title: In vivo identification of uric acid stones with dual-energy CT: diagnostic performance evaluation in patients.
abstract: BACKGROUND
  To prospectively investigate the in vivo diagnostic performance of dual-energy (DE) computed tomography (CT) for the differentiation between uric acid (UA)-containing and non-UA-containing urinary stones.
  
  
  METHODS
  DE CT scans were performed in 180 patients with suspected urinary stone disease using a dual-source CT scanner in the DE mode (tube voltages 80 and 140 kV). Urinary stones were classified as UA-containing or non-UA-containing based on CT number measurements and DE software results. Sensitivity, specificity, positive predictive values (PPV), and negative predictive values (NPV) for the detection of UA-containing urinary stones were calculated using the crystallographic stone analysis as the reference standard.
  
  
  RESULTS
  DE CT detected 110/180 patients (61%) with urinary stone disease. In 53 patients, stones were sampled. Forty-four out of 53 stones (83%) were non-UA-containing; and nine stones (17%) were UA-containing. The software automatically mapped 52/53 (98%) stones. One non-UA-containing stone (UA, 2 mm) was missed; one UA-containing stone (3 mm) was misclassified by software analysis. The sensitivity, specificity, PPV, and NPV for the detection of UA-containing stones was 89% (8/9, 95% CI: 52-100%), 98% (43/44, 95% CI: 88-100%), 89% (8/9, 95% CI: 52-100%), and 98% (43/44, 95% CI: 88-100%).
  
  
  CONCLUSIONS
  Our results indicate that DE dual-source CT permits for the accurate in vivo differentiation between UA-containing and non-UA-containing urinary stones.
authors.affiliation: Institute of Diagnostic Radiology, University Hospital Zurich, Raemistr. 100, 8091, Zurich, Switzerland. paul.stolzmann@usz.ch
authors.forename: Paul
authors.initials: P
authors.lastname: Stolzmann
authors.forename: Marko
authors.initials: M
authors.lastname: Kozomara
authors.forename: Natalie
authors.initials: N
authors.lastname: Chuck
authors.forename: Michael
authors.initials: M
authors.lastname: Müntener
authors.forename: Sebastian
authors.initials: S
authors.lastname: Leschka
authors.forename: Hans
authors.initials: H
authors.lastname: Scheffel
authors.forename: Hatem
authors.initials: H
authors.lastname: Alkadhi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018360:Crystallography, X-Ray; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012372:ROC Curve; D011857:Radiographic Image Interpretation, Computer-Assisted; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014527:Uric Acid; D014545:Urinary Calculi / Q000737:chemistry / Q000000981:diagnostic imaging*
chemical_list: D014527:Uric Acid