Study of measuring system of x-ray spectrum for reduction of patient dose at medical x-ray diagnosis.

(1)用CdTe和CdZnTE探测器测量的诊断x射线光谱的校正我们尝试使用最近开发的低成本CdTe和CdZnTE探测器进行诊断x射线光谱的直接测量。由于探测到的光谱与真实光子光谱不一致，采用了剥离法进行校正。CdTe探测器得到的结果不如Ge探测器精确，而CdZnTe探测器得到的结果与之一致。我们分析了通过0.03mmMo或0.025 mmmrh滤波器和使用50 μ m针孔准直器系统在28kV和50ma下测量的乳房x射线光谱。CdZnTe探测器所获得的结果与美国放射卫生局（BRH）公布的Ge探测器所测量的x射线光谱形状一致。(2)散射x射线光谱的测量：采用锥形准直器和铅束阻挡器，分别测量了通过物体和物体的主散射和散射x射线光子光谱，并根据辐照场面积的变化分别测量了多个反散射网格（以下简称网格）。根据这些结果，可以估计栅格去除散射x射线的效果。(3)最佳放射线因素分析我们提出了一种利用心理物理分析确定胸片最佳管电压的新方法。利用屏幕的x射线光子光谱和灵敏度光谱，得到了肺场最高密度和纵隔最低密度正好覆盖最佳密度范围的最佳管电压。(4)屏膜系统的图像质量（MTF，粒度）分析。我们得到了速率增益屏膜系统调制传递函数（MTF）的管电压依赖性。在空间频率小于3mm^<-1>时，前后两侧的mtf值随管电压的增大而减小。我们表明，为了解释这一现象，不仅要考虑K-x射线，还要考虑屏幕中产生的相干和非相干散射x射线光子。在2.0mm^<-1>频率处的心理物理维纳谱值可代替心理物理均方根粒度用于影像学斑驳的评价。获得心理物理维纳谱所需的时间比获得心理物理均方根粒度所需的时间更少。少

(1) Correction of diagnostic x-ray spectra measured with CdTe and CdZnTE detectorsWe have attempted to perform the direct measurement of diagnostic x-ray spectra using low-cost CdTe and CdZnTe detectors, which have been developed recently. Since detected spectra did not coincide with the true photon spectra, a correction by stripping procedure was applied. The results obtained with CdTe detector were less exact than those with a Ge detector, but those with CdZnTe detector agreed with it.We analyzed mammographic x-ray spectra penetrated through 0.03mmMo or 0.025mmRh filter and objects measured using 50-mu m pinhole colimator system at 28kV and 50mAs. The obtainable results with CdZnTe detector agree with mammographic x-ray spectral shape measured using Ge detector published by Bureau of Radiological Health (BRH) in U.S.A..(2) Measurement of scattered x-ray spectraBy using a conical collimator and a lead beam stopper, primary and scattered x-ray photon spectra through an object and an an … More ti-scatter grid (abbreviated as grid, hereafter) were measured separately, varying the irradiation field area. From these results, the effects of grids for removing scattered x-rays were able to estimate.(3) Analysis of optimum radiographic factorsWe proposed a new method for determining the optimum tube voltage of a chest radiograph using psychophysical analysis. An optimum tube voltage, by which the highest density in the lung-field and the lowest density in the mediastin just covered the optimum density range, was obtained using x-ray photon spectrum and sensitivity spectrum of the screen.(4) Analysis of image quality (MTF,granularity) of a screen-film systemWe have obtained the tube voltage dependence of the modulation transfer function (MTF) of a rate-erath screen-film system. The values of the MTFs for the front and back sides at spatial frequencies of less than 3mm^<-1> decreased with the tube voltage. We showed that to explain this phenomenon, not only K-x rays but coherent and incoherent scattered x-ray photons yielded in the screens had to be taken into consideration.The value of psychophysical Wiener spectrum at a frequency of 2.0mm^<-1> can be used for the evaluation of radiographic mottle instead of the psychophysical RMS granularity. The time to obtain the psychophysical Wiener spectrum can be reduced more than it to obtain the psychophysical RMS granularity. Less