Renal calculus composition analysis using dual-energy CT: a prospective observational study

To analyze preoperatively the composition of renal calculi using dual-energy computed tomography (DECT) and compare it with reference standard biochemical stone analysis. Eighty-one participants who were diagnosed with renal calculi underwent DECT at 80 kVp and 140 kVp. Spectral analysis was performed, and the energy map generated was used to classify the calculus based on available preset data. Average Hounsfield units (HU) were calculated for the two energy levels, and ratio of HU was derived (DE ratio) and calculus was categorized into different stone compositions. Hounsfield units of each calculus was measured at 120 kVp standard dose CT, and Hounsfield density (HU/largest transverse diameter) was derived. Comparison of results of spectral analysis and DE ratio was done and correlated with the biochemical laboratory analysis as reference standard wherever available. Spectral analysis and CT prediction of stone were performed for all 81 patients. CT prediction of stone based on DE ratio into “uric acid,” “struvite,” “calcium oxalate” and “calcium carbonate apatite” was performed. Assessment of stone composition by biochemical analysis was done for 65 patients who eventually underwent PCNL for stone extraction. Both DE ratio and spectral analysis were able to differentiate calculus into various types based on composition with statistically significant p values. However, spectral analysis proved to be marginally better in renal stone characterization particularly for mixed stones. The DE ratio for uric acid stones was derived as 0.9–1.1, 0.9–2.3 for mixed stones and 1.0–2.4 for calcium stones. Spectral analysis promises a practical approach to predicting calculus composition preoperatively, thereby avoiding unnecessary surgical intervention.