Several different test protocols were used to measure the sensitometric response, the modulation transfer function (MTF), the veiling glare and the Wiener spectrum of two x-ray image intensifier (II) tubes. These data provided the means to calculate summary measures of imaging performance, i.e., the noise equivalent quanta, NEQ, or the detective quantum efficiency, DQE, as a function of spatial frequency. Results are presented to show the differences between an older versus a newer generation II tube, i.e., DQE equals 0.3 +/- 0.03 and 0.6 +/- 0.06 at 0.5 lp/mm, respectively. The eventual goal of this work is to achieve some consensus on methodology for these measurements and to validate the use of algorithmic observers in quantitating imaging performance in the clinical environment.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.