A strict determination of scan timing is needed for dynamic multi-phase scanning and 3D-CT angiography (3D-CTA) by multi-detector row CT (MDCT). In the present study, contrast media arrival time (T_<AR>) was measured in the abdominal aorta at the bifurcation of the celiac artery for confirmation of circulatory differences in patients. In addition, we analyzed the process of formation of the time-density curve (TDC) and examined factors that affect the time to peak aortic enhancement (T_<PA>). Mean T_<AR> was 15.57±3.75 s. TDCs were plotted for each duration of injection. The rising portions of TDCs were superimposed on one another. TDCs with longer injection durations were piled up upon one another. Rise angle was approximately constant in response to each flow rate. Rise time (T_R) showed a good correlation with injection duration (T_<ID>). T_R was 1.01T_<ID> (R^2=0.994) in the phantom study and 0.94T_<ID>-0.60 (R^2=0.988) in the clinical study. In conclusion, for the selection of optimal scan timing it is useful to determine T_R at a given point and to determine the time from T_<AR>.
