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Ho:YAG laser lithotripsy in non-contact mode: optimization of fiber to stone working distance to improve ablation efficiency

Abstract

Purpose

To evaluate how variable working distances between the laser fiber and the stone influence ablation volume.

Methods

A laser fiber was fixed on a robotic arm perpendicular to an artificial stone. A single laser pulse was triggered at different working distances (0–2.0 mm in 0.2 mm increments) between the distal fiber tip and the stone. To achieve a measurable impact, pulse energy was set to 2 and 3 J, with either short or long pulse duration. Ablation volume was calculated with an optical microscope. Experiments were repeated five times for each setting.

Results

Highest ablation volume was observed with a long pulse of 3 J at a working distance of 0.4 mm between the laser fiber and the stone surface (p value < 0.05). At 2 J, the highest ablation volume was noticed with a short pulse in contact mode. However, ablation volume of the latter was not significantly greater than with a long pulse of 2 J at a working distance of 0.4 mm (p value > 0.05). Compared to lithotripsy in contact mode, triggering a single long pulse at 0.4 mm increased ablation volume by 81% (p value = 0.016) at 2 J and by 89% (p value = 0.034) at 3 J.

Conclusions

For Ho:YAG laser lithotripsy, ablation volume may be higher in non-contact mode using long pulses, rather than in direct contact to the stone. Findings of the current study support the need of further studies of lithotripsy in non-contact mode.

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Abbreviations

Ho:YAG:

Holmium:yttrium–aluminum–garnet

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Acknowledgements

We would like to express our greatest appreciation to Prof. Gregory Altshuler, Prof. Nathaniel M. Fried and Viktoriya Vinnichenko for their valuable suggestions and proofreading of this article.

Funding

Prof. Olivier Traxer is a consultant for Coloplast, Rocamed, Olympus, EMS and Boston Scientific. Dr. Steeve Doizi is a consultant for Coloplast. Dr. Vincent De Coninck is supported by the EUSP scholarship from the European Association of Urology and by a grant from the Belgische Vereniging voor Urologie (BVU). Dr. Etienne Xavier Keller is supported by a Travel Grant from the University Hospital Zurich and by a grant from the Kurt and Senta Herrmann Foundation.

Author information

VDC: protocol/project development, data collection or management, data analysis, manuscript writing/editing. EXK: protocol/project development, data collection or management, data analysis, manuscript writing/editing. PC: protocol/project development, data collection or management, data analysis. LD: protocol/project development. EE: protocol/project development. SD: protocol/project development, data analysis. LB: protocol/project development, data analysis. OT: protocol/project development, data collection or management, data analysis, manuscript writing/editing.

Correspondence to Olivier Traxer.

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We did not perform research involving human participants and/or animals.

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De Coninck, V., Keller, E.X., Chiron, P. et al. Ho:YAG laser lithotripsy in non-contact mode: optimization of fiber to stone working distance to improve ablation efficiency. World J Urol 37, 1933–1939 (2019). https://doi.org/10.1007/s00345-018-2589-8

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Keywords

  • Distance
  • Ho:YAG
  • Laser
  • Nephrolithiasis
  • Non-contact