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Evaluation of urinary tract stone chemical composition in vivo using dual-energy computerized tomography (CT).
Sergei Zorkin, MD, PhD, Artak Akopyan, MD, PhD, Dmitry Shakhnovskiy, MD, Aleksandra Mazo, MD, PhD, Lidia Vorobyova, MD, PhD.
SCCH RAMS, Moscow, Russian Federation.

In modern pediatric urology recurrent urolithiasis is a common problem. Based on a stone composition it is possible to establish the most appropriate dietary and pharmacological regimen for prevention of recurrent stone formation. The goal of this study was to evaluate the accuracy of dual-energy CT assessing the composition of urinary tract stones in vivo using X-ray diffraction as the reference standard.
Sixty seven patients (median age 4 years, range 6 months-18 years) with urolithiasis underwent a dual-energy (tube voltages, 140 and 80 kVp) unenhanced abdominal CT. We evaluated each stone volume, density in Hounsfield units (HU) and composition. All patients were treated with extracorporeal shock wave lithotripsy (ESWL). We performed X-ray diffraction of collected stone samples. Then agreement of dual-energy CT and X-ray diffraction results was assessed using Cohen kappa coefficient. The correlation among stone composition, volume and CT density was estimated using the Kruskal-Wallis test.
All patients had single urinary tract stone. Fifty nine stones were in kidneys and 8 were in ureters. The median stone volume was 0,392 cm3 (Range 0,035-8,172 cm3); median CT density was 1030 HU (Range 200-1900 HU). According to X-ray diffraction 59 stones were calcium oxalate, one xanthine, one cysteine, two uric acid and four were of mixed composition. CT allowed us to identify composition in all cases of single component stones. In mixed composition stones all chemical components were also identified, depending on stone region. Statistical analysis revealed substantial agreement between dual-energy CT and X-ray diffraction (Cohen κ = 0,712). Stone composition had statistically significant correlation with a CT density (p= 0,00932) and no correlation with a stone volume (p = 0,836).
Dual-energy CT scan demonstrated excellent accuracy in determining urinary tract stone chemical composition, including mixed stones.

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