We investigated the effects of imaging and display conditions on the detectability of low‐contrast objects in digital subtraction angiographic (DSA) images. The test images were produced by superimposition of low‐contrast objects on a uniform noisy background obtained with a DSA system. We employed 18‐alternative forced‐choice (18‐AFC) experiments and predictions based on statistical decision theory to study the dependence of the threshold contrasts of the test objects on the object size, incident x‐ray exposure, display window width, and display medium. The results indicated that the threshold contrast decreased with increasing object size, and that the detectability of an object of a given size increased with increasing incident x‐ray exposure and decreasing width of the display window. We found that the signal‐to‐noise ratio (SNR) obtained from theperceivedstatistical decision theory model, which includes the observer's internal noise, can accurately predict the detectability of low‐contrast objects in DSA images. The threshold SNR corresponding to 50% correct detection in the 18‐AFC experiments had a constant value of 3.8, in agreement with results reported previously for screen–film systems. The theoretical model will be useful for prediction of the performance of a DSA system based on its physical characteristics, and for evaluation of the tradeoff between patient exposure and diagnostic accuracy for a given DSA unit.