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DoublePulse™ Technology

    The Trimedyne laser (1210-VHP) is only Holmium:YAG laser that  features  the DoublePulse™ waveform, which allows the user to deliver more energy to hard substances with less risk of damaging surrounding soft tissues.

     The Holmium:YAG laser works by generating both heat and an acoustic shock bubble.  Acoustic shock is one mechanism responsible for stone migration in ureteroscopy, when utilizing a laser as the lithotrite.  Our DoublePulse™ technology allows greater calculi fragmentation, while reducing the potential risk of ureteral wall injury encountered with single pulse mode.  The net result is rapid stone ablation with less risk of damaging the ureteral wall or other soft tissue and reduced calculi migration.

 

TRANSIENT CAVITATION AND ACOUSTIC EMISSION PRODUCED BY DIFFERENT LASER LITHOTRIPTERS

Pei Zhong, Ph.D., Hon-Leung Tong, M.S., Franklin Hadley Cocks, Ph.D., Margaret S. Pearle, M.D., Ph.D. and Glenn M. Preminger, M.D.

Abstract: Transient cavitation and shockwave generation produced by pulsed-dye and holmium:YAG laser lithotripters were studied using high-speed photography and acoustic emission measurements. In addition, stone phantoms were used to compare the fragmentation efficiency of various laser and electrohydraulic lithotripters. The pulsed-dye laser, with a wavelength (504 nm) strongly absorbed by most stone materials but not by water, and a short pulse duration of ~ 1 µsec, induces plasma formation on the surface of the target calculi. Subsequently, the rapid expansion of the plasma forms a cavitation bubble, which expands spherically to a maximum size and then collapses violently, leading to strong shockwave generation and microjet impingement, which comprises the primary mechanism for stone fragmentation with short-pulsed lasers. In contrast, the holmium laser, with a wavelength (2100 nm) most strongly absorbed by water as well as by all stone materials and a long pulse duration of 250 to 350 µsec, produces an elongated, pear-shaped cavitation bubble at the tip of the optical fiber that forms a vapor channel to conduct the ensuing laser energy to the target stone (Moss effect). The expansion and subsequent collapse of the elongated bubble is asymmetric, resulting in weak shockwave generation and microjet impingement. Thus, stone fragmentation in holmium laser lithotripsy is caused primarily by thermal ablation (drilling effect).

Introduction: Several types of laser, including pulsed-dye, alexandrite and holmium:YAG, are currently used for intracorporeal lithotripsy. These lasers differ significantly in wavelength, pulse duration, pulse energy, and therefore the mechanism of stone fragmentation and treatment efficiency. Although the physical processes in laser treatment are generally believed to include an initial optical breakdown in water or on the stone surface, with simultaneously generated plasma expansion and cavitation bubble formation, followed by subsequent shockwave emission and microjet formation produced by bubble collapse, the exact mechanism of action has not always been clearly elucidated. A fundamental understanding of the laser-stone interaction is critical for the effective and safe use of laser lithotripters, as well as for technical improvement in lasertripsy technology.

In this study, we utilized high-speed photography combined with acoustic pressure measurements to characterize the transient cavitation bubble oscillation and associated acoustic emission generated by holmium and pulsed-dye laser lithotripters. Stone fragmentation produced by different laser lithotripters, as well as by an electrohydraulic lithotripter (EHL) using a standard stone phantom, was compared. The implications of the study results relating to the improvement of lasertripsy technology are discussed.

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