title: Determination of renal stone composition with dual-energy CT: in vivo analysis and comparison with x-ray diffraction.
abstract: OBJECTIVE
  To preoperatively assess the composition of urinary stones by using dual-energy computed tomography (CT), with postoperative in vitro x-ray diffraction analysis as the reference standard.
  
  
  METHODS
  Institutional review board approval was obtained, and all participants provided written informed consent. Twenty-seven patients aged 50-64 years with renal stones, who were scheduled for stone extraction with percutaneous nephrolithotomy (PCNL), preoperatively underwent nonenhanced single-source dual-energy multidetector CT with 2-mm section thickness, 1-mm increments, 140 kVp, and 250 mAs. Regions of interest were drawn on low- and high-energy images, and low- and high-energy attenuation ratios were calculated for each stone scanned in vivo. The attenuation ratios for the patients were compared with those for an in vitro stone library phantom model of 37 stones with known chemical compositions. After surgery, the extracted stones were analyzed by using x-ray diffraction. The results of in vivo multidetector CT and ex vivo chemical analysis were compared.
  
  
  RESULTS
  Dual-energy low- and high-energy attenuation ratios measured with the phantom were less than 1.1 for uric acid, 1.1-1.24 for cystine, and greater than 1.24 for calcified stones. Struvite stones had attenuation ratios that overlapped with calcified stone ratios and thus could not be assessed reliably. Four patients had mixed stones (<75% of a single component), and one patient had a struvite stone. Of 27 patients, 22 (82%) (exact confidence interval [CI]: 68%, 92%) received a correct diagnosis with dual-energy CT: all six (100%; exact CI: 54%, 100%) patients with uric acid stones, 15 (79%; exact CI: 62%, 95%) of the 19 patients with calcium stones, and the one (100%) patient with a cystine stone. The patient with a struvite stone did not receive a correct dual-energy CT-based diagnosis.
  
  
  CONCLUSIONS
  Dual-energy multidetector CT may enable accurate in vivo characterization of kidney stone composition.
authors.affiliation: Department of Urology, Hadassah Hebrew University Medical Center, POB 12000, Jerusalem, Israel.
authors.forename: Guy
authors.initials: G
authors.lastname: Hidas
authors.forename: Ruth
authors.initials: R
authors.lastname: Eliahou
authors.forename: Mordechai
authors.initials: M
authors.lastname: Duvdevani
authors.forename: Phillipe
authors.initials: P
authors.lastname: Coulon
authors.forename: Laurent
authors.initials: L
authors.lastname: Lemaitre
authors.forename: Ofer N
authors.initials: ON
authors.lastname: Gofrit
authors.forename: Dov
authors.initials: D
authors.lastname: Pode
authors.forename: Jacob
authors.initials: J
authors.lastname: Sosna
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D011446:Prospective Studies; D012016:Reference Values; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014961:X-Ray Diffraction