Objective: The purpose of this study was to investigate the influence of heart rate, slice thickness, and calcification density on absolute value and variability of calcium score using 64-slice multidetector computed tomography (MDCT).
Methods and materials: Three artificial arteries containing each 3 lesions with varying density were scanned using a moving cardiac phantom at rest and at 50 to 110 beats per minute (bpm) at 10-bpm intervals on a 64-slice MDCT. Images were reconstructed at slice thicknesses (increment) of 0.6 (0.4), 0.75 (0.5), 1.5 (1.5), and 3.0 (3.0) mm. The amount of calcium was expressed as an Agatston score, volume score, and equivalent mass.
Results: Absolute coronary artery calcium (CAC) scores decreased [average -37% for low density calcification (LDC)] or increased [average +32% for high density calcification (HDC)] at heart rates over 60 bpm depending on slice thickness and scoring method. Thinner slice thicknesses yielded higher CAC scores. Variability of the CAC scores increased with increasing heart rates especially for low density calcifications (8% at rest vs. 50% at 110 bpm). Variability also increased for thicker slices (average 6% for 0.6 mm vs. 18% for 3.0 mm). Variability was lower for HDC compared with LDC (approximately 5% for HDC vs. 27% for LDC at 70 bpm, averaged over all methods and slice thicknesses).
Conclusion: CAC-scoring is strongly influenced by cardiac motion, calcification density, and slice thickness. CAC scores increase for high density calcifications and decrease for low density calcifications at increasing heart rates. Heart rate should be reduced on 64-slice MDCT to obtain a lower degree of variability of CAC-scoring, preferably below 70 bpm. A thinner slice thickness further enhances the reproducibility.