title: Detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy CT.
abstract: OBJECTIVE
  To evaluate the detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy computed tomography (CT).
  
  
  METHODS
  This retrospective HIPAA-compliant study was institutional review board approved. All included patients had previously consented to the use of their medical records for research. Sixty-two patients (38 men, 24 women; age range, 35-91 years) had undergone CT urography, which consisted of nonenhanced and pyelographic-phase dual-energy CT performed by using a dual-source scanner. Commercial software was used to create virtual nonenhanced images by suppressing the iodine signal from the pyelographic-phase dual-energy CT scans. Two radiologists, in consensus, evaluated the virtual nonenhanced images for the presence of stones. Sensitivity for detecting stones was calculated on a per-stone basis. Sensitivity, specificity, and accuracy were also calculated on a per-renal unit (defined as the intrarenal collecting system and ureter of one kidney) basis. The true nonenhanced scan was considered the reference standard. A jackknife method was used because any patient may have multiple stones.
  
  
  RESULTS
  Of 62 patients with 122 renal units, 21 patients with 25 renal units had a total of 43 stones (maximal transverse diameter range, 1-24 mm; median, 3 mm). The overall sensitivity for detecting stones was 63% (27 of 43 stones) per stone. Sensitivities were 29% (four of 14 stones) for 1-2-mm stones, 64% (nine of 14 stones) for 3-4-mm stones, 83% (five of six stones) for 5-6-mm stones, and 100% (nine of nine stones) for 7-mm or larger (7, 7, 7, 8, 8, 9, 11, 15, and 24 mm) stones. All three ureteral stones (3, 4, and 8 mm) were correctly identified. The sensitivity, specificity, and accuracy for detecting stones on a per-renal unit basis were 65% (17 of 26 renal units), 92% (88 of 96 renal units), and 86% (105 of 122 renal units), respectively.
  
  
  CONCLUSIONS
  Virtual nonenhanced images generated at pyelographic-phase dual-energy CT enabled the detection of urinary stones with moderate accuracy. The detection of small (1-2-mm) stones was limited.
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Naoki
authors.initials: N
authors.lastname: Takahashi
authors.forename: Terri J
authors.initials: TJ
authors.lastname: Vrtiska
authors.forename: Akira
authors.initials: A
authors.lastname: Kawashima
authors.forename: Robert P
authors.initials: RP
authors.lastname: Hartman
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Primak
authors.forename: Joel G
authors.initials: JG
authors.lastname: Fletcher
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016001:Confidence Intervals; D003287:Contrast Media; D005260:Female; D006801:Humans; D007472:Iohexol; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012984:Software; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014545:Urinary Calculi / Q000000981:diagnostic imaging*; D014567:Urography
chemical_list: D003287:Contrast Media; D007472:Iohexol