One of the most successful applications of digital radiography systems thusfar has been the imaging of vasculature opacified by intravenously administered contrast agents using temporal subtraction. Because the contrast in the arterial structures of interest is small as a consequence of the dilution due to the intravenous injection, it is essential that such imaging systems have high contrast sensitivity. This paper discusses means to assess the contrast sensitivity of imaging systems using iodinated phantoms and temporal subtraction. A difference image is shown demonstrating a 1 mm vessel containing 0.5 mg/cm2 of iodine, i.e. less than 1% radiographic contrast. Initial CDD results are presented. Dependence of CDD analysis on video signal level is demonstrated. The effects of x-ray scatter and image intensifier veiling glare are predicted and measured experimentally. Contrast levels in two digital fluorographic clinical procedures are estimated.