CT triple-phase liver (protocol)

The triple-phase liver CT protocol is a useful examination in the assessment of focal liver lesions, hypervascular liver metastases and endocrine tumors.

It involves a dedicated late arterial phase, portal venous phase and delayed phase acquisition. Not to be confused with a four-phase which involves the addition of a non-contrast series.

NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on CT hardware and software, radiologists' and referrers' preference, institutional protocols, patient factors (e.g. allergy) and time constraints. 

Terminology

For some departments and/or radiologists, a triple-phase may instead be used to refer to an initial non-contrast phase followed by a late arterial and portal venous phases. 

Indications

Suspected liver lesions such as hepatocellular carcinoma, focal nodular hyperplasia, adenoma, and hemangioma.

Purpose

Differentiating liver lesions on non-contrast studies is difficult due to the homogeneity of the liver tissue on CT however this exam helps solve that problem. The portal vein accounts for~75% of the liver's blood supply with the remainder from the hepatic artery, so a later arterial phase is required for the best enhancement of the parenchyma.

To help characterize the vascularity of hypervascular liver lesions. This examination is most typically utilized to differential a hepatocellular carcinoma from other lesions.

A hepatocellular carcinoma, a highly vascular primary lesion, will demonstrate hyperenhancement in the arterial phase and venous or delayed phase washout whilst a hemangioma should match the blood pool in each phase (same as the aorta in arterial etc).

Technique

• patient position

  • supine with their arms above their head

• scout 

  • diaphragm to iliac crests

• scan extent 

  • diaphragm to iliac crests

    • some departments will perform a full abdomen and pelvis in the portal venous phase

• scan direction

  • craniocaudal

• contrast injection considerations (bolus tracking)

  • monitoring slice (region of interest)

    • level of the diaphragmatic hiatus or first lumbar vertebra at the aorta

• threshold

  • 150 HU

• volume

  • 100-120 mL of non-ionic contrast at 3 to 5 mL/s (a higher flow rate will equal great enhancement ²) 

• scan delay ¹

  • late arterial phase

    • ​15-30 seconds post bolus trigger (35-45 s after injection)

  • portal venous phase

    • ​60-75 seconds post-injection (independent of arterial timing)

  • delayed phase

    • 2-5 minutes

• ​respiration phase

  • ​inspiration, breath-hold

Practical points

• an understanding of how each phase should appear is important ¹

  • late arterial phase

    • portal vein enhanced, no hepatic vein enhancement

      • hepatocellular carcinoma may only show enhancement in the late arterial phase so this is very important

  • portal venous phase

    • portal veins, hepatic veins (via antegrade flow) enhanced

  • delayed phase

    • portal and hepatic veins slightly enhanced by a lot less than on the portal venous phase

• slice thickness less than or equal to 5 mm

• if the patient has received an injection of drug-eluting beads such as Lipiodol a four-phase liver protocol should be considered