2. Two lesions are seen within the lateral segment of the left lobe of the liver (yellow arrows). They appear mildly hyperintense on T2 images and mildly hypointense on precontrast T1 images. On arterial-phase and portal-venous-phase images, the lesions demonstrate rim enhancement; they appear hypointense on 5-minute and 20-minute delayed hepatobiliary-phase imaging. Thin-slab MinIP of the 20-minute delayed images showed no other lesions.
This is a straightforward example of the detection and characterization of metastatic disease in the liver. Metastases such as those from colorectal cancer are typically hyperintense on T2 imaging and show rim enhancement on contrast-enhanced T1 imaging. As metastatic lesions contain no functioning hepatocytes, they appear hypointense on delayed hepatobiliary-phase imaging. It is important to review the precontrast T1 images, which often depict these lesions well. Diffusion-weighted imaging showed restricted diffusion within these lesions (not shown).

3. CT scan (not shown) demonstrated the presence of 2 large metastatic lesions within the right lobe of the liver. The MRI study is somewhat limited by the patient’s large body habitus (150 kg). Despite this limitation, numerous lesions are detected on multiple different sequences with much greater conspicuity than that seen on the CT scan. Lesions demonstrate restricted diffusion and are mildly hyperintense on T2 imaging. Arterial-phase and portal-venous-phase T1 imaging shows rim enhancement and central hypointensity. Delayed hepatobiliary-phase imaging at 20 minutes provides excellent visualization of these lesions, while MinIP images depict innumerable additional rounded metastatic lesions with much greater conspicuity (white arrows).
The exact role of hepatobiliary gadolinium-based contrast agents for the detection and characterization of metastatic disease in the liver is not fully defined. However, early evidence suggests that a greater disease burden can be detected using MRI compared with CT, and perhaps to a greater degree using hepatobiliary contrast agents. The use of delayed 20-minute hepatobiliary-phase imaging with high space resolution and optimized flip angle (40°) in conjunction with thin-slab MinIP images is a useful means for screening for liver lesions. However, all available sequences, including diffusion-weighted imaging, T2, and T1 imaging (both precontrast and postcontrast) should be used for comprehensive detection and characterization of these lesions.

4. Contrast-enhanced CT shows a 1
Contrast-enhanced CT shows a 1.6-cm lesion within segment 5 of the liver. On T2 imaging it appears mildly hyperintense (yellow arrow). It is heterogeneous on T1 imaging with central hyperintensity and peripheral hypointensity relative to liver (red arrow). In addition, a second smaller lesion (not seen on CT) that is hypointense on precontrast T1 imaging is also noted. This lesion is hyperintense on T2 imaging (yellow arrow).
Contrast-enhanced T1 images in the arterial phase show brisk enhancement of the larger lesion. Portal-venous-phase imaging shows hypointensity within the 2 lesions and identifies a third hypointense lesion (white arrow). Delayed 20-minute hepatobiliary-phase imaging shows 1 additional lesion (blue arrowhead) for a total of 4 lesions on this slice, one of which is very small and best appreciated on thin-slab MinIP images.
This example demonstrates MRI’s ability to both detect and characterize metastatic disease. Greater disease burden was observed on MRI than on CT. The clinical consequences of improved visualization of metastatic disease burden are uncertain, and prospective outcomes studies will be necessary to determine whether improved visualization of metastatic disease leads to improved outcomes. Intuitively, it very is difficult to argue that more accurate visualization and quantification of metastatic disease burden is anything but beneficial. However, current staging and treatment guidelines were established using CT as the imaging modality for detection of disease burden. Therefore, continued improvement in visualization of metastatic disease may require modification of staging and treatment guidelines.
This example also demonstrates the role of delayed hepatobiliary-phase imaging for detecting very small lesions in the liver, particularly on thin-slab MinIP images. Again, is essential for the interpreting physician to remember that delayed hepatobiliary-phase imaging is insufficient for diagnosis of metastatic disease. All sequences must be used for complete characterization of lesions.
Finally, the central hyperintensity in the larger lesion seen on precontrast T1-weighted imaging is suggestive of metastatic melanoma from the presence of melanin. This is not a constant feature of melanoma but is commonly seen and is consistent with the patient’s known diagnosis.

5. Two large lesions are seen within segments 7 and 8 of the liver
Two large lesions are seen within segments 7 and 8 of the liver. The larger lesion (segment 8) has a lobulated border. Both lesions appear moderately hyperintense on T2 imaging and hypointense on precontrast T1 imaging. Minimal rim enhancement is seen on the arterial-phase and portal-venous-phase images. Profound hypointensity relative to the adjacent liver parenchyma is seen on the 20-minute delayed hepatobiliary-phase images. The lesions exhibit restricted diffusion on diffusion-weighted imaging. Other lesions were identified on other slices (not shown).
This case shows typical MRI findings of metastatic disease within the liver. Delayed hepatobiliary-phase imaging is not necessary to either detect or characterize lesions of this size, although the best contrast between lesion and liver is seen on the delayed images. We have found that high-resolution delayed hepatobiliary-phase images provide accurate means of measuring the dimensions of metastatic lesions and therefore may be useful for follow-up studies where accurate size measurements are necessary. High contrast offered by delayed-phase imaging may be a useful means of volumetric measurements of these lesions as well, although further research is needed to demonstrate this.

6. Numerous large masses of varying size and appearance are seen throughout the liver. Overall these lesions appear moderately hyperintense on T2 imaging, demonstrate restricted diffusion, and are hypointense on precontrast T1 imaging. On arterial-phase imaging, brisk heterogeneous enhancement is noted, with persistent and progressive enhancement in the portal-venous phase. Ninety-minute delayed hepatobiliary-phase imaging shows hypointensity of these lesions relative to the adjacent liver, although there is some heterogeneous internal enhancement that is increased from precontrast T1-weighted imaging but still hypointense relative to liver. Improved conspicuity of these lesions is seen in comparison to the other contrast-enhanced images, although these lesions have similar conspicuity to the precontrast T1-weighted imaging.
Metastatic renal cell carcinoma often presents as “hypervascular” metastases, demonstrating avid enhancement in the arterial phase of the dynamic T1-weighted acquisition, unlike typical lesions (such as colorectal metastases) that show slow progressive rim enhancement. All imaging features are consistent with metastatic disease and the overall pattern is suggestive of hypervascular metastases such as RCC. In addition to RCC, typical hypervascular metastases include melanoma, neuroendocrine tumors (including carcinoid and pancreatic islet cell tumors), breast carcinoma, and thyroid carcinoma.
Delayed hepatobiliary-phase imaging is not necessary for this diagnosis. However, the fact that delayed hepatobiliary-phase imaging can be performed during free breathing (contrast enhancement is in a pseudosteady state, unlike bolus phase when contrast concentration changes rapidly), allowing acquisition with very high spatial resolution imaging and excellent SNR performance. This feature may be helpful to provide accurate depiction of both the number of lesions and more precise definition of their borders and size to evaluate treatment response on follow-up studies.