In vivo determination of renal stone composition with dual-energy computed tomography

Background: Composition of renal stones influences management of patients with renal stone disease. Currently stone composition can only be analysed ex vivo after stone extraction or passage, but recent introduction of dual-energy computed tomography (CT) to clinical practice has raised interest in the ability of this technology to determine composition of renal stones in vivo. Objectives: To determine renal stone composition in patients using single-source dual-energy rapid-peak kilovolt (kVp) switching CT. Method: Nineteen patients with renal stones for percutaneous nephrolithotomy were evaluated with single-source dual-energy computed tomography on a Discovery CT 750HD. The Gemstone Spectral Imaging (GSI) effective atomic number (Z(eff)) and attenuation at 70 keV monochromatic energy were used to predict the stone composition. Infrared spectroscopy and x-ray diffraction of stones after extraction served as the reference standard. Results: Two (10.5%) of the 19 stones had uric acid as major component. The other 17 (89.5%) were calcium-based stones. No statistically significant difference between the GSI Zeff and calculated effective atomic number (Z) for stone compounds was found. The GSI Zeff and attenuation could differentiate between uric acid and non-uric acid stones. No differentiation between different calcium stones could be made. Conclusion: Uric acid and non-uric acid renal stones can be differentiated with single-source dual-energy in vivo. The GSI Zeff reflects the dominant material in polycrystalline stones.