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Brunsing et al. Hepatoma Res 2020;6:59 I http://dx.doi.org/10.20517/2394-5079.2020.50 Page 7 of 16
[50]
comparing NC-AMRI to US for HCC surveillance , but similar studies will be needed in non-Asian
populations before this approach can be widely recommended. Ultimately, the performance and clinical
utility of this approach will be determined mainly by DWI, which provides higher lesion conspicuity than
the other sequences, thus optimizing this sequence will be essential.

DYNAMIC AMRI
Imaging
Dynamic contrast-enhanced AMRI (Dynamic-AMRI), one of two AMRI strategies that utilize GBCAs,
acquires dynamic contrast enhanced images using T1-weighted images with fat suppression following
administration of an extracellular contrast agent. The dynamic component refers to images acquired at
predetermined and successive phases to detect and characterize HCCs based on the vascular alterations of
hepatocarcinogenesis. These phases include the following:

Pre-contrast imaging
The pre-contrast images provide a baseline from which all post-contrast images are assessed for contrast
enhancement. Pre-contrast images also allow detection of intrinsic T1 hyperintense observations, and for
confirming that any hyperintensity on post contrast images represents true contrast enhancement. With
modern MRI systems, it is possible to collect IP/OOP images simultaneously with the pre-contrast T1-
weighted images (i.e., no additional acquisition is needed). If such images are acquired, they may permit
assessment of relative fat or iron content relative to liver, as described for NC-AMRI.

Arterial phase imaging
Arterial phase (AP) is the time point after contrast injection at which tumor enhancement via arterial
inflow is expected to be maximal. This usually occurs when portal veins are moderately to fully enhanced
but the hepatic veins are not yet enhanced by antegrade flow. Appropriate timing of the AP is essential and
[51]
can be achieved with reasonable consistency using current bolus-tracking technology or other methods .
This sequence is used to assess arterial phase hyperenhancement (APHE), meaning enhancement greater
than background liver parenchyma in the AP. Thought to reflect the arterialization of HCC during
hepatocarcinogenesis, APHE is one of the defining imaging features of HCC and is required for imaging-
[9]
based diagnosis in high-risk patients, per Liver Imaging Reporting and Data System (LI-RADS) .

Portal venous phase imaging
Portal venous phase (PVP) is the time point after contrast injection at which the portal veins are fully
[9]
enhanced and the hepatic veins are enhanced by antegrade flow , occurring approximately 40 sec after AP
when the liver is expected to be at its peak enhancement. Portal and hepatic vein anatomy and patency are
assessed on this phase, including the presence of tumor in vein, which indicates macrovascular invasion.
Washout appearance and enhancing capsule appearance, other defining imaging features of HCC, may be
detected if present.

Delayed phase imaging
Delayed phase (DP) images are usually acquired 2-5 min after injection. Washout appearance and
enhancing capsule appearance are usually most conspicuous on the DP images.

Reporting
Reporting of dynamic-AMRI is based on the major features of HCC as defined by LI-RADS [Figure 4]. An
exam detecting a mass, meeting criteria for HCC (i.e., LR-5), should be reported as a positive result. The
reporting and follow-up recommendations for exams showing indeterminate lesions (i.e., LR-3 or LR-4)
based on Dynamic-AMRI has not been standardized.