title: Dual-energy CT iodine-subtraction virtual unenhanced technique to detect urinary stones in an iodine-filled collecting system: a phantom study.
abstract: OBJECTIVE
  The objective of our study was to evaluate the feasibility of virtual unenhanced images reconstructed from a dual-energy CT scan to depict urinary stones in an iodine solution in a phantom study.
  
  
  METHODS
  Twenty urinary stones of different sizes (1.4-4.2 mm in short-axis diameter) were placed in plastic containers. The containers were consecutively filled with different concentrations of iodine solution (21, 43, 64, 85, and 107 mg/dL; CT attenuation value range, 510-2,310 H at 120 kVp). Dual-energy CT was repeated with 80-140 and 100-140 kVp pairs, two collimation-slice thickness combinations, and the presence or absence of a 4-cm-thick oil gel around the phantom. The iodine-subtraction virtual unenhanced images were reconstructed using commercial software. The images were evaluated by three radiologists in consensus for the visibility of the stones and the presence of residual nonsubtracted iodine. Stone visibility rates were compared between the 80-140 and 100-140 kVp pairs and the five different iodine concentrations.
  
  
  RESULTS
  Stone visibility rates with the 80-140 kVp pair were 99%, 93%, 96%, 94%, and 3% and those with the 100-140 kVp pair were 98%, 95%, 99%, 94%, and 99% for an iodine concentration of 21, 43, 64, 85, and 107 mg/dL, respectively. The poor visibility rate with 80-140 kVp and 107 mg/dL iodine concentration was due to the failure of iodine subtraction.
  
  
  CONCLUSIONS
  Dual-energy CT iodine-subtraction virtual unenhanced technique is capable of depicting urinary stones in iodine solutions of a diverse range of concentrations in a phantom study.
authors.affiliation: Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA.
authors.forename: Naoki
authors.initials: N
authors.lastname: Takahashi
authors.forename: Robert P
authors.initials: RP
authors.lastname: Hartman
authors.forename: Terri J
authors.initials: TJ
authors.lastname: Vrtiska
authors.forename: Akira
authors.initials: A
authors.lastname: Kawashima
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Primak
authors.forename: Oleksandr P
authors.initials: OP
authors.lastname: Dzyubak
authors.forename: Jayawant N
authors.initials: JN
authors.lastname: Mandrekar
authors.forename: Joel G
authors.initials: JG
authors.lastname: Fletcher
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D007455:Iodine; D008954:Models, Biological; D019047:Phantoms, Imaging; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014545:Urinary Calculi / Q000000981:diagnostic imaging*
chemical_list: D007455:Iodine