Category: New Technology: Stones

MP5-15 - Stone/tissue discrimination and fiber breakage control for laser lithotripsy: using an aiming beam in more ways

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

Introduction & Objective :

Ureteroscopic lithotripsy with a laser is a safe procedure generally. However, there is a remaining risk of damaging or perforating ureter or kidney tissue. We have realized a set-up where stone autofluorescence excited by a green aiming beam is exploited for stone- tissue discrimination. This has already been used for in vivo measurements and was now modified to additionally monitor fiber breakage or severe damage by measuring the aiming beam’s reflection at the fiber tip.

Methods :

An advanced fiber-fiber-coupling set-up for a Holmium laser including a green aiming beam for real-time lock-in measurement of reflection and fluorescence signals was used in in vitro studies with human renal calculi (n>20), porcine calix and endoscope components. Both signals were recorded during application of Holmium laser pulses using intact as well as damaged fibers.

Results :

The autofluorescence was 4-130 times higher on stone than on tissue /endoscope components. The signal decreases only linearly for fiber-stone distance <1mm (fiber diameter 365µm) and quadratically for longer distances – i.e. the fluorescence was measurable in non-contact mode. The signal was still well above detection threshold even with severely damaged fibers (worst measured decrease: 75%). The reflection signal amplitude dropped with inferior fiber tip surface quality (fiber breakage detection). Combined evaluation of fluorescence and reflection amplitude gives additional information on the fiber position - when the reflection signal rises without simultaneous increase of the fluorescence signal, the fiber is positioned near tissue or a lithotripsy tool.

Conclusions : Our experiments confirmed that autofluorescence excited by a green aiming beam can be exploited for stone detection in laser lithotripsy and showed that additional information can be collected by simultaneously measuring the reflection signal. Both signals complement each other for monitoring of the correct position of the treatment fiber and checking its status (broken or intact) in real-time. By integrating our set-up into a laser system one can realize an automatic feedback control preventing the laser from being fired when the fiber is not placed near urinary calculi.  This will improve the precision and therefore safety of ureteroscopic procedures tremendously.

Birgit Lange

Medizinisches Laserzentrum Lübeck GmbH
Luebeck, Schleswig-Holstein, Germany

Dr. rer. nat. Birgit Lange, Medizinisches Laserzentrum Lübeck GmbH.

Since October 2009: Scientific employee at the Medical Laser Center Lübeck, working, among other things, in the field of fiber based methods for stone-tissue-differentiation for laser lithotripsy.
2007-2009: Development engineer with Dr. Johannes Heidenhain GmbH, Traunreut.
2001-2007: Scientific employee at the Max-Planck-Institut für Quantenoptik, Garching (Phd study).
1995-2001: Physics-study at the Ruprecht-Karls-Universität Heidelberg.

Jens Cordes

University Hospital Schleswig-Holstein (Campus Luebeck)
Luebeck, Schleswig-Holstein, Germany

Ralf Brinkmann

Luebeck, Schleswig-Holstein, Germany