Table 3. Diagnosis of Hepatocellular Carcinoma.

Imaging Modality	Role in HCC Diagnosis	Assessment of “Washout” Appearance
		Timing	Degree	Preconditions
Multiphasic contrast-enhanced CT	First- and second-line imaging study	Portal venous phase or delayed phase	All	No targetoid appearance on contrast-enhanced images
Multiphasic MRI using extracellular contrast agent	First- and second-line imaging study	Portal venous phase or delayed phase	All	Neither marked T2 hyperintensity nor targetoid appearances on diffusion-weighted images or contrast-enhanced images
Multiphasic MRI using hepatocyte-specific contrast agent	First- and second-line imaging study	Portal venous phase or delayed phase or hepatobiliary phase	All
Contrast-enhanced US using blood-pool contrast agent	Second-line imaging study	Late vascular phase (≥ 60 seconds)	Mild	No rim or peripheral globular enhancement on arterial phase; no early washout (<60 seconds); no punch-out pattern washout within 120 seconds
Contrast-enhanced US using Kupffer cell-specific contrast agent	Second-line imaging study	Late vascular phase (≥ 60 seconds) or Kupffer phase	Mild (if late vascular phase)

1. Imaging diagnosis: in high-risk patients (chronic hepatitis B, chronic hepatitis C, and cirrhosis), a liver nodule ≥ 1 cm detected by surveillance test can be diagnosed as an HCC if it shows radiological hallmarks of HCC. When an imaging diagnosis of HCC cannot be made with confidence on a first-line imaging study, an additional second-line imaging study can be applied. (1) Major imaging features are defined as arterial phase hyperenhancement and washout appearance on portal venous, delayed, or hepatobiliary phases on dynamic contrast-enhanced CT or dynamic contrast-enhanced MRI (extracellular contrast agent or hepatocyte-specific contrast agent). These criteria should be applied only to a lesion that does not show either marked T2 hyperintensity or targetoid appearances on diffusion-weighted images or contrast-enhanced images. (2) When contrast-enhanced ultrasound (blood-pool contrast agent or Kupffer cell-specific contrast agent) is performed as a second-line imaging study, arterial phase hyperenhancement and mild and late (≥ 60 seconds) washout are radiological hallmarks of HCC. These criteria should be applied only to a lesion that does not show rim or peripheral globular enhancement on the arterial phase.

2. Pathologic diagnosis: if the patient does not have any risk factor for HCC or the nodule does not show typical radiological hallmarks of HCC, a biopsy can be performed for confirmative diagnosis.

HCC = hepatocellular carcinoma, CT = computed tomography, MRI = magnetic resonance imaging, US = ultrasonography.