Fiber fragmentation during laser lithotripsy

Laser lithotripsy (LISL) in combination with a bare fiber can lead to fragmentation of the fiber tip. Fiber fragmentation of four lithotripsy laser systems was measured under clinical conditions (calcium sulphate stone, covered with water), a q-switched alexandrite laser, a pulsestretched alexandrite laser and two different dye lasers were used. The threshold for fiber fragmentation for pulses of gaussian shape was 200MW/cm² peak powerdensity. The q-switched alexandrite laser leads to fragmentation rates of 100mm/1000 pulses at typical pulseenergies (50mJ, 150ns), whereas fiber fragmentation did not occur if dye lasers were used (80mJ, 1,3μs; 80mJ, 2,5μs) due to their longer pulselengths and lower powerdensities respectively. Using a pulsestretched alexandrite laser fragmentation could be avoided if pulselengths above 1μs were used. We demonstrate that during LISL the fiber fragments which are produced will be embedded in the ureter wall and therefore subsequent formation of stenoses may be possible.