Background and Purpose: The effect of laser pulse width on calculus retropulsion during ureteroscopic
lithotripsy is poorly defined because of the limited availability of variable pulse-width lasers. We used an adjustable
pulse-width Ho:YAG laser to test the effect of pulse width on in vitro phantom-stone retropulsion
and fragmentation efficiency.
Methods and Materials: An Odyssey 30 Ho:YAG laser (Convergent Laser Technologies, Oakland, CA) with adjustable pulse width (350 or 700 sec) was used to treat spherical 10-mm plaster calculi in a model ureter (N 40) and calix (N 16) utilizing 200- and 400- m fibers (10 Hz, 1.0 J). Calculi were placed in a waterfilled
clear polymer tube, and laser energy was applied continuously in near contact until the stone had moved 8 cm. The time (seconds) and energy (joules) needed to cause the stone to traverse this distance was recorded. Stones were also placed in a stainless-steel mesh calix model in which retropulsion was limited. Laser energy was applied for 5 minutes at each pulse width. A laser-energy meter (Molectron Detector Inc, Portland OR) was used to quantify fiber transmission efficiency after 1 minute of continuous lithotripsy for each fiber at each pulse width.
Results: Retropulsion was greater for stones treated at 350 sec, indicated by a shorter time to traverse the model ureter. For the 200- m fiber at 350 sec, the average time was 11.5 seconds v 20.3 seconds at 700 sec (P 0.001). The average total energy delivered was 114.9 J at 350 sec v 199.8 J at 700 sec (P 0.001). For
the 400- m fiber at 350 sec, the average time was 5.8 seconds v 11.9 seconds at 700 sec (P 0.001). The average total energy was 57.1 J at 350 sec v 127.3 J at 700 sec (P 0.001). In the caliceal model, at 350 and 700 sec with the 200- and 400- m fibers, mass loss was 34.9% and 33.4% (P 0.8) and 14.6% and
21.6% (P 0.04), respectively. The reduction in energy transmission at 350 sec and 700 sec with the 200- m fiber after 60 seconds of continuous lasing was 8.82% v 9%, respectively (P 0.95). For the 400- m fiber, the transmission loss was 18.4% at 350 sec v 4.4% at 700 sec (P 0.0002).
Conclusion: When treating ureteral calculi, retropulsion can be reduced by using a longer pulse width without compromising fragmentation efficiency. For caliceal calculi, the longer pulse width in combination with a 400- m fiber provides more effective stone fragmentation.
Background and Objectives: The purpose of this study was to investigate the effect of optical pulse duration on
stone retropulsion during Ho:YAG (l¼2.12 mm) laser lithotripsy.
Study Design/Materials and Methods: A clinical
Ho:YAG laser with pulse durations was employed to fragment calculus phantoms and to evaluate stone phantom retropulsion. At a given pulse energy, optical pulse
durations were divided into two discrete conditions: short pulse (sp: 120 190 mseconds at FWHM) and long pulse (sp: 210 350 mseconds at FWHM). Plaster of Paris calculus phantoms were ablated at different energy levels using optical fibers of varying diameters (273, 365, and 550 mm in core size). The dynamics of the recoil action of a calculus phantom was monitored using a high-speed camera; the laser-induced craters were evaluated with optical coherent tomography (OCT). Bubble formation and collapse were recorded with a fast flash photography setup, and acoustic transients were measured with a hydrophone.
Results: Shorter pulse durations produced more stone retropulsion than longer pulses at any given pulse energy. Regardless of pulse duration, higher pulse energy and larger fibers resulted in larger ablation volume and retropulsion (P<0.05). For shorter pulse durations, more rapid bubble expansion was observed and higher amplitudes of the collapse pressure wave were measured (P<0.05).
Conclusion: Less retropulsion and equivalent fragmentation occurred when Ho:YAG pulse duration increased.
