title: Dual-Energy CT for Quantification of Urinary Stone Composition in Mixed Stones: A Phantom Study.
abstract: OBJECTIVE
  The purpose of this study was to assess the feasibility of using dual-energy CT to accurately quantify uric acid and non-uric acid components in urinary stones of mixed composition.
  
  
  METHODS
  A total of 24 urinary stones were analyzed with micro CT to serve as the reference standard for uric acid and non-uric acid composition. These stones were placed in water phantoms to simulate body attenuation of slim to obese adults and scanned with a third-generation dual-source CT scanner by use of dual-energy modes adaptively selected on the basis of phantom size. CT number ratio, which is distinct for different materials, was calculated for each pixel of the stones. Each pixel was then classified as uric acid and non-uric acid by comparison of the CT number ratio with preset thresholds ranging from 1.10 to 1.70. Minimal, maximal, and root-mean-square errors were calculated by comparing composition with the reference standard, and the threshold with the minimal root-mean-square error was determined. A paired t test was performed to compare the stone composition determined with dual-energy CT with the reference standard obtained with micro CT.
  
  
  RESULTS
  The optimal CT number ratio threshold ranged from 1.27 to 1.55, dependent on phantom size. The root-mean-square error ranged from 9.60% to 12.87% across all phantom sizes. Minimal absolute error ranged from 0.04% to 1.24% and maximal absolute error from 22.05% to 35.46%. Dual-energy CT and the reference micro CT did not differ significantly on uric acid and non-uric acid composition (paired t test, p = 0.20-0.96).
  
  
  CONCLUSIONS
  Accurate quantification of uric acid and non-uric acid composition in mixed stones is possible with dual-energy CT.
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: Alice
authors.initials: A
authors.lastname: Huang
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
authors.forename: Juan Montoya
authors.initials: JM
authors.lastname: Cardona
authors.affiliation: 1 Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.|2 Present address: Department of Radiology, University of Texas Southwestern, Dallas, TX.
authors.forename: Xinhui
authors.initials: X
authors.lastname: Duan
authors.affiliation: 3 Department of Anatomy and Cell Biology, Indiana University, Indianapolis, IN.
authors.forename: James C
authors.initials: JC
authors.lastname: Williams
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: D006801:Humans; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014545:Urinary Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging*; D055114:X-Ray Microtomography
keywords: dual-energy CT; mixed stones; stone composition; urinary stones