title: Electron-beam CT: the effect of using a correction function on coronary artery calcium quantitation.
abstract: OBJECTIVE
  The purpose of the study was to determine if use of a correction function derived from a phantom with known calcium density reduces variation in coronary artery calcium scores measured with electron-beam computed tomography (CT) and to evaluate the influence of body girth, as measured by body mass index (BMI), on coronary artery calcium-score variability in a clinical screening cohort.
  
  
  METHODS
  Two hundred fifty consecutive patients underwent two electron-beam CT examinations with a standardized phantom. Region-of-interest (ROI) measurements of the phantom were correlated with the patient BMI. In a subset of 28 patients with low but positive coronary artery calcium scores, ROI values of the phantom were used as a correction for signal attenuation.
  
  
  RESULTS
  Patient BMI was not significantly correlated to signal attenuation. Application of a correction function resulted in a small but insignificant decrease in interscan coronary artery calcium-score variation. The interscan coronary artery calcium score variation was 24.5% +/- 23.9; it decreased to 24.3% +/- 21.6 with use of the 75 mg/cm3 portion of the phantom and to 22.2% +/- 21.4 with use of the 150 mg/cm3 portion of the phantom.
  
  
  CONCLUSIONS
  The use of a coronary artery calcium phantom does not reduce interscan variation sufficiently to warrant regular clinical usage. Interscan variation in the coronary artery calcium score is not significantly influenced by patient BMI.
authors.affiliation: Department of Radiological Sciences, UCLA School of Medicine, USA.
authors.forename: L E
authors.initials: LE
authors.lastname: Greaser
authors.forename: H C
authors.initials: HC
authors.lastname: Yoon
authors.forename: R T
authors.initials: RT
authors.lastname: Mather
authors.forename: M
authors.initials: M
authors.lastname: McNitt-Gray
authors.forename: J G
authors.initials: JG
authors.lastname: Goldin
mesh_terms: D000704:Analysis of Variance; D001161:Arteriosclerosis / Q000000981:diagnostic imaging; D001824:Body Constitution; D015992:Body Mass Index; D002114:Calcinosis / Q000000981:diagnostic imaging; D002118:Calcium / Q000032:analysis*; D015331:Cohort Studies; D017023:Coronary Angiography / Q000379:methods*; D003327:Coronary Disease / Q000000981:diagnostic imaging*; D003331:Coronary Vessels / Q000737:chemistry; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008403:Mass Screening; D009765:Obesity / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D012044:Regression Analysis; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D002118:Calcium