Computed Tomography Evaluation of Urinary Stones Densities Compared to in Vitro Analysis of Its Chemical Composition

Recently, the use of noncontrast spiral computerized tomography (NCCT) has gained widespread acceptance in the evaluation of urinary stone patients. It has long been used clinically to evaluate the causes of radiolucent filling defects using Hounsfield units (HU) to distinguish calculi from tumor or blood clots, and to identify nonurologic causes of flank pain (Smith R etal ). Urinary stones have a significantly higher CT attenuation than the surrounding soft tissues and are virtually always visible on NCCT. Knowing the composition of a urinary calculus is frequently a key factor in determining its most appropriate management. Should the urine be alkalinized? Will the stone be amenable to extracorporeal shock wave lithotripsy (ESWL), or should ureteroscopy or percutaneous lithotripsy be attempted? Different techniques have been used to assist in determining the correct chemical composition of calculi. Urine pH, urinary crystals, prior stone history and the presence of urea-splitting organisms (Ramakumar S,etal). Several in vitro studies have suggested that NCCT can demonstrate measured differences in radiodensity among different urinary stones (Mitchenson HD etal,).With these clinical problems in mind, we sought to determine whether the composition of urinary calculi could be predicted by their CT characteristics in an attempt to find out the best technique for distinguishing the various stones compositions, provided that it is clinically practical and would not require repeated imaging of the patients.