Spiral computed tomography: role in determination of chemical compositions of pure and mixed urinary stones--an in vitro study.

Objectives: To determine the chemical composition of pure and mixed urinary calculi by multislice helical computed tomography (CT) in an in vitro setting. CT is becoming the preferred radiologic examination in diagnosis and management of calculus disease. The management of calculus disease can be facilitated by ascertaining the stone composition. Unnecessary shock wave treatment could be avoided if the fragility of the stones could be predicted at diagnosis.

Methods: A total of 107 stones (86 pure and 21 mixed) were measured in a multislice helical scanner within an air-filled environment. The scans were performed at two energy levels, 80 kV and 120 kV, with a 1-mm slice thickness. The chemical compositions of the urinary stones were assessed on the basis of the differences in the densities measured in Hounsfield units. The stones were assigned to six different groups according to the density measured in Hounsfield units: uric acid, struvite, cystine, calcium phosphate, calcium oxalate monohydrate, and calcium oxalate dihydrate.

Results: The differences in the density measured by multislice helical CT at 120 kV for the six groups of pure stones were statistically significant. The densities of the different regions within the mixed stones were also significantly different statistically from each other. The densities of the different regions measured in the mixed stones were not different from the densities of the corresponding pure stones. This finding supports the idea that different chemical compositions within a stone can be identified by their densities measured by multislice helical CT.

Conclusions: The chemical compositions of both pure and mixed stones can be determined by multislice helical CT in an in vitro setting. The feasibility of in vivo determinations remains to be clarified.