Effect of firing rate on the performance of shock wave lithotriptors

• Published in: BJU international 2008-12, Vol.102 (11), p.1681-1686
• Main Authors: Pishchalnikov, Yuri A., McAteer, James A., Williams Jr, James C.
• Format: Article
• Language: English
• Subjects: acoustic output; Acoustics; Biological and medical sciences; cavitation bubbles; Humans; Kidney Calculi - therapy; Lithotripsy - instrumentation; Lithotripsy - methods; Lithotripsy - standards; Medical sciences; Nephrology. Urinary tract diseases; shock wave lithotripsy
• ISSN: 1464-4096; 1464-410X
• DOI: 10.1111/j.1464-410X.2008.07896.x

OBJECTIVE To determine the mechanism that underlies the effect of shock wave (SW) rate on the performance of clinical lithotripters. MATERIALS AND METHODS The effect of firing rate on the pressure characteristics of SWs was assessed using a fibre‐optic probe hydrophone (FOPH 500, RP Acoustics, Leutenbach, Germany). Shock waves were fired at slow (5–27 SW/min) and fast (100–120 SW/min) rates using a conventional high‐pressure lithotriptor (DoLi‐50, Dornier MedTech America, Inc., Kennesaw, GA, USA), and a new low‐pressure lithotriptor (XX‐ES, Xi Xin Medical Instruments Co. Ltd, Suzhou, PRC). A digital camcorder (HDR‐HC3, Sony, Japan) was used to record cavitation fields, and an ultrafast multiframe high‐speed camera (Imacon 200, DRS Data & Imaging Systems, Inc., Oakland, NJ, USA) was used to follow the evolution of bubbles throughout the cavitation cycle. RESULTS Firing rate had little effect on the leading positive‐pressure phase of the SWs with the DoLi lithotriptor. A slight reduction (≈7%) of peak positive pressure (P+) was detected only in the very dense cavitation fields (≈1000 bubbles/cm3) generated at the fastest firing rate (120 SW/min) in nondegassed water. The negative pressure of the SWs, on the other hand, was dramatically affected by firing rate. At 120 SW/min the peak negative pressure was reduced by ≈84%, the duration and area of the negative pressure component was reduced by ≈80% and ≈98%, respectively, and the energy density of negative pressure was reduced by >99%. Whereas cavitation bubbles proliferated at fast firing rates, HS‐camera images showed the bubbles that persisted between SWs were very small (