Methods to Quantify Coronary Artery Calcifications in Cardiac CT

Three different ways are commonly used to describe the amount of coronary artery calcium: calculation of the Agatston score, calculation of a volume score and calculation of absolute calcium mass.

The traditional way to describe the calcified coronary artery plaque burden was established by Agatston et al. [19] in 1990. This score is determined by multiplying the area of a calcified coronary artery plaque by a density co-factor chosen on the basis of the peak attenuation of the lesion. The total Agatston score is then calculated as a sum score of all lesions identified within the entire coronary artery tree.

A calcium volume score is simply calculated as the number of voxels of all calcified plaques multiplied by the volume of one voxel. However, it must be noted that a volume score does not necessarily stand for the real volume of coronary artery calcifications, because the definition of calcium is threshold dependent [18].

The absolute calcium mass is as a uniform measure of calcified coronary artery plaque burden that is calculated by multiplying the volume of every calcified plaque with its density value followed by multiplying the sum of all measurements with a scanner- and scan protocol-specific calibration factor. Using the absolute calcium mass instead of the Agatston score or the volume score improves inter-study reproducibility and therefore guarantees a better comparability of calcium measurements even if the data sets are obtained from different scanner types and/ or different scan protocols [1, 18].

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