Definition:

Post-contrast phase acquired with extracellular agents after the portal venous phase and with the following characteristics:

• Portal and hepatic veins are enhanced but less than in portal venous phase.
• Liver parenchyma is enhanced but usually less than in portal venous phase.

Comments:

• Delayed phase is required for MRI and suggested for CT (it is required by OPTN for both CT and MRI).
• Delayed phase usually should be acquired at around 3-5 minutes.
• The term delayed phase applies to CT or MRI with extracellular agents and to MRI with extracellular agents with modest hepatocellular uptake (e.g., gadobenate).
• It does not apply to MRI with agents with strong hepatocellular uptake (e.g., gadoxetate disodium). With such agents:
• The term “transitional phase” or “late dynamic phase” is preferred for images acquired shortly after portal venous phase.
• The term “hepatobiliary phase” or “hepatocyte phase” is preferred for even more delayed images showing biliary excretion and peak enhancement of liver parenchyma.