Contrast Kinetics - Breast MRI
Key Concept
Analysis of how a lesion takes up and releases Gadolinium over time.
- "Wash-in" (Early Phase): First 2 minutes. Reflects vascularity/angiogenesis.
- "Wash-out" (Delayed Phase): 2–7 minutes. Reflects interstitial space/leakiness.
Golden Rule: Morphology trumps kinetics. A spiculated mass with a Type 1 curve is still suspicious.
1. The Kinetic Curves (Time-Intensity Curves)
The curve is generated by placing a Region of Interest (ROI) over the most avidly enhancing part of the lesion (avoiding necrosis/cysts).
Type 1: Persistent (Progressive)
- Shape: Continual increase in signal intensity over time. No plateau or loss of signal.
- Interpretation: usually Benign.
- PPV for Malignancy: Low (~6%).
- Typical Lesions:
- Fibroadenoma (myxoid type).
- Normal parenchyma / PASH.
- Trap: ~10% of invasive cancers show Type 1 (especially Lobular CA and Mucinous CA).
Type 2: Plateau
- Shape: Initial rapid rise, then flattens out (signal stays relatively constant,
10%). - Interpretation: Indeterminate / Suspicious.
- PPV for Malignancy: Intermediate (varies widely, but often quoted ~7-28% risk).
- Typical Lesions:
- Fibroadenoma (sclerotic).
- DCIS.
- Some invasive cancers.
Type 3: Washout
- Shape: Rapid initial rise followed by a distinctive drop in signal intensity (>10% decrease) in the delayed phase.
- Interpretation: Malignant until proven otherwise.
- PPV for Malignancy: High (>29–87%).
- Pathophysiology: Malignant vessels are leaky (shunts) with small interstitial space
contrast enters fast and leaves fast. - Typical Lesions:
- Invasive Ductal Carcinoma (IDC).
- High-grade tumours.
- Trap: Lymph nodes and proteinaceous cysts can sometimes show washout-like features (but T2 signal helps differentiate).
2. Assessment Strategy
Step 1: Qualitative (Visual)
- Look at the subtraction images.
- Does it enhance?
- Internal Enhancement Patterns:
- Homogeneous: Uniform (often benign or small CA).
- Heterogeneous: Variable (suspicious).
- Rim Enhancement: High PPV for malignancy (central necrosis/fibrosis with active periphery). Exceptions: Fat necrosis, inflamed cyst.
- Dark Internal Septations: Highly specific for Fibroadenoma.
Step 2: Quantitative (The Curve)
- Place a small ROI on the "hot spot" (fastest enhancing area).
- Do not include the whole tumour (averaging dilutes the washout).
- Do not include necrosis (no enhancement).
3. Important Caveats (The "Exam Traps")
Morphology > Kinetics
A Type 3 (Washout) curve in a smooth, oval mass with dark internal septations is likely a Fibroadenoma.
A Type 1 (Persistent) curve in a spiculated, architectural distortion is likely Invasive Lobular Carcinoma (ILC).
Never downgrade a morphologically suspicious lesion based on a benign curve.
False Negatives (Malignancy with "Benign" Kinetics)
- Invasive Lobular Carcinoma (ILC): Often diffuses gently; Type 1 or 2 curve common.
- Mucinous Carcinoma: Large interstitial space holds contrast; Type 1 (persistent) curve is classic.
- DCIS: Often shows plateau or even persistent enhancement (non-mass enhancement).
False Positives (Benign with "Malignant" Kinetics)
- Lymph Nodes: Intense washout is normal for nodes (look for the hilum).
- Inflammation/Mastitis: Hypervascularity can mimic washout.
- Fibroadenoma: Cellular/young FA can sometimes show washout (though plateau is more common).
4. Reporting Terminology (BI-RADS)
- Initial Phase (first 2 mins):
- Slow
- Medium
- Rapid
- Delayed Phase (after 2 mins):
- Persistent
- Plateau
- Washout
Example Dictation:
"The mass demonstrates rapid initial enhancement with delayed washout (Type 3 kinetics), concerning for malignancy."
