title: Differentiating calcium oxalate and hydroxyapatite stones in vivo using dual-energy CT and urine supersaturation and pH values.
abstract: OBJECTIVE
  Knowledge of urinary stone composition can guide therapeutic intervention for patients with calcium oxalate (CaOx) or hydroxyapatite (HA) stones. In this study, we determined the accuracy of noninvasive differentiation of these two stone types using dual-energy CT (DECT) and urine supersaturation (SS) and pH values.
  
  
  METHODS
  Patients who underwent clinically indicated DECT scanning for stone disease and subsequent surgical intervention were enrolled. Stone composition was determined using infrared spectroscopy. DECT images were processed using custom-developed software that evaluated the ratio of CT numbers between low- and high-energy images. Clinical information, including patient age, gender, and urine pH and supersaturation profile, was obtained from electronic medical records. Simple and multiple logistic regressions were used to determine if the ratio of CT numbers could discriminate CaOx from HA stones alone or in conjunction with urine supersaturation and pH.
  
  
  RESULTS
  Urinary stones (CaOx n = 43, HA n = 18) from 61 patients were included in this study. In a univariate model, DECT data, urine SS-HA, and urine pH had an area under the receiver operating characteristic curve of 0.78 (95% confidence interval [CI] 0.66-0.91, P = .016), 0.76 (95% CI 0.61-0.91, P = .003), and 0.60 (95% CI 0.44-0.75, P = .20), respectively, for predicting stone composition. The combination of CT data and the urinary SS-HA had an area under the receiver operating characteristic curve of 0.79 (95% CI 0.66-0.92, P = .007) for correctly differentiating these two stone types.
  
  
  CONCLUSIONS
  DECT differentiated between CaOx and HA stones similarly to SS-HA, whereas pH was a poor discriminator. The combination of DECT and urine SS or pH data did not improve this performance.
authors.affiliation: Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905.
authors.forename: Yu
authors.initials: Y
authors.lastname: Liu
authors.forename: Mingliang
authors.initials: M
authors.lastname: Qu
authors.forename: Rickey E
authors.initials: RE
authors.lastname: Carter
authors.forename: Shuai
authors.initials: S
authors.lastname: Leng
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Ramirez-Giraldo
authors.forename: Giselle
authors.initials: G
authors.lastname: Jaramillo
authors.forename: Amy E
authors.initials: AE
authors.lastname: Krambeck
authors.forename: John C
authors.initials: JC
authors.lastname: Lieske
authors.forename: Terri J
authors.initials: TJ
authors.lastname: Vrtiska
authors.forename: Cynthia H
authors.initials: CH
authors.lastname: McCollough
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002129:Calcium Oxalate / Q000737:chemistry* / Q000652:urine*; D003937:Diagnosis, Differential; D017886:Durapatite / Q000737:chemistry* / Q000652:urine*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016482:Urinalysis / Q000379:methods; D014545:Urinary Calculi / Q000737:chemistry / Q000000981:diagnostic imaging*; D055815:Young Adult
chemical_list: D002129:Calcium Oxalate; D017886:Durapatite
keywords: Dual-energy CT; composition characterization; urinary stones; urine pH; urine supersaturation