A method is described for determination of an initialization time point of imaging of a region of interest of an object to be examined. A slice of the object is selected for bolus-tracking images in which the flow of a fluid flowing toward the region of interest is observable. A plurality of bolus-tracking images of the slice is taken. Time-density curves are determined based upon intensity values assigned to the individual image points acquired in the plurality of bolus-tracking images for the selected slice. Individual image points are divided into groups according to similarity of time-density curves assigned to the individual image points. Finally, the time at which an intensity value assigned to one of the groups exceeds a threshold value is determined. Also described are a method for carrying out the imaging of a region of interest； an initialization time point determination device； and a computed tomography system.
