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 one of the strongest independent predictors of future cardiovascular events. 1

What is CT Calcium Scoring?

• CT calcium scoring uses electrocardiogram-gated multidetector computed tomography (CT) to detect and quantify calcium deposits in coronary arteries, which serve as a reliable marker of coronary atherosclerosis and vascular age 1
• The scan is performed using a prospectively ECG-triggered scanning mode with 2.5-3.0 mm thick axial images obtained through the heart 1
• The radiation dose is relatively low (approximately 0.37-1.5 mSv), comparable to or slightly lower than screening mammography (0.44-0.56 mSv) 1
• The test requires only a few heartbeats to complete, with best-quality data acquired during mid-diastole when cardiac motion is minimal 1

How Calcium Scoring Works

• The Agatston score is the most widely used scoring system in clinical practice and research 1
• The scoring algorithm identifies calcific lesions as having CT density >130 Hounsfield units and area >1 mm² 1
• A weighting factor (1-4) is assigned based on CT density, and the calcium score is calculated by multiplying the lesion area by this weighting factor 1
• The total calcium score is computed by summing scores of all calcified lesions and can be expressed as a percentile adjusted for sex and race 1
• Scores can be calculated for individual coronary arteries as well as the entire coronary tree 1

Clinical Significance and Risk Prediction

• CAC is a robust marker for risk assessment and prediction of future atherosclerotic cardiovascular disease (ASCVD) events in asymptomatic patients without known coronary artery disease 1
• CAC is superior to traditional risk factor assessments and other non-traditional markers (like carotid intimal thickness, ankle-brachial index, C-reactive protein) for predicting cardiovascular risk 1
• The degree of CAC represents atherosclerotic burden, with cardiovascular risk increasing as calcium scores increase, especially when scores exceed 300-400 1
• A calcium score of zero (CAC=0) indicates excellent prognosis with very low risk (<1% annually) for cardiac death or myocardial infarction 1

Clinical Applications and Guidelines

• CT calcium scoring is particularly valuable for risk stratification in patients with intermediate (7.5-20%) or borderline (5-7.5%) 10-year ASCVD risk 1
• The 2019 ACC/AHA preventive guidelines recommend calcium scoring as a reasonable guide for shared decision-making in adults aged 40-75 years with intermediate ASCVD risk 1
• Patients with intermediate risk but no coronary calcification can be reclassified into a lower-risk group, potentially avoiding statin therapy 1
• The American College of Cardiology/American Heart Association recommends screening for clinically silent ischemia when calcium scores exceed 400 1

Important Considerations and Limitations

• CT calcium scoring should be seen primarily as a marker of atherosclerosis and not of degree of stenosis 1
• The CAC area typically represents only about 20% of the total atherosclerosis burden, as not all plaques contain calcium 1
• Due to radiation exposure and low prevalence of calcification in younger individuals, calcium scoring is generally not recommended for men under 40 and women under 50 years of age 1
• The calcium score can be affected by technical factors including image acquisition parameters and reconstruction algorithms 2

Future Directions

• Newer techniques are being developed to assess coronary calcium from contrast-enhanced coronary CT angiography (CCTA), potentially eliminating the need for a separate non-enhanced scan 3, 4, 2
• These approaches could reduce radiation exposure by approximately one-third while maintaining accurate cardiovascular risk assessment 2
• Advanced scoring methods like the Calcium Coverage Score, which represents the percentage of coronary arteries affected by calcific plaque, may provide additional prognostic information 5