Fast raster scanning system for active dose field formation

A fast system for raster scanning of a 250 MeV beam is described. The system provides the active formation of a dose field with dimensions 40×40 cm² with a rate of 1000 lines and 10 shots per second. The principal feature of the system is that only switch mode devices (thyristors) are used in power circuits. This removes the limitations on the commutated power, allows to increase scanning frequency and makes the system more reliable.     

Scanning X-ray microscopy based on Kumakhov optics and a raster X-ray source

The concept of scanning X-ray microscopy has been practically implemented for the first time using a cylindrical polycapillary structure of the Kumakhov X-ray optics and a scanning microfocus X-ray source. The scanning X-ray microprobe is provided by electron-beam scanning of a focal spot over the target in a transmission X-ray tube equipped with an output cylindrical polycapillary structure.     

Radiation dose from a linear slit scanning X-ray machine with full-body imaging capabilities

Doses for a range of examinations and views using digital X-ray equipment with full-body linear slit scanning capabilities (Statscan) have been compared with those from other published studies. Entrance doses (free-in-air) were measured using a dosimeter, and effective doses were generated using a Monte Carlo simulator. Doses delivered by the linear slit scanning system were significantly lower than those from conventional X-ray equipment. Effective doses were between 9 and 75% of the United Nations Scientific Committee Report on the Effects of Ionising Radiation doses for standard examinations. This dose reduction can be explained by the properties of linear slit scanning technology, including low scatter, beam geometry, the use of a digital detector and the use of higher than usual tube voltages.     

Two-dimensional imaging without scanning by multifocal multiphoton microscopy

We describe multifocal multiphoton microscopy giving images without laser scanning. A multitude of 8 x 8 laser beams is focused into a sample yielding two-photon excitation in a plane. The focal spots are arranged in a rectangular array with close spacing between individual points (approximately 0.5 microm). The fluorescence emission from the sample is recorded with a CCD camera, but, owing to the close distance between the beams, they can no longer be regarded as individual points but rather as an illumination of the plane that is covered by the array of focal points. The axial sectioning capability is comparable with an ordinary single-beam two-photon microscope. Interference between the beams that could compromise the axial sectioning capability does not occur in our setup owing to small temporal delays between the individual beams. The axial sectioning capability of the setup is discussed in detail by means of the step response in which the foci are scanned axially into a uniformly fluorescent medium.     

Individual multiwall carbon nanotubes spectroscopy by scanning transmission X-ray microscopy

Scanning transmission X-ray microscopy (STXM) has been used to probe the electronic structure of individual multiwall carbon nanotubes by chemical mapping at the nanoscale. Carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of individual structures are shown to be able to differentiate carbon nanotubes from onionlike carbon nanoparticles and to differentiate nanotubes synthesized by different growth methods. Imaging of the very same region by both STXM and transmission electron microscopy is shown to be a very useful and complementary approach.     

X-ray imaging tubes

The important parameters of X-ray imaging tubes are considered in relation to their main components, the X-ray detection screen, the photocathode, the electron optics and the output screen. These parameters define the performance which can be achieved in terms of noise, contrast and resolution. Possible further improvements are also discussed.     

X-ray colour imaging

A prototype X-ray colour imaging system has been assembled using the principle of tomographic energy-dispersive diffraction imaging (TEDDI). The new system has been tested using samples of nylon-6, aluminium powder and deer antler bone. Non-destructive three-dimensional images of the test objects have been reconstructed on a 300 microm scale with an associated diffraction pattern at each voxel. In addition, the lattice parameters of the polycrystalline material present in the sampled voxels have been determined using full pattern refinement methods. The use of multiple diffracted parallel colour X-ray beams has allowed simultaneous spatially resolved data collection across a plane of the sample. This has simplified the sample scan motion and has improved data collection times by a factor scaling with the number of detector pixels. The TEDDI method is currently limited to thin samples (approx. 1-2mm) with light atoms owing to the very low detection efficiency of the silicon detector at X-ray energies above 25 keV. We describe how these difficulties can be removed by using semiconductor detectors made from heavier atomic material.     

联合空间与角度的符号相干系数平面波成像北大核心CSCD

超声平面波成像是近年来一种应用较广泛的超快速超声成像方法,多角度相干平面波复合(Coherent Plane Wave Compounding,CPWC)成像在不过多损失速率的情况下,提升成像质量。但普通的CPWC方法只是简单复合多个角度延时叠加(Delay and Sum,DAS)后的数据,并未考虑到单个角度内以及多个角度之间数据的相关性。文章提出了一种联合空间与角度的符号相干系数(Angular Spatial Sign Coherence Factor,asSCF)平面波成像方法,将空间符号相干因子和角度符号相干因子创新性地融合到波束合成的过程中,充分考虑信号之间的相关性,旨在提升多角度复合成像质量。进行了仿真实验、仿体实验以及在体组织实验,对asSCF-CPWC方法、单一的符号相干系数法以及传统CPWC方法成像进行对比,结果发现asSCF-CPWC方法具有更好的横向分辨能力和成像对比度。     

X-ray dark-field imaging modeling

Dark-field images are formed from x-ray small-angle scattering signals. The small-angle scattering signals are particularly sensitive to structural variation and density fluctuation on a length scale of several tens to hundreds of nanometers, offering a unique contrast mechanism to reveal subtle structural features of an object. In this study, based on the principle of energy conservation, we develop a physical model to describe the relationship between x-ray small-angle scattering coefficients of an object and dark-field intensity images. This model can be used to reconstruct volumetric x-ray small-angle scattering images of an object using classical tomographic algorithms. We also establish a relationship between the small-angle scattering intensity and the visibility function measured with x-ray grating imaging. The numerical simulations and phantom experiments have demonstrated the accuracy and practicability of the proposed model.     

Absorption coefficient imaging by near-field scanning optical microscopy in bacteria

We present a method for obtaining a position-dependent absorption coefficient from near-field scanning optical transmission microscopy. We show that the optical transmission intensity can be combined with the topography, resulting into an absorption coefficient that simplifies the analysis of different materials within a sample. The method is tested with the dye rhodamine 6G, and we show some analysis in biological samples such as bacteria KIebsiella pneumoniae and Pseudomonas aeruginosa. The calculated absorption coefficient images show important details of the bacteria, in particular for P. aeruginosa, in which membrane vesicles are clearly seen.     

Vortex imaging in superconducting films by scanning hall probe microscopy

We have used a low noise Scanning Hall Probe Microscope (SHPM) to study vortex structures in superconducting films. The microscope has high magnetic field (2.9×10^–8T/Hz at 77K) and spatial resolution, 0.85m. Magnetic field profiles of single vortices in High T_c YBa₂Cu₃O_7– thin films have been successfully measured and the microscopic penetration depth of the superconductor has been extracted as a function of temperature. Flux penetration into the superconductor has been imaged in real time (8s/frame).     

Hard X-ray imaging by a spherical compound refractive lens

Hard X-ray imaging by a spherical compound refractive lens is presented. The lens is composed of 123 biconcave microlenses with a size of 200 μm in diameter. Each microlens was formed by the epoxy between two bubbles, which were injected into an epoxy-filled glass capillary. The focal length of the lens is 114 mm at 8.05 keV. The light source was obtained by using a copper anode X-ray tube without a filter. The lens can be achieved a spatial resolution of 5 μm with field of view of about 700 μm, and 1–3 μm resolution may be obtainable by using monochromator and diaphragm.     

Three-dimensional trace element analysis by confocal X-ray microfluorescence imaging

A three-dimensional (3D) variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method is based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector. The experimental arrangement represents a significant generalization of regular two-dimensional (2D) scanning micro-XRF and employs a detector half-lens whose focus coincides with that of the focused incoming beam. The detection volume defined by the intersection of the exciting beam and the energy-dependent acceptance of the polycapillary optics is 100-350 mum(3). Minimum detection limits are sub-ppm, and sensitivities are comparable with regular scanning XRF. Next to the reduction of in-sample single/multiple scattering, the setup provides the possibility of sample depth scans with an energy-dependent resolution of 10-35 mum in the energy range of 3-23 keV and the possibility of performing 3D-XRF analysis by simple XYZ linear scanning. This provides a suitable alternative to X-ray fluorescence tomography. The method is illustrated with results of the analysis of solid inclusions in diamond and fluid inclusions in quartz.     

Charge contrast imaging of suspended nanotubes by scanning electron microscopy

A method of rapidly identifying and imaging suspended nanotubes by scanning electron microscopy is reported. Nanotubes are visible in high contrast and even at low magnification. The contrast can be explained by considering the effect that the charge on the nanotube has on the substrate. The proposed mechanism is general and should apply to any charged nanostructure in proximity to a surface or interface. This represents a new contrast mechanism in scanning electron microscopy.     

成像式光栅自准直测角方法研究

针对目前光电自准直仪难以做到既有高分辨力同时又有大的测量范围的不足,提出一种成像式光栅自准直测角方法。该方法将成像式光栅方法、自准直测角技术相结合,利用标尺光栅像和指示光栅形成的光栅副反映被测物体的角度变化。试验结果表明,该系统接收到的光栅信号稳定,满足光栅计数的要求,成像式光栅自准直测角方法原理可行。该方法避免了光栅副间隙带来的误差,具有大量程及较高的分辨力。     

Correlation analysis for angular compounding in strain imaging

Spatial angular compounding for elastography is a new technique that enables the reduction of noise artifacts in elastograms. This technique is most effective when the angular strain estimates to be averaged or compounded are uncorrelated. In this paper, we present a theoretical analysis of the correlation between pre- and postcompression radio-frequency echo signals acquired from the same location but at different beam insonification angles. The accuracy of the theoretical results is verified using radiofrequency pre- and postcompression echo signals acquired using a real-time clinical scanner on tissue-mimicking uniformly elastic and homogenous phantoms. The theory predicts an increased signal decorrelation with an increase in the beam-steered insonification angle as the applied strain increases and for increasing depths in the medium. Theoretical results provide useful information regarding the correlation of the angular strain estimates obtained from different beam angles that helps in finding optimum compounding schemes for elastography.