Study of X‐Ray Imaging with Toroidally Bent Crystal

We developed a focusing imager with a toroidally bent crystal imager. The imager can be used in X‐ray imaging of laser fusion experiments. This article discusses the focusing properties of toroidally bent crystal in Bragg geometry. Simulations of spatial resolution for toroidally bent crystals with different conditions including source size and detector position were done using the ray‐tracing method. The applicable conditions for optimized two‐dimensional (2D) imaging of X‐ray source are proposed. Toroidally bent crystal of mica with curvature radius 290 mm in the meridional plane and 190 mm in the sagittal plane is used as imaging element in the experiments. The high‐quality visible 2D X‐ray image was obtained with the imaging plate due to the high collection efficiency of the bent crystal imaging system. It is demonstrated that the toroidally bent mica crystal could be used in X‐ray imaging. By analyzing the image information of the sagittal direction, we find out that the toroidal crystal imager has spatial resolution about 34 µm.     

Attenuated total reflection-Fourier transform infrared imaging of large areas using inverted prism crystals and combining imaging and mapping

Attenuated total reflection-Fourier transform infrared (ATR-FT-IR) imaging is a very useful tool for capturing chemical images of various materials due to the simple sample preparation and the ability to measure wet samples or samples in an aqueous environment. However, the size of the array detector used for image acquisition is often limited and there is usually a trade off between spatial resolution and the field of view (FOV). The combination of mapping and imaging can be used to acquire images with a larger FOV without sacrificing spatial resolution. Previous attempts have demonstrated this using an infrared microscope and a Germanium hemispherical ATR crystal to achieve images of up to 2.5 mm x 2.5 mm but with varying spatial resolution and depth of penetration across the imaged area. In this paper, we demonstrate a combination of mapping and imaging with a different approach using an external optics housing for large ATR accessories and inverted ATR prisms to achieve ATR-FT-IR images with a large FOV and reasonable spatial resolution. The results have shown that a FOV of 10 mm x 14 mm can be obtained with a spatial resolution of approximately 40-60 microm when using an accessory that gives no magnification. A FOV of 1.3 mm x 1.3 mm can be obtained with spatial resolution of approximately 15-20 microm when using a diamond ATR imaging accessory with 4x magnification. No significant change in image quality such as spatial resolution or depth of penetration has been observed across the whole FOV with this method and the measurement time was approximately 15 minutes for an image consisting of 16 image tiles.     

Characterization of a CCD-based digital x-ray imaging system for small-animal studies: properties of spatial resolution

A digital x-ray imaging system was designed for small-animal studies. This system is a fiber-optics taper-coupled imaging system with two CCD arrays uniquely jointed. The x-ray source of the system has a small focal spot of 20 microm. This digital imaging system contains specially designed shelves to provide magnification levels, ranging from 1.5x to 5x. The system is characterized in terms of its properties of spatial resolution. An observer-based spatial resolution measurement was conducted with a line-pair target and a sector test pattern. The modulation transfer function of the system, with different magnifications, was studied by use of a 10-microm lead slit. The average resolutions at 50% and 5% modulations at 1x magnification were measured as 3.9 and 8.4 lp/mm, respectively, where lp indicates line pairs. With 5x magnification, the 50% and the 5% modulations provided 13.2- and 29.9-lp/mm, respectively, average spatial resolutions. The measurements showed consistency between the two individual CCD arrays; the difference in resolution between the two CCDs is less than 1%, even at high magnifications.     

Evaluation of bent-crystal x-ray backlighting and microscopy techniques for the Sandia Z machine

X-ray backlighting and microscopy systems for the 1-10-keV range based on spherically or toroidally bent crystals are discussed. These systems are ideal for use on the Sandia Z machine, a megajoule-class x-ray facility. Near-normal-incidence crystal microscopy systems have been shown to be more efficient than pinhole cameras with the same spatial resolution and magnification [Appl. Opt. 37, 1784 (1998)]. We show that high-resolution (< or = 10 microm) x-ray backlighting systems using bent crystals can be more efficient than analogous point-projection imaging systems. Examples of bent-crystal-backlighting results that demonstrate 10-microm resolution over a 20-mm field of view are presented.     

Noninterferometric quantitative phase imaging with soft x rays

We demonstrate quantitative noninterferometric x-ray phase-amplitude measurement. We present results from two experimental geometries. The first geometry uses x rays diverging from a point source to produce high-resolution holograms of submicrometer-sized objects. The measured phase of the projected image agrees with the geometrically determined phase to within +/-7%. The second geometry uses a direct imaging microscope setup that allows the formation of a magnified image with a zone-plate lens. Here a direct measure of the object phase is made and agrees with that of the magnified object to better than +/-10%. In both cases the accuracy of the phase is limited by the pixel resolution.     

A Simulator for X-ray images

A simulator for X-ray images is presented based on a virtual X-ray source and a virtual human body obtained from tomographic slices. In the simulator it is possible to modify the tube potential, the anodic current, the exposure time, the filtration and some geometric parameters such as source-skin distance, orientation and field size. The virtual body consists of a three-dimensional voxel matrix in which CT numbers for each point of the body are stored. The interactions of X rays passing through the body are evaluated using the pencil beam technique. The image is obtained by computing the dose absorbed by the detector and converting it into optical density using a proper response function. The image spatial resolution is limited by the voxel size. The influence of each parameter on the image quality can be observed interactively. The dose absorbed in each point of the body is an important parameter obtained as output of the simulator.     

Experimental spatial sampling study of the real-time ultrasonic pulse-echo BAI-mode imaging technique

The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique has been developed to inspect the seal integrity of hermetically sealed, flexible food packages. With a focused 17.3-MHz transducer acquiring radio frequency (RF) echo data in a static rectilinear stop-and-go pattern, this technique was able to reliably detect channel defects as small as 38 /spl mu/m in diameter and occasionally detect 6-/spl mu/m-diameter channels. This contribution presents our experimental spatial sampling study of the BAI-mode imaging technique with a continuous zigzag scanning protocol that simulates a real-time production line inspection method in continuous motion. Two transducers (f/2 17.3 MHz and f/3 20.3 MHz) were used to acquire RF echo data in a zigzag raster pattern from plastic film samples bearing rectilinear point reflector arrays of varying grid spacings. The average BAI-value difference (/spl Delta/BAI) between defective and intact regions and the contrast-to-noise ratio (CNR) were used to assess image quality as a function of three spatial sampling variables: transducer spatial scanning step size, array sample grid spacing, and transducer -6-dB pulse-echo focal beam spot size. For a given grid size, the /spl Delta/BAI and CNR degraded as scanning step size in each spatial dimension increased. There is an engineering trade-off between the BAI-mode image quality and the transducer spatial sampling. The optimal spatial sampling step size has been identified to be between one and two times the -6-dB pulse-echo focal beam lateral diameter.     

Resolution of a reflection hologram recorded with a slit

Resolution of the reconstructed image is evaluated for the reflection hologram recorded by use of a slit. Sharp and deep images are obtained because the resolution in the vertical direction is higher than that of the conventional reflection holograms and is independent of the size of the illuminating light source. In contrast, the resolution in the horizontal direction depends on the light-source size in this direction. The optimum source size is discussed in connection with the balance in the resolutions for both directions. A method for obtaining the vertical parallax by use of multiple slits is proposed, and application of the proposed hologram to the heads-up display is also demonstrated.     

Röntgenröhren in der Medizintechnik

X‐Ray Tubes in Medical Imaging Applications The application of X‐rays in medical diagnostics has become an essential element in everyday life. Every hospital or imaging center uses X‐ray radiation to get an insight into the human body within shortest time. The technology which is used to take an image of the mandible or to create a full body scan of an emergency patient by computer tomography within a few seconds is the same. This article describes shortly the history of the invention of X‐rays. The creation of X‐rays is explained by a simple schematic. The relevance and function of the cathode to create free electrons is very important. The evolution form simple thermal filaments to electron field emitters is described. The innovation of liquid metal bearings is also essential to realize high power X‐ray tubes by effectively removing the heat from the anode. After a short excursion to the medical applications of X‐Ray imaging a completely new approach of X‐ray source is described.     

Analysis of structural distortion in Eshelby twisted InP nanowires by scanning precession electron diffraction

Transmission electron microscopes (TEM) are widely used in nanotechnology research. However, it is still challenging to characterize nanoscale objects; their small size coupled with dynamical diffraction makes interpreting real- or reciprocal-space data difficult. Scanning precession electron diffraction ((S)PED) represents an invaluable contribution, reducing the dynamical contributions to the diffraction pattern at high spatial resolution. Here a detailed analysis of wurtzite InP nanowires (30–40 nm in diameter) containing a screw dislocation and an associated wire lattice torsion is presented. It has been possible to characterize the dislocation with great detail (Burgers and line vector, handedness). Through careful measurement of the strain field and comparison with dynamical electron diffraction simulations, this was found to be compatible with a Burgers vector modulus equal to one hexagonal lattice cell parameter despite the observed crystal rotation rate being larger (ca. 20%) than that predicted by classical elastic theory for the nominal wire diameter. These findings corroborate the importance of the (S)PED technique for characterizing nanoscale materials.

     

含孤立物体场景的高速、高密度三维面形采集

提出了一种用于采集含空间孤立物体场景的高速、高密度三维面形采集方法。该方法将三幅图案高速投影到被测物体上并同步采集图像,从而实现场景三维形貌及纹理的高速记录。其中两幅图案是互相具有π相移的正弦条纹,采用傅里叶变换法求解变形条纹相位。将拍摄到的两幅变形条纹图相加可得到物体表面纹理。另一幅图案用来确定条纹级次,实现绝对相位测量,解决高速形貌采集中孤立物体相位展开难题。它由一系列宽度与正弦条纹周期相同的竖条构成,采用三种灰度对竖条编码。每个竖条由单一灰度或两种在竖直方向上周期性分布的灰度构成,这样可编6个码。将竖条按由这些码构成的伪随机序列排列,得到编码图案。测量时,对拍摄的编码图案解码,通过子序列匹配来确定对应正弦条纹的级次。设计了采用DLP投影仪及高速摄像机的高速测量系统。采用提出的方法实现了640×480分辨率下每秒60帧和320×240分辨率下每秒120帧的三维形貌及纹理采集。     

Efficient three-dimensional imaging from a small cylindrical aperture

Small-diameter cylindrical imaging platforms, such as those being considered in the development of in vivo ultrasonic microprobes, pose unique image formation challenges. The curved apertures they provide are incompatible with many of the commonly used frequency-domain synthetic aperture imaging algorithms. At the same time, their frequently small diameters place limits on the available aperture and the angular resolution that may be achieved. We obtain a three-dimensional, frequency-domain imaging algorithm for this geometry by making suitable approximations to the point spread function for wave propagation in cylindrical coordinates and obtaining its Fourier transform by analogy with the equivalent problem in Cartesian coordinates. For the most effective use of aperture, we propose using a focused transducer to place a virtual source a short distance from the probe. The focus is treated as a diverging source by the imaging algorithm, which then forms images on deeper cylindrical shells. This approach retains the simplicity and potential angular resolution of a single element, yet permits full use of the available probe aperture and a higher energy output. Computer simulations and experimental results using wire targets show that this imaging technique attains the resolution limit dictated by the operating wavelength and the transducer characteristics     

Spatial analysis of time of flight-secondary ion mass spectrometric images by ordinary kriging and inverse distance weighted interpolation techniques

Ordinary kriging and inverse distance weighted (IDW) are two interpolation methods for spatial analysis of data and are commonly used to analyze macroscopic spatial data in the fields of remote sensing, geography, and geology. In this study, these two interpolation techniques were compared and used to analyze microscopic chemical images created from time of flight-secondary ion mass spectrometry images from a patterned polymer sample of fluorocarbon (C(x)F(y)) and poly(aminopropyl siloxane) (APS, a.k.a. siloxane). Data was eliminated from the original high-resolution data set by successive random removal, and the image file was interpolated and reconstructed with a random subset of points using both methods. The statistical validity of the reconstructed image was determined by both standard geographic information system (GIS) validation statistics and evaluating the resolution across an image boundary using ASTM depth and image resolution methodology. The results show that both ordinary kriging and IDW techniques can be used to accurately reconstruct an image using substantially fewer sample points than the original data set. Ordinary kriging performed better than the IDW technique, resulting in fewer errors in predicted intensities and greater retention of original image features. The size of the data set required for the most accurate reconstruction of the original image is directly related to the autocorrelation present within the data set. When 10% of the original siloxane data set was used for an ordinary kriging interpolation, the resulting image still retained the characteristic gridlike pattern. The C(x)F(y) data set exhibited stronger spatial correlation, resulting in reconstruction of the image with only 1% of the original data set. The removal of data points does result in a loss of image resolution; however, the resolution loss is not directly related to the percentage of sample points removed.     

Chemical imaging of surface reactions by multiplexed capillary electrophoresis

A new technique for in situ imaging of surface reactions and screening heterogeneous catalysts by using multiplexed capillary electrophoresis was developed. By bundling together the inlets of a large number of capillaries, an aligned imaging probe can be created that can be used to sample directly products formed at a surface with spatial resolution determined by the outer diameter of the capillaries. In this work, we used surfaces made of platinum, iron, or gold wires to generate electrochemical products for imaging. Various shapes were recorded including crosses, squares, and triangles. A model multifunctional catalytic surface consisting of both iron and platinum electrodes in the shape of a cross was also imaged successfully. Each of the two wires produced a different electrochemical product that could be subjected to capillary electrophoresis to provide chemical selectivity. On the basis of the collected data, we were able to distinguish the products from each wire in the reconstructed image.     

Soft-x-ray Gabor holography by use of a backilluminated CCD camera

A soft-x-ray Gabor hologram was recorded directly by means of a cooled backilluminated CCD camera, and numerical reconstruction was performed. Synchrotron radiation from a bending magnet with beam line 11A at the Photon Factory, National Laboratory for High Energy Physics, Japan, was used. X rays were monochromatized to a wavelength of 2.34 nm with a grasshopper monochromator and focused on a pinhole of diameter 1.0 mum with a zone plate. A specimen was illuminated with soft x rays transmitted through the pinhole, and a shadowgraph with a magnification ratio of 33 at the CCD plane was digitized directly. The transverse resolution of the reconstructed image was estimated to be 1.5 mum, which was in good agreement with a theoretical value.     

Principles of Highly Resolved Determination of Texture and Microstructure using High‐Energy Synchrotron Radiation

Diffraction imaging with hard X‐rays (high‐energy synchrotron radiation) using the detector sweeping techniques allows measurement of the texture and microstructure of polycrystalline materials with high orientation‐ and location‐resolution. These techniques provide continuous two‐dimensional images of different sections and projections of the six‐dimensional “orientation‐location” space. For the high orientation resolution case, it is possible to measure the orientation and location coordinates of up to 10⁵ individual grains simultaneously. From these parameters, the grain size and shape can also be obtained, yielding the complete orientation stereology of the polycrystalline aggregate, which is required for its complete characterization. For the high location resolution case, the intensity at any point of the diagrams corresponds to a pole density as a function of the orientation‐location space.     

Photoacoustic tomography using a Mach-Zehnder interferometer as an acoustic line detector

A three-dimensional photoacoustic imaging method is presented that uses a Mach-Zehnder interferometer for measurement of acoustic waves generated in an object by irradiation with short laser pulses. The signals acquired with the interferometer correspond to line integrals over the acoustic wave field. An algorithm for reconstruction of a three-dimensional image from such signals measured at multiple positions around the object is shown that is a combination of a frequency-domain technique and the inverse Radon transform. From images of a small source scanning across the interferometer beam it is estimated that the spatial resolution of the imaging system is in the range of 100 to about 300 mum, depending on the interferometer beam width and the size of the aperture formed by the scan length divided by the source-detector distance. By taking an image of a phantom it could be shown that the imaging system in its present configuration is capable of producing three-dimensional images of objects with an overall size in the range of several millimeters to centimeters. Strategies are proposed how the technique can be scaled for imaging of smaller objects with higher resolution.     

用于二维线纹测量的二维动态光电显微镜

对二维线纹标准样板进行溯源测量时,需要对十字刻线进行高分辨力瞄准。利用二维动态光电显微镜,将二维样板十字刻线分别成像在相互垂直的两组狭缝上,狭缝宽度与刻线像的宽度基本一致,方向与刻线像平行,且在像空间上沿宽度方向错开约一个狭缝宽度的距离。当二维线纹样板沿某一方向运动时,对应方向被测刻线的像先后呈现在一组狭缝中,导致通过该组狭缝的光通量依次发生变化,对应的两个光电接收器的电信号存在相位差;信号处理系统根据两路电信号的相位关系,在信号交叉位置发出瞄准脉冲,锁定坐标测量系统,即得到该方向被测刻线的位置;分别对十字交叉刻线的两条刻线进行瞄准,即可得到对应交叉点的坐标。     

Image properties of polycrystalline storage films

Polycrystalline storage films are applied in various fields of x-ray radiography. Depending on the application, different requirements exist for the sensitivity and spatial resolution of the film, and these are related to light scattering in the film. Scattering is controlled by optical properties of the storage medium, e.g., the scattering length by the grain size, the absorbance by the choice of the binder, and the geometric boundary conditions by the film thickness. A method treating the scattering of light as a diffusionlike process is presented. The sensitivity, resolution, and other image properties are determined from the optical properties. The influence of the scattering length, absorbance, and thickness on image parameters is calculated and discussed. The results indicate that optimizing the image properties of the film can be achieved by a reduction of the absorbance and an increase in film thickness to the penetration depth of the x rays. Furthermore, it is shown that the resolution of the film can be set strictly according to the requirements of an individual application if the scattering length in the medium is adjusted.