WO1992016154A1

WO1992016154A1 - Material-paring device by means of laser light

Info

Publication number: WO1992016154A1
Application number: PCT/DE1992/000219
Authority: WO
Inventors: Kristian Hohla; Johannes Agethen
Original assignee: Technolas Lasertechnik Gmbh
Priority date: 1991-03-13
Filing date: 1992-03-13
Publication date: 1992-10-01
Also published as: DE4108146A1; DE4108146C2

Abstract

A device for paring material, in particular biological tissues, has a laser system that generates laser pulses and a fiber-optic light guide system with fiber-optic light guides (1) gathered into a bundle (2) to which the laser pulses (6) are coupled and that guide the laser pulses (6) to the spot where material is to be pared. The bundle (2) is subdivided into at least two groups of fiber-optic light guides (1) and each laser pulse (6) is not coupled to at least one group of fiber-optic light guides (1).

Description

Device for removing material with laser light

Description

Technical field

The invention relates to a device for removing material and, in particular, biological tissue, with a laser system that generates laser pulses and a light-guiding device that has bundled light-guiding fibers into which the laser pulses are coupled. and direct the laser pulse to the point at which material is to be removed.

In laser surgery, for example, laser systems are used which, due to their high light output, evaporate tissue in such a short time and thus remove it in such a way that there is practically no heat load for the surrounding non-irradiated tissue. A wide variety of laser systems, including so-called excimer lasers which emit light in the UV range, have been used for such laser-induced processes.

The ablation processes described above are also referred to as photoablation and are used above all in microsurgery (angioplasty, ophthalmology, orthopedics, etc.) in order to remove tissue as gently as possible.

In addition, photoablation is also used to machine workpieces or the like. State of the art

The known devices for photoablation generally have a light guide device which guides the laser light to the point at which material, for example tissue, is to be removed.

In microsurgical operations, the light guide device is integrated in so-called surgical handpieces or flexible catheters and must therefore have great flexibility.

For this reason, thin optical fibers are generally used as the light-guiding device. Since optical fibers are destroyed by the laser light when it exceeds a certain specific power density, the optical fiber device has a plurality of fibers which are combined into a bundle. This enables high-energy laser pulses to be transported.

Especially in the area of angioplasty, i.e. Vascular surgery, however, has the following problem:

Each laser pulse only detects and removes a limited depth of tissue. This tissue-specific depth, which corresponds approximately to the penetration depth of the laser light, is only a few μm. So far, efforts have been made to apply the greatest possible amount of energy or power to the largest possible area in order to remove as much tissue as possible per laser pulse.

However, the speed of operation does not depend

only from the energy per laser pulse and the area acted upon, but also from the repetition rate (repetition rate) of the laser pulses. In known generic devices for removing material and in particular biological tissue, the repetition rate is essentially not limited by the physically possible repetition rate of the laser system, but by the thermal stress on the tissue that is too high at higher pulse rates .

Typically, the repetition rate in known generic devices for removing material is less than about 25 Hz.

Furthermore, the following further problem arises in the procedure as is customary in known generic devices for removing material:

For example, in angioplasty, excimer lasers are used, which emit total energies between 30 and 80 mJ at the fiber bundle exit (depending on the fiber bundle diameter). The individual fibers in the bundle are applied simultaneously and as evenly as possible with the laser beam. In laser systems with other wavelengths, such as neodymium-YAG lasers, holmium or dye lasers, however, much higher laser pulse energies must be used in order to achieve an ablation effect.

Due to the rapid evaporation of the tissue - the evaporation processes typically take place in the microsecond range - a shock wave forms which penetrates into the surrounding tissue. The high pressure gradients that occur can lead to considerable disruptions and damage to the environment. Damage to the tissue and the cell layers, which are relatively far away from the ablated area, is therefore often undamaged. avoidable. There are traumatic changes that can lead to considerable tissue irritation. As a result, renewed growth of the cell layers is observed, whereby restenosis (re-narrowing) can start.

The laser, originally intended as the atraumatic tool, has therefore proven to be quite damaging in the um area.

Description of the invention

The invention has for its object to provide a device for removing material and in particular biological tissue with a laser system, in which the removal process is carried out gently, so that it has no or only a negligibly small damaging effect on the environment, for example owns a healthy tissue environment.

An inventive solution to this problem is specified in claim 1. Developments of the invention are the subject of the dependent claims

The invention is based on the knowledge that the cause of the traumatic damage to the surroundings of the ablated area is the ablation process per se, but rather the shock wave associated with the ablation process in the conventional procedure. Therefore, the procedure according to the invention is such that the generation of shock waves during ablation is avoided as far as possible.

Surprisingly, this can be achieved in that a device for removing material and in particular biological tissue according to the upper handle of claim 1, and this device is further developed according to the invention in that the bundle is divided into at least two groups of optical fibers and that each laser pulse is not coupled into at least one group of optical fibers.

In other words, the light is coupled into the optical fiber bundle in such a way that it is separated in time and space in such a way that the individual optical fibers or groups are deliberately acted upon in time and in serial spatial order by at least one laser pulse each.

The invention is based on the idea that the formation of the shock wave is a direct consequence of the high energy per laser pulse, which is necessary when the light is applied over the entire Kätheterguer cutting surface in order to achieve "usable" removal rates.

According to the invention, therefore, only one laser pulse is coupled into a single optical fiber or a group of fibers, which only irradiates a small area and whose energy is so low that it does not trigger any or no traumatic shock wave. As a result of the scanning movement of the light spot over the area to be ablated, the thermal load on the area affected by the light spot is low, so that the pulse repetition frequency can be increased significantly in a device according to the invention compared to the prior art (claim 7). In this way, despite the “scanning movement” that the laser beam executes over the entire area to be ablated, and the reduced energy per laser pulse, the same or even higher removal rates as in the prior art can be achieved. It is advantageous here if the energy of each laser pulse is dimensioned such that the depth of its effect in the tissue corresponds approximately to the spot diameter (claim 11).

The maximum achievable pulse repetition frequency is consequently no longer determined by the traumatic effect, but (except by the performance of the laser) only by the fact that the time interval between two laser pulses must be selected so that the shock wave of the first laser pulse is already so has greatly diluted that an overlay with the shock wave, which is generated by the laser pulse transported by the adjacent optical fiber or group, no longer causes a traumatic effect.

Since pressure waves typically travel at a few 1000 m / sec. spread out and the tissue depth within which damage is to be avoided is a maximum of 1 mm, a minimum time between two pulses of approximately 10 seconds is calculated.

If light is applied to the individual fibers with a pulse repetition frequency of less than 10 Hz, the pressure waves generated do not overlap. Because of the reduced energy, each individual pressure wave is significantly smaller, so that it has no pain or traumatic effect.

The basic idea according to the invention therefore consists in sequentially applying laser pulses to the individual optical fibers of the bundle, a typical pulse repetition frequency being used, for example, in the area of angioplasty for each fiber is approximately 25 laser pulses per second (but not significantly more), so that the same total deposited energy is obtained as if a conventional device were operated with 25 laser pulses per second.

Since the operating data of, for example, excimer lasers enable an operating mode in which the individual optical fibers are subjected to a pulse repetition frequency of 25 Hz, this form of gentle treatment is possible with known laser systems.

The basic concept according to the invention thus differs not only because of the fact that the laser beam - in contrast to the prior art - is "scanned" into an optical fiber bundle, but also fundamentally from the devices in the prior art, in which a " scanning movement "of the laser beam is used:

Thus, in the device described in US Pat. No. 4,538,608, the "scan movement" of the scanning beam is used to ablate an area which is substantially larger than the area which is associated with a "stationary" beam and a correspondingly widened beam spot could be processed therapeutically.

In contrast, in WO 87/01819 the continuous, ie non-pulsed, laser beam is focused on a small spot in order to obtain a large opening angle of the beam and thus a therapeutic effect essentially only in the focal plane. The scan movement serves exclusively to be able to process a comparatively large spot with this focused beam. The reduction of the pulse power or the energy while increasing the pulse repetition frequency to avoid traumatically effective shock waves is not addressed in either publication.

In claim 2 it is claimed that the optical fibers are aligned in such a way that the light exit surfaces of optical fibers, the light entry surfaces of which are adjacent, are also adjacent. For this purpose, the optical fibers can be arranged in the bundle regularly and in particular in a linear manner (claim 3).

This arrangement of the optical fibers has a number of advantages:

If a scanning device is provided according to claim 4, each of which applies a laser pulse to a specific group of optical fibers, the "scanning pattern" of the scanning device is imaged on the light entry surfaces of the optical fibers on the light exit surfaces, so that even when several optical fibers are exposed to a laser pulse at the output the optical fibers are defined and reproducible conditions.

The fact that the coupling of a laser pulse into very specific optical fibers leads to an exit of this laser pulse at a precisely defined point can also be used to achieve a spatially resolved detection of the ablated material:

In the embodiment described in claim 8, a shock or pressure wave sensor is provided which detects the shock wave or pressure wave triggered by each individual laser pulse. An evaluation unit records the respective impact or pressure wave in association with the optical fiber or group of optical fibers acted upon by the triggering laser pulse. The maximum value and the amplitude of the shock wave triggered by a laser pulse with a certain pulse duration and with a certain energy depend on the material that the laser pulse hits:

For example, there are different shock wave profiles for plaque and calcined tissue than for normal tissue. Thus, the detection of the generated shock wave in association with the respectively applied optical fiber or group of optical fibers and thus - i.e. on the basis of the features of claims 2 and 3, the location where the laser pulse strikes, a statement about the type of ablated material.

In principle, any pressure sensors, for example intracorporeal sensors, which are arranged in a ring around the distal end of the optical fiber bundle can be used as the shock or pressure wave sensor.

A further development is characterized in which it is not necessary to arrange a sensor intracorporeally. Rather, the shock or pressure wave sensor can be arranged extracorporeally, since it detects the shock or pressure wave transmitted by the bundle of optical fibers.

The property of a device according to the invention that the pulsed laser beam sequentially scans the area to be ablated can also be used for an optical determination of the type of material to be ablated: For this purpose, an optical sensor is provided which detects the wavelength distribution of the fluorescent light triggered by each individual laser pulse. An evaluation unit determines the material of the affected area from the wavelength distribution in association with the optical fiber or group of optical fibers acted upon by the triggering laser pulse. For details of the determination of the ablated material from the light "returning" in the light guide, reference is made, for example, to WO 88/08279, to which reference is expressly made to explain all of the details that are not explained here.

In principle, any scanning devices, for example the scanning devices described in WO 87/01819, can be used as the scanning device which generates the "scanning" movement of the pulsed laser beam over the optical fiber bundle.

In view of the fact that a pulsed laser beam is used in the device according to the invention, however, it makes sense to use the simple scanning devices characterized in claims 5 and 6.

According to these claims, the scanning device can have a mirror or a prism arrangement mounted on a rotating disk.

Brief description of the drawing

The invention is described below by way of example without limitation of the general inventive idea on the basis of exemplary embodiments with reference to the drawing. Show it: 1 shows a simplified illustration to explain the mode of operation for tissue ablation with a conventional multifiber bundle,

2 shows a conventional arrangement for simultaneous laser beam coupling into a multifiber bundle,

3 shows a simplified illustration to explain the function of a device according to the invention with mirror deflection, and

4 shows a cross section through a device according to the invention with a rotating prismatic disk.

Representation of exemplary embodiments

In the following figures, the same elements are provided with the same reference numerals, so that when these elements reappear, a new idea is dispensed with.

1 shows the distal region of a device for removing tissue 4. The device has a large number of optical fibers 1, which are arranged in a bundle 2 and integrated into a catheter 2 ¹ .

FIG. 2 shows that, in known devices for photoablation, the individual fibers 1 in the multifiber bundle 2 are exposed to laser light. For this purpose, a laser beam 6 generated by a laser system (not shown) is emitted from an optical imaging or focusing lens 7 (or a lens system) onto the coupling surface 8 'of the multifiber bundle 2 while at the same time adapting the beam spot to the size and shape the coupling surface 8 'shown. All individual optical fibers 1 which are guided within the multifiber bundle 2 are thus irradiated with laser light simultaneously and as uniformly as possible. Due to the 8 "at each laser pulse at the output of the multifiber bundle 2 exiting light energy, the layers of tissue 4 lying directly against the (distal) catheter head are subjected to such a high thermal load that the tissue evaporates.

Due to the explosive expansion of tissue material 3, the ablated material is displaced to the side in front of the catheter head and, on the other hand, a shock wave 5, which spreads into the surrounding tissue area, occurs, which can lead to tissue and cell line damage.

3 shows a device according to the invention, in which the individual laser pulses of the laser system, which in turn is not shown, are sequentially coupled into individual optical fibers 1 contained in the multifiber bundle 2.

For this purpose, the laser beam 6 is imaged via the focusing lens 7 and a deflection unit, which has a mirror 9 rotatably mounted about a pivot axis D, in each case on individual optical fibers 1 or groups in such a way that different optical fibers or groups are acted upon one after the other become. In order to make the mirror guidance as simple as possible, in the embodiment shown the individual optical fibers, which are combined to form a multifiber bundle 2 in a catheter (not shown), are arranged linearly. Different, regular spatial arrangements of optical fibers are also conceivable (e.g. triangle, rectangle, etc.). By rotating the mirror 9 about the axis of rotation D in a synchronized manner, ie synchronized with the laser pulses, all the optical fibers 1 or groups are successively illuminated or struck. However, the clock frequency of the mirror adjustment does not necessarily have to match the repetition rate of the laser system, ie more than one light pulse can be transmitted per beam image on an optical fiber 1 or group.

According to the invention, a shock or pressure wave sensor 10 is also provided, which detects the shock wave or pressure wave 5 triggered by each individual laser pulse. The shock or pressure wave sensor 10 is arranged extracorporeally and detects the shock or pressure wave 5 transmitted by the bundle 2 of optical fibers 1. An evaluation unit (not shown) determines the respective shock or pressure wave from the output signal of the sensor 10 in association with the optical fiber 1 or group of optical fibers acted upon by the triggering laser pulse.

FIG. 4 shows a further embodiment of the invention, which differs from the embodiment shown in FIG. 3 by the design of the deflection unit, which in this embodiment is a disk 11 with prisms 12 'that can be rotated about an axis R , 12 ", .. is formed.

The laser beam 6 also passes through an optical imaging lens 7 and then passes through a prism 12 'embedded in the edge region of the disk 11 rotating about the axis R, which deflects the beam 6 onto an optical fiber 1 or group of the bundle 2.

The prisms (only two are shown in the cross-sectional representation, namely 12 ', 12 ") are arranged radially in the edge region of the disk 11 in such a way that the laser beam passes through the prisms (12, 12 ', ...) one after the other and is deflected differently. The speed of rotation of the disk then indicates the average pulse rate of the arrangement.

The methods of sequential scanning can also be used to activate only parts of the catheter cross section. In this case, optical fibers are specifically excluded from the radiation, which is technically easy to implement in the deflection devices shown. This is of particular interest if a suitable detection method is used which allows the tissue in front of the catheter to be recognized.

Furthermore, different locations can also be irradiated with the light from different lasers.

Another advantage of this beam deflection method is that the same energy can be applied to each individual fiber. This is very difficult with simultaneous illumination of the bundle, since each laser beam has more or less pronounced inhomogeneities. The total average power, which is thus transported by a fiber 1, can be increased not inconsiderably in this way, so that there is a considerable increase in the cutting speed.

The frequency of the laser pulses must be increased accordingly, the energy of the individual laser pulse is reduced accordingly.

The above consideration should be clarified with the following numerical example: Approx. 50 optical fibers 1 are arranged in a typical angioplasty catheter.

With a pulse repetition rate of 25 Hz per fiber 1, the laser must be operated with a total repetition rate of 1,250 Hz. At the same time, the individual pulses must be mapped onto a single fiber or onto a group of fibers. The laser beam must be scanned over the entrance surface 8 'of the fiber bundle 2, so to speak. The laser pulse frequency is in orders of magnitude below the limit frequency of 10 Hz estimated above.

The device according to the invention can thus be easily implemented in practice by arranging any scanning or scanning device on the light-entry-side (proximal) end 8 'of the optical fibers, which deflects the laser pulses in such a way that the laser pulses Entry surfaces of the individual fibers 1 "scanned".

Industrial applicability

The invention can be used both in the field of medical technology and for material processing of technical workpieces.

Claims

Patent claims

1. Device for removing material (4) and in particular biological tissue, with a laser system that generates laser pulses, and a light-guiding device that has bundled (2) optical fibers (1) into which the laser pulses be coupled in and which guide the laser pulse to the point at which material is to be removed, characterized in that the bundle (2) is divided into at least two groups of optical fibers and that each laser pulse is not divided into at least one group of optical fibers is coupled.

2. Device according to claim 1, characterized in that the optical fibers (1) are aligned such that the light exit surfaces (8 ") of optical fibers (1), whose light entry surfaces (8 ') are adjacent, are adjacent.

3. Apparatus according to claim 2, characterized in that the optical fibers (1) are arranged regularly and in particular linearly in the bundle.

4. Device according to one of claims 1 to 3, characterized in that a scanning device is provided, each of which applies a specific group of Licht¬ optical fibers (1) with a laser pulse.

5. The device according to claim 4, characterized in that the scanning device has a pivotable mirror (9).

6. The device according to claim 4, characterized in that the scanning device has a on a rotating disc (11) attached prism arrangement (12 ', 12 ", ...).

7. Device according to one of claims 1 to 6, characterized in that the maximum repetition rate per optical fiber (1) or group is 25 Hz.

8. Device according to one of claims 1 to 7, characterized in that a shock or Druckwellen¬ sensor (10) is provided which detects the shock wave or pressure wave triggered by each individual laser pulse, and that an evaluation unit, the respective shock or pressure wave in association with the optical fiber (1) or group of optical fibers acted upon by the triggering laser pulse.

9. The device according to claim 8, characterized in that the shock or Druckwellen¬ sensor (10) is arranged extracorporeally, and the shock wave or pressure wave transmitted by the bundle (2) of optical fibers (1) is detected.

10. Device according to one of claims 1 to 9, characterized in that an optical sensor is provided hen, which detects the wavelength distribution of the fluorescent light triggered by each individual laser pulse, and that an evaluation unit from the wavelength distribution in association with that with the triggering laser pulse acted upon optical fiber (1) or group of optical fibers determined the material of the area affected.

11. Device according to one of claims 1 to 10, characterized in that the energy of each laser pulse is dimensioned such that the depth of its effect in the tissue (4) corresponds approximately to the spot diameter and / or that it has no traumatically effective impact or Pressure wave triggers.

12. Device according to one of claims 1 to 11, characterized in that the laser system has an excimer laser.