title: Diagnostic utility of attenuation measurement (Hounsfield units) in computed tomography stonogram in predicting the radio-opacity of urinary calculi in plain abdominal radiographs.
abstract: OBJECTIVE
  (1) To determine the best cut-off level of Hounsfield units (HU) in the CT stonogram that would predict the appearance of a urinary calculi in plain KUB X-ray; (2) to estimate the sensitivity and specificity of the best cut-off HU; and (3) to determine whether stone size and location affect the in vivo predictability.
  
  
  METHODS
  A prospective cross-sectional study of patients aged 18-85 diagnosed with urolithiases on CT stonogram with concurrent plain KUB radiograph was conducted. Appearance of stones was recorded, and significant difference between radiolucent and radio-opaque CT attenuation level was determined using ANOVA. Receiver operating characteristics (ROC) curve determined the best HU cut-off value. Stone size and location were used for factor variability analysis.
  
  
  RESULTS
  A total of 184 cases were included in this study, and the average urolithiasis size on CT stonogram was 0.84 cm (0.3-4.9 cm). On KUB X-ray, 34.2 % of the urolithiases were radiolucent and 65.8 % were radio-opaque. Mean value of CT Hounsfield unit for radiolucent stones was 358.25 (±156), and that for radio-opaque stones was 816.51 (±274). ROC curve determined the best cut-off value of HU at 498.5, with the sensitivity of 89.3 % and specificity of 87.3 %. For >4 mm stones, the sensitivity was 91.3 % and the specificity was 81.8 %. On the other hand, for =<4 mm stones, the sensitivity was 60 % and the specificity was 89.5 %.
  
  
  CONCLUSIONS
  Based on the constructed ROC curve, a threshold value of 498.5 HU in CT stonogram was established as cut-off in determining whether a calculus is radio-opaque or radiolucent. The determined overall sensitivity and specificity of the set cut-off HU value are optimal. Stone size but not location affects the sensitivity and specificity.
authors.affiliation: St. Luke's Medical Center, Quezon City, Philippines. auhc_ekim@yahoo.com
authors.forename: Michael E
authors.initials: ME
authors.lastname: Chua
authors.forename: Glenn T
authors.initials: GT
authors.lastname: Gatchalian
authors.forename: Michael Vincent
authors.initials: MV
authors.lastname: Corsino
authors.forename: Buenaventura B
authors.initials: BB
authors.lastname: Reyes
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging; D007669:Kidney Calculi / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D014057:Tomography, X-Ray Computed; D014514:Ureteral Calculi / Q000000981:diagnostic imaging* / Q000473:pathology; D001743:Urinary Bladder / Q000000981:diagnostic imaging; D001744:Urinary Bladder Calculi / Q000000981:diagnostic imaging* / Q000473:pathology; D055815:Young Adult