Diagnostic X-ray Spectra Including Scatter and Scatter Rejection Methods

Abstract

  The scattered radiation is generated by an object in medical X-ray diagnosis. It degrades the quality of an X-ray image. For a quantitative estimation of this effect, it is necessary to determine X-ray spectra including scatter as fundamental data. We have carried out the Monte Carlo simulation for a 70kV tube voltage, an object of 20-cm acrylic resin and fields of 2, 4, 8, 15 and 30 cmφ. The maximum incident angle was varied as 5°, 13°, 20° and 90° to investigate the grid effect. The object-detector distance was varied from 1 to 60 cm to investigate the Groedel effect. The results showed that scatter fractions decreased noticeably by the Groedel effect for the 2to 8-cmφ fields, but they did not decrease prominently for the 15- and 30-cmφ fields. The effect of the higher grid ratio appeared for the smaller angle of the collimator. For the 15- and 30-cmφ fields we have obtained angular dependence relations of scatter spectra, mean energies, and exposures. As a result , the larger scatter angle yielded the lower mean energy and the lower exposure. These phenomena were caused by the Compton effect. The results obtained by experiments using a plannar Ge detector, conic Pb collimators and beam stoppers coincided with the above results.