title: Serial electron beam CT measurements of coronary artery calcium: Has your patient's calcium score actually changed?
abstract: OBJECTIVE
  The objective of our study was to develop a model for determining the smallest statistically significant change in the coronary artery calcium score (CAC) between serial measurements in a given subject.
  
  
  METHODS
  We assembled a convenience sample of 2,217 pairs of repeated electron beam CT coronary calcium scans acquired in quick succession. Each scan consisted of forty 100-msec, 3-mm sections obtained at 60% of the ECG R-R interval. A single observer quantified calcium in each scan independent of knowledge of calcium quantity in the repeated scan. We then modeled a relationship between the variation of the differences between repeated measurements of calcium and the magnitude of the calcium score and formulated 95% repeatability coefficient equations for the Agatston and volumetric CAC score. The equations allow determining the smallest statistically significant interval change in the calcium score between two serial measurements in a given subject.
  
  
  RESULTS
  In a subject with measurable CAC at baseline, the smallest statistically significant interval change is +/- (4.930 x square root of baseline Agatston CAC score) or +/- (3.445 x square root of baseline volumetric CAC score). In a subject with no measurable CAC at baseline, a follow-up CAC score exceeding 11.6 Agatston units or 9.5 mm3 qualifies for statistically significant progression. The results were similar in men and women.
  
  
  CONCLUSIONS
  By examining repeatability of quantitative electron beam CT measurements of coronary calcium as a function of the magnitude of the calcium score, we developed a model to determine the smallest statistically significant change between serial measurements in a given subject.
authors.affiliation: Department of Medicine, Section of Cardiology (M/C 715), University of Illinois at Chicago College of Medicine, Chicago, IL 60612, USA. sevrukova@mir.wustl.edu
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Sevrukov
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bland
authors.forename: George T
authors.initials: GT
authors.lastname: Kondos
mesh_terms: D000368:Aged; D002114:Calcinosis / Q000000981:diagnostic imaging* / Q000473:pathology; D003327:Coronary Disease / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*