The present invention relates to a computed tomography system (10) and a corresponding method which enable tracking of a contrast material bolus and which involve a reduced radiation dose. The proposed computed tomography system (10) comprises an acquisition unit including an X ray source (18) and an X ray detector (30) for acquiring projection data sets (42 44 46) a reconstruction unit (41) for reconstructing a planning image (48) from a first projection data set (42) an identification unit (52) for identifying a region of interest (40) in the planning image (48) a selection unit (54) for selecting a projection angle (60) through the region of interest (40) a calculator (62) for calculating a target projection value (64) for a projection of said region of interest (40) with the selected projection angle (60) a control unit (32) for controlling said acquisition unit to acquire a second reduced projection data set (44) including projection data from projections of said region of interest (40) with the selected projection angle (60) and a comparator (68) for comparing projection values of the second projection data set (44) with the target projection value (64) wherein the control unit (32) is adapted to control the acquisition unit to initiate the acquisition of a third projection data set (46) based on the comparison result (70) and to reconstruct a diagnostic image (50) from the third projection data set (46).
