title: In vivo characterization of urinary calculi on dual-energy CT: going a step ahead with sub-differentiation of calcium stones.
abstract: BACKGROUND
  The role of dual-energy computed tomography (DECT) in characterization of urinary calculi is evolving and literature regarding differentiation of calcium calculi is sparse and confounding.
  
  
  OBJECTIVE
  To evaluate the capability of DECT in assessing the urinary calculi composition in vivo, especially in differentiating various types of calcium calculi.
  
  
  METHODS
  One hundred and twenty patients underwent DECT for characterization of urinary calculi. Seventy patients with 114 calculi, including 93 calcium stones, were retrospectively analyzed. DE ratios and attenuation differences were compared using ANOVA and receiver-operating-characteristic (ROC) analysis was done to predict cut-off values, in particular for detecting calcium-oxalate-monohydrate (COM) stones.
  
  
  RESULTS
  DE ratio ≤1.14 accurately detected uric acid calculi, ≥1.29 was definitive for calcium and intermediate values were characteristic of cystine stones. DE ratios were significantly different between group 1 (COM [n = 32]; mean 1.376 ± 0.041), group 2 ([calcium oxalate dihydrate (COD) + COM] [n = 51]; 1.416 ± 0.048), and group 3 ([carbonate apatite (CaP) + COD + COM] [n = 10]; 1.468 ± 0.038) (group 1 vs. 2, P = 0.001; 1 vs. 3, P = 0.000; 2 vs. 3, P = 0.004). More importantly, pure COM calculi (group 1) had significantly lower DE ratio compared with mixed calcium calculi (groups 2 and 3) (P = 0.000). Attenuation differences (between low and high kV images) could not distinguish between COM and mixed calculi. ROC analysis for detection of COM calculi yielded AUC of 0.770 with cut-off DE ratio 1.385 (sensitivity 65.6%, specificity 82%) and value <1.335 was seen only with COM calculi (100% specificity).
  
  
  CONCLUSIONS
  DECT can be employed for in vivo differentiation of various types of calculi and for detection of relatively lithotripsy-resistant COM calculi.
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences (AIIMS), New Delhi, India.
authors.forename: Sudeep
authors.initials: S
authors.lastname: Acharya
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences (AIIMS), New Delhi, India.
authors.forename: Ankur
authors.initials: A
authors.lastname: Goyal
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences (AIIMS), New Delhi, India.
authors.forename: Ashu Seith
authors.initials: AS
authors.lastname: Bhalla
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences (AIIMS), New Delhi, India raju152@yahoo.com.
authors.forename: Raju
authors.initials: R
authors.lastname: Sharma
authors.affiliation: Department of Urology, All India Institute of Medical Sciences (AIIMS), New Delhi, India.
authors.forename: Amlesh
authors.initials: A
authors.lastname: Seth
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences (AIIMS), New Delhi, India.
authors.forename: Arun Kumar
authors.initials: AK
authors.lastname: Gupta
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging; D008297:Male; D012372:ROC Curve; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014545:Urinary Calculi / Q000000981:diagnostic imaging*
keywords: CT; Urinary; adults; calcifications/calculi; kidneys