递变电压下投影融合图像重建研究

针对变电压投影数据中的不完全投影数据重建问题,提出基于投影数据线性融合的变电压CT重建算法。该算法根据最佳灰度带提取递变电压投影序列中的有效信息,利用线性融合的方法,把低电压下的投影数据通过线性关系融合到相邻高电压投影数据上,依此类推直至最高电压,获得一幅完整信息的高动态投影数据,并利用TV-ART算法重建。实验表明:线性融合算法不仅实现了变电压图像信息的完整重建,像素值也更加稳定。     

基于结构先验的变电压CT成像

为获得更高质量的CT重建图像,建立了基于结构先验的变电压CT成像方法。该方法对同一像素点在不同电压下满足最佳灰度带的有效投影数据进行叠加迭代重建,得到递变电压的重建结果,通过设定阈值,将低电压下投影数据的重建结果分为两个部分,将边缘的结构部分先验地运用到高电压下投影数据的重建结果里,以此弥补变电压重建图像过程中的信息缺失。仿真实验表明:该方法能够获得完整的工件信息,重建图像质量高,像素值也更加稳定。     

基于多周循环步进式插值扫描轨迹的工业CT柔性检测技术研究

为了在一次CT检测过程中同时实现被检工件的精细检测与内部缺陷快速发现的两种检测需求,提出了一种新型CT检测方案。该方案将一种改进的圆形CT投影扫描轨迹与不完全投影插值算法有效融合,实现了投影采集与最优图像实时重建的同步进行。为验证该技术的可行性,设计了相应的扇束CT仿真平台及试验模体,仿真试验结果表明,该检测技术在CT扫描过程中可及时发现被检工件的内部缺陷,扫描结束后可获得工件的精细CT图像,有效满足了工业CT用户在多种检测目的之间自由切换的柔性检测需求。     

探测器分块排列的CT系统及其图像重建

为解决CT系统中扫描视野受限及低剂量成像问题,提出一种探测器分块排列的CT系统及其稀疏角度CT图像迭代重建方法。探测器分块排列可扩大CT图像物体扫描视野,稀疏角度采集投影数据能有效降低辐射剂量,同时采用ART-TV迭代算法重建CT图像。仿真实验表明:该方法可有效扩大CT系统扫描视野,在稀疏角度获取投影数据采集方式下,利用ART-TV迭代重建算法可重建优质CT图像,实现降低辐射剂量的目的。     

体素投影分类ART算法快速重建CT图像

为克服CT图像重建中代数重建算法(ART)不足,基于体素投影分类的方法,提出了一种快速计算加权因子的策略,进而提出了重建CT图像的快速ART算法。相比于常用Siddon方法计算加权因子的ART算法,虽然该算法的重建精度略逊,但是解决了原ART算法计算非常费时和所需存储空间大的问题。仿真实验结果证明了该算法的有效性。     

伪彩色数字高程模型在工业CT断层图像检查中的应用

在工业CT断层图像缺陷检测应用中，提出了将数字高程模型DEM与伪彩色技术一起应用于二维灰度图像缺陷检测领域的算法流程。应用该算法流程，能够充分利用CT断层灰度图像信息，获得清晰的视觉检查效果，从而大大增强了系统检测缺陷的能力。在大型工业CT图像重建与检查分系统中采用该算法流程已经取得了较为理想的效果。     

平板X射线源重叠投影的线性迭代重建

为解决平板X射线源多个射线源同时照射时产生的投影重叠问题带来的图像重建困难,本研究提出了一种基于平板X射线源重叠投影的CT图像重建方法。该方法引入线性修正因子修正投影重叠带来的非线性,然后使用联合代数重建算法(SART)实现CT图像的重建。实验表明,该方法可以实现平板X射线源重叠投影直接重建CT图像,但是随着平板X射线源阵列数增大,重建图像质量下降。     

基于基图像TV模型的CT射束硬化校正方法

X射线CT中,X射束硬化导致重建图像中出现伪影,严重影响了图像质量。论文深入分析了射束硬化对原始投影数据的影响,并提出了一种基于基图像TV模型的射束硬化校正方法。该方法首先依据射束硬化的物理特征建立了带有可调参数的初步校正模型;其次,在不同的可调参数条件下,原始投影数据经该模型预处理变换得到多组预处理投影序列;再次,分别对预处理投影序列进行重建得到一系列校正基图像;最后,将基图像的线性组合作为最终重建图像。其中,加权系数的最优解是以最终重建图像的全变分(Total Variation,TV)函数作为目标函数,通过迭代法求得。为验证该算法,对真实的铝柱体模和工业检测件进行了实验,结果表明,该算法对射束硬化引起的杯状和条状伪影均有显著的抑制效果。     

X射线能谱CT最佳参数选取方法研究

X射线能谱CT重建图像质量的好坏主要由CT系统的性能和设置参数综合确定。在CT系统性能稳定的情况下,实际成像过程中往往需要通过调节各种参数以达到最佳成像结果。X光机的电压和电流由于在参数相近的图像重建结果中无法直观地判断哪个参数下图像质量更佳,因此需要引入定量的判据。基于此问题设计了一种综合评价方法,即通过引入三种图像质量评价体系:灰度平均梯度、均方根误差和峰值信噪比,对比分析X光机不同电流下能谱CT图像重建结果,综合确定X射线光机电流设定的最佳值。该方法也适用于其他单一参数调整下相似重建图像的优劣区分。     

全帧CCD探测器CT扫描数据读出与拖影校正研究

以光纤耦合全帧CCD方式制作的X射线探测器在实验室高精度X射线CT扫描中广泛应用。由于X射线的强穿透特性,全帧CCD探测器通常工作在无快门模式,图像拖影是该模式下必定存在的伪影。本文针对全帧CCD探测器CT扫描图像拖影校正进行研究,提出了非曝光行校正法校正投影图像拖影,避免了利用暗像元校正法校正投影图像拖影时可能会带来的条形伪影;针对动态曝光CT扫描,设计了基于辐射屏蔽的投影图像感兴趣区域快速读出模式,通过降低电荷转移时间有效抑制投影图像拖影的产生,提高探测器有效信号动态范围。实验结果表明：应用非曝光行校正法能有效校正投影图像拖影、提高投影图像质量;采用投影图像感兴趣区域快速读出模式可有效解决动态曝光CT扫描图像拖影校正难题。     

Preparation of Zn/TiO2 powder and its photocatalytic performance for oxidation of P-nitrophenol

Zn-doped TiO2 catalysts were prepared using a sol-gel method and characterized by XPS,UV-Vis, BET, XRD in this study. Under the irradiation of simulant sunlight, the photocatalytic activity for the degradation of p-nitrophenol was studied too. After irradiation for 2.5 h, the degradation percentage of p-nitrophenol could rise to more than 80 %. The results showed that the spectrum absorption band edge of Zn/TiO2 powder does not broaden obviously comparing with pure TiO2 powder. Zinc exists as Zn （11）. When calcined at 973 K, there is a new phase as ZnTiO3 in Zn/TiO2 catalyst. The order of photocatalytic activity of Zn/TiO2 catalysts calcined at different temperatures for p-nitrophenol is 773 K 〉 673 K 〉 873 K 〉 573 K 〉 973 K and the photocatalytic activity of Zn/TiO2 catalyst calcined at 773 K is better than TiO2 catalysts heated at the same temperature, and outclasses that of commercial TiO2 catalyst. It also showed that the photocatalytic degradation of p-nitrophenol follows first-order kinetics under the irradiation of simulant sunlight.     

Current status of radiation therapy for prostate cancer

Radiotherapy for the treatment of prostate cancer has been extensively explored in the past. Along with the comprehensive understanding of the biology of prostate cancer and rapid advances in terms of technology, the out- come of treatment for the patients with prostate cancer has improved. The authors review radiotherapy as the primary treatment for the disease, with particular emphasis on the technological advances from both the radiobiological and radiophysics aspects. Nonconventional fractionated irradiation like hyper- or hypo-fractionation has been imple- mented in the clinic, the final results still need to be confirmed in the future. Technological advances like IMRT, IGRT, in the last two decades have significantly improved the delivery of external radiotherapy to the prostate. This has re- sulted in an overall increase in the total dose that can be safely delivered to the prostate, which has led to modest im- provements in the biochemical outcome. However, establishing the standard therapy for prostate cancer remains con- troversial. It is hoped that the next decades will bring continued advances in the development of biologicals that will further improve current clinical outcomes.     

The control system for SSRF injection and extraction

This paper introduces the injection and extraction control system design for SSRF,which is a distributed control system aimed at stability and reliability of the pulse power supplies,PPS(Personnel Protection System)and MPS(Machine Protection System).The hardware environment is mainly based on PLC(Programmable Logic Con- troller),and ARM(Advanced RISC Machine)is also applied for studying stability of the power supplies.WinCC and EPICS(Experimental Physics and Industrial Control System)have been selected as the platforms of SCADA(Super- visory Control and Data Acquisition).For unifying the interfacing to the control computer,all front-end equipments are connected via Industrial Ethemet.     

水平管内含空气蒸汽强制对流冷凝换热模型研究

为研究含空气蒸汽在水平管内强制对流冷凝换热特性,基于对传热传质过程的分析,建立了管内为环状流与波状流条件下的流动冷凝换热模型。从潜热、显热和液膜3个环节对整个换热过程进行建模,最终得到计算局部冷凝换热系数的理论关系式。模型预测结果与实验数据的对比表明,二者相对偏差在±20%以内,验证了该换热模型的准确性与适用性。通过进一步的研究发现：从换热管入口至出口,随着冷凝的进行,管内换热主要热阻由液膜热阻向气液界面的凝结热阻转变;主流气体对流换热过程基本可忽略。     

Investigations on landmine detection by BF3 detector

Experiments were carried out to investigate the possible use of neutron backscattering for the detection of polyethylene (PE) sample buried in the soil. In detection of landmine by neutrons, the neutron detector and its shield play an important role. In this paper, the effects of graphite, heavy water, polyethylene and boric acid moderators on the flux of back scattered neutrons were investigated. We have also experimentally verified the effect of BF3 detector shield and obtained good agreement with theory.     

Web Services interface of SSRF archive data analysis system

Accelerator database stores various static parameters and real-time data of accelerator. SSRF (Shanghai Synchrotron Radiation Facility) adopts relational database to save the data. We developed a data retrieval system based on XML Web Services for accessing the archive data. It includes a bottom layer interface and an interface applicable for accelerator physics. Client samples exemplifying how to consume the interface are given. The users can browse, retrieve and plot data by the client samples. Also, we give a method to test its stability. The test result and performance are described.     

Assessment of radioactivity levels in some oil samples from the western desert, Egypt

Distributions of natural gamma-emitting radionuclides were determined in 93 oil samples collected from some petroleum fields in the western desert of Egypt. The radioisotope activities in the area under investigation lay in the range of (21 ± 4) to (38 ± 13) Bq?L-1 for 226Ra, (9 ± 2) to (15 ± 5) Bq?L-1 for 232Th, and (154 ± 28) to (303 ± 54) Bq?L-1 for 40K. The mean values were 27, 12, and 201 Bq?L-1, respectively. Among oils, variations in radionuclide ac- tivities could be on account of differences in TDS, HCO3, and Ba, with high or low pH. In this environment, oil prop- erties differently affected the mobilization of natural radionuclides. The range of 226Ra variation had been compared with available data from other countries. The calculated absorbed dose rate ranged from 22.33 to 32.66 nGy?h-1 in lo- cation (B) and (E) respectively, which was less than the accepted value.     

Preparation and properties of 117m Sn(IV)-TTHMP in in-vitro and in small animals

In this work,TTHMP was synthesized and labelled with 117m Sn.The preparation conditions,stability and lipophilicity of 117m Sn(IV)-TTHMP were investigated.Biodistribution of the complex in rabbits and mice was studied.It was found that the quantity of TTHMP and pH value of the prepararion solution had vital effects on the labeling yield of 117m Sn(IV)-TTHMP.It was also found that 117m Sn(IV)-TTHMP was hydrophilic and stable at room temperature and 37℃ in open air 117m Sn(IV)-TTHMP showed unexpectedly high bone uptake and bone-to-blood ratio in the animals.This made it potentially useful as an reagent for skeletal scintigraphy and radiotherapy of bone tumors.     

The role of AGFA high-energy CR in the calibration and quality control of multileaf collimators （MLC）

Linear accelerators equipped with multileaf collimators （MLC） are becoming more common and are widely used in the intensity-modulated radiotherapy （IMRT）. There is an imperative need to ensure the commissioning specification of the linear accelerators for the sake of quality assurance （QA） and quality control （QC）. This paper is aimed to investigate the role of AGFA high-energy CR （Computed Radiography） in calibrating dynamic multileaf collimators and evaluating the accuracy of the leaf position. The result shows that AGFA high-energy CR can easily and conveniently be used to calibrate MLC and verify its position. Hence, the application of AGFA high-energy CR is proved to be an accurate and time-saving method for routine MLC QC, especially when MLC calibration adjustments are required.     

Gamma radiation levels in the ambient environment of the QNPP Base

Monitoring results of gamma dose rate level in 1992～2004 in the ambient environment of the Qinshan Nuclear Power Plants(QNPP)Base,the northeast of Zhejiang Province,are reported in this paper.It is shown that the gamma dose rate of five monitoring sites of 2.5 km to QNPP Base is 84～113 nGy/h,with an average of 96 nGy/h in the 13 years.The average value is close to the background level of 93 nGy/h prior to operation of the QNPP Base,and is lower than the monitoring result of 101 nGy/h at the reference site in Hangzhou City.Within 50 km from the QNPP Base,the cumulative dose rate of the thermoluminescent dosimeter(TLD)is 90 nGy/h,which is lower than the back- ground level of 111 nGy/h.