Fundamental Studies for the High Intensity Flash X-ray generators for Biomedical Radiography

介绍了用于生物医学照相的高强度闪光X射线发生器的基础研究。单次闪光X射线发生器如下：(A)用于进行软X射线照相的高强度类型(小于100千伏)；(B)用于获取人体深处组织的X光照片的低阻抗高强度类型(小于120千伏)；以及(C)便携式(小于200千伏)。每个发生器都具有控制X射线强度、能谱分布和有效焦斑大小的功能，主要由高压发生器、脉冲聚光器、气隙系统、涡轮分子泵和场发射闪光X射线管组成。两种类型的三脉冲X射线发生器由高压产生单元、分压单元、三个高压产生单元、三个用于便携式产生的高压脉冲器和一个多路并联脉冲开关…组成更多的系统，一个有三个端子的大功率气体二极管，一个涡轮分子泵，和三个带有冷阴极的远程X射线管。对于单管发生器，脉冲发生器通过分压单元将脉冲器充电到相同或不同的电压，并使用SF_6通过大功率气体二极管连接到X射线管。对于三管发生器，由于三个脉冲器直接连接到管上，而没有二极管，因此可以同时获得三个X射线输出。单管型和三管型的最小时间间隔分别约为100US和3US。X射线强度与充电电压的3次方或4次方成正比。脉冲宽度小于300 ns，随着充电电压的增加和插入在X射线窗口外的金属滤光片厚度的增加，X射线质量(平均谱分布)变得困难。通过减小阳极角、减小阴极直径、减小阴阳极间距和插入金属滤光片，可以减小有效焦斑尺寸。高速X射线照相系统由两种延迟开关组成：(A)直接开关和(B)激光开关、延迟脉冲发生器、CR系统和FX发生器。当射线照相对象触发延迟开关时，产生一个短电脉冲，并将其传输到延迟脉冲发生器。当延迟的X射线脉冲传输到高速脉冲开关系统时，产生了准确的延迟X射线脉冲。接下来，当射线照相对象在最佳射线照相条件下被照射到受控X射线时，穿透的X射线产生数字图像。由于两种延迟开关的时间分辨率都小于20 ns，X射线产生的总时间分辨率小于1微米S。通过控制射线条件，可以进行各种高速生物医学照相，如频闪照相、连续延迟照相、能量减影照相和连续三维分析。较少

Fundamental studies for the high intensity flash x-ray generators for biomedical radiography are described. The single flash x-ray generators are as follows: (a) a high intensity type (less than 100kV) for performing the soft radiography, (b) a low-impedance and high intensity type (less than 120kV) for obtaining radiographs of tissues deep inside of the human body, and (c) a portable type (less than 200kV). Each generators had the control functions for the x-ray intensity, the spectrum distribution, and the effective focal spot size, and mainly consisted of the following essential components: a high voltage generator, a pulse condenser, a gas gap system, a turbo molecular pump, and a flash x-ray tube using field emission.Two types of the triple-pulsed x-ray generators consisted of the following components: a high-voltage generating unit, a voltage divider unit, three high-voltage generating unit, three high-voltage pulsers used for a portable generator, a tiple parallel impulse switch … More ing system, a high-power gas diode having three terminals, a turbo molecular pump, and three remote x-ray tubes having cold cathode. For the single-tube generator, the pulsers were charged to the same or different voltages by using a voltage divider unit and were connected to the x-ray tube through a high-power gas diode using SF_6. For the triple-tube generator,since three pulsers were connected directly to the tubes without a diode, three x-ray outputs could be obtained simultaneously. The minimum time intervals for the single-tube and the triple-tube types were about 100 and 3us, respectively. The x-ray intensities increased in proportion to the third or fourth power of the charging voltage. The pulse width was less than 300ns, and the x-ray quality (average spectrum distribution) became hard according to increases in the charging voltage and increases in the thickness of metal filters inserted outside of the x-ray window. The effective focal spot size could be reduced by decreasing the anode angle, decreasing the cathode diameter, decreasing the anode-cathode space, and inserting the metal filters.The high-speed radiographic system consisted of the following components: two types of delay switches,i. e. (a) direct switching and (b) laser switching, a delayed pulse generator, a CR system,and an FX generator. When the radiographic object triggered the delay switch, a short electric pulse was produced and was transmitted to the delayed pulse generator. An accurate delayed x-ray pulse was produced when the delayed pulse was transmitted to the high-speed impulse switching system. Next, when the radiographic object was exposed to the controlled x-rays under the optimum radiographic conditions, the permeating x-rays produced the digital image. Since the time resolutions for two types of delay switches were less than 20ns, the total time resolution for the x-ray production was less than 1<micrn>s. Various kinds of high speed biomedical radiography, e. g., the stroboscopic radiographgs, the continuous delayed radiographs the energy subtraction radiographs, and the continuous three-dimensional analysis could be performed by controlling the radiographic conditions. Less