The ability of the acoustic energy/stone burden ratio to predict gallstone clearance in biliary lithotripsy.

The relationship between acoustic energy, stone burden, and stone clearance in biliary extracorporeal shock wave therapy (ESWL) is unclear. We hypothesized that there is a consistent relationship between these parameters that enables gallstone clearance to be predicted. Using a porcine model and various gallstone burdens, we performed biliary ESWL with varying energy levels and number of shock waves. The acoustic energy/stone burden ratio (AE/SB) was calculated that incorporated these variables. Stone clearance increased with higher energy settings and fewer stones present (p less than 0.005). The relationship between AE/SB ratio and stone clearance was logarithmic (r 2 = 0.82). The plateau of this curve showed optimal stone clearance at approximately 20 joules/g, beyond which point the benefit of further ESWL may not outweigh the risks. This relationship between AE/SB ratio and stone clearance may be able to predict the optimal energy required and probable outcome of biliary ESWL prior to the procedure.