CT examination
All patients underwent abdominal CE-CT examination using two 64-slice spiral CT scanners (Siemens, Forchheim, Germany or Philips Medical Systems, Cleveland, OH, USA). The parameters of CT imaging were set as follows: for Siemens, 120 kV tube voltage, 150–250 mA tube current, 0.5 s tube rotation time, 64 × 0.6 mm detector collimation, 350 × 350 mm field of view, 5 mm section thickness and 1-1.25 mm reconstruction interval; for Philips, 120 kV tube voltage, 200–250 mA tube current, 0.5 s tube rotation time, 64 × 0.625 mm detector collimation, 350 × 350 mm field of view, 5 mm section thickness and 1-1.5 mm reconstruction interval. Subsequently, arterial phase (delay 30–40 s) and the portal venous phase (delay 60–70 s) images were obtained after 2 mL/kg of iodinated contrast medium was injected intravenously at a rate of 3 ml/s.