The efficacy of non-contrast helical computed tomography in the prediction of urinary stone composition in vivo.

The composition of urinary stones was predicted on the basis of the differences in their Hounsfield unit (HU) densities as detected by in vivo non-contrast helical computed tomography (NCHCT). A total of 87 stones, which had been obtained from patients admitted to the emergency department with acute flank pain, were analysed biochemically. These stones had been visualized by NCHCT before spontaneous passage, ureteroscopic extraction or surgical removal, and their HU densities had been recorded. The HU densities of the stones were compared with the results of biochemical analysis. The mean HU densities of the stones composed of calcium oxalate (n = 54), struvite (n = 19) and uric acid (n = 14) were 812 +/- 135, 614 +/- 121 and 413 +/- 143, respectively. The differences between the mean HU densities of these three stone types were statistically significant. This initial clinical study demonstrated that in vivo NCHCT analysis may be used to predict the composition of urinary stones.