A feasibility study of X‐ray phase‐contrast mammographic tomography at the Imaging and Medical beamline of the Australian Synchrotron

Results are presented of a recent experiment at the Imaging and Medical beamline of the Australian Synchrotron intended to contribute to the implementation of low‐dose high‐sensitivity three‐dimensional mammographic phase‐contrast imaging, initially at synchrotrons and subsequently in hospitals and medical imaging clinics. The effect of such imaging parameters as X‐ray energy, source size, detector resolution, sample‐to‐detector distance, scanning and data processing strategies in the case of propagation‐based phase‐contrast computed tomography (CT) have been tested, quantified, evaluated and optimized using a plastic phantom simulating relevant breast‐tissue characteristics. Analysis of the data collected using a Hamamatsu CMOS Flat Panel Sensor, with a pixel size of 100 µm, revealed the presence of propagation‐based phase contrast and demonstrated significant improvement of the quality of phase‐contrast CT imaging compared with conventional (absorption‐based) CT, at medically acceptable radiation doses.     

Three dimensional accurate morphology measurements of polystyrene standard particles on silicon substrate by electron tomography

Polystyrene latex (PSL) nanoparticle (NP) sample is one of the most widely used standard materials. It is used for calibration of particle counters and particle size measurement tools. It has been reported that the measured NP sizes by various methods, such as Differential Mobility Analysis, dynamic light scattering (DLS), optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), differ from each other. Deformation of PSL NPs on mica substrate has been reported in AFM measurements: the lateral width of PSL NPs is smaller than their vertical height. To provide a reliable calibration standard, the deformation must be measured by a method that can reliably visualize the entire three dimensional (3D) shape of the PSL NPs. Here we present a method for detailed measurement of PSL NP 3D shape by means of electron tomography in a transmission electron microscope. The observed shape of the PSL NPs with 100 nm and 50 nm diameter were not spherical, but squished in direction perpendicular to the support substrate by about 7.4% and 12.1%, respectively. The high difference in surface energy of the PSL NPs and that of substrate together with their low Young modulus appear to explain the squishing of the NPs without presence of water film.     

Characteristics of Friedel pairs and diffraction contrast tomography with non‐perpendicular rotation axis

The characteristics of Friedel pairs in diffraction contrast tomography (DCT) are studied in the condition that the rotation axis of the sample is not exactly perpendicular to the incident X‐ray direction. For the rotation axis approximately aligned along the vertical direction, the Friedel pairs close to the horizontal plane are insensitive to the non‐perpendicularity of the rotation axis, and can be used to refine the sample‐to‐detector distance and X‐ray energy, while the Friedel pairs close to the vertical direction are sensitive to the non‐perpendicularity of the rotation axis, and can be used to determine the rotation axis orientation. The correct matching proportion of Friedel pairs decreases with increasing non‐perpendicularity of the rotation axis. A method of data processing considering rotation axis misalignment is proposed, which significantly increases the correct matching and indexing proportions of the diffraction spots. A pure aluminium polycrystalline sample is investigated using DCT at beamline 4W1A of Beijing Synchrotron Radiation Facility. Based on the analysis of Friedel pairs, the sample‐to‐detector distance and X‐ray energy are refined to be 8.67 mm and 20.04 keV, respectively. The non‐perpendicular angle of the rotation axis is calculated to be 0.10°. With these refined geometric parameters, the matching proportion of the spatial position of diffraction spots is 90.62%. Three‐dimensional reconstruction of the sample with 13 grains is realised using the algebraic reconstruction technique. It is demonstrated that the precise correction of the orientation of the sample rotation axis is effective in DCT suffering from rotation axis misalignment, and the higher accuracy in determining the rotation axis is expected to improve the reconstruction precision of grains.     

Combination of HAADF‐STEM and ADF‐STEM Tomography for Core–Shell Hybrid Materials

Characterization of core–shell type nanoparticles in 3D by transmission electron microscopy (TEM) can be very challenging. Especially when both heavy and light elements coexist within the same nanostructure, artifacts in the 3D reconstruction are often present. A representative example would be a particle comprising an anisotropic metallic (Au) nanoparticle coated with a (mesoporous) silica shell. To obtain a reliable 3D characterization of such an object, a dose‐efficient strategy is proposed to simultaneously acquire high‐angle annular dark‐field scanning TEM and annular dark‐field tilt series for tomography. The 3D reconstruction is further improved by applying an advanced masking and interpolation approach to the acquired data. This new methodology enables us to obtain high‐quality reconstructions from which also quantitative information can be extracted. This approach is broadly applicable to investigate hybrid core–shell materials.     

Data-fusion of high resolution X-ray CT,SEM and EDS for 3D and pseudo-3D chemical and structural characterization of sandstone

When dealing with the characterization of the structure and composition of natural stones, problems of representativeness and choice of analysis technique almost always occur. Since feature-sizes are typically spread over the nanometer to centimeter range, there is never one single technique that allows a rapid and complete characterization. Over the last few decades, high resolution X-ray CT (μ-CT) has become an invaluable tool for the 3D characterization of many materials, including natural stones. This technique has many important advantages, but there are also some limitations, including a tradeoff between resolution and sample size and a lack of chemical information. For geologists, this chemical information is of importance for the determination of minerals inside samples. We suggest a workflow for the complete chemical and structural characterization of a representative volume of a heterogeneous geological material. This workflow consists of combining information derived from CT scans at different spatial resolutions with information from scanning electron microscopy and energy-dispersive X-ray spectroscopy.     

地震CT勘探原理及其在公路隧道病害诊断中的应用

地震CT勘探是一种新的地球物理方法。具有分辨率高、可靠性强、信息量大、图象直观的特点。可以广泛地用于线路、场地、隧道、边坡等项目的工程地质勘查和病害诊断。在元磨高速公路芭蕉箐隧道的地质病害诊断中应用地震CT进行勘探,取得了良好的效果。     

A Non-linear Algorithm of Photoelastic Tomography for the Axisymmetric Problem

A non-linear algorithm of photoelastic tomography for the measurement of axisymmetric stress fields has been elaborated. It is free of any assumptions concerning the value of the birefringence or rotation of the principal stress axes along the light rays. The algorithm is based on the measurement of characteristic directions and phase retardation in two parallel sections of the test object. Stress components are presented in the form of power series along the radial coordinate. A differential evolution algorithm has been used for finding the stress field parameters, which fit the measurement data best. Application of the method is illustrated by residual stress measurement in a drinking glass.     

弹性动力学反问题的发展和展望

本文介绍了弹性动力学反问题的理论和方法及其在工程实际中的应用。对本学科的当前发展，重点介绍了Ｂｏｒｎ近似的线性化方法和利用弹性波的层析成象技术的理论基础，同时对一些实验技术作了简要介绍。对本学科的进一步发展值得注意解决的问题作了展望。     

Surface and volume non-invasive methods for the structural monitoring of the bass-relief ‘Madonna con Bambino’ (Gorizia,Northern Italy)

Abstract

Structural analysis of marble statues, carried out by non-invasive and in situ methods, is crucial to define the state of conservation of the artworks and to identify the deterioration phenomena that can affect them. In this work, we combined in situ non-destructive techniques, ultrasonic tomography (US), ultraviolet-induced visible fluorescence (UV-IF) and X-ray fluorescence (XRF) to study the bass-relief ‘Madonna con Bambino’ (Gorizia, Italy). The US revealed the presence of some metallic pivots, associated with areas of high sound velocity; moreover, a more degraded area has been identified in the lower part of the bass-relief. The acquired UV-IF image confirmed the presence of surface degradation, allowing a preliminary evaluation of the extension of a fracture, from surface to bulk. In addition, the different materials (both original and/or integrations) that compose the studied surface have been identified. The XRF has contributed to define the nature of the inorganic materials applied during undocumented previous restoration works on the surface as filler for lacunae.     

Second harmonic magnetoacoustic responses of magnetic nanoparticles in magnetoacoustic tomography with magnetic induction

Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles(MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses(2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction(MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.