Study of fiber-tip damage mechanism during Ho:YAG laser lithotripsy by high-speed camera and the Schlieren method
2015
Fiber-tip degradation, damage, or burn back is a common problem during the ureteroscopic laser lithotripsy procedure
to treat urolithiasis. Fiber-tip burn back results in reduced transmission of laser energy, which greatly reduces the
efficiency of stone comminution. In some cases, the fiber-tip degradation is so severe that the damaged fiber-tip will
absorb most of the laser energy, which can cause the tip portion to be overheated and melt the cladding or jacket
layers of the fiber. Though it is known that the higher the energy density (which is the ratio of the laser energy fluence
over the cross section area of the fiber core), the faster the fiber-tip degradation, the damage mechanism of the fibertip
is still unclear. In this study, fiber-tip degradation was investigated by visualization of shockwave, cavitation/bubble
dynamics, and calculus debris ejection with a high-speed camera and the Schlieren method. A commercialized, pulsed
Ho:YAG laser at 2.12 um, 273/365/550-um core fibers, and calculus phantoms (Plaster of Paris, 10x10x10 mm cube)
were utilized to mimic the laser lithotripsy procedure. Laser energy induced shockwave, cavitation/bubble dynamics,
and stone debris ejection were recorded by a high-speed camera with a frame rate of 10,000 to 930,000 fps. The
results suggested that using a high-speed camera and the Schlieren method to visualize the shockwave provided
valuable information about time-dependent acoustic energy propagation and its interaction with cavitation and
calculus. Detailed investigation on acoustic energy beam shaping by fiber-tip modification and interaction between
shockwave, cavitation/bubble dynamics, and calculus debris ejection will be conducted as a future study.
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