The effect of stone size on comminution efficiency in shock wave lithotripsy
We have investigated the relationship between stone size and stone comminution (SC) in shock wave lithotripsy (SWL). Begostone phantoms of cylindrical shape in 4-, 7- and 10-mm size (W x H) groups were prepared with appropriately equal total mass (i.e., 1.5 g) in a tube holder and treated in an electromagnetic shock wave lithotripter field at various locations and doses. The results reveal a close correlation between SC and the average peak pressure, P+(avg), incident on the stone among differnet size groups. The P+(avg) threshold to initiate stone fragmentation and the slope of SC vs ln (P+(avg)) curve in water were found to increase with decreased stone size. In 1,3-butanediol where cavitation is suppressed, the P+(avg) threshold was found to be similar to the value in water yet the slope of the SC curve was significantly reduced at decreased stone size. Altogether, these results demonstrate a clear dependency of the P+(avg) threshold and rate of SC on stone size, as well as the importance of cavitation in producing efficiency stone comminution during SWL.
