title: CT attenuation values of blood and myocardium: rationale for accurate coronary artery calcifications detection with multi-detector CT.
abstract: OBJECTIVE
  To determine inter-session and intra/inter-individual variations of the attenuations of aortic blood/myocardium with MDCT in the context of calcium scoring. To evaluate whether these variations are dependent on patients' characteristics.
  
  
  METHODS
  Fifty-four volunteers were evaluated with calcium scoring non-enhanced CT. We measured attenuations (inter-individual variation) and standard deviations (SD, intra-individual variation) of the blood in the ascending aorta and of the myocardium of left ventricle. Every volunteer was examined twice to study the inter-session variation. The fat pad thickness at the sternum and noise (SD of air) were measured too. These values were correlated with the measured aortic/ventricular attenuations and their SDs (Pearson). Historically fixed thresholds (90 and 130 HU) were tested against different models based on attenuations of blood/ventricle.
  
  
  RESULTS
  The mean attenuation was 46 HU (range, 17-84 HU) with mean SD 23 HU for the blood, and 39 HU (10-82 HU) with mean SD 18 HU for the myocardium. The attenuation/SD of the blood were significantly higher than those of the myocardium (p < 0.01). The inter-session variation was not significant. There was a poor correlation between SD of aortic blood/ventricle with fat thickness/noise. Based on existing models, 90 HU threshold offers a confidence interval of approximately 95% and 130 HU more than 99%.
  
  
  CONCLUSIONS
  Historical thresholds offer high confidence intervals for exclusion of aortic blood/myocardium and by the way for detecting calcifications. Nevertheless, considering the large variations of blood/myocardium CT values and the influence of patient's characteristics, a better approach might be an adaptive threshold.
authors: Department of Radiology, University Hospital of Lausanne, Rue du Bugnon 46, 1011 Lausanne, Switzerland; Quantitative Medical Imaging International Institute, Digital Imaging Research center, Faculty of Computing, Information Systems and Mathematics, University of Kingston, London, United Kingdom.
authors: Salah D
authors: SD
authors: Qanadli
authors: Department of Radiology, University Hospital of Lausanne, Rue du Bugnon 46, 1011 Lausanne, Switzerland.
authors: Anne-Marie
authors: AM
authors: Jouannic
authors: Quantitative Medical Imaging International Institute, Digital Imaging Research center, Faculty of Computing, Information Systems and Mathematics, University of Kingston, London, United Kingdom.
authors: Jamshid
authors: J
authors: Dehmeshki
authors: Department of Radiology, University Hospital of Lausanne, Rue du Bugnon 46, 1011 Lausanne, Switzerland.
authors: Tri-Linh
authors: TL
authors: Lu
mesh_terms: D000368:Aged; D002114:Calcinosis / Q000175:diagnosis* / Q000000981:diagnostic imaging; D003331:Coronary Vessels / Q000000981:diagnostic imaging*; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D014057:Tomography, X-Ray Computed