X射线管的焦点仿真设计研究

在X射线管中焦点的形状和尺寸对影像质量起着决定性作用。本文使用CST Studio Suite软件进行仿真设计，研究了栅极电压和聚焦结构对焦点的影响，开展了焦点形成机理、电极结构与静电聚焦等理论分析，为X射线管的结构设计提供规律参照。     

高频数字X射线管灯丝发射特性对比研究

选择X射线DR摄影系统用国产与进口X射线管,进行灯丝发射特性对比研究,评估国产X射线管满足高频数字X射线机使用的有效性。采用万东50kW高频高压发生器,在相同负载条件下,分别测试进口和国产X射线管的大小焦点灯丝初级电压、灯丝初级电流、高压初级电流,并将灯丝初级电压和初级电流换算成灯丝次级电压和次级电流进行数据分析。对应选择的多档kV,在25~100mA管电流范围内,两种X射线管的小焦点发射特性均呈线性。在125~630mA管电流范围内,两种X射线管的大焦点发射特性呈线性。在相同管电压情况下,进口X射线管小焦点发射效率高于国产X射线管平均9%左右;进口X射线管大焦点发射效率低于国产X射线管平均2%左右。国产X射线管灯丝发射特性能够匹配国产高频数字X射线机,满足临床X射线诊断使用。配套DR专用摄影系统时,可将小焦点实际焦点宽度适当减小,既可提高影像质量,也可降低灯丝损耗。     

X射线管结构与焦斑关系研究

X射线管是X射线机的心脏,是产生X射线的源泉<参考文献原文>。其焦斑大小及分布对整机图像清晰度起着决定性的作用。通过对X射线管结构特点、焦斑产生机理、电极结构与焦斑相关性实验的测试数据及理论分析等多方面的论述,探讨了X射线管结构尺寸对焦斑的影响。通过系列实验及理论分析表明:X射线管阴极结构对焦斑有巨大的影响。借助计算机模拟仿真计算,合理设计阴极结构,能够获取大小适中、分布均匀的焦斑,从而达到改善X射线机图像清晰度的目的。     

碳纳米管场发射微焦点高速X射线管

具有快速启动和高速拍照特性的微焦点X射线管具有广泛的应用需求。一种基于碳纳米管场致发射阴极阵列的微焦点X射线管研制成功。采用由微波等离子体化学气相沉积方法制备出的高度定向的、具有优异场致发射性能的碳纳米管微束阵列作为X射线管的冷阴极,以此设计出由六边型铜网为栅极的多级式高分辨率电子光学系统,使该X射线管可以实现高速脉冲拍照特性。当栅极电压为2.7kV时,总发射电流达到2mA,碳纳米管相应的发射电流密度达到2.5A/cm2,此时X射线的焦斑尺寸为39μm,从而可以实现高分辨率X射线成像。     

微焦X射线管电子发射系统的二维模拟

微焦点X射线管是一种焦斑尺寸在1~100μm的X光管。由于它具有高的空间分辨率,这种光管被广泛用于生物医学、生化动力学、工业无损检测、X射线显微镜以及微型CT等行业。电子发射系统是X射线管的关键部分,基于MATLAB平台分别使用蒙特卡洛法、有限差分法和龙格库塔法对电子发射系统的热发射、聚焦电场电位、电子束轨迹进行了模拟。以给定阴极尺寸的良好对焦X射线管为模型,分析了模拟数据,得出最佳焦距为15.0 mm,与标称相同。说明模拟方法具有可行性,模拟结果具有一定可信度。实际生产过程中对于设计好尺寸的阴极可以通过此方法找到理论最佳焦距并测试,将对实际生产中的对焦问题起到一定的指导和借鉴作用。     

X射线管中电子束聚焦技术的探讨

在x射线管中,焦点的大小和形状对影象起着决定性的作用。焦点中电子分布不均匀现象不仅会损坏光学焦点的性能,而且降低了管子的功率。焦点的大小和形状是由电极的形状和尺寸所决定。聚焦极形状和集射     

反射式X射线管阳极钨靶的模拟优化设计

反射式X射线管已广泛应用于放射诊疗、工业探伤、安全检查等领域。阳极靶作为X射线管的关键部件，对X射线管的性能有着决定性的作用。本文采用基于蒙特卡罗方法的MCNP软件对能量为160 keV电子束在反射式X射线管钨靶上的轫致辐射规律进行了模拟研究，研究了出束方向的光强随阳极靶厚和靶角的变化规律，比较了焦点长度方向和宽度方向一定锥角范围内X射线出射谱的特点，最终给出了X射线管靶厚和靶角设计的优化方案，对于提高X射线管亮度和能谱一致性具有一定的理论指导意义。     

X射线管灯丝参数及其温度分布计算的研究

X射线管的焦点尺寸、功率和寿命是评价X射线管性能的主要技术指标,这些参数主要取决于灯丝的参数设计和工作时的温度分布。首先根据X射线管灯丝的典型电压、最大工作电流以及最大管电流的设计要求,利用灯丝热辐射表面积与热电子发射表面积相等的方法,推导了X射线管灯丝直径和长度参数的计算公式,同时可以获得灯丝的最高平均工作温度;再结合傅里叶导热微分方程,提出等间隔温度迭代的方法从灯丝两端开始计算温度,并引入螺旋遮挡系数δ进行修正,研究了灯丝在不同灯丝电压下的温度分布以及热电子发射分布。实验测量了X射线管在不同灯丝电压下的灯丝电流和管电流,用测量的灯丝电流计算灯丝温度分布,通过热电子发射电流公式转换为管电流,最后与实验测量的管电流值进行比较,结果表明两者变化趋势一致,最大误差小于±7.7%。     

冷阴极X射线管关键部件的设计与仿真

利用CST粒子工作室软件设计仿真了一种高电子通过率冷阴极微焦点X射线管。重点分析X射线管阴极结构、栅网和聚焦极的结构与电压、阳极电压等关键因素对电子束聚焦束斑的影响,特别是设计了一种独特的阴极凹槽结构,使阴极电子束发射的散角减小了21.84°,并使电子枪通过率从54.3%增加至74.59%。在此基础上设计的碳纳米管X射线管在阳极电压为70 kV时,电子通过率可达到75%,电子束焦点约为56 μm,聚束比为5∶1,可为冷阴极微焦点X射线管的设计和加工提供参考。     

准点X光源成像实验台架的研制

为了研究医学系统中乳腺癌早期诊断的关键技术，研制了一台用于准点X光源成像实验台架。该实验台架由脉冲触发器电源和脉冲X射线管组成，其中脉冲触发器电源由Marx发生器、火花隙开关、电容分压器及输出段构成，采用紧凑可移动化的设计；脉冲X射线管利用冷阴极反射轰击阳极靶韧致辐射出X射线的机理，该方法可有效提高辐射出X射线点源位置的重复率，并且根据不同的驱动电压可调节阴阳极的材料及距离，保证在脉冲X射线管输出X射线光子能量≥15 keV的情况下，X射线点源尺寸可以达到≤100 μm的设计指标。Simplorer模拟结果表明：在脉冲X射线管阻抗为57 Ω时，脉冲触发器输出指标为电压169 kV，上升时间≤10 ns，脉宽≤100 ns。     

Correction for resolution nonuniformities caused by anode angulation in computed tomography

Most X-ray tubes comprise a rotating anode that is bombarded with electrons to produce X-rays. A substantial amount of heat is generated, and to increase the area of the anode exposed to the electrons, without increasing the apparent size of the focal spot, the focal track of the anode is generally beveled with a very shallow angle (typically 5 degrees-7 degrees in a computed tomography (CT) tube). Due to the line focus principle, this allows a fairly large area of the focal track to be exposed to electrons while retaining a fairly small effective projected focal spot. One side effect of anode angulation is that the focal spot appears different from different positions in the detector array; the effective focal spot size at a constant distance from the tube will be larger for a peripheral detector channel than for a central one. These differences in the effective size of the focal spot across the field-of-view lead to worse resolution in the periphery than in the center of reconstructed images. In this work we describe a method for achieving more uniform resolution in fanbeam CT images by correcting for these focal spot angulation effects. We do so by modeling the effects as a series of local blurrings in the space of transmitted CT intensities and determining the effective coefficients of the corresponding discrete convolutions. The effect of these blurrings can then be compensated for in the sinogram domain through the use of a penalized-likelihood sinogram restoration model we have recently developed.     

Fast circular tomography device for cardiac imaging: image deflection mechanism and evaluation

A circular tomography system for cardiac imaging is described and measurements of the detector system are presented. Fast tomographic motion is obtained with a custom-made rotating focal spot X-ray tube combined with servo-operated scanning mirrors that deflect the optical image between a large field of view image intensifier and television camera. The motion of the deflection mirrors is locked in frequency and phase to the position of the focal spot with precision analog electronics. Initial measurements on the system components indicate that circular tomograms of the beating heart can be obtained in 1/60 s at rates as high as 30/s. Image degradation due to focal spot tracking error is minimal; however, the optical temporal lag of a P-20 type image intensifier output phosphor results in a factor of three contrast loss for millimeter-sized objects. A linear system analysis in conjunction with the measured temporal step response of the phosphor is in good agreement with the magnitude of this contrast loss.     

利用整体毛细管X光半会聚透镜会聚同步辐射

为了进一步开展基于整体毛细管X光半会聚透镜和同步辐射的微区X射线分析,利用整体毛细管X光半会聚透镜和超环面镜的组合会聚了同步辐射。在8 keV能量点,利用超环面镜,将面积为2.3 mm×26 mm,竖直发散度和水平发散度分别近似为0和1.1 mrad的同步辐射光束会聚为面积为0.9 mm×0.3 mm,水平和竖直发散度分别为1.4 mrad和0.1 mrad的束斑,然后利用整体毛细管X光半会聚透镜将束斑会聚成直径为21.4μm的微焦斑,该整体毛细管X光半会聚透镜对束斑的传输效率为7.9%,该透镜焦距和焦斑处单位面积上的强度(功率密度)增益分别为13.3 mm和59。     

用三区三元相位滤波器提高近场光存储系统的焦深

为了提高近场固体浸没透镜光存储系统的焦深,设计了三区三元相位滤波器.设计建立在矢量衍射理论基础上,应用MATLAB优化工具箱优化设计出可以获得最大焦深的滤波器结构参数.在设计过程中,我们限定记录光斑的大小与没有滤波器时的光斑大小相等,而光斑的强度减小一半,所设计的滤波器可以使近场固体浸没透镜光存储系统的焦深提高1.6倍...     

The sensitivity to technological innovations of the doses delivered by optimized mammography systems

Multiparameter optimizations have been carried out to study the effects of hypothetical technological advances on the patient doses required to maintain a given image quality in mammography. The assumed advances include: improvement in the power loading limits of the tube focal spot, increased absorption efficiency for a given detector resolution, increases in detector system gain, and changes in the exposure time limitations that result from patient motion. The optimization permits system geometry, kVp of the examination, filtration, detector resolution, focal spot size, and grid characteristics to vary simultaneously and self-consistently subject to image quality as well as technological constraints. The effects of technological innovations were measured by systematically varying the technological constraints to reflect hypothetical improvements and comparing the resulting minimized doses, required to maintain constant image quality, to a baseline optimized system derived from a set of baseline technological capabilities.     

X射线辐照下材料电子发射特性的模拟

稳态 X 射线管是一种重要的 X 射线辐照模拟装置,在辐照效应等研究领域有重要应用。采用蒙特卡罗模拟方法计算了 50 kV,150 kV 和 225 kV 管电压下的 X 射线能谱,并对 X 射线辐照下电子发射进行了模拟;研究了准直孔直径分别为 2 mm,4 mm 和 6 mm 条件下 X 射线的焦斑分布和电子发射弥散情况,以及不同能谱的 X 射线轰击到聚乙烯、聚酰亚胺、Si、SiO₂、Cu、Ta 和 W等样品上产生的电子发射能谱和电流强度等特性,为 X 射线辐照下材料电子发射特性的实验研究和设计提供一定的理论基础和指导。     

Electron flow in the conventional X-ray tube

The electron-flow pattern in a conventional X-ray tube is analyzed with a ray-tracing computer program. It is shown that the emission is temperature-limited (TL) in a forward-facing sector, and space-charge-limited (SCL) in sectors on each side. The angle of the TL sector varies directly with the anode voltage and inversely with the filament temperature, generally in the range 90°-160°. TheAlines of the focal spot are shown to be direct images of points near the 2 and 4 o'clock positions on the cathode, while theBlines are inverted images of points near 1 and 5 o'clock.     

关于检测抛物面反射镜质量的技术研究

为了对小尺寸抛物面反射镜进行质量检测, 采用平行光聚焦的方法测量焦距, 旋转被测反射镜的方法测量偏心角, 再结合图像处理的方法测量弥散斑大小, 并提出了一种减小测量误差的方法; 对这些测量方法进行了理论分析和实验验证, 得到了待测反射镜的焦距、偏心角和弥散斑大小。结果表明, 焦距的相对误差在0.1%以内, 偏心角误差在7%以内, 弥散斑大小小于0.2mm, 测量结果可靠。该方案设计为其它小口径的非球面的检测提供了很好的思路, 并且为减小测量误差、提高测量精度提供了很好的研究方法。     

Image restoration in computed tomography: estimation of the spatially variant point spread function

An indirect method for determining the point-spread-function (PSF) in computed tomography (CT) is described. Unlike experimental techniques in which a resolution phantom is scanned to obtain the system PSF, the approach estimates the parameters of a model which describes the two-dimensional X-ray beam profile at each point as a convolution of the appropriately scaled focal spot intensity and detector sensitivity distributions. The model was validated by experimental measurement of the focal spot intensity distribution. Using known X-ray beam profiles, the PSF of a CT scanner can be derived by simulating the data collection process and applying conventional image reconstruction techniques. Visual comparison of directly measured and computed PSFs reveals an asymmetry resulting from misregistration of the phantom wires and the image grid.     

基于四象限探测器的光纤焦比退化的测量方法

为开展提高光纤焦比退化测量精度方法的研究,提出了一种基于四象限探测器的光纤焦比退化的测量方法。该方法是光纤的出射光斑打到四象限探测器上,通过偏转镜扫描四象限探测器靶面,获得探测器上的光斑位置灵敏度,间接获得出射光斑实际尺寸,进而得出光纤的焦比退化。并对光斑位置灵敏度与光斑半径的关系进行了分析,同时探究了四象限探测器的沟道宽度对光纤焦比退化的影响。