CT examination of the liver with hypodense shadows is a more general descriptive diagnosis and does not represent a specific disease, manifesting as a different density from the liver parenchyma, suggesting the occurrence of a lesion, which requires a specific enhancement examination to confirm the diagnosis. Enhancement scans are CT scans performed after contrast is injected from a vein into a blood vessel to detect lesions not found on plain scan and to help determine the nature of the lesion. Since contrast is injected intravenously, staging scans are performed in the arterial, portal, venous and equilibrium phases depending on where the contrast is located. The following are the times of staging scans after contrast injection: 1) arterial phase: 30-35 seconds for scanning; 2) portal phase: 60-75 seconds for scanning; 3) venous phase: 100-120 seconds for scanning; 4) equilibrium phase: 2-5 minutes for scanning.