[Usefulness of high energy radiation using copper filter on CR chest radiography]

The bone contrast on chest radiographs obtaind with computed radiography (CR, hereafter) is not decreased enough compaired with that for screen/film combination, even if we use a high tube voltage. This may be because the Exporsure Data Recognizer which can normalize the density and contrast of the chest images is performed. In order to increase the diagnostic accuracy for the lung disease,we propose to use a copper additional filter to decrease the bone contrast. Consequently, in order to have satisfied the bone contrast and the patient expousure dose, additional 0.3 mm copper filter and effective energy was 59.3 keV or more were required of the tube voltage of 140kV. Further, the effective energy of 140 kV tube voltage with a 0.7 mm copper, which is the maximum thickness of the additional filter within 50 m seconds in exporsure time, was 68 keV. Concluding these results, optimum range of additional copper filter is from 0.3 mm to 0.7 mm in chest high voltage radiography using CR. The bone contrast decreases sufficiently, if we use X-rays which have effective energy within this range. Our method is also useful to reduce patient dose.