Definition:
In LI-RADS, the arterial phase refers to the hepatic arterial phase unless otherwise specified. The arterial phase is a post-contrast injection time range in which images have the following characteristics:
- Hepatic artery and branches are fully enhanced.
- Hepatic veins not yet enhanced by antegrade flow.
Comments:
- Arterial phase imaging is required for both CT and MRI.
- Hepatic arterial phase may be subclassified as early and late hepatic arterial phase.
- Early hepatic arterial phase: portal vein is not yet enhanced.
- Late hepatic arterial phase: portal vein is enhanced.
- Late hepatic arterial phase is strongly preferred for HCC diagnosis and staging, because the degree of enhancement in HCC usually is higher in the late than in the early hepatic arterial phase. Some HCCs may show hyper-enhancement only in the late hepatic arterial phase.
Potential pitfalls and challenges:
- At MRI, aorta may not be brightly enhanced.
- With short bolus durations, contrast material bolus may pass beyond aorta by time of image acquisition.