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Measurement of avalanche size and position resolution of RPCs with different surface resistivities of the high voltage provider

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Chinese Physics C 2010年第5期34卷 565-570页

作者：岳骞李元景叶瑾程建平王义李金吴昱城 Department of Engineering Physics Tsinghua University key laboratory of particle & radiation imaging Tsinghua University

The effects of surface resistivity of the high voltage provider on the space dispersion of the induced charge of a prototype Resistive Plate Chamber （RPC） have been studied experimentally and theoretically. The results of both experiment and theory agree and confirm that a two-Gaussian function can be used to fit the dispersion of the induced charge of the RPC. It is shown that the Gaussian function with the narrower width is mainly due to the expansion of the avalanche charge in the gas gap of the RPC, and the Gaussian function with the larger width is due to the charge dispersion when it passes through the resistive carbon film. This will be useful in the RPC design when one wants to make an RPC with high position resolution.

关键词： RPC surface resistivity avalanche size position resolution

An industrial CT system for monitoring a running aero-engine

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Nuclear Science and Techniques 2014年第6期25卷 24-30页

作者：常铭肖永顺陈志强 Department of Engineering Physics Tsinghua University key laboratory of particle & radiation imaging Tsinghua University

In order to improve aerodynamic performance and efficiency, monitoring the geometry and position information of the internal structure with the aero-engine under various operational statuses is an important task. In this paper, a novel design of industrial computed tomography(ICT) system with a linac as X-ray source is proposed to complete the task. The major advantage of the proposed system is that it can provide visualized images of internal structures of the running aero-engine without physical disturbance, which makes it possible to extract the accurate geometry information. The main idea behind this design is to measure the projection data from various views for reconstructions making use of the rotations of the aero-engine blades, instead of the mechanical rotations in the conventional ICT system. However, due to high speed rotation of the aero-engine blades,the system faces more challenges than conventional ICT systems both in data acquisitions and reconstruction algorithms. The challenges and corresponding solutions are presented in this paper. In conclusion, the proposed ICT system provides a powerful tool for monitoring the running aero-engines.

关键词：航空发动机叶片工业CT系统运行工业计算机断层扫描空气动力性能信息通信系统内部结构线性加速器

Twin image removal in X-ray fluorescence holography with two energies

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Chinese Physics C 2008年第12期32卷 1016-1020页

作者：陈淼鑫李政 key laboratory of particle & radiation imaging (tsinghua university) Ministry of EducationDepartment of Engineering Physics Tsinghua University

In the last decade, X-ray fluorescence holography has been developed for the study of 3D atomic arrangements in solids. However, it encounters the twin image problem which may disturb the reconstructed atomic images. In this paper, the formation of twin image is discussed and we propose a modified two-energy algorithm to remove the twin image. The simulation shows that the method is valid and more efficient than the multiple-energy algorithm proposed by Barton.

关键词： X-ray holography twin image

Design of a compact C-band high brightness photoinjector for an ultra-fast electron diffraction

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Chinese Science Bulletin 2013年第36期58卷 4577-4581页

作者： LIU XiaoHan TANG ChuanXiang QIAN HouJun CHEN HuaiBi HUANG WenHui key laboratory of particle & radiation imaging Ministry of Education Department of Engineering Physics Tsinghua University

A compact C-band high brightness photoinjector for ultra-fast electron diffraction(UED)is under development at tsinghua *** C-band photoinjector,operating at 5.172 GHz,uses a 1.45-cell C-band RF gun as the electron *** design of the RF gun has addressed the physics,beam dynamics and mechanical aspects,and based on these design studies,a prototype has been *** order to obtain optimized performance for the UED,beam dynamics simulation has been carried out using the particle tracking code Astra for the photoinjector consisting of an alternative multi-cell RF gun design and a C-band compressor *** beam dynamics parameters that are optimized include the bunch length,peak current,horizontal emittance,and position of the minimum bunch length.

关键词：电子衍射 C波段高亮度紧凑型设计微波电子枪束流动力学束团长度

A curve-based material recognition method in MeV dual-energy X-ray imaging system

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Nuclear Science and Techniques 2016年第1期27卷 13-20页

作者： Zhi-Qiang Chen Tiao Zhao Liang Li Department of Engineering Physics Tsinghua University key laboratory of particle and radiation imaging (tsinghuauniversity) Ministry of Education

High-energy dual-energy X-ray digital radiography imaging is mainly used in the material recognition of cargo inspection. We introduce the development history and principle of the technology and describe the data process flow of our system. The system corrects original data to get a dual-energy transparence image. Material categories of all points in the image are identified by the classification curve,which is related to the X-ray energy spectrum. For the calibration of classification curve, our strategy involves a basic curve calibration and a real-time correction devoted to enhancing the classification accuracy. Image segmentation and denoising methods are applied to smooth the image. The image contains more information after colorization. Some results show that our methods achieve the desired effect.

关键词： X射线成像系统校准曲线材料识别识别方法数据处理流程透明图像分类精度实时校正

Diffraction-induced edge contrast enhancement for terahertz imaging

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Chinese Optics Letters 2009年第8期7卷 690-693页

作者：王迎新赵自然陈志强张丽康克军 Department of Engineering Physics Tsinghua UniversityKey Laboratory of Particle and Radiation Imaging (Tsinghua University)Ministry of Education of China

Contrast enhancement is particularly important for imaging of weakly absorbing materials. We demonstrate the inherent contrast-enhancement effect at the edges of a transparent object by using a conventional pulsed terahertz imaging setup without additional modification of the system design. We provide both experimental and theoretical evidence suggesting that this effect is a consequence of the frequency-dependent energy loss of the terahertz radiation induced by edge diffraction. The influence of the phase step of the broadband terahertz pulses on the edge contrast is discussed.

关键词： Energy dissipation

Simulation study of a photo-injector for brightness improvement in Thomson scattering X-ray source via ballistic bunching

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Chinese Physics C 2014年第2期38卷 75-81页

作者：丁云泽杜应超张振黄文会 Department of Engineering Physics Tsinghua University key laboratory of particle & radiation imaging (tsinghua university) Ministry of Education

Increasing the peak brightness is beneficial to various applications of the Thomson scattering X-ray source. A higher peak brightness of the scattered X-ray pulse demands a shorter scattering electron beam realized by beam compression in the electron beam-line. In this article, we study the possibility of compressing the electron beam in a typical S-band normal conducting photo-injector via ballistic bunching, through just adding a short RF linac section right behind the RF gun, so as to improve the peak brightness of the scattered x-ray pulse. Numerical optimization by ASTRA demonstrates that the peak current can increase from 50 A to 300 A for a 500 pC, 10 ps FWHM electron pulse, while normalized transverse RMS emittance and RMS energy spread increases very little. Correspondingly, the peak brightness of the Thomson scattering X-ray source is estimated to increase about three times.

关键词： beam compression ballistic bunching Thomson scattering X-ray source

A practical image reconstruction and processing method for symmetrically off-center detector CBCT system

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Nuclear Science and Techniques 2013年第4期24卷 17-22页

作者： HAO Jia ZHANG Li LI Liang CHEN Zhiqiang KANG Kejun Department of Engineering Physics Tsinghua University key laboratory of particle & radiation imaging (tsinghua university) Ministry of Education

CBCT scanners have been widely used in angiography,radiotherapy guidance,mammography and oral maxillofacial *** cut detector size,reduce manufacturing costs and radiation dose while keeping a reasonable FOV,the flat panel detector can be placed off-center *** scanning configuration extends the FOV ***,each projection is transversely truncated,bringing errors and artifacts in *** this paper,a simple but practical method is proposed for this scanning geometry based on truncation compensation and the modified FDK *** simulations with jaw phantom were conducted to evaluate the accuracy and practicability of the proposed method.A novel CBCT system for maxillofacial imaging is used for clinical test,which is equipped with an off-center small size flat panel *** show that reconstruction accuracy is acceptable for clinical use,and the image quality appears sufficient for specific diagnostic *** provides a novel solution for clinical CBCT system,in order to reduce radiation dose and manufacturing cost.

关键词： CT系统检测器 CB 图像重建 CT扫描仪平板探测器对称辐射剂量

Slice-wise reconstruction for low-dose cone-beam CT using a deep residual convolutional neural network

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Nuclear Science and Techniques 2019年第4期30卷 53-61页

作者： Hong-Kai Yang Kai-Chao Liang Ke-Jun Kang Yu-Xiang Xing Department of Engineering Physics Tsinghua University key laboratory of particle and radiation imaging Ministry of Education Tsinghua University

Because of the growing concern over the radiation dose delivered to patients, X-ray cone-beam CT(CBCT) imaging of low dose is of great interest. It is difficult for traditional reconstruction methods such as Feldkamp to reduce noise and keep resolution at low doses. A typical method to solve this problem is using optimizationbased methods with careful modeling of physics and additional constraints. However, it is computationally expensive and very time-consuming to reach an optimal solution. Recently, some pioneering work applying deep neural networks had some success in characterizing and removing artifacts from a low-dose data set. In this study,we incorporate imaging physics for a cone-beam CT into a residual convolutional neural network and propose a new end-to-end deep learning-based method for slice-wise reconstruction. By transferring 3D projection to a 2D problem with a noise reduction property, we can not only obtain reconstructions of high image quality, but also lower the computational complexity. The proposed network is composed of three serially connected sub-networks: a cone-to-fan transformation sub-network, a 2D analytical inversion sub-network, and an image refinement sub-network. This provides a comprehensive solution for end-to-end reconstruction for CBCT. The advantages of our method are that the network can simplify a 3D reconstruction problem to a 2D slice-wise reconstruction problem and can complete reconstruction in an end-to-end manner with the system matrix integrated into the network design. Furthermore, reconstruction can be less computationally expensive and easily parallelizable compared with iterative reconstruction methods.

关键词： Cone-beam CT Slice-wise Residual U-net Low dose Image denoising