title: Split-bolus dual-energy CT urography: protocol optimization and diagnostic performance for the detection of urinary stones.
abstract: OBJECTIVE
  Prospective protocol optimization, determination of image quality and diagnostic performance of virtual non-enhanced images (VNEI) derived from split-bolus dual-energy computed tomography (DECT) urography in patients with urinary stones.
  
  
  METHODS
  IRB-approved, prospective study of 100 patients who, after written informed consent, underwent single-energy, non-enhanced CT and split-bolus, contrast-enhanced DECT (30 + 50 mL of contrast media; combined nephro-urographic acquisition). DECT was performed using setting A (80/140 kVp) in the first 20, and setting B (100/140 kVp) in the second 20 patients. Tin filtration was used in all patients. After a pre-analysis of VNEI quality, 60 additional patients were examined using setting B. Two readers qualitatively and quantitatively determined image quality of all weighted-average DECT images regarding urinary tract opacification (n = 100), and all VNEI regarding quality of iodine subtraction and urinary stone detection (n = 80). True nonenhanced (TNEI) images were the standard of reference for statistical analysis (inter-reader variability and diagnostic performance characteristics).
  
  
  RESULTS
  The urinary tract was completely opacified in 94% (94/100) of patients. Iodine subtraction was improved (p < 0.01) and image noise of VNEI was lower (p < 0.05) in DECT setting B. On VNEI, 83% (86/104) of urinary stones were correctly identified and 17% (18/104) were missed. Stones missed (2.5 mm, 1-4) were significantly smaller than stones correctly identified (5 mm, 2-27; p < 0.001). Diagnostic accuracy was 98% on a per-renal-unit basis and 96% on a per-patient basis. Inter-reader agreements were excellent (κ = 0.91-1.00; ICC = 0.86-0.99).
  
  
  CONCLUSIONS
  Split-bolus DECT urography was technically feasible and quality of VNEI was improved with the 100/140 kVp setting. Detection of urinary stones <4 mm on VNEI was limited.
authors.affiliation: Department of Radiology, University Hospital Zurich, Raemistrasse 100, 8091, Zurich, Switzerland, christoph.karlo@gmail.com.
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Karlo
authors.forename: Ralph
authors.initials: R
authors.lastname: Gnannt
authors.forename: Anna
authors.initials: A
authors.lastname: Winklehner
authors.forename: Michael A
authors.initials: MA
authors.lastname: Fischer
authors.forename: Olivio F
authors.initials: OF
authors.lastname: Donati
authors.forename: Daniel
authors.initials: D
authors.lastname: Eberli
authors.forename: Tullio
authors.initials: T
authors.lastname: Sulser
authors.forename: Hatem
authors.initials: H
authors.lastname: Alkadhi
authors.forename: Paul
authors.initials: P
authors.lastname: Stolzmann
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media; D005260:Female; D006801:Humans; D007472:Iohexol / Q000031:analogs & derivatives; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods; D013382:Subtraction Technique; D014545:Urinary Calculi / Q000000981:diagnostic imaging*; D014567:Urography / Q000379:methods*
chemical_list: D003287:Contrast Media; D007472:Iohexol; C038192:iopromide