FUNDAMENTAL STUDY ON THE PREDICTION OF RENAL CALCULI DESTROYED BY EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY : EVALUATION OF STONE MINERAL CONTENT USING DUAL ENERGY X-RAY ABSORPTIOMETRY

In vitro fracture study of renal calculi was performed to predict the destruction of stones by extracorporeal shock wave lithotripsy (ESWL). The mineral density (MD) and mineral content (MC) were measured using dual energy x-ray absorptiometry (DEXA), which is widely used for quantitative measurements of bone salt. MD and MC values obtained from 46 calculi correlated well with the numbers of ESWL shots (r=0.0807, r=0.811, respectively).MD and MC values obtained from 26 calculi of approximately the same sizes were assessed for the strength of calculi against the shock wave, and they showed better correlation with the nymbers of ESWL shots (r=0.783, r=0.763, respectively) than the CT values (r=0.719). Thesefore, MD and MC values reflected the fragility and strength of the calculi extremely well. In addition, multivariate analysis of the MD and MC and stone thicknesses improved the prediction accuracy as compared with simple variate analysis of MD or MC in predicting the number of ESWL shots. It is suggested that the destruction of renal calcuil by ESWL can be reliably predicted using measurements of MD and MC by DEXA and stone thicknesses.