WO1991005332A1 - Process and device for generating laser-induced shock wave - Google Patents

Abstract

Process for transmitting extremely high light intensities via light guide systems for the generation of shock waves to shatter bodily accretions, in which two or more successive pulses are transmitted via a light guide, whereby the slope of the leading edge of the shock wave is determined by the displacement in time of the individual shock pulses, and a device for implementing the process.

Description

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Method and device for producing

 laser-induced shock waves

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Description

The invention relates to a method in the preamble

of claim 1 specified type and a device for

Execution of the procedure.

The transmission of extremely high light intensities

Light guide systems, especially optical fibers, are from beson their interest in creating an optical breakthrough at the end of these light guide systems, which in turn acts as a source for secondary shock waves that can be used, for example, to erode and destroy material surfaces, membranes or concretions. In the medical field of application, shock waves generated in this way are used to crush the concretions of the kidneys, bladders, galls, pakreas and saliva stones.

The state of the art should be based on the

Figures 1 to 5, which form simple explanatory representations, are briefly described:

It is known to use short-pulsed laser systems to generate shock waves. Here, in particular for the generation of shock waves in a liquid environment, after transmission of the light pulses through optical waveguide 3, focusing optics 1, according to FIG. 1, are provided, or materials are introduced into the optical beam path that have the lowest possible breakthrough threshold, be it in form of solid surfaces, such as in the case of the so-called optoacoustic transducer 2 - according to FIG. 2 - or in the form of small suspended particles 4 in the liquid - according to FIG. 3 Particles are generated and can only be secondary to the Target structure work. If additional focusing auxiliary measures, such as distal optics 1 or 5 - according to FIG. 5 - are used, the radiation can also be focused on the target structure to be destroyed and the breakthrough can be achieved directly on the surface. However, it is difficult to achieve focus diameters in the output of an optical waveguide that are significantly smaller than the output aperture of the optical waveguide by means of optical focusing aids, especially when there is an additional requirement that the diameter of the focusing optics should not be significantly greater than the diameter of the optical waveguide. to achieve a high flexibility of the system. It is also known to use high-intensity light pulses directly at the output of the fiber by placing them on the target structure to generate shock waves. However, the optical breakthrough can only be achieved if the energy density (J / cm ² ) is high enough, ie the fibers are sufficiently thin. On the other hand, there is then the difficulty on the coupling-in side of coupling high-energy pulses into the fiber, because then very often the power density in the fiber input exceeds the destruction threshold. According to the prior art, this problem is solved by using lasers with particularly long pulse lengths, which leads to a reduction in the pulse peak power while maintaining the total energy. On the other hand, this has the problem that the pressure amplitudes of the shock wave front are lower at the fiber output, since the energy is built up over a longer period of time and insofar as the efficiency of the shock wave destruction falls. Another disadvantage of all existing systems that do not generate the shock wave on or in the surface of the target material is that the degree of conversion of laser energy into shock wave energy is significantly less than 10%. It is only when the shock wave is generated directly in the target structure that conversion efficiencies of greater than 60% can be achieved. The invention is based on the object of specifying a method and a device for generating laser-induced shock waves in which the conversion efficiency is increased. This object is achieved with the characterizing features of claim 1.

The invention is based, among other things, on the knowledge that the damage thresholds of optical light guide systems not only have an integral upper limit power density both on the surface and in volume, but that the damage threshold is both wavelength and time-dependent. According to the invention, the energy for generating the optical breakthrough is transmitted in the form of two or more successive pulses through the optical waveguide, the time offset of the starting points of the individual pulses being determined by the desired steepness of the shock wave front. The method is used to transmit extremely high light intensities, which generate shock waves by means of an optical breakthrough in order to crush body concrements. By transmitting the energy in the form of two or more successive pulses, the destruction threshold of the optical light guide systems is not exceeded. There is an additional increase in the total energy that can be transmitted if the second pulse lies in a different wavelength range than in the embodiment with a pulsed, simultaneously frequency-doubled NdtYAG laser with Q-switching.

In the case of a short-wave guide pulse, the refractive index of the target structure changes and the coupling of subsequent pulses improves.

There is an additional increase in the total energy that can be transmitted if a subsequent pulse, for example the second pulse, forms in a different wavelength range, preferably the first harmonic of the first pulse. In a preferred exemplary embodiment, the radiation of a pulsed simultaneous frequency-doubled Nd: YAG laser with Q-switching is used. In addition to the fact that the limitation of the transferability of high-energy laser pulses by light guiding systems can be partially lifted by the multi-pulse transmission, it has also been shown that the refractive index of the target structure changes when a short-wave guide pulse is used using non-linear optical effects. The resulting increase in Absorption improves the coupling of subsequent pulses, since the threshold for the optical breakthrough of the subsequent pulse or pulses has been significantly reduced. The first pulse with the higher photon energy ignites a plasma at the target structure, which is "pumped" as a good absorber with the subsequent pulses. The resulting greater energy content of the plasma in turn leads to an improvement in the efficiency of the conversion of laser energy into shock wave energy.

A preferred embodiment of a device for carrying out the method according to the invention has a multi-fiber catheter, which transmits the frequency-multiplied pulse as a guide pulse over a part of the fibers and transmits the fundamental wavelength through the remaining fibers with a time delay, or in which a double or multiple pulse is passed over each fiber becomes.

Another inexpensive embodiment of the multifiber catheter includes a central channel, for either an additional large diameter fiber for additive large single pulses, or an additional fiber for the guiding pulse, or a dormina basket, or a flexible endoscope, or for adding a liquid to reduce the Breakthrough threshold, or for flushing or suction.

A device for performing the method according to the invention enables an increase in effectiveness in the generation of shock waves. For the laser-induced generation of shock waves, extremely high light intensities are transmitted via optical fibers and thus an optical breakthrough is generated at the exit point, which in turn triggers shock waves that are used to erode and destroy material surfaces, membranes or concretions. When the shock waves are triggered, not only the target objects are eroded, but also the fiber end. A device is therefore created which prevents the fiber output from becoming ineffective due to geometrical changes in the generation of shock waves or that "combustion products", in particular in medical applications, remain at the shock wave generation site.

When applying the shock waves to target structures of different hardness, it has been shown that with certain materials there is an increased erosion or wear of the distal fiber end. There are first indications that in medical applications of shock waves generated in this way, optical fiber residues remain which were found in the corresponding organ during later operations.

When using a fiber without distal optics, the shock waves on the target structure are generated almost in direct contact. The threshold for fiber destruction is very different for different wavelengths. The destruction thresholds of the target structures also show a corresponding wavelength dependency, so that it is assumed that the processes for fragmenting the target structure and the fiber end are the same. In the known devices of this type, the possibility of transmitting higher energies is limited by the threshold for the destruction of the fiber end, so that the shock wave generation becomes ineffective for some applications.

Here it has been shown that the fiber end of an optical fiber can in principle be protected in two different ways.

On the one hand, the location of the triggering of the shock wave can be spatially separated from the coupling out of the radiation at the fiber end by introducing a suitable material between the fiber end and the trigger point for the shock waves. A material which is harder than quartz and is therefore not fragmented by the shock waves is preferred, since it has a higher destruction threshold. On the other hand, protection can be achieved by applying a material to the fiber end that elastically to quasi-plastically dampens the shock waves striking the fiber end. The requirements for the material are sufficient transparency in the spectral range of the laser radiation used, short-term biological compatibility and mechanical damping of the shock wave. Tough, highly viscous polymers that have both elastic and plastic deformability are particularly suitable.

Synthetic resins from various classes of material, such as epoxy resins, in the form of a sight have proven particularly useful nellklebers, polyurethane resins (DD varnishes), polyvinyl acetate (or a corresponding adhesive).

Advantageous developments of the invention are characterized in the subclaims or are shown in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. FIG. 5 shows an exemplary embodiment of a device for carrying out the method according to the invention,

FIG. 5a shows a diagram to illustrate the temporal course of the pulses in an exemplary embodiment of the method according to the invention,

6 shows an overall view of a laser catheter for use with the method according to the invention, FIG. 7 shows a sectional view of FIG. 6 and

Figures 8 to 12 different embodiments of devices for performing the method according to the invention.

In a preferred embodiment, a Q-switched Nd: YAG laser or a Q-switched alexandrite laser is used for this. The radiation from the laser is doubled in frequency by a doubler crystal connected downstream of the actual laser generator, and the reason in a downstream optical beam path Wave 6 (cf. FIG. 5) and the frequency-doubled wave 7 are spectrally divided, the fundamental wave being delayed in time with respect to the frequency-doubled wave via an optical delay line 8 with two deflection prisms 8a and 8b, and then both together via a wavelength-selective beam splitter 10 onto the input aperture 9 of the optical fiber 14 are focused.

It has proven to be particularly favorable to let both the radiation of the fundamental wave and the frequency-doubled one first pass through an aperture 11, which in turn is imaged onto the entrance aperture of the optical waveguide via an imaging lens 13.

For the two wavelengths, care must be taken to ensure that the diaphragms are positioned at optically conjugated points, which overall means that the beam waist 12 of the laser radiation lies just before the actual surface of the optical waveguide and that the diaphragm overexposes the optical core of the Optical fiber is avoided. In particular, there is an advantage of the double or multi-pulse method with different frequencies, e.g. the harmonic and the respective base emissions, in that the breakthrough threshold for the subsequent main pulse of the base emission can be lowered so much by the nonlinear optical change in refractive index and partial increase in absorption of the target structure when using so-called bare fibers, the breakthrough threshold is already reached on the target structure and thus complex optical fo kissing units or optomechanical end converters can be omitted.

The time offset of two successive pulses is shown in detail in FIG. 5a. The laser power p is plotted as a function of time t. It can be seen here that a second pulse 15 with a wavelength of 1064 nm follows a first pulse 16 of 532 nm offset by approximately one pulse width. The amplitude of the second pulse 15 continues approximately the first pulse 16 in such a way that the two superimposed pulses form a total pulse with a rising edge which is reduced compared to the falling edge of the second pulse.

In a continuation of the inventive concept for increasing the pulse energy that can be transmitted via a fiber and for lowering the breakdown threshold at the target structure, a fiber bundle can be used instead of or in addition to the individual fiber, as shown in a side view in FIG. 6, and this with an enlarged overall cross section and thus increased energy transmission Maintains flexibility of the light guide system. FIG. 7 shows a cross section through an embodiment with 15 fibers.

In the arrangement shown in FIG. 6 in a side view, the coupling takes place from a plug 17 via a Y-piece 18. A central channel 19 forming an inner lumen serves to receive, for example, a guide wire. The multifaset is then connected to the Y-piece catheter with its distal exit opposite the Y-piece.

The sectional view shown in FIG. 7 shows an equidistant annular arrangement of the fibers 19a around the central channel 19.

In the further exemplary embodiment of a multifiber catheter that contains such a fiber bundle, the technique of the multiple pulse can be implemented in two different ways.

1. The frequency-multiplied pulse is transmitted as a guide pulse through part of the fibers. With a time delay, the fundamental wavelength is transmitted through the remaining fibers and thus improved coupling to the target structure is used to generate shock waves. 2. In a second embodiment, a double or multiple pulse is transmitted over each fiber, so that the wavelength-dependent increase in the destruction threshold of the fiber and thus the increased energy transmission possibility is additionally exploited.

In one embodiment of the multifiber catheter with a central channel, the following options for increasing the efficiency in generating shock waves are favorable:

1. an additional fiber with a large diameter in order to transmit additively large single pulse energies Support in the crushing of body stones, especially in the case of so-called "problem stones". 2. an additional fiber which, in a simplified embodiment of the double-pulse application, transmits the guide pulse to lower the breakdown threshold, while the fibers of the fiber bundle deliver the single pulse to pump the plasma.

3. a dormina basket for fixing a coronary body.

4. a flexible endoscope for visual control of the process.

5. Add a liquid to lower the breakthrough threshold. 6. Flush or suction.

The various options can also be combined or used alternately. FIG. 8 shows an arrangement in which the quartz fiber 21 guides the light via a hard intermediate plate 22 to the target structure 23, on which the shock waves are triggered. Suitable materials for the intermediate plate are all substances which are transparent in the corresponding wavelength range and which have a greater hardness than quartz, such as sapphire or diamond tan. FIG. 9 shows a variant of the solution according to the invention by using a focusing sapphire tip 24 which, in addition to being more stable against destruction by the shock waves, also offers the advantage of focusing the radiation with the effect of a higher power density. This enables an increase in the transmitted energy of approximately 60%.

Figure 10 shows an embodiment with a coating of a transparent and highly viscous plastic 25, which prevents fragmentation of the fiber end surface.

This coating is preferably drop-shaped (FIG. 11), so that a focusing end member is produced, which in turn offers the advantage of focusing the radiation and generating a higher power density. With this arrangement, an increase in the transmitted energy by approximately 100% compared to the bare fiber end surface is possible.

In addition, the coating of the fiber end surface can also be carried out over a longer length of the fiber (FIG. 12), so that when a tough plastic is used, the coating also acts as an additional protective jacket if the fiber end breaks and no fragments of the fiber remain at the application site.

The invention is not limited to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable, which of the solution shown are fundamentally different Makes use of explanations.

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Claims

Patent claims 1.Procedure for the transmission of extremely high light intensities via light guide systems for the generation of shock waves for the destruction of body concretions, so that two or more successive pulses are transmitted via an optical waveguide, the steepness of the shock wave front being determined by the time offset of the individual pulses. 2. The method of claim 1, d a d u r c h g e k e n n z e i c hn e t that the second pulse is in a different wavelength range. 3. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that a Q-switched Nd: YAG or alexandrite laser is used, the radiation of which is frequency-doubled, spectrally divided and the fundamental wave is guided over an optical delay line. 4. The method according to claim 1, characterized in that the fundamental wave and the frequency-doubled wave together through an aperture step through and be focused on the entrance aperture of an optical waveguide. 5. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that a thin fiber is used without distal focusing aid and the optical breakthrough is ignited by the higher-frequency guide pulse. 6. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the laser energy for triggering the shock waves is pumped into the resulting plasma by the subsequent pulses. 7. The method according to claim 6, d a d u r c h g e k e n n z e i c h n e t that a fiber bundle is used instead of the single fiber. 8. The method of claim 7, d a d u r c h g e k e n n z e i c h n e t that a 'part of the fibers of the higher-frequency guide pulse and the remaining fibers, the fundamental wavelength is transmitted with a time delay. 9. The method according to claim 7, characterized in that a double or multiple pulse is transmitted over each fiber. 10. The method of claim 7, d a d u r c h g e k e n n z e i c h n e t that the individual fibers are controlled sequentially by at least three fibers of the multifiber catheter. 11. Apparatus for carrying out the method according to claim 10, so that an additional thick fiber is provided in the central channel of the multifiber catheter for the application of large individual pulse energies. 12. The apparatus of claim 10, d a d u r c h g e k e n n z e i c h n e t that a fiber is provided in the central channel for transmitting the guide pulse, while the longer-wave pulses are transmitted in the fibers of the catheter. 13. The apparatus of claim 10, d a d u r c h g e k e n n z e i c h n e t that a Dormina basket for fixing a body concrement or a flexible endoscope for observing the process can be advanced in the central channel, a liquid can be applied to lower the breakthrough threshold or this is used for flushing or suction. 14. Device for protecting the fiber end face of optical fibers in the production of laser-induced Shock waves with short-pulsed laser systems, for a method according to claim 1, characterized in that the location of the coupling out of the optical fiber is spatially separated from the location of the shock wave generation. 15. The apparatus of claim 14, d a d u r c h g e k e n n z e i c h n e t that the space between the distal end and the location of the shock wave generation is filled with a spacer made of a material that is harder than quartz and is transparent to the laser radiation used. 16. The apparatus of claim 14, d a d u r c h g e k e n n z e i c h n e t that the spacer consists of sapphire or diamond and / or forms a focusing tip. 17. The apparatus of claim 14, d a d u r c h g e k e n n z e i c h n e t that the spacer consists of a highly viscous synthetic resin that dampens the shock waves quasi-elastic. 18. The apparatus according to claim 17, characterized in that the spacer by a uniform coating of the fiber end made of synthetic resin or a teardrop-shaped coating made of synthetic resin is formed, the latter acting focusing for the laser radiation. 19. The apparatus of claim 18, d a d u r c h g e k e nn z e i c h n e t that the coating of synthetic resin completely encloses the shape of the free-prepared quartz fiber tip and additionally a part of the fiber jacket as a tough coating, so that the tip remains connected to the coating even when the fiber breaks. 20. The apparatus of claim 18, d a d u r c h g e k e n n, z e i c h n e t that the synthetic resin from epoxy resin, in particular from a corresponding quick-curing adhesive, from polyurethane resin, in particular from a DD varnish, or from polyvinyl acetate, in particular a corresponding made-up adhesive.  * * * * *