Transient Cavitation and Acoustic Emission Produced by Different Laser Lithotripters

Abstract

Transient cavitation and shockwave generation produced by pulsed-dye and holmium:YAG laser lithotripters were studied using high-speed photography and acoustic emission measurements. In addition, stone phantoms were used to compare the fragmentation efficiency of various laser and electrohydraulic lithotripters. The pulsed-dye laser, with a wavelength (504 nm) strongly absorbed by most stone materials but not by water, and a short pulse duration of approximately 1 microsec, induces plasma formation on the surface of the target calculi. Subsequently, the rapid expansion of the plasma forms a cavitation bubble, which expands spherically to a maximum size and then collapses violently, leading to strong shockwave generation and microjet impingement, which comprises the primary mechanism for stone fragmentation with short-pulse lasers. In contrast, the holmium laser, with a wavelength (2100 nm) most strongly absorbed by water as well as by all stone materials and a long pulse duration of 250 to 350 microsec, produces an elongated, pear-shaped cavitation bubble at the tip of the optical fiber that forms a vapor channel to conduct the ensuing laser energy to the target stone (Moss effect). The expansion and subsequent collapse of the elongated bubble is asymmetric, resulting in weak shockwave generation and microjet impingement. Thus, stone fragmentation in holmium laser lithotripsy is caused primarily by thermal ablation (drilling effect).

Elastic Waves of a Single Elasto-Hydrodynamically Lubricated Contact

“…The third zero frequency cannot be identified, which can be a result of several causes, such as cavitation, signalto-noise ratio or an uncertain defined contact time. Even though Zong et al [14] demonstrate cavitation excites high frequencies, which would be in line with covering zero frequencies such as in this case for third order and higher orders, the uncertain defined contact time in the EHL case is the most plausible explanation for the covering of the zero frequencies of third order and higher, which is observed in both simulation and measurement. Signal-tonoise ratio can be eliminated, due to the fact that covering of the zero frequencies of third and higher order is present in the simulations.…”

“…The difficulties of the complex nature of an EHL contact itself remain. This complexity of an EHL contact is also a reason for fundamental research in acoustic emission to focus on fundamental sources such as transient forces [13] or cavitation [14] which both occur in an EHL contact. However, studying fundamental sources is just a first step towards the study of full EHL contacts.…”

Fiber-optic manipulation of urinary stone phantoms using holmium:YAG and thulium fiber lasers

“…8,12,16,[20][21][22] Some of these reports have shown images of small residual effects of the bubble collapse behind the fiber tip. 12,19 This is presumably due to a collapsing bubble-induced pressure wave propagating in the axial direction of the fiber, both toward and away from the fiber tip.…”

“…Previous investigators have shown that for both increased absorption and longer pulse durations, the cavitation bubble becomes elongated and multiple cavitation bubbles may form. [15][16][17] Indirect evidence of this is seen in both the results for the TFL microsphere experiments and the shockwave-induced luminescence observed emanating from two distinct points in front of the fiber tip [ Fig. 6(a)].…”

“…The area of luminescence appeared oval and resembled the shape of holmium-induced cavitation bubbles reported by other investigators. 12,15,16,18,19 …”