A system for imaging a subject with a contrast agent is provided. The system includes an X-ray source, an X-ray detector, and a controller. The X-ray source is operative to transmit X-rays through the subject. The X-ray detector is operative to receive the X-rays after having passed through the subject. The controller is in electronic communication with the X-ray source and the X-ray detector and operative to: generate a target contrast level based at least in part on a contrast adjustment factor； determine when a level of the contrast agent in a first plurality of images of the subject acquired via the X-ray source and the X-ray detector reaches the target contrast level； and acquire a second plurality of images of the subject via the X-ray source and the X-ray detector after the level of the contrast agent has reached the target contrast level.
