OBJECTIVE: The purpose of this article is to evaluate in vivo the chemical composition of urinary stones using dual-source and dual-energy CT, with crystallography as the reference standard.
MATERIALS AND METHODS: Forty patients (mean [± SD] age, 49 ± 17 years) with known or suspected nephrolithiasis underwent unenhanced abdominal CT for urinary tract evaluation using a dual-energy technique (tube voltages, 140 and 80 kVp). For each stone 5 mm or larger in diameter, we evaluated the site, diameter, CT density, surface (smooth vs rough), and stone composition. Patients were treated with extracorporeal shock wave lithotripsy (n = 34), percutaneous nephrolithotomy (n = 4), or therapeutic ureterorenoscopy (n = 2). Collected stones underwent crystallography, and the agreement with the results of dual-energy CT was calculated with the Cohen kappa coefficient. The correlation among stone composition, diameter, and CT density was estimated using the Kruskal-Wallis test.
RESULTS: Thirty-one patients had a single stone and nine had multiple stones, for a total of 49 stones. Forty-five stones were in the kidneys, and four were in the ureters; 23 had a smooth surface and 26 had a rough surface. The mean stone diameter was 12 ± 6 mm; mean CT density was 783 ± 274 HU. According to crystallography, stone composition was as follows: 33 were calcium oxalate, seven were cystine, four were uric acid, and five were of mixed composition. Dual-energy CT failed to identify four stones with mixed composition, resulting in substantial agreement between dual-energy CT and crystallography (Cohen κ = 0.684). Stone composition was not correlated with either stone diameter (p = 0.920) or stone CT density (p = 0.185).
CONCLUSION: CT showed excellent accuracy in classifying urinary stone chemical composition, except for uric acid-hydroxyapatite mixed stones.
AJR Am J Roentgenol. 2011 Jul;197(1):W76-83. doi: 10.2214/AJR.10.5217
PMID: 21700999 [PubMed - indexed for MEDLINE]
Impressive pictures demonstrate the capability of the dual energy CT to identify the stone composition in the patient before treatment in correlation to the stone analysis after stone removal. There were problems with the exact diagnosis of mixed stones. 4 of 5 mixed stones were not correctly identified. I wonder how precise the technique is in term of stone analysis: 33 of 49 stones were identified as Calcium oxalate. But we know from stone analysis that only 1/3 of CaOx stones have one component only.
Something is wrong with the software and the co-authoring urologist: "Referring to the manufacturer's standard settings, the software displayed calcium stones in blue and noncalcium stones in red." "By varying these settings, we were also able to differentiate three types of stones among noncalcium stones—uric acid, hydroxyapatite, and cystine ". Hydroxyapatite identified as a noncalcium stone?