Accurate measurement of characteristic curves of II-TV digital systems by use of aluminum stepwedge technique.

In order to determine accurately the relative x-ray intensities transmitted through the different steps of an aluminum stepwedge and incident on an image intensifier (II)-TV digital system, we used a 100-mm camera which was attached to the II output. The characteristic curves of an II-TV digital system, which relate the output pixel value to the input relative x-ray intensity, were determined at 65 and 90 kV by the use of the aluminum attenuation curves measured at the two energies. We found that the two curves agreed within the experimental errors; this result indicates that the characteristic curve does not depend on the x-ray beam quality used. Furthermore, for accurate measurement of the characteristic curve, it is necessary to collimate the x-ray beams to a narrow width, approximately 0.6 X 10 cm, so that the effect of veiling glare from the thinner to the thicker parts of the stepwedge is eliminated.