The invention relates to an imaging system for generating a series of images of a subject. Fluid boli are generated at a first location of the subject, wherein each fluid bolus comprises a sequence of sub-boli and wherein images of the series of images are acquired at a second location of the subject, after the fluid boli have been flowed to the second location. A sub-bolus length is determined based on at least one image of the already acquired images of the series of images, wherein a further fluid bolus comprising a sequence of sub-boli is generated at the first location, wherein at least one of the sub-boli has the determined sub-bolus length, and wherein a further image of the series of images is acquired at the second location of the subject, after the further fluid bolus has been flowed from the first location to the second location.