Coronary artery calcium (CAC) scoring and cardiac computed tomographic angiography (CCTA) are comparatively new noninvasive imaging modalities that have experienced a rapid accumulation of scientific evidence for their clinical utility in the diagnosis, prognosis, and therapeutic planning for coronary heart disease. This technology offers a wide range of clinical applications and has value for a diverse range of patients.
Quantitation of coronary artery calcification by noncontrast cardiac computed tomography (CCT) for CAC scoring predicts future cardiovascular events in asymptomatic patients beyond what is conferred by assessment using traditional clinical risk-score calculators. The evaluation of coronary artery calcification has been widely accepted by the medical community as a powerful noninvasive screening tool due to the fact that atherosclerosis remains the only pathology known to be associated with coronary calcification (Fig. 28-1).1 Furthermore, the correlation between the degree of vessel calcification and the overall atherosclerotic burden is well established, both through histopathologic determination and invasive imaging modalities such as intravascular ultrasound imaging.2–5
Computed tomography showing absence (A,B) and presence (C,D) of coronary artery calcium, used to compute a coronary calcium score. Figures A and C are volume rendered, while figures B and D are axial cross-sectional images.
CAC quantification may be performed by noncontrast electron beam computed tomography (EBCT) or multidetector row computed tomography (MDCT) scanners using electrocardiographic (ECG) gating. The standardized CAC protocol calls for axial imaging with prospective ECG triggering, with tube voltage of 120 kVp and tube current set at 120 to 150 milliampere-seconds (mAs), with the field of view limited to the heart and lungs using a scan length defined by the carina and the base of the heart. CAC scoring requires only a few seconds of scanning time and the overall study may be performed in 10 to 15 minutes. CAC scoring generally remains a screening tool; as such, patients selected for CAC evaluation with MDCT scanners should have minimal radiation exposure. The use of prospective ECG triggering enables performance of CAC scoring with very low-radiation doses that are less than the environmental exposure to radiation due to background radon exposure for an individual living at sea level for a year. The dose–length product (DLP) and effective radiation dose (E) should be maintained at less than 200 mGy × cm and 3.0 mSv, respectively.6 Performed within guideline-suggested parameters, imaging results in a total radiation exposure that should average 1 to 1.5 mSv.2
Calculation of Coronary Artery Calcium Score
The Agatston score is the most commonly used tool for CAC scoring and best supported by the literature. The Agatston score is a semi-automated tool to calculate a weighted sum of the area of coronary calcification, wherein each calcified area is multiplied ...