Category: New Technology: Stones

MP5-4 - Comparison of vapor bubbles induced by an Holmium:YAG Laser and a SuperPusled Thulium Fiber Laser. Toward high speed lithotripsy at KHz repetition rate.

Fri, Sep 21
10:00 AM - 12:00 PM

Introduction & Objective :

The Thulium fiber laser (TFL) is being explored as an alternative to Ho:YAG Laser, the current gold standard laser source for lithotripsy. A greater efficiency of this technology is expected, as its wavelength of 1940 nm more closely matches the water absorption peak, providing an absorption coefficient about five times higher than Ho:YAG.
The aim of this study was to use high speed imaging to evaluate in vitro TFL induced bubbles, in order to determine the influence of these parameters on bubble formation, and how these bubbles differ from the Ho:YAG Laser.


Methods :

A 50W SuperPulsed surgical laser prototype of TFL (IPG Photonics, Oxford, MA) with a wavelength of 1940 nm, and a 30W Holmium:YAG laser MH1 (Rocamed, Monaco) were used in this study. Images of the laser activation were recorded at the tip of a 272 µm fiber immersed in a saline bath, using a Photron APX-RS 3000 high-speed camera, with a setting of 15 000 frames per second. Laser pulses were characterized using a photodiode connected to an oscilloscope. The recorded images were analysed with the software Photron FastCAM Viewer 2.4 (Photron Limited).


Results :

The TFL produces an almost uniform square shaped temporal energy profile, very different from the pulse generated by the holmium, which shows a peak of energy at the beginning of impulsion with a spherical shaped vapor bubble, followed by a linear decrease of the signal.
In contrast to the holmium laser, for which the size of the bubble increases with energy and pulse duration, TFL produces, when the pulse duration increases, a vapor channel with a stream of small bubbles, each locally expanding and collapsing axially out of phase with the other bubbles (called Moses effect).
Nevertheless, the lifetime of this stream of bubble is correlated to energy and pulse duration, and each bubble expands and collapses completely, before the generation of the next bubble, without overlap. We could deduce an exponential relationship between the pulse duration and the repetition frequency of the bubbles: for each pulse duration, TFL produces much more bubbles than Ho:YAG laser.


Conclusions : Due to its wavelength, TFL impulsion produces a uniform energy profile: Moses effect is possible, each bubble grows and collapses without interference, and more frequently than with the Ho:YAG laser. Further studies are necessary to confirm that this bubble number superiority leads to a lithotripsy superiority.

Paul H.L. Chiron

MD, FEBU
Sorbonne Université, GRC n°20, Groupe de Recherche Clinique sur la Lithiase Urinaire, AP-HP, Hôpital Tenon, F-75020 Paris, France
Saint Mandé, Ile-de-France, France

Laurent L. Berthe

Paris, Ile-de-France, France

Vincent De Coninck

Urologist
AZ Klina
Brasschaat, Antwerpen, Belgium

Vincent De Coninck graduated as a medical doctor from the Free University of Brussels, Belgium (VUB) in 2011. He became a certified urologist in 2017 after a training at the University Hospital of Brussels (Prof. Dr. Dirk Michielsen) and OLV Aalst (Prof. Dr. Alex Mottrie), where he developed a special interest in the minimal invasive treatment of benign and malignant pathologies. In the same year, he became Fellow of the European Board of Urology.
In 2018, he completed a one-year fellowship program of the Endourological Society in Paris, France under the supervision of Prof. Dr. Olivier Traxer. During that fellowship, he also obtained a diploma in urolithiasis, organized by Dr. Michel Daudon at the Sorbonne University in Paris, France. Afterwards, he was trained in HoLEP by Dr. Karin Lehrich in Berlin, Germany.
Currently, he is completing a three-month fellowship under the supervision of Dr. Guido Giusti in Milan, Italy. In December 2018, he will start working as an endourologist in AZ Klina, Brasschaat, Belgium. He will focus on the medical and surgical treatment of kidney stones and benign prostatic obstruction (HoLEP) and he will continue publishing articles relating to the management of patients with renal stone disease.

Etienne X. Keller

Fellow of the ES
Sorbonne Université, GRC n°20, Groupe de Recherche Clinique sur la Lithiase Urinaire, AP-HP, Hôpital Tenon, F-75020 Paris, France
Paris, Ile-de-France, France

Steeve S. Doizi

Urologist
Sorbonne Université, GRC n°20, Groupe de Recherche Clinique sur la Lithiase Urinaire, AP-HP, Hôpital Tenon, F-75020 Paris, France
Paris, Ile-de-France, France

Olivier O. Traxer

Professor
Sorbonne Universite, GRC n020 Lithiase Renale, AP-HP, Hospital Tenon, F-75020 Paris, France
Paris, Ile-de-France, France