Rare-earth and calcium tungstate intensifying screens, a comparative study of relative speed, radiation doses and resolving power.

Abstract

Using calcium tungstate (CaWO4) and rare-earth intensitying screens, their relative speeds were compared in exposures of a pelvis phantom, and radiation doses were measured at several kilovoltages. Using a slit pattern, the resolving power was assessed by a modified contrast-frequency response and by direct viewing of the radiographs. In the comparison of the rare-earth and CaWO4 screens the following differences were found: (1) A great reduction in the radiation dose can be achieved by the use of the fast screen types, yet at the cost of some loss of resolving power; (2) the film contrast can be improved by a reduction in the kilovoltage without an increase in the radiation dose; (3) the short exposure times and the characteristic course of the dose curve necessitate an adjustment of the phototimer or a change of the control unit; and (4) with the slower screen type tested, the resolving power can be improved without increasing the radiation dose.