title: Dual-energy CT in patients suspected of having renal masses: can virtual nonenhanced images replace true nonenhanced images?
abstract: OBJECTIVE
  To qualitatively and quantitatively compare virtual nonenhanced (VNE) data sets derived from dual-energy (DE) computed tomography (CT) with true nonenhanced (TNE) data sets in the same patients and to calculate potential radiation dose reductions for a dual-phase renal multidetector CT compared with a standard triple-phase protocol.
  
  
  METHODS
  This prospective study was approved by the institutional review board; all patients provided written informed consent. Seventy one men (age range, 30-88 years) and 39 women (age range, 22-87 years) underwent preoperative DE CT that included unenhanced, DE nephrographic, and delayed phases. DE CT parameters were 80 and 140 kV, 96 mAs (effective). Collimation was 14 x 1.2 mm. CT numbers were measured in renal parenchyma and tumor, liver, aorta, and psoas muscle. Image noise was measured on TNE and VNE images. Exclusion of relevant anatomy with the 26-cm field of view detector was quantified with a five-point scale (0 = none, 4 = >75%). Image quality and noise (1 = none, 5 = severe) and acceptability for VNE and TNE images were rated. Effective radiation doses for DE CT and TNE images were calculated. Differences were tested with a Student t test for paired samples.
  
  
  RESULTS
  Mean CT numbers (+/- standard deviation) on TNE and VNE images, respectively, for renal parenchyma were 30.8 HU +/- 4.0 and 31.6 HU +/- 7.1, P = .29; liver, 55.8 HU +/- 8.6 and 57.8 HU +/- 10.1, P = .11; aorta, 42.1 HU +/- 4.1 and 43.0 HU +/- 8.8, P = .16; psoas, 47.3 HU +/- 5.6 and 48.1 HU +/- 9.3 HU, P = .38. No exclusion of the contralateral kidney was seen in 50 patients, less than 25% was seen in 43, 25%-50% was seen in 13, and 50%-75% was seen in four. Mean image noise was 1.71 +/- 0.71 for VNE and 1.22 +/- 0.45 for TNE (P < .001); image quality was 1.70 HU +/- 0.72 for VNE and 1.15 HU +/- 0.36 for TNE (P < .0001). In all but three patients radiologists accepted VNE images as replacement for TNE images. Mean effective dose for DE CT scans of the abdomen was 5.21 mSv +/- 1.86 and that for nonenhanced scans was 4.97 mSv +/- 1.43. Mean dose reduction by omitting the TNE scan was 35.05%.
  
  
  CONCLUSIONS
  In patients with renal masses, DE CT can provide high-quality VNE data sets, which are a reasonable approximation of TNE data sets. Integration of DE scanning into a renal mass protocol will lower radiation exposure by 35%.
authors.affiliation: Department of Clinical Radiology, University of Munich-Grosshadern Campus, Marchioninistr 15, 81377 Munich, Germany. anno.graser@med.lmu.de
authors.forename: Anno
authors.initials: A
authors.lastname: Graser
authors.forename: Thorsten R C
authors.initials: TR
authors.lastname: Johnson
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Hecht
authors.forename: Christoph R
authors.initials: CR
authors.lastname: Becker
authors.forename: Christianne
authors.initials: C
authors.lastname: Leidecker
authors.forename: Michael
authors.initials: M
authors.lastname: Staehler
authors.forename: Christian G
authors.initials: CG
authors.lastname: Stief
authors.forename: Henriette
authors.initials: H
authors.lastname: Hildebrandt
authors.forename: Myrna C B
authors.initials: MC
authors.lastname: Godoy
authors.forename: Myra E
authors.initials: ME
authors.lastname: Finn
authors.forename: Flora
authors.initials: F
authors.lastname: Stepansky
authors.forename: Maximilian F
authors.initials: MF
authors.lastname: Reiser
authors.forename: Michael
authors.initials: M
authors.lastname: Macari
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001822:Body Burden; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult