemachse (9) rotierbaren, Gantry angeordnet ist, das Quellen/Detektor-System (F, D) aufweisend: 1.1. eine Rontgenstrahlenquelle mit einer Gitterstruktur (13, G 0 ), welche gitterartig angeordnete Streifen von Emissionsmaxima und Emissionsminima einer erzeugten Rontgenstrahlung mit einer Gitterperiode (p 0 ) emittiert, wobei ein in zwei Ebenen aufgeweiteter Strahlenfacher von Rontgenstrahlen mit einem maximalen Facherwinkel (2xφ max ) in der Rotationsebene der Gantry und einem Z-Winkel (2xζ max ) senkrecht zur Rotationsebene der Gantry entsteht, 1.2. eine Detektoranordnung mit einer Vielzahl von nebeneinander angeordneten Gitter/Detektor-Modulen, welche jeweils in Strahlrichtung hintereinander angeordnet aufweisen: 1.2.1. mindestens ein Phasengitter (G 1i ), zur Erzeugung eines Interferenzmusters, 1.2.2. ein Analysengitter (G 2i ) mit unmittelbar anschliesendem Detektor mit einer Vielzahl von Detektorelementen, zur Bestimmung von Phase, mittlerer Strahlungsintensitat (I med ) und Amplitude (I amp ) der mittleren Intensitat der Strahlung je Detektorelement bei Relativverschiebung einer der vorgelagerten Gitterstrukturen,...

Röntgen-CT-System zur Erzeugung tomographischer Phasenkontrast- oder Dunkelfeldaufnahmen

We report how a method which requires a simple experimental setup, in principle equivalent to the one for doing classical absorption tomography, can yield phase information in three dimensions in only one single step As an alternative to two steps approaches (phase retrieval and reconstruction of the object function applying a conventional filtered backprojection algorithm), AV Bronnikov suggested an algorithm which provides direct 3D reconstruction of the refractive index from the intensity distributions measured in a single plane (pure phase object) and from the intensity distributions measured in two planes (mixed phase‐amplitude object) We adapted the original algorithm in order to retrieve the 3D reconstruction of the refractive index from the intensity distributions measured in a single plane also for the case of mixed weakly absorbing‐phase object The results show that the contrast is increased, while keeping dose minimal and spatial resolution equivalent to the conventional absorption based technique

/pdf/a-new-method-for-phase-contrast-tomography-3lxoqc9qkl.pdf

C. David

Papers

Dynamical theory for diffractive x-ray imaging of one-dimensional periodic objects

Sub-micrometer focusing setup for high-pressure crystallography at the Extreme Conditions beamline at PETRA III

Anordnung und Verfahren zur projektiven und/oder tomographischen Phasenkontrastbildgebung mit Röntgenstrahlung

Röntgen-CT-System zur Erzeugung tomographischer Phasenkontrast- oder Dunkelfeldaufnahmen

A New Method for Phase Contrast Tomography