Imaging Choice for Liver Mass Evaluation
Both MRI with IV contrast and multiphase CT with IV contrast are considered equivalent first-line imaging modalities for evaluating liver masses >1 cm, though MRI demonstrates superior lesion characterization and detection sensitivity, particularly for smaller lesions. 1
Clinical Context Determines Optimal Modality
The choice between MRI and CT depends critically on the clinical scenario:
For Normal Liver Without Known Malignancy (Lesions >1 cm)
- Multiphase CT with IV contrast and MRI with IV contrast are equivalent alternatives for characterizing indeterminate liver lesions 1
- Either modality alone provides sufficient diagnostic information to guide management 1
- The American College of Radiology designates these as "usually appropriate" with equal appropriateness ratings 1
For Patients With Known Extrahepatic Malignancy
- MRI with IV contrast is preferred over CT for lesions of any size, though both remain appropriate 1
- MRI demonstrates superior sensitivity for detecting metastases, particularly lesions <1 cm 1
- For subcentimeter lesions specifically, MRI is the sole recommended modality 1, 2
For Chronic Liver Disease/Cirrhosis
- MRI with extracellular contrast agent is the preferred modality, with sensitivity of 83.1% and accuracy of 86.6% for hepatocellular carcinoma 2
- Both MRI and multiphase CT remain appropriate alternatives for lesions >1 cm 1
- MRI with hepatobiliary agents (gadoxetic acid) provides additional hepatocyte-specific information 1, 2
Technical Superiority of MRI
MRI provides superior lesion characterization compared to CT across multiple parameters:
- Better detection of arterial hypervascularization: 97.6% for MRI vs 81.5% for CT 2
- Superior capsule visualization: 85.5% for MRI vs 33.9% for CT 2
- Higher sensitivity for subcentimeter lesions: 60% sensitivity in chronic liver disease 1
- Enhanced tissue characterization through T1/T2 weighting, diffusion-weighted imaging, and hepatobiliary-specific contrast agents 3, 4
Practical Decision Algorithm
Step 1: Determine lesion size and clinical context
- Lesions <1 cm with known malignancy → MRI with IV contrast 1, 2
- Lesions >1 cm without malignancy → Either MRI or CT acceptable 1
- Lesions in cirrhotic liver → Prefer MRI, CT acceptable 1, 2
Step 2: Consider patient-specific factors
- Renal insufficiency → Limits both modalities but affects contrast choices 2
- Pacemakers/metallic implants → Contraindication to MRI, use CT 2
- Contrast allergies → Modality-specific considerations 2
- Local expertise and equipment availability 2
Step 3: Optimize technical parameters
- For CT: Multiphase acquisition (arterial, portal venous, delayed phases), 2.5-5 mm slice thickness, 3-5 mL/s contrast injection rate 1
- For MRI: Include T1/T2 sequences, in-phase/out-of-phase imaging, dynamic post-gadolinium imaging with arterial phase timing 3, 4
Critical Technical Requirements
Both modalities require proper technique to achieve diagnostic accuracy:
- Multiphase imaging is mandatory - single-phase studies are inadequate 1
- Arterial phase timing is critical for detecting hypervascular lesions and acute hepatitis 3
- Thin slice reconstruction (≤5 mm) improves lesion detection and characterization 1
- Portal venous phase provides highest sensitivity for most lesion detection 1
Common Pitfalls to Avoid
- Do not rely on noncontrast or single-phase CT - these have limited sensitivity and require repeat imaging with proper multiphase technique 1
- Benign lesions are more common than metastases even in cancer patients (51-80% of lesions <1-1.5 cm are benign), so avoid overdiagnosis 2
- Peripheral ring enhancement on arterial phase has 98% positive predictive value for malignancy but must be distinguished from perilesional enhancement seen in benign lesions 1
- CT has significantly lower sensitivity for hypovascular metastases (74%) compared to hypervascular lesions 1
When Results Are Equivocal
If initial cross-sectional imaging is indeterminate: