On coronary CT angiography (CCTA), a lesion is identified with a CT attenuation of −30 HU within a coronary plaque. This finding indicates:
- A Heavily calcified stable plaque
- B Intraluminal thrombus
- C Lipid-rich necrotic core (low-attenuation plaque) ✓
- D Stent restenosis
Correct answer: C. Lipid-rich necrotic core (low-attenuation plaque)
Explanation
A CT attenuation value of <30–50 HU within a coronary plaque on CCTA represents a lipid-rich necrotic core, which is a feature of vulnerable (high-risk) plaque prone to rupture. Other high-risk plaque features on CCTA include napkin-ring sign, positive remodelling (remodelling index >1.1), and spotty calcium. Calcified stable plaques are hyperdense (>130 HU). Intraluminal thrombus appears as a filling defect within the lumen, not within the plaque. Stent restenosis appears as lumen narrowing within the stent struts.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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