title: Individual selection of X-ray tube settings in computed tomography coronary angiography: Reliability of an automated software algorithm to maintain constant image quality.
abstract: OBJECTIVE
  To evaluate a software tool that claims to maintain a constant contrast-to-noise ratio (CNR) in high-pitch dual-source computed tomography coronary angiography (CTCA) by automatically selecting both X-ray tube voltage and current.
  
  
  METHODS
  A total of 302 patients (171 males; age 61±12years; body weight 82±17kg, body mass index 27.3±4.6kg/cm(2)) underwent CTCA with a topogram-based, automatic selection of both tube voltage and current using dedicated software with quality reference values of 100kV and 250mAs/rotation (i.e., standard values for an average adult weighing 75kg) and an injected iodine load of 222mg/kg.
  
  
  RESULTS
  The average radiation dose was estimated to be 1.02±0.64mSv. All data sets had adequate contrast enhancement. Average CNR in the aortic root, left ventricle, and left and right coronary artery was 15.7±4.5, 8.3±2.9, 16.1±4.3 and 15.3±3.9 respectively. Individual CNR values were independent of patients' body size and radiation dose. However, individual CNR values may vary considerably between subjects as reflected by interquartile ranges of 12.6-18.6, 6.2-9.9, 12.8-18.9 and 12.5-17.9 respectively. Moreover, average CNR values were significantly lower in males than females (15.1±4.1 vs. 16.6±11.7 and 7.9±2.7 vs. 8.9±3.0, 15.5±3.9 vs. 16.9±4.6 and 14.7±3.6 vs. 16.0±4.1 respectively).
  
  
  CONCLUSIONS
  A topogram-based automatic selection of X-ray tube settings in CTCA provides diagnostic image quality independent of patients' body size. Nevertheless, considerable variation of individual CNR values between patients and significant differences of CNR values between males and females occur which questions the reliability of this approach.
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Charité Campus Mitte, Berlin, Germany. Electronic address: tahir.durmus@charite.de.
authors.forename: Tahir
authors.initials: T
authors.lastname: Durmus
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Charité Campus Mitte, Berlin, Germany.
authors.forename: Reny
authors.initials: R
authors.lastname: Luhur
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Charité Campus Mitte, Berlin, Germany.
authors.forename: Tareef
authors.initials: T
authors.lastname: Daqqaq
authors.affiliation: SCOSSiS Statistical Consulting, Berlin, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Schwenke
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Charité Campus Mitte, Berlin, Germany.
authors.forename: Gesine
authors.initials: G
authors.lastname: Knobloch
authors.affiliation: Department of Radiology, Klinikum Ernst von Bergmann, Potsdam, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Huppertz
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Charité Campus Mitte, Berlin, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Hamm
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Charité Campus Mitte, Berlin, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lembcke
mesh_terms: D000368:Aged; D000465:Algorithms; D049628:Body Size; D000072226:Computed Tomography Angiography / Q000379:methods / Q000592:standards*; D017023:Coronary Angiography / Q000379:methods / Q000592:standards*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging; D003331:Coronary Vessels / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D012016:Reference Values; D015203:Reproducibility of Results; D012984:Software / Q000592:standards*; D014965:X-Rays
keywords: CT; Cardiac CT angiography; Coronary artery disease; Tube current; Tube voltage