What is CT (Computed Tomography) calcium scoring?

CT Calcium Scoring: A Powerful Tool for Cardiovascular Risk Assessment

CT calcium scoring is a non-invasive imaging technique that quantifies coronary artery calcification to assess atherosclerotic burden and predict cardiovascular risk, serving as the single best predictor of future cardiovascular events in asymptomatic individuals. 1

What is CT Calcium Scoring?

CT calcium scoring uses electrocardiogram-gated multidetector computed tomography (CT) to detect and quantify calcium deposits in the coronary arteries. This technique:

• Measures coronary artery calcification (CAC), a reliable marker of coronary atherosclerosis and vascular age 1
• Provides a numerical score (Agatston score) that correlates with atherosclerotic burden and future cardiovascular risk
• Requires minimal radiation exposure (0.37-1.5 mSv), comparable to or slightly less than screening mammography 1

Technical Aspects

• Performed using ECG-gated multidetector CT or electron beam tomography 1
• Images acquired during mid-diastole to minimize cardiac motion 1
• Calcification defined as lesions with CT density >130 Hounsfield units and area >1 mm² 1
• The Agatston score calculation:
  • Assigns a weighting factor (1-4) based on calcium density
  • Multiplies lesion area by weighting factor
  • Sums scores of all calcified lesions 1
• Results can be expressed as absolute scores or percentiles adjusted for age, sex, and race 1

Clinical Significance and Risk Stratification

CAC scoring provides powerful prognostic information:

• Superior to traditional risk factor assessments for predicting future cardiovascular events 1
• Outperforms other non-traditional markers like carotid intimal thickness, ankle-brachial index, and C-reactive protein 1
• Risk increases proportionally with CAC score 1

Risk Categories Based on CAC Score

CAC Score	Risk Category	Clinical Implication
0	Very low risk	"Power of zero" - excellent prognosis with <1% annual risk of cardiac death/MI [1]
1-100	Mild risk	Increased risk compared to zero score
101-400	Moderate risk	Significantly elevated risk
>400	High risk	Substantially increased risk; may warrant screening for silent ischemia [1]

Clinical Applications

CAC scoring is particularly valuable for:

1. Risk reclassification in intermediate-risk patients:

   • Nearly one-fifth of US adults aged 45-79 years have intermediate (7.5%-20%) 10-year ASCVD risk 1
   • CAC scoring can reclassify these patients into lower or higher risk categories 1
   • Helps guide decisions about statin therapy 1

2. Guiding preventive therapy decisions:

   • Zero CAC score may allow withholding statin therapy even with risk-enhancing factors 1
   • High CAC scores strongly indicate need for aggressive preventive measures 1

3. Motivating patient adherence:

   • Visualization of coronary calcium can improve patient motivation for lifestyle changes and medication adherence 1
   • Patients with detected CAC show better blood pressure control, lipid levels, and risk factor management 1

Monitoring Disease Progression

• Follow-up scans may be considered at 3-5 year intervals 1
• CAC progression (>15% annualized change) associated with >3-fold increase in mortality 1
• Most meaningful in patients with initial CAC=0 who have diabetes or multiple risk factors 1
• Limited value in patients with baseline CAC>400 who are already high-risk 1

Limitations and Considerations

• Not recommended for routine screening in men <40 years and women <50 years due to low prevalence of detectable calcium 1
• Radiation exposure, though low, should be considered 1
• Statin therapy may increase CAC scores over time, complicating interpretation of serial scans 1
• Detects only calcified plaque, which represents approximately 20% of total atherosclerotic burden 1
• Primarily a marker of atherosclerosis burden, not stenosis severity 1

Special Populations

• In patients with kidney disease, correlation between CAC scores and angiographic CAD may be poor due to medial vascular calcification rather than intimal calcification 1
• In younger patients, non-calcified plaque may be present without detectable calcium 1

CT calcium scoring provides valuable information about cardiovascular risk that can guide clinical decision-making and preventive strategies, particularly in intermediate-risk patients where traditional risk assessment may be insufficient.