title: Radiation Dose Reduction in Dual-Energy CT: Does It Affect the Accuracy of Urinary Stone Characterization?
abstract: OBJECTIVE
  The purpose of this article is to assess the effect of radiation dose reduction in dual-energy CT (DECT) on the performance of renal stone characterization using a patient cohort.
  
  
  METHODS
  CT data from 39 unenhanced DECT examinations performed for stone characterization were retrospectively analyzed in this study. Reduced-dose images were simulated at 75%, 50%, and 25% of the routine dose using a previously validated noise-insertion algorithm. Differentiation between uric acid (UA) and non-UA stones was performed using a fixed cutoff value for the dual-energy ratio. ROC analysis was performed to determine optimal cutoff values and the associated sensitivity and specificity.
  
  
  RESULTS
  Of the 206 stones found, 43 were UA and 163 were non-UA. The mean (± SD) volume CT dose index (CTDIvol) was 16.0 ± 4.0 mGy at the 100% dose level. The mean noise in 100-kV images increased from 40.9 ± 6.8 HU at 100% dose to 46.8 ± 8.8 HU, 57.7 ± 12.5 HU, and 85.4 ± 22.9 HU at 75%, 50%, and 25% dose levels, respectively. Using the default cutoff value, for stones 10 mm(3) or larger, the sensitivity/specificity were 100.0%/98.8%, 82.8%/98.8%, and 89.3%/98.7%, at 75%, 50%, and 25% dose levels, respectively. ROC analysis showed varying optimal cutoff values at different dose levels. The sensitivity and specificity improved with use of these optimal cutoff values. Differentiation capability decreased for stones smaller than 10 mm(3).
  
  
  CONCLUSIONS
  At 75% of the 16-mGy routine dose, the sensitivity and specificity for differentiating UA from non-UA stones were minimally affected for stones 10 mm(3) or larger. The use of optimal cutoff values for dual-energy ratio as dose decreased (and noise increased) provided improved performance.
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Mingliang
authors.initials: M
authors.lastname: Qu
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Lifeng
authors.initials: L
authors.lastname: Yu
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Daniel Gomez
authors.initials: DG
authors.lastname: Cardona
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Yu
authors.initials: Y
authors.lastname: Liu
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Xinhui
authors.initials: X
authors.lastname: Duan
authors.affiliation: 2 Department of Radiology, Shanghai Ninth People's Hospital, Shanghai, China.
authors.forename: Songtao
authors.initials: S
authors.lastname: Ai
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.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Maria
authors.initials: M
authors.lastname: Shiung
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D014527:Uric Acid / Q000737:chemistry; D014545:Urinary Calculi / Q000000981:diagnostic imaging*
chemical_list: D014527:Uric Acid
keywords: dual-energy CT; dual-energy ratio; radiation dose reduction; renal stone composition; uric acid stones; urinary stones