High resolution detection of internal structure of renal calculi by helical computerized tomography

Purpose: There is considerable interest in using radiological imaging to predict kidney stone fragility before patient treatment. Case series of shock wave lithotripsy show that shock wave lithotripsy is repeated and/or ancillary procedures are done to remove shock wave resistant stones in a significant number of cases. If the fragility of stones were predicted at diagnosis, unnecessary shock wave treatment would be avoided. However, plain radiography allows little discrimination of stone type and simple numerical analysis of computerized tomography (CT) images by measuring Hounsfield units has been shown to be limited in its ability to predict stone fragility. Materials and Methods: Urinary stones of known composition were imaged by helical CT in vitro at various slice widths and the images were assessed using a range of window settings. Results: Visualization of stone structure was greatly enhanced using bone windows and a narrow slice width. Surface structure, such as crystalline leaves of calcium oxalate dihydrate, and internal structure showing the heterogeneity of composition or cracks were detected. Stones of similar mineral composition differed dramatically in terms of CT visible structure. Conclusions: Using a narrow slice width and bone windows greatly improves the visualization of kidney stone structure on helical CT. These results open up new possibilities for determining the relationship of stone structure and fragility for shock wave lithotripsy.