Repeatability Limits for Measurement of Coronary Artery Calcified Plaque with Cardiac CT in the Multi-Ethnic Study of Atherosclerosis

OBJECTIVE: The purposes of this study were to examine the repeatability of the findings of coronary artery calcification (CAC) measured with CT on repeated scans, to estimate 95% repeatability limits for CAC, and to use these limits to quantify detectable change in CAC over time. SUBJECTS AND METHODS: The Multi-Ethnic Study of Atherosclerosis is a prospective cohort study with 6,814 participants 45-84 years old and free of clinical cardiovascular disease at enrollment. Agreement for presence of CAC was assessed for 6,742 participants who had baseline replicate scans on which a CAC score of 0 indicated no coronary calcification. Among 3,380 participants with baseline CAC, the 95% repeatability limits were established with a quantile regression model. Detectable change in CAC during follow-up was defined by an increase or decrease beyond the baseline repeatability limit. RESULTS: At baseline, 274 (4.1%) of the rescan pairs were discordant (presence or absence of CAC). Greater body mass index was associated with a discordant pair (trend, p < 0.05). The upper 95% repeatability limits were (0.17 x Agatston score) + (4.89 x sq rt(Agatston score)) + (0.44 x body mass index) - 10.84 for Agatston score and (0.16 x volumetric calcium score) + (4.30 x sq rt(volumetric calcium score)) + (0.23 x body mass index) - 5.00 for volumetric calcium score. Rescan repeatability was comparable for electron beam and 4-MDCT scanners. At 2.5 years of average follow-up (range, 0.9-5.0 years), a detectable increase in Agatston and volumetric calcium scores was observed in 1,027 (36.3%) and 1,020 (36.0%), respectively, of 2,832 participants with baseline CAC. CONCLUSION: The repeatability limits derived can be used to evaluate whether an increase in CAC score exceeds that expected from measurement error alone.