title: Characterisation of urinary stones in the presence of iodinated contrast medium using dual-energy CT: a phantom study.
abstract: OBJECTIVE
  To develop a dual-energy CT (DECT) method for differentiating uric acid (UA) from non-UA stones in the presence of iodinated contrast medium.
  
  
  METHODS
  Thirty UA and 45 non-UA stones were selected after infra-red spectroscopic analysis and independently placed in a 1.5-ml vial, which was filled first with saline and then with increasing concentrations of iodine. For each condition, tubes were put in a 35-cm water phantom and examined using a dual-source CT system at 100 and 140 kV. Virtual unenhanced images created from CT data sets of the stones in iodine-containing solutions provided position and volume information. This map was used to calculate a CT number ratio to differentiate stone type. A region-growing method was developed to improve the ability to differentiate between UA and non-UA stones with iodinated contrast medium.
  
  
  RESULTS
  The sensitivity for detecting UA stones was 100 % for unenhanced images but fell to 18 % with 20 mgI/ml iodine solution and 0 % for higher concentrations. With region growing, the sensitivity for detecting UA stones was increased to 100 %, 82 %, 57 %, 50 % and 21 % for iodine solutions of 20, 40, 60, 80 and 100 mgI/ml.
  
  
  CONCLUSIONS
  The region-growing method improves differentiation of UA from non-UA stones on contrast-enhanced DECT urograms.
  
  
  CONCLUSIONS
  Computed tomography is widely used to assess renal tract calculi. Dual-energy CT can assess stone composition and provide virtual unenhanced images. However, iodinated contrast medium affects the volume estimation for urinary stones. CTR of stones is altered by the surrounding iodine in CT urograms. The region-growing method improves the identification of uric acid stones.
authors.affiliation: Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA. wang.jia2@mayo.edu
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.forename: Mingliang
authors.initials: M
authors.lastname: Qu
authors.forename: Xinhui
authors.initials: X
authors.lastname: Duan
authors.forename: Naoki
authors.initials: N
authors.lastname: Takahashi
authors.forename: Akira
authors.initials: A
authors.lastname: Kawashima
authors.forename: Shuai
authors.initials: S
authors.lastname: Leng
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D003287:Contrast Media; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007472:Iohexol; D019047:Phantoms, Imaging; D012372:ROC Curve; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014545:Urinary Calculi / Q000737:chemistry / Q000000981:diagnostic imaging*; D014567:Urography / Q000379:methods
chemical_list: D003287:Contrast Media; D007472:Iohexol