V1718: Laser fibers, pulse energy and retropulsion - what we can see and what we can’t

Video

Introduction and Objectives
To evaluate through high-speed video analysis how retropulsion is affected by pulse energy, laser fiber diameter, the use of different lithotripters and by any other observable aspect.

Methods
Uniformly artificial stones (made of BegoStone plus®) immersed in saline and inside a polypropylene cylinder were put in direct contact with a laser fiber tip, through which a single laser pulse was fired. Three different laser lithotripters were tested, using for each of them two different laser fiber diameters, a smaller one (200-273 µm) and larger one (550-600 µm) at various pulse energies (0.2-3.5 J). All experiences were recorded with high-speed video, the distance the stone travelled measured and each video analyzed in order to detect any unexpected event.

Results
As pulse energy rises, so does the distance the artificial stones travels after laser impact, whatever the lithotripter or laser fiber diameter used. At equal energy levels, larger laser fiber diameters are associated with significantly greater stone displacement, regardless of the level of pulse energy or the laser lithotripter used. High-speed video analysis detected other interesting effects: if the laser fiber tip is inside a fragmentation crater, retropulsion increases considerably (sometimes over 40% more retropulsion); formation of cavitation bubbles and their resulting shockwaves were recorded, showing that even those stones that are not in direct contact with the laser fiber tip may be affected over considerably large distances; with very high pulse energies (2.0 J or higher), the sudden stone displacement produces a turbulence wave which pushes the stone even further away than the retropulsion effect alone.

Conclusions
Higher energy levels and larger laser fiber diameters promote an increased retropulsion effect. Retropulsion and stone position is significantly affected whether the laser fiber tip is barely touching the stone, inside a fragmentation crater or even at a substantially wider distance from the stone surface.

High-speed video analysis can bring new insights concerning laser lithotripsy, and reveal details that might otherwise remain concealed to the human eye.

Funding: none