title: Differentiation of kidney stones using dual-energy CT with and without a tin filter.
abstract: OBJECTIVE
  The aim of this in vitro study was to examine the capability of three protocols of dual-energy CT imaging in distinguishing calcium oxalate, calcium phosphate, and uric acid kidney stones.
  
  
  METHODS
  A total of 48 calcium oxalate, calcium phosphate, and uric acid human kidney stone samples were placed in individual containers inside a cylindric water phantom and imaged with a dual-energy CT scanner using the following three scanning protocols of different combinations of tube voltage, with and without a tin filter: 80 and 140 kVp without a tin filter, 100 and 140 kVp with a tin filter, and 80 and 140 kVp with a tin filter. The mean attenuation value (in Hounsfield units) of each stone was recorded in both low- and high-energy CT images in each protocol. The dual-energy ratio of the mean attenuation values of each stone was computed for each protocol.
  
  
  RESULTS
  For all three protocols, the uric acid stones were significantly different (p < 0.001) from the calciferous stones according to their dual-energy ratio values. For differentiating calcium oxalate and calcium phosphate stones, the difference between their dual-energy ratio values was statistically significant, with different degrees of significance (range, p < 0.001 to p = 0.03) for all three protocols. On the basis of the values of the area under receiver operating characteristic curve (AUC) of calcified stone differentiation, the three protocols were ranked in the following order: the 80- and 140-kVp tin filter protocol (AUC, 0.996), the 100- and 140-kVp tin filter protocol (AUC, 0.918), and the 80- and 140-kVp protocol (AUC, 0.871).
  
  
  CONCLUSIONS
  The tin filter added to the high-energy tube and the use of a wider dual-energy difference are important for improving the stone differentiation capability of dual-energy CT imaging.
authors.affiliation: The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD 21287, USA. gfung2@jhmi.edu
authors.forename: George S K
authors.initials: GS
authors.lastname: Fung
authors.forename: Satomi
authors.initials: S
authors.lastname: Kawamoto
authors.forename: Brian R
authors.initials: BR
authors.lastname: Matlaga
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Taguchi
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhou
authors.forename: Elliot K
authors.initials: EK
authors.lastname: Fishman
authors.forename: Benjamin M W
authors.initials: BM
authors.lastname: Tsui
mesh_terms: D000704:Analysis of Variance; D002129:Calcium Oxalate / Q000032:analysis; D002130:Calcium Phosphates / Q000032:analysis; D006801:Humans; D066298:In Vitro Techniques; D007669:Kidney Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D012372:ROC Curve; D014001:Tin; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*; D014527:Uric Acid / Q000032:analysis
chemical_list: D002130:Calcium Phosphates; D002129:Calcium Oxalate; D014527:Uric Acid; D014001:Tin; C020243:calcium phosphate