title: Repeatability limits for measurement of coronary artery calcified plaque with cardiac CT in the Multi-Ethnic Study of Atherosclerosis.
abstract: 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.
  
  
  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.
  
  
  CONCLUSIONS
  The repeatability limits derived can be used to evaluate whether an increase in CAC score exceeds that expected from measurement error alone.
authors.affiliation: Department of Biostatistics, Collaborative Health Studies Coordinating Center, University of Washington, 6200 NE 74th St, Building 29, Suite 310, Seattle, WA 98115, USA.
authors.forename: Hyoju
authors.initials: H
authors.lastname: Chung
authors.forename: Robyn L
authors.initials: RL
authors.lastname: McClelland
authors.forename: Ronit
authors.initials: R
authors.lastname: Katz
authors.forename: J Jeffrey
authors.initials: JJ
authors.lastname: Carr
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Budoff
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002114:Calcinosis / Q000000981:diagnostic imaging* / Q000208:ethnology*; D017023:Coronary Angiography / Q000706:statistics & numerical data*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging* / Q000208:ethnology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*; D014481:United States / Q000208:ethnology