title: In vivo evaluation of the chemical composition of urinary stones using dual-energy CT.
abstract: OBJECTIVE
  The purpose of this article is to evaluate in vivo the chemical composition of urinary stones using dual-source and dual-energy CT, with crystallography as the reference standard.
  
  
  METHODS
  Forty patients (mean [± SD] age, 49 ± 17 years) with known or suspected nephrolithiasis underwent unenhanced abdominal CT for urinary tract evaluation using a dual-energy technique (tube voltages, 140 and 80 kVp). For each stone 5 mm or larger in diameter, we evaluated the site, diameter, CT density, surface (smooth vs rough), and stone composition. Patients were treated with extracorporeal shock wave lithotripsy (n = 34), percutaneous nephrolithotomy (n = 4), or therapeutic ureterorenoscopy (n = 2). Collected stones underwent crystallography, and the agreement with the results of dual-energy CT was calculated with the Cohen kappa coefficient. The correlation among stone composition, diameter, and CT density was estimated using the Kruskal-Wallis test.
  
  
  RESULTS
  Thirty-one patients had a single stone and nine had multiple stones, for a total of 49 stones. Forty-five stones were in the kidneys, and four were in the ureters; 23 had a smooth surface and 26 had a rough surface. The mean stone diameter was 12 ± 6 mm; mean CT density was 783 ± 274 HU. According to crystallography, stone composition was as follows: 33 were calcium oxalate, seven were cystine, four were uric acid, and five were of mixed composition. Dual-energy CT failed to identify four stones with mixed composition, resulting in substantial agreement between dual-energy CT and crystallography (Cohen κ = 0.684). Stone composition was not correlated with either stone diameter (p = 0.920) or stone CT density (p = 0.185).
  
  
  CONCLUSIONS
  CT showed excellent accuracy in classifying urinary stone chemical composition, except for uric acid-hydroxyapatite mixed stones.
authors.affiliation: Dipartimento di Radiologia, Centro Diagnostico Italiano, Milan, Italy.
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Manglaviti
authors.forename: Silvia
authors.initials: S
authors.lastname: Tresoldi
authors.forename: Chiara Stefania
authors.initials: CS
authors.lastname: Guerrer
authors.forename: Giovanni
authors.initials: G
authors.lastname: Di Leo
authors.forename: Emanuele
authors.initials: E
authors.lastname: Montanari
authors.forename: Francesco
authors.initials: F
authors.lastname: Sardanelli
authors.forename: Gianpaolo
authors.initials: G
authors.lastname: Cornalba
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000328:Adult; D000368:Aged; D002129:Calcium Oxalate / Q000032:analysis*; D003553:Cystine / Q000032:analysis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014463:Ultrasonography; D014527:Uric Acid / Q000032:analysis*; D014545:Urinary Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging*
chemical_list: D002129:Calcium Oxalate; D014527:Uric Acid; D003553:Cystine