It is now well recognized that Coronary Artery Disease (CAD) is part of the spectrum of
cardiovascular diseases (CVDs) that have common underlying risk factors and may manifest as
myocardial infarction, stroke or death.
CAD is a pathological process characterized by the accumulation of atherosclerotic plaque in
the epicardial arteries, whether obstructive or non-obstructive; it can have long and stable
periods, but it can also become unstable at any time.
It is unknown whether the high risk provided by the presence of obstructive coronary artery
atherosclerotic disease is due to stenosis per se, or due to its correlation with the total
burden of atherosclerotic plaque. Studies suggest that calcified atherosclerotic burden, not
stenosis, is the main predictor of future events of cardiovascular disease (myocardial
infarction and cerebrovascular disease) and death in patients with coronary artery disease.
Atherosclerosis imaging allows measurable assessments of disease progression and activity,
revealing early signs of potential drug effects. Non-invasive methods are preferable for
serial imaging in drug trials because of the potential risks associated with invasive
procedures. High participant dropout rates are also observed when invasive methods are used.
Therefore, coronary artery calcium scanning offers a simple, non-invasive, rapid, and
reliable method to quantify coronary calcium, which is pathognomonic for established
atherosclerosis. It is a powerful screening tool for asymptomatic patients at low or
intermediate risk of CVD, including those with diabetes mellitus, and can potentially improve
adherence to lifestyle advice and medication.
Coronary artery calcium can be quantified by non-contrast-enhanced CT using the Agatston
score, which is currently the most widely used method. Conceptually, the Agatston score is
the sum of the scores for all calcified coronary lesions, representing both the total area
and the maximum density of coronary calcification. The area of the lesion is multiplied by
the density factor that is determined by pre-defined cut points. The density factor is used
so that the regions with higher attenuation contribute more strongly to the final calcium
score. A CT attenuation threshold of 130 Hounsfield units (HU) is used for calcium detection,
and only contiguous voxels totaling an area greater than 1 mm2 are counted as "lesions" to
reduce the influence of image noise. Standardized categories have been developed for the
calcium score with scores of 0 indicating the absence of calcified plaque, 1 to 10 minimal
plaque, 11 to 100 mild plaque, 101 to 400 moderate plaque, and > 400 severe plaque.
In 2017, the Society of Cardiovascular Computed Tomography (SCCT) and the Society of Thoracic
Radiology (STR) proposed the CAC-DRS as a way to standardize communication regarding CAC
findings on non-contrast-enhanced CT scans. CAC-DRS categories are defined as Ax/Ny, where A
represents the Agatston score group (where A0, A1, A2, and A3 represent CAC of 0, CAC of
1-99, CAC of 100-299, and CAC ≥ 300, respectively), and N represents the number of vessels
affected by CAC, ranging from 0 to 4 for the major epicardial coronary arteries.,
respectively), and N represents the number of vessels affected by CAC, which varies from 0 to
4 for the main epicardial coronary arteries.