Differences Between Coronary Artery Calcium (CAC) Scan and Coronary Computed Tomography Angiography (CCTA)
CAC scan and CCTA are distinct cardiac imaging tests with different capabilities, techniques, and clinical applications, with CCTA providing more comprehensive anatomical information about coronary arteries compared to CAC scoring alone.
Basic Differences
CAC Scan:
- Definition: Non-contrast CT scan that quantifies calcium deposits in coronary arteries
- Technique: ECG-gated non-contrast CT scan 1
- Measurement: Calcified plaque burden reported as Agatston score 1
- Radiation dose: Lower radiation exposure (typically 1-3 mSv) 1
- Contrast: Does not require contrast administration 1
- Duration: Brief scan time
CCTA:
- Definition: Contrast-enhanced CT scan that visualizes coronary artery lumen and wall
- Technique: ECG-gated CT scan with intravenous contrast 1
- Visualization: Direct visualization of coronary stenosis severity, extent, and distribution 2
- Radiation dose: Higher radiation exposure (3-12 mSv with dose reduction techniques) 1
- Contrast: Requires intravenous contrast administration 1
- Duration: Longer scan time, requires heart rate control (typically ≤60 bpm) 1
Clinical Applications and Capabilities
CAC Scan:
- Detects and quantifies calcified plaque only
- Excellent for risk stratification in asymptomatic individuals 1
- High sensitivity (96-100%) but lower specificity (40-66%) for obstructive CAD 1
- Cannot detect non-calcified plaque or visualize coronary lumen
- CAC=0 has excellent negative predictive value (>95%) for obstructive CAD 1
- Primarily used for risk assessment rather than diagnosis 1
CCTA:
- Visualizes both calcified and non-calcified plaque 1
- Directly assesses coronary lumen and stenosis severity 1
- Evaluates plaque characteristics (calcified, non-calcified, mixed) 1
- Higher sensitivity (85-95%) and specificity for obstructive CAD 1
- Excellent negative predictive value (98%) for excluding obstructive CAD 1
- Can assess plaque burden, distribution, and location 2
- Can evaluate arterial remodeling and other plaque features 1
Clinical Value and Decision-Making
When to Use CAC:
- Risk stratification in asymptomatic individuals
- Gatekeeper for further testing in low-to-intermediate risk symptomatic patients 3
- When radiation dose and contrast exposure are concerns
- To decide whether to initiate or intensify preventive therapies
When to Use CCTA:
- Evaluation of patients with chest pain and low-intermediate pretest probability of CAD 1
- When detailed coronary anatomy is needed
- When non-calcified plaque assessment is important
- In emergency department for evaluation of acute chest pain 1
- When functional information about coronary stenosis is needed (with newer CT-FFR techniques) 1
Combined Approach
Recent evidence suggests that combining CAC with CCTA improves diagnostic performance:
- Adding CAC to CCTA improves diagnostic accuracy for obstructive CAD (AUC: 87% vs. 80% for CCTA alone) 4
- Particularly valuable when CCTA findings are non-diagnostic 4
- CAC can serve as a gatekeeper: patients with CAC=0 may not need CCTA, while those with elevated CAC may benefit from CCTA 3
Important Considerations
- Both tests expose patients to radiation, though modern techniques have reduced doses significantly
- CCTA requires iodinated contrast, which is contraindicated in some patients with kidney disease
- Image quality of CCTA is affected by high heart rates, arrhythmias, and severe calcification
- CAC scoring is less affected by these technical factors but provides less diagnostic information
In summary, CAC provides information about calcified plaque burden and is excellent for risk stratification, while CCTA offers comprehensive anatomical assessment of the coronary arteries including both calcified and non-calcified plaque, stenosis severity, and plaque characteristics.