To evaluate the ability of noncontrast computed tomography (NCCT) to predict stone composition and fragility for treatment with extracorporeal shock wave lithotripsy (SWL).

A total of 103 stones from patients who had undergone different open surgical procedures were scanned with a 64 detector row helical computed tomography (CT) scanner using 1-mm collimation at 2 energy levels of 80 and 120 kV. The chemical compositions of the urinary stones were assessed on the basis of the differences in the densities measured in Hounsfield units (HU). Stones were then broken in an electromagnetic lithotripter until complete fragmentation, and number of shock waves was counted.

After exclusion of the groups with few calculi, 46 pure stones (18 uric acid, 22 calcium oxalate monohydrate, 6 struvite) and 48 mixed stones were included in the statistical analysis. For measurements at 120-kV, 80-kV, and dual-energy CT values, the overall difference between the densities of the stones was statistically significant; however there was a cross-over in densities between all stone groups. There were significant positive correlations at 120-kV, 80-kV, and dual-energy CT values between stone density and number of shock waves required for complete fragmentation. Stones with HU >1000 required statistically significant higher number of shock waves.

Multidetector CT is not an accurate method for detection of human stone compositions; however a high stone CT attenuation value is s significant predictor of failure to fragment renal stones by SWL.