FIG. 6.

Stone breakage for wide and narrow focal zone lithotripters. Gypsum model stones held in a 2-mm mesh basket were positioned on-axis and at 5 mm and 10 mm off-axis in the plane of the target point of the lithotripter. SWs were fired at settings in the range of clinical treatment for the LG-380 (PL-9, 19 MPa), XX-ES (9.3 kV, 17 MPa), and Storz SLX (PL-9, 90 MPa) at 60 SW/min until no fragments remained in the basket. The Storz SLX was more effective at breaking stones positioned on-axis than either the LG-380 or the XX-ES (P<0.01). Breakage efficiency fell faster, however, for the narrow focal width SLX than for either of the two wide focal width lithotripters, with the SLX needing three times as many SWs to break stones positioned 5 mm off-axis as at the focus (P<0.001 vs on-axis). For the XX-ES, stones had to be moved to 10 mm off-axis for a significant increase in number of SWs to breakage (P<0.05), but this needed on average 34% more SWs than on-axis. The LG-380 needed a similar increase in number of SWs at 10 mm, on average 31% more than on-axis. *P<0.05, **P<0.001 vs SWs on-axis (distance=0).