A diagnostic imaging system includes an x-ray source (16), which is rotated around an examination region (20). A subject, disposed on a couch (30), is translated longitudinally through the examination region (20). The x-ray source (16) is pulsed at selected angular location(s), e.g. one or both of 6 and 12 o'clock, to transmit x rays through the subject as it is being translated through the examination region (20). The transmitted radiation is being detected by a radiation detector (22) and is reconstructed by an image processor (52) into a two-dimensional projection pilot scan image. A subject contour is calculated and is used along with the radiation attenuation data by a dose calculator (60) to determine the minimum radiation dose required to produce a constant quality image.