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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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