Pattern Analysis of Laser Fiber Degradation According to the Laser Setting: In Vitro Study of the Double-Firing Phenomenon

Abstract

Background: It is essential to understand the mechanism of the various causes of laser fiber damage and an ideal method of reducing endoscope damage induced by laser emission in multiple sites. This study classified the different patterns of laser fiber degradation according to laser settings and analyzed the role of cavitation bubbles to find a desirable way of minimizing endoscope damage.

Methods: A total of 118 laser fibers were analyzed after 1-,3-, and 5-min laser emission to artificial stones under the settings of 1 J-10 Hz, 1 J-20 Hz, 1 J-30 Hz, and 2 J-10 Hz. Every 3 cm from the fiber tip was marked and examined with a digital microscope and a high-speed camera. The images of the fibers and the movement of cavitation bubbles were taken with a distance of 1 to 5 mm from the gel.

Results: Seven types of fiber damage (charring, limited and extensive peeled-off, bumpy, whitish plaque, crack, and break-off) coincided during laser emission. Damages rapidly increased with emission time > 3 minutes regardless of the laser settings. The damaged lengths covered 5 mm on average, and the fibers at 5-min emission were significantly shorter than others. The fiber durability of 1J-10Hz setting was better than other settings after 3-min laser emission. Backward movement of the cavitation bubbles was found at the 1-mm distance from the gel, and the damaged lengths were longer than the diameters of the cavitation bubbles because of their proximal movement.

Conclusion: The damage patterns of the laser fiber tips were classified into seven types. The heat damage around the surface of the laser fiber can be increased according to the high-energy or high-frequency laser setting, a short distance to the stone, a short distance from the tips of flexible ureteroscopes, no cutting laser fiber procedures, and the inappropriate use of irrigation fluid or laser fiber jacket.

Keywords: Lasers; Pattern of Degradation; Ureteroscopes.

Fig. 1. Patterns of laser fiber degradation. Types of laser fiber damages. (A) Charring, (B) Limited peeled off, (C) Extensive peeled off, (D) Bumpy, (E) Bumpy, (F) Crack, (G) Break off.

Fig. 2. Cavitation around the tip of the laser fiber. Single shot of laser emission with the energy of 1 J, 40,000 frames per second, and 1 microsec minimum exposure time.

Fig. 3. Size differences of cavitation bubbles according to the laser power (J). Migration of the bubbles at the distance of 1 mm.

Fig. 4. Laser tip during flexible ureteroscopic surgery. The laser fiber cannot be advanced > 3 mm from the tip of the flexible ureteroscope to reach the stone when the laser fiber almost escapes from the stones because of the acute deflection angle in a lower pole (A) or in a diverticular space (B). Change in the lengths of the intact part of the laser fibers are shown before and after pop-dusting techniques for 5 minutes. The laser setting of 1 J-20 Hz (C, D) showed longer remnant laser fibers than 1 J-30 Hz (E, F).