Effect of lithotripter focal width on stone comminution in shock wave lithotripsy.
Using a reflector insert, the original HM-3 lithotripter field at 20 kV was altered significantly with the peak positive pressure (p(+)) in the focal plane increased from 49 to 87 MPa while the -6 dB focal width decreased concomitantly from 11 to 4 mm. Using the original reflector, p(+) of 33 MPa with a -6 dB focal width of 18 mm were measured in a pre-focal plane 15-mm proximal to the lithotripter focus. However, the acoustic pulse energy delivered to a 28-mm diameter area around the lithotripter axis was comparable ( approximately 120 mJ). For all three exposure conditions, similar stone comminution ( approximately 70%) was produced in a mesh holder of 15 mm after 250 shocks. In contrast, stone comminution produced by the modified reflector either in a 15-mm finger cot (45%) or in a 30-mm membrane holder (14%) was significantly reduced from the corresponding values (56% and 26%) produced by the original reflector (no statistically significant differences were observed between the focal and pre-focal planes). These observations suggest that a low-pressure/broad focal width lithotripter field will produce better stone comminution than its counterpart with high-pressure/narrow focal width under clinically relevant in vitro comminution conditions.
Qin
Jun
J
Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, USA.
Simmons
W Neal
WN
Sankin
Georgy
G
Zhong
Pei
P
D000162:Acoustics / Q000295:instrumentation; D002137:Calculi; D004867:Equipment Design; D008096:Lithotripsy / Q000295:instrumentation*; D008422:Materials Testing; D008962:Models, Theoretical; D009038:Motion; D019047:Phantoms, Imaging; D011312:Pressure; D013997:Time Factors; D014160:Transducers, Pressure