title: Feasibility of discriminating uric acid from non-uric acid renal stones using consecutive spatially registered low- and high-energy scans obtained on a conventional CT scanner.
abstract: OBJECTIVE
  The objective of our study was to show the feasibility of distinguishing between uric acid (UA) and non-UA renal stones using two consecutive spatially registered low- and high-energy scans acquired on a conventional CT system.
  
  
  METHODS
  A total of 33 patients undergoing clinically indicated dual-source dual-energy CT examinations to differentiate UA from non-UA renal stones were enrolled in this study. Immediately after patients underwent clinically indicated dual-source dual-energy CT, two consecutive scans (one at 80 kV and one at 140 kV) were obtained on a conventional CT scanner over the region limited to the stones identified on the dual-source scans. After 3D deformable registration of the 80- and 140-kV images, UA and non-UA stones were identified using commercial software. The sensitivity, specificity, and accuracy of stone classification were calculated using the dual-source results as the reference standard.
  
  
  RESULTS
  A total of 469 stones were identified in the dual-source examinations (26 UA and 443 non-UA stones). The average in-plane stone diameter was 4.4 ± 2.5 (SD) mm (range, 2.0-18.9 mm). The overall sensitivity, specificity, and accuracy for identifying UA stones were 73.1%, 90.1%, and 89.1%, respectively. The sensitivity, specificity, and accuracy were 94.7%, 96.9%, and 96.8% for stones 3 mm or larger (n = 341 [19 UA and 322 non-UA]).
  
  
  CONCLUSIONS
  Accurate differentiation of UA from non-UA renal stones is feasible using two consecutively acquired and spatially registered conventional CT scans.
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St, SW, Rochester, MN 55905.
authors.forename: Shuai
authors.initials: S
authors.lastname: Leng
authors.forename: Maria
authors.initials: M
authors.lastname: Shiung
authors.forename: Songtao
authors.initials: S
authors.lastname: Ai
authors.forename: Mingliang
authors.initials: M
authors.lastname: Qu
authors.forename: Terri J
authors.initials: TJ
authors.lastname: Vrtiska
authors.forename: Katharine L
authors.initials: KL
authors.lastname: Grant
authors.forename: Bernhard
authors.initials: B
authors.lastname: Krauss
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schmidt
authors.forename: John C
authors.initials: JC
authors.lastname: Lieske
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003937:Diagnosis, Differential; D005240:Feasibility Studies; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007669:Kidney Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging*; D008875:Middle Aged; D011829:Radiation Dosage; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014527:Uric Acid / Q000737:chemistry*; D055815:Young Adult
chemical_list: D014527:Uric Acid
keywords: CT; deformable registration; dual-energy CT; renal stone; stone composition