Energy and angular dependence of x-ray absorption and its effect on radiographic response in screen--film systems.

The relationship between the film density and the x-ray energy absorbed in the screens, and the effect of the components of a screen--film system on x-ray absorption in the screen phosphor has been studied. It is concluded that, to a good approximation, the total absorbed x-ray energy can be calculated ignoring components other than the phosphor, and that the absorbed energy is related to the film density through the characteristic curve of the film. This simple relationship provides a basis for the theoretical prediction of the radiographic performance of an imaging system. Analytical expressions have been derived for the energy absorbed in model screens containing one or two high-atomic-number elements. For incident energies above the K-edge of the high-Z elements, the contribution of the K x-rays to energy absorption was included by use of a K-reabsorption factor. This factor was determined for eight screen pairs as a function of incident photon energy and incident angle.