A method for determining a time for acquiring contrast-enhanced images from a CT scanner of a subject into whom a contrast medium has been injected, the method including: identifying a region of interest in an initial CT image of the body of a subject; defining an attenuation data segment corresponding to the region of interest by reprojecting the region of interest in the initial image; receiving attenuation data within the segment from a subsequent scan of the patient; and independently processing the attenuation data received within the segment to estimate an optimal time for performing a diagnostic scan of the body, without reconstructing all or a portion of the CT image.