Shadow effects in simulated ultrasound images derived from computed tomography images using a focused beam tracing model

Simulation of ultrasound images based on computed tomography (CT) data has previously been performed with different approaches. Shadow effects are normally pronounced in ultrasound images, so they should be included in the simulation. In this study, a method to capture the shadow effects has been developed, which makes the simulated ultrasound images appear more realistic. The method using a focused beam tracing model gives diffuse shadows that are similar to the ones observed in measurements on real objects. Ultrasound images of a cod (Gadus morhua) were obtained with a BK Medical 2202 ProFocus ultrasound scanner (BK Medical, Herlev, Denmark) equipped with a dedicated research interface giving access to beamformed radio frequency data. CT images were obtained with an Aquilion ONE Toshiba CT scanner (Toshiba Medical Systems Corp., Tochigi, Japan). CT data were mapped from Hounsfield units to backscatter strength, attenuation coefficients, and characteristic acoustic impedance. The focused beam tracing model was used to create maps of the transmission coefficient and scattering strength maps. Field II was then used to simulate an ultrasound image of 38.9 × 55.3 × 4.5 mm, using 10(6) point scatterers. As there is no quantitative method to assess quality of a simulated ultrasound image compared to a measured one, visual inspection was used for evaluation.     

Beam Hardening Correction Base on Monte Carlo Simulation Method

For the empirical beam hardening correction in computerized tomography (CT), it is necessary to measure an attenuation curve for the material. The attenuation curve depends on the X ray machine operation parameters and object material, etc. If any measuring condition changes, a new attenuation curve has to be measured. This approach is time consuming and difficult to implement. A new method of beam hardening correction is presented in this paper, which is based on Monte Carlo simulation of the attenuation characteristic. An aluminium object is scanned and the projection data is corrected by the empirical beam hardening correction and by the simulation based correction. The results of the reconstructed images confirm the correctness of the simulation based method. The simulation based correction has been applied successfully to CT projection data of several test samples, with the material of aluminum, steel and copper.     

基于蒙特卡罗模拟的射束硬化校正方法

传统的射束硬化校正方法, 通常需要针对每一种材料测量该材料对射线的吸收曲线. 由于吸收曲线对实验条件有很大的依赖性, 每当改变X光机电压或者被测工件的材料等条件时,需要重新测量吸收曲线才能完成硬化校正过程. 这种方法费事费时. 本文提出了基于蒙特卡罗模拟计算物质吸收曲线的硬化校正方法. 实验中, 分别用本方法和传统的硬化校正方法对铝工件进行硬化校正, 经过比较, 确认本方法是有效的. 然后用该方法对不同材料(铝、铁和铜)的工件进行校正. 实验结果表明, 本方法能有效消除各种材料工件图像中的硬化伪影, 是快速的和切实可行的.     

Numerical simulation and design of a thermionic electron gun

This paper reports the simulation of an electron gun. The effects on the beam quality of some parameters on the beam quality were studied and optimal choices were identified. It gives numerical beam qualities for a common electrostatic triode gun, and the dependencies on design parameters such as electrode geometries and bias voltages to these electrodes are shown. An electron beam of diameter 5 mm with energy of 5 ke V was assumed for the simulation process. Some design parameters were identified as variable parameters in the presence of space charge.These parameters are the inclination angle of emission electrode, the applied voltage to the focusing electrode, the gap width between the emission electrode and the focusing electrode and the diameter of the focusing electrode. The triode extraction system is designed and optimized by using CST software(for Particle Beam Simulations). The physical design of the extraction system is given in this paper. From the simulation results, it is concluded that the inclination angle of the emission electrode is optimized at 22.5?, the applied voltage to the focusing electrode was optimized and found to be Vfoc =-600 V, the optimal separation distance(gap between emission electrode and focusing electrode) is 4 mm, and the optimal diameter of the emission electrode is 14 mm. Initial results for these efforts aimed at emittance improvement are also given.     

Image – Based “film” dosimetry in NILPRP SSDL

This paper presents the 1D, 2D & 3D dose distribution determination method using the Real Time Dosimetry (RTD) system in NILPRP Secondary Standard Dosimetry Laboratory (SSDL). MULTIDATA has extended the RTD system to perform traditional film dosimetry tasks directly on images. Image-based film dosimetry provided the benefits of traditional film analysis in a faster, more intuitive process for commissioning, quality assurance and beam data libraries in radiation beam applications.     

Wood engraving by Q-switched diode-pumped frequency-doubled Nd:YAG green laser

Laser deep engraving is one of the most promising technologies to be used in wood carver operations. In this method, a laser beam is used to ablate a solid wood bulk, following predetermined patterns. The sculpture is obtained by repeating this process on each successive thin layer. Obviously, in order to achieve larger material removal rates, the process needs a controllable variation of the depth to carve a 3D (three dimensional) profiles.The degree of precision of the shape, the removal rate and the surface quality during the engraving process strictly depend on the materials properties, the laser source characteristics and the process parameters.The aim of this work is to investigate the influence of the process parameters on the material removal rates by engraving panels made of different types of wood using a Q-switched diode-pumped Nd:YAG green laser working with a wavelength λ=532 nm. The examined parameters were: the mean power that depends on the pulse frequency, the beam speed and the number of laser scansions, also called repetitions. The working parameters and the engraved depth were related and an energy-based model was proposed in order to predict the latter.Experimental results showed that the Q-switched diode-pumped frequency-doubled Nd:YAG green laser can be successfully used to machine different types of wood, obtaining decorative drawing and 3D engraved geometries without burning. However, an accurate selection of the wood types and the process parameters is necessary in order to obtain deep engraving without carbonization and a homogeneous carving.     

High speed imaging for material parameters calibration at high strain rate

To describe the material behaviour at high strain rates dynamic experimental tests are necessary, and appropriate constitutive models are to be calibrated accordingly. A way to achieve this is through an inverse procedure, based on the minimization of an error function calculated as the difference between experimental and numerical data coming from Finite Element analysis. This approach, widely used in the literature, has a heavy computational cost associated with the minimization process that requires, for each variation of the material model parameters, the execution of FE calculations. In this work, a faster but yet effective calibration procedure is studied Experimental tests were performed on an aluminium alloy AA6061-T6, by means of a direct tension-compression Split Hopkinson bar. A fast camera with a resolution of 192 × 128 pixels and capable of a sample rate of 100,000?fps captured images of the deformation process undergone by the samples during the tests. The profile of the sample obtained after the image binarization and processing, was postprocessed to derive the deformation history; afterwards it was possible to calculate the true stress and strain, and carry out the inverse calibration by analytical computations. The results of this method were compared with the ones coming from the Finite Element approach.     

ECR源低能强流高电荷态离子束四维发射度测量仪的研制

为全面研究ECR（Electron Cyclotron Resonance）离子源引出的高电荷态离子束流品质,获取ECR离子源引出离子束流的横向四维相空间分布,提高向加速器的注入效率,中国科学院近代物理研究所研制了一台高精度Pepper Pot型发射度测量仪PEMiL（Pepper pot Emittance Meter in Lanzhou）。根据使用需求,利用KBr晶体喷涂技术取代传统的CsI闪烁体成像技术,解决了束流光斑重叠效应,获得了边界清晰的束流图像;并开发了相应的数据处理分析程序,以分析处理得到的束流横向四维相空间分布。利用PEMiL获得了75 keV,170 eμA的O5+束流横向四维发射度。分析结果表明:PEMiL测量分析后的束流发射度结果可靠性高,荧光屏电荷累积效应造成的发射度差异不超过25%,PEMiL可作为ECR离子源引出离子束流品质诊断的有效装置。     

Beam analysis of scanning electron microscope according to the mirror effect phenomenon

In a scanning electron microscope the influence of electronic beam parameters on the electron-mirror images has been investigated. A simple theoretical model for scanning electron beam behavior in terms of beam and surface potentials is presented. The derived expression relates the scanning beam parameters and parameters of an irradiation region. Influence of a beam (the size and current), scanning potential, working distance, trapped charge and the irradiated area on electron mirror images are defined. Results show that the electron beam current has a considerable effect on the deduced mirror images in comparison with the other beam parameters. So it could be adapted for adjusting the phenomena of mirror effect. Moreover, the trapped charges have been calculated and the results examined in comparison with experimental data.     

Processing of concretes with a high power CO2 laser

Laser material processing, being a non-contact process, minimizes many of the complexities involved in the decontamination and decommissioning of nuclear facilities. A high power laser beam incident on a concrete surface can produce spalling, glazing or vaporization, depending upon the laser power density and scan speed. This paper presents effect of various laser processing parameters on the efficiency of material removal by surface spalling and glazing. The size of laser beam at constant fluence or energy density had significantly different effect on the spalling process. In thick concrete block cutting the flow or removal of molten material limits the cutting depth. By employing repeated laser glazing followed by mechanical scrubbing process cutting of 150 mm thick concrete block was carried out. Gravitation force was utilized for molten materials to flow out while drilling holes on vertical concrete walls. The dependence of the incident laser beam angle on drilling time was experimentally studied.     

Effect of focus position on informational properties of acoustic emission generated by laser-material interactions

To achieve desired accuracy, precision and surface roughness during laser-material removal process, monitoring and control of the process parameters related to laser, optics, workpiece material and its motion are required. Focus position, defined as a gap between the focusing lens and the surface of the sample workpiece, is one of the most critical process parameters, which determines the projection of the intensity of the laser beam on the surface to be ablated and therefore directly affects volume and geometry of the material removed and there by machining quality. In this paper, acoustic emission (AE) generated by laser-material interactions was statistically analyzed with respect to the variations in the focus position. The study involved on-line measurements of the AE signal from the laser-material interaction zone as a function of the focus position and the width of the machined trenches. Several basic statistical parameters, e.g. average amplitude, variance and power spectrum density were analyzed to select distinct informational parameters. Pattern recognition analysis of three informational parameters based on variances within frequency diapasons of 20-180, 180-300, and 300-500 kHz was used for reliable classification of the focus position and width of the machined trenches. The results provide important information for future development of on-line monitoring and control systems for laser-material removal process.     

移动式加速器在快中子照相中的应用

介绍了移动式加速器的工作原理、结构和调试过程。该加速器具有体积小、重量轻、束流稳定度高、束斑直径小的特点。移动式加速器是首次在中国工程物理研究院应用于快中子照相。在调试过程中测试了小型移动式加速器的束流稳定性等参数,采用伴随粒子方法测量了直流中子产额。通过移动加速器和数字照相系统的组合,获得了初步图像。     

Free carrier modulation of a sub-bandgap CW laser beam: A Si optoelectronic chopper

In this work we introduced two beam photocarrier cross-modulation for creation of an optically driven photonic laser beam modulator using a semiconductor wafer as the active medium. Unlike other laser beam modulators, the process of modulation of an unmodulated sub-bandgap laser beam was made possible by generating a spatially- and free-carrier density-wave-dependent infrared absorption coefficient in the bulk of the semiconductor, following absorption of a collinear super-bandgap modulated laser beam. The experimental results showed that the modulation efficiency strongly depends on the transport parameters of the semiconductor material and on the power of the super-bandgap laser beam.     

Beam hardening correction for a cone-beam CT system and its effect on spatial resolution

In this paper, we present a beam hardening correction (BHC) method in three-dimension space for a cone-beam computed tomography (CBCT) system in a mono-material case and investigate its effect on the spatial resolution. Due to the polychromatic character of the X-ray spectrum used, cupping and streak artifacts called beam hardening artifacts arise in the reconstructed CT images, causing reduced image quality. In addition, enhanced edges are introduced in the reconstructed CT images because of the beam hardening effect. The spatial resolution of the CBCT system is calculated from the edge response function (ERF) on different planes in space. Thus, in the CT images with beam hardening artifacts, enhanced ERFs will be extracted to calculate the modulation transfer function (MTF), obtaining a better spatial resolution that deviates from the real value. Reasonable spatial resolution can be obtained after reducing the artifacts. The 10% MTF value and the full width at half maximum (FWHM) of the point spread function with and without BHC are presented.     

Reflection mode holographic recording in methylene blue-sensitized polyvinyl alcohol acrylamide films

Photopolymer systems can produce good image quality holograms that does not require any post-processing and are environmentally stable with good diffraction efficiency. The present work reports the development of a methylene blue-sensitized polyvinyl alcohol acrylamide (MBPVA/AA) photopolymer system for recording white light reflection holograms. Reflection gratings were recorded in the photopolymer films with different concentrations of methylene blue (MB). Various parameters affecting the holographic properties of the samples were also studied. The holographic performance of the material is found to depend on its chemical composition and the recording parameters.     

Folded shift multiplexing

Shift multiplexing is a holographic recording method that uses a spherical reference wave. We extend the principle to a thin slab of holographic material that acts as a waveguide. Total internal reflection folds the reference spherical beam in one dimension. We demonstrate that the shift selectivity with the folded spherical beam is independent of the slab thickness but depends instead on the numerical aperture of the coupled spherical wave. A shift selectivity of 0.5 microm has been achieved with a 1-mm-thick LiNbO3 crystal and 50 high-definition data pages are recorded with this method.     

Pulsed laser deposition—UV laser sources and applications

Progress in material research and processing industry is fueled by the technique of pulsed laser deposition (PLD). High energy excimer lasers enable this technique since every material is amenable to their high photon energies. Spectral properties, temporal pulse and laser beam parameters of state of the art excimer lasers will be compared with frequency converted Nd:YAG lasers. Both quality and longevity of the deposited layers strongly depend on the degree of accuracy achieved in the thin film ablation and subsequent deposition process.     

In situ investigation on rapid microstructure evolution in extreme complex environment by developing a new AFBP-TVM sparse tomography algorithm from original CS-XPCMT

A new sparse tomography method for observing the rapid internal microstructure evolution of material, called the Algebraic Filtered-Back-Projection and Total Variation Minimization (AFBP-TVM) iteration sparse reconstruction algorithm, was proposed in this paper. The new algorithm was developed by combining the two techniques of the Algebraic Reconstruction Technique (ART) and the Filtered-Back-Projection (FBP) on the basis of analysis in linear space. A series of numerical reconstruction experiments were conducted to validate the new algorithm. The results indicated the new algorithm can obtain satisfactory reconstruction images from 1/6 of the projections that were used in traditional algorithms. So the time spent on projection acquisition process can be reduced to 1/6 of that in traditional tomography method. The quality of images reconstructed by new algorithm was better than other algorithms, which was evaluated by three quantitative parameters. The normalized average absolute distance criterion and the normalized mean square criterion, which were used to evaluate the relative error of the reconstruction results (smaller value means better quality of reconstruction), decreased from 0.3758 to 0.1272 and from 0.1832 to 0.0894 respectively. The standardized covariance criterion, which was used to evaluate the similarity level (greater value means higher accuracy of reconstruction), increased from 92.72% to 99.30%. Finally, the new algorithm was validated under actual experimental conditions. The results indicated that the AFBP-TVM algorithm obtained better reconstruction quality than other algorithms. It meant that the AFBP-TVM algorithm may be a suitable method for in situ investigation on material's rapid internal microstructure evolution in extreme complex environment.     

参考光波面质量对全息存储质量影响的数值模拟研究

采用数值模拟方法研究了不同种类参考光波面质量对再现图像质量的影响.针对全息实验实际情况,对二值图像建立了傅里叶变换全息图记录和读出的物理模型,分别考察采用一般平面波参考光、高斯光束球面波参考光和散斑参考光时的读出图像质量,并以信噪比损失作为衡量图像质量的定量工具.模拟结果表明,在理想平面波参考光和球面波参考光的情形,全息读出图像质量非常好,与输入图像相比信噪比损失在0.6dB以下.但是对于散斑参考光,尽管其极优的位移选择性提供了高密度存储的可能性,但再现图像质量明显变差,信噪比损失在5dB以上,实现有效的数据存储位密度将是十分困难的.为了兼顾存储密度和再现质量,应该考虑优化参考光的途径.     

光纤组束激光的工业加工应用前景分析

为了分析光纤组束激光的工业加工应用前景,对组束激光的角偏移和腔耦合效率进行了理论分析和数值计算,结果表明组束激光输出功率可以达到10kW量级。结合双光栅组束结构,对组束激光的光束质量进行控制,结果表明此条件下优化的组束激光光束质量可以达到1.4左右。光纤组束激光在输出功率和光束质量两方面均满足工业加工的应用需求。