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Objectives: Although the Agatston score is a commonly used quantification method, rescan reproducibility is suboptimal, and different CT scanners result in different scores. In 2007, McCollough et al (Radiology 2007;243:527-538) proposed a standard for coronary artery calcium quantification. Advancements in CT technology over the last decade, however, allow for improved acquisition and reconstruction methods. This study aims to investigate the feasibility of a reproducible reduced dose alternative of the standardized approach for coronary artery calcium quantification on state-of-the-art CT systems from 4 major vendors., Materials and Methods: An anthropomorphic phantom containing 9 calcifications and 2 extension rings were used. Images were acquired with 4 state-of-the-art CT systems using routine protocols and a variety of tube voltages (80-120 kV), tube currents (100% to 25% dose levels), slice thicknesses (3/2.5 and 1/1.25 mm), and reconstruction techniques (filtered back projection and iterative reconstruction). Every protocol was scanned 5 times after repositioning the phantom to assess reproducibility. Calcifications were quantified as Agatston scores., Results: Reducing tube voltage to 100 kV, dose to 75%, and slice thickness to 1 or 1.25 mm combined with higher iterative reconstruction levels resulted in an on average 36% lower intrascanner variability (interquartile range) compared with the standard 120 kV protocol. Interscanner variability per phantom size decreased by 34% on average. With the standard protocol, on average, 6.2 ± 0.4 calcifications were detected, whereas 7.0 ± 0.4 were detected with the proposed protocol. Pairwise comparisons of Agatston scores between scanners within the same phantom size demonstrated 3 significantly different comparisons at the standard protocol (P < 0.05), whereas no significantly different comparisons arose at the proposed protocol (P > 0.05)., Conclusions: On state-of-the-art CT systems of 4 different vendors, a 25% reduced dose, thin-slice calcium scoring protocol led to improved intrascanner and interscanner reproducibility and increased detectability of small and low-density calcifications in this phantom. The protocol should be extensively validated before clinical use, but it could potentially improve clinical interscanner/interinstitutional reproducibility and enable more consistent risk assessment and treatment strategies., Competing Interests: Conflicts of interest and sources of funding: G.D.v.P. was supported in part by an unconditional grant from PUSH: a collaboration between Siemens Healthineers and the University Medical Center Groningen; the sponsor had no role in the conceptualization, interpretation of findings, writing, or publication of the article. D.M. has no activities related to the present article; he is a shareholder of and a consultant for Segmed, Inc. K.N. received institutional research support from Siemens Healthineers, Bayer Healthcare, GE Healthcare, and HeartFlow Inc. L.J.O.'s institution received a grant from Canon Medical Systems to hire a doctoral candidate to investigate subtraction CT and disclosed no other relevant relationships. D.F. has no activities related to the present article; he received research support from Siemens Healthineers and GE Healthcare, is on the speakers' bureau at Siemens Healthineers, and has ownership interest in iSchemaView; he disclosed no other relevant relationships. M.J.W. has no activities related to the present article and received a research grant from Philips Healthcare; he is a cofounder, advisor, and stockholder of Segmed, Inc; he disclosed no other relevant relationships. J.W., N.R.v.d.W., M.J.W.G., R.W.v.H., F.d.L., R.H.J.A.S., and T.L. have nothing to disclose., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)