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

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(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