title: Virtual non-contrast in second-generation, dual-energy computed tomography: reliability of attenuation values.
abstract: OBJECTIVE
  To evaluate the reliability of attenuation values in virtual non-contrast images (VNC) reconstructed from contrast-enhanced, dual-energy scans performed on a second-generation dual-energy CT scanner, compared to single-energy, non-contrast images (TNC).
  
  
  METHODS
  Sixteen phantoms containing a mixture of contrast agent and water at different attenuations (0-1400 HU) were investigated on a Definition Flash-CT scanner using a single-energy scan at 120 kV and a DE-CT protocol (100 kV/SN140 kV). For clinical assessment, 86 patients who received a dual-phase CT, containing an unenhanced single-energy scan at 120 kV and a contrast enhanced (110 ml Iomeron 400 mg/ml; 4 ml/s) DE-CT (100 kV/SN140 kV) in an arterial (n=43) or a venous phase, were retrospectively analyzed. Mean attenuation was measured within regions of interest of the phantoms and in different tissue types of the patients within the corresponding VNC and TNC images. Paired t-tests and Pearson correlation were used for statistical analysis.
  
  
  RESULTS
  For all phantoms, mean attenuation in VNC was 5.3±18.4 HU, with respect to water. In 86 patients overall, 2637 regions were measured in TNC and VNC images, with a mean difference between TNC and VNC of -3.6±8.3 HU. In 91.5% (n=2412) of all cases, absolute differences between TNC and VNC were under 15HU, and, in 75.3% (n=1986), differences were under 10 HU.
  
  
  CONCLUSIONS
  Second-generation dual-energy CT based VNC images provide attenuation values close to those of TNC. To avoid possible outliers multiple measurements are recommended especially for measurements in the spleen, the mesenteric fat, and the aorta.
authors.affiliation: Department of Radiology, Medical University Vienna/Vienna General Hospital, Vienna, Austria. michael.toepker@meduniwien.ac.at
authors.forename: Michael
authors.initials: M
authors.lastname: Toepker
authors.forename: Thomas
authors.initials: T
authors.lastname: Moritz
authors.forename: Bernhard
authors.initials: B
authors.lastname: Krauss
authors.forename: Michael
authors.initials: M
authors.lastname: Weber
authors.forename: Gordon
authors.initials: G
authors.lastname: Euller
authors.forename: Thomas
authors.initials: T
authors.lastname: Mang
authors.forename: Florian
authors.initials: F
authors.lastname: Wolf
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Herold
authors.forename: Helmut
authors.initials: H
authors.lastname: Ringl
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media / Q000008:administration & dosage; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted; D015203:Reproducibility of Results; D012189:Retrospective Studies; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014584:User-Computer Interface; D014867:Water / Q000008:administration & dosage
chemical_list: D003287:Contrast Media; D014867:Water