DE4108146C2 - Device for removing material with laser light - Google Patents

Description

The invention relates to a device for Removal of material, especially biological Tissue, with a laser system that generates laser pulses, which via a focusing and deflection device in too a bundle of optical fibers can be coupled, which direct the laser pulse into place, on which material is to be removed, the Bundles in at least two groups of optical fibers is divided so that the individual groups of light Conducting fibers can be subjected to laser pulses one after the other.  

For example, laser systems are used in laser surgery me used because of their high light output Vaporize tissue in such a short time that practical no heat load for the non-irradiated, healthy Tissue occurs. For such laser-induced processes A wide variety of laser systems, including for some time so-called excimer lasers, which Emit light in the UV range, used.

The removal processes described above will also known as photoablation mechanisms and fin especially in microsurgery (angioplasty, Oph thalmology, orthopedics etc.) application to possible very gentle way to remove tissue.

They are usually used in microsurgical operations so-called surgical handpieces, for example catheters used in which the laser light in so-called Optical fibers are routed to the point where Material, d. H. for example, tissue can be removed should. The ability of optical fibers to laser light transport, however, is limited because from a spec power density the fibers by the laser light be destroyed.

Because - to get a flexible catheter, for example ten - thin fibers must be used, which are summarized, have the surgical hand usually cut up many fibers so that laser pulses high energy can be transported, so that poss can be operated as quickly and efficiently as possible.  

Especially in the area of angioplasty, i.e. H. the vessel Surgery, however, has the following problem: Everyone Laser pulse only detects and removes a limited amount of tissue depth. This tissue-specific depth, which is roughly the Penetration depth of the laser light corresponds. Is only few around. So far, efforts have been made to as high a surface density of energy or power as possible To reach fiber output. The operation speed speed does not only depend on the energy per laser pulse, but also from the repetition rate (repititions rate) of the laser pulses. This is known in front directions for removing material and in particular of biological tissue, using a laser system Values of less than approx. 25 Hz limited, as at high The pulse rates are too high for thermal stress on the tissue becomes.

To achieve high operating speeds is you've been striving in the past so much Energy as possible per laser pulse through the fiber bundle to lead. For example, in angioplasty Excimer lasers worked at the fiber bundle exit (depending on fiber bundle diameter) total energies between between 30 and 80 mJ. The individual fibers in the Bundles become the same at the same time, if possible moderately exposed to the laser beam. With laser system with a different wavelength, such as Neo dym-YAG lasers, holmium or dylaser, however, must who uses much higher laser pulse energies to achieve an ablation effect.

Because of the rapid evaporation of the tissue - the Evaporation processes typically take place in the microscope customer area - a shock wave forms  penetrates into the surrounding tissue. Which occurs in the process high pressure gradients can lead to considerable Disruptions and damage in the environment. Damage to the tissue and the cell layers, the rela tiv far from the ablated area is therefore inevitable. Traumatic ver Changes that lead to considerable tissue irritation can. As a result, the growth of Cell layers observed, causing restenosis (How narrowing).

The laser, originally as the atraumatic tool praised, proves to be quite in the µm range harmful. The reason for this is likely - as according to the invention has been recognized - not the ablation process by se, but the one with the ablation process conventional shock wave associated laser systems.

The aforementioned shock wave problem is neither in the DE 37 42 553 A1 addressed from which a laser beam device for a laser workstation system goes and to be regarded technologically as the state of the art is. The core idea is still in US 4,967,745 of shock wave generation, especially since one Laser catheter tip is described, the one physical separation between what is to be irradiated Material and the light exit surface of a light guide fiber provides.

The invention has for its object a Vorrich device for removing material and in particular to indicate biological tissue with a laser system, in which the removal process is carried out gently, so that he has no or only a negligibly small one  harmful effect on the remaining material, especially on the healthy tissue environment, be sits.

An inventive solution to this problem is in Claim 1 specified. Developments of the invention are the subject of the subclaims.

The invention is based on the basic idea that it To solve this task, the Erzeu avoid shock waves during ablation.

Surprisingly, this basic idea can be realized that continue from a device to remove material and especially biological chemical tissue, with a laser system, the laser pulse generated in a bundle of light Conducting fibers can be coupled, which the laser pulse to the Manage the point at which material is to be removed, is assumed.

According to the invention, such a device is thereby further developed that the succession of two lasers pulse, which is inserted into the bundle of optical fibers be coupled, is chosen such that the Light application per laser pulse within the ab shock waves arising in time do not overlay. For this purpose, the bundle is at least in a known manner divided two groups of optical fibers so that each laser pulse into at least one group of Optical fibers are not coupled.

In other words, the light is coupled in the optical fiber bundle so temporally and spatially separately that the individual optical fibers or group  pen separated in time and in serial spatial order follow at least one laser pulse each time are irradiable.

The invention is based on the idea that the formation of the shock wave is a direct result of the high energy per laser pulse that is applied to the tissue over the entire cross-sectional area of the catheter. If only a single fiber from the laser fiber bundle is irradiated with the laser light, much less energy is released at the catheter outlet; consequently, the shock wave is significantly reduced. The same also applies to the amount of tissue that is ablated. In order to compensate for this effect, the fibers of the bundle are sequentially irradiated with laser light with the device according to the invention, that is, each fiber is acted upon individually in a time sequence with light. The time interval between two laser pulses must be chosen so that the shock wave of the first laser pulse has already been thinned so far that an overlay with the pressure wave emitted by the adjacent fiber can be excluded. Since pressure waves typically travel at a few 1000 m / sec. spread and the tissue depth within which damage is to be avoided is a maximum of 1 mm, a minimum time between two pulses is calculated to be about 10 ^-6 sec. On the other hand, if the individual fibers with a frequency of less than 10⁶ Hz If light is supplied, the pressure waves that form will not be able to overlap. Every single pressure wave will be much smaller since it is only generated by the energy of a single fiber.

The idea of the invention is therefore that individual fibers of the bundle sequentially with laser pulse, in the area of angioplasty each fiber no more than 25 laser pulses per second should receive. This way, the same effect achieved as if all fibers had 25 lasers simultaneously received pulse per second. The frequency of the laser pulses must be increased accordingly, the energy of the individual laser pulse is down accordingly puts.

The following example is intended to illustrate the above consideration:
Approx. 50 optical fibers are arranged in a typical Angliopalasty catheter. With a single fiber frequency of 25 Hz, the laser would have to be operated at a repetition rate of 1,250 Hz. At the same time, the individual pulses must be mapped to each individual fiber. The laser beam must be scanned over the fiber bundle, so to speak. The laser pulse frequency is in orders of magnitude below the limit frequency of 10⁶ Hz estimated above. The device according to the invention can be implemented in practice, for example, by arranging a scanning device at the light entrance (proximal) end of the optical fibers, which deflects the laser pulses in such a way that the laser impulse "scans" the light entry surfaces of the individual fibers.

Because the operating data of excimer lasers, for example this form of operation is possible gentle handling possible with known laser systems.

The invention is based on execution examples with reference to the drawing exempla described.

Fig. 1 is a simplified diagram for explaining the operation for tissue ablation with a conventional multi-fiber bundle,

Fig. 2 shows a conventional arrangement for simultaneous Laserstrahleinkopplung in a multi-fiber bundle,

Fig. 3 is a simplified representation for explaining the function of a device according to the invention with mirror deflection and

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

The device for removing tissue 4 shown in FIG. 1 has a catheter 2 , in the interior of which a large number of optical fibers 1 are guided. In the previously used photoablation techniques, the individual fibers in the bundle are simultaneously exposed to the laser beam. Due to the light energy exiting per laser pulse at the output of the fiber, the tissue immediately adjacent to the catheter head is subjected to such high thermal stresses that the tissue evaporates. Due to the explosive expansion of tissue material 3 , the abla tated material in front of the catheter head is pushed to the side on the one hand, and on the other hand, a shock wave 5 spreads into the surrounding tissue area, which leads to said tissue and cell damage.

In Fig. 2, the previously used in laser light coupling is shown in so-called multifiber bundles. Here, the laser beam 6 coming from the laser system passes through an optical imaging lens 7 , which adjusts the light beam in size and shape to the geometrical conditions of the coupling surface of a multifunctional bundle 8 . All individual optical fibers that are guided within the multi-fiber bundle are irradiated simultaneously and as evenly as possible with laser light.

A device for sequentially coupling light into individual optical fibers contained in a multifiber bundle is shown in FIG. 3. The laser beam 9 is spatially imaged onto an individual optical fiber or group by means of an imaging lens 10 and a mirror which is rotatably mounted about the axis of rotation D. In order to make the mirror guidance as simple as possible, the individual optical fibers, which come together to form a multi-fiber bundle 12 , are arranged linearly. Any deviating, regular spatial arrangement of optical fibers is also conceivable (e.g. triangle, rectangle, etc.). By clockwise rotation of the mirror 11 about the axis of rotation D who in succession in accordance with the repetition rate of the pulsed laser thus illuminates all optical fibers or groups in succession.

The clock frequency of the mirror adjustment must, however not necessarily with the repetition rate of the Laser system match, d. H. per beam image  more than one can be on an optical fiber or group Light pulse are transmitted.

Another device according to the invention is shown in FIG. 4. The laser beam 13 also passes through an optical imaging lens 14 and then passes a specially in the edge region of a rotating disc 16 rotating around the axis R prism 15 , which focuses the beam 13 on an optical fiber or group 17 . The radial attachment of a plurality of prisms (in the cross-sectional view only two are shown - 15 , 15 ') is provided in the edge region of the disc 17 such that the laser beam the prisms ( 15 , 15 ',...) In time one behind the other penetrates, with the beam image capturing each optical fiber or group in succession during the rotation of the disk 16 . The Rotationsgeschwin speed of the disc then indicates the average pulse rate of the arrangement.

The methods of sequential scanning can also only parts of the catheter cross section are used for this to activate. Optical fibers are targeted here exempt from radiation, which is technically in the shown devices is easy to implement. This is of particular interest if one Appropriate detection method is used, which he leaves the tissue in front of the catheter to know.

Another advantage of this beam deflection method Added to this is the fact that every single fiber with the same energy can be applied. This is at a simultaneous illumination of the bundle only very much  difficult because every laser beam more or less has pronounced inhomogeneities. The entire mitt performance that is thus transported through a fiber can be increased significantly in this way be, so that there is a significant increase in Cutting speed results.

Claims (8)

1. Device for removing material ( 4 ), in particular of biological tissue, with a laser system that generates laser pulses, which can be coupled into a bundle of optical fibers ( 1 ) via a focusing and deflection device, which transmit the laser pulse to the Conduct point at which material is to be removed, the bundle being divided up into at least two groups ( 17 ) of optical fibers, so that the individual groups of optical fibers can be acted upon one after the other with laser pulses, characterized in that the succession of two laser pulses, which in the bundle ( 8 , 12 ) of optical fibers are coupled, is chosen such that the shock waves generated by the light application per laser pulse within the material to be removed do not overlap. 2. Device according to claim 1, characterized in that the maximum Re petition frequency of the laser pulses is 10 MHz. 3. Apparatus according to claim 1 or 2, characterized in that the maximum re petitionsrate with which an optical fiber ( 1 ) is acted upon by a laser pulse is 25 Hz. 4. Device according to one of claims 1 to 3, characterized in that the optical fibers rule moderate, preferably linear, within the light guide fiber bundle are arranged.   5. Device according to one of claims 1 to 4, characterized in that the light coupling into each individual optical fiber or group can be carried out via a mirror ( 11 ). 6. Device according to one of claims 1 to 5, characterized in that the light coupling into each individual optical fiber or group by a, on a rotating disc ( 16 ) attached, prism arrangement ( 15 , 15 ',...) Can be performed . 7. Device according to one of claims 1 to 6, characterized in that the energy of each laser pulses is such that the depth of its effect in the Material corresponds approximately to the spot diameter. 8. Device according to one of claims 1 to 7, characterized in that the laser system a Has excimer laser.