WO1992020288A1

WO1992020288A1 - Device for making surgical incisions with combined thermal and ionizing laser beams

Info

Publication number: WO1992020288A1
Application number: PCT/CA1992/000214
Authority: WO
Inventors: Kurt E. Schirmer
Original assignee: Schirmer Kurt E
Priority date: 1991-05-23
Filing date: 1992-05-22
Publication date: 1992-11-26
Also published as: CA2043072A1; JPH06507328A; AU1697792A; EP0586414A1

Abstract

In the cutting with a laser beam there are in the target point material changes which affect the repeated application and efficiency of the laser beam. Provisions are made to send a thermal laser beam (4) and a photodisruptive laser beam (5) and to combine the two into one output beam having a common optical axis, in which the photodisruptive laser beam (5) and the thermal light beam (4) travel simultaneously. The different laser types cause different effects on target point, whereby a higher rate of disruption is achieved by concentrating pressure and heat in the same space and brief time span at the target point to provide execution of incisions in substances. Vascularized tissue is ablated without bleeding by the combined use of the argon (2) and the Nd:YAG laser (3).

Description

DEVICE FOR MAKING SURGICAL INCISIONS WITH ' COMBINED THERMAL AND IONIZING LASER BEAMS

TECHNICAL FIELD

This invention concerns a device for cutting into material, in particular human and animal tissue or the like with a focused light beam.

BACKGROUND ART

In particular, because of the sharp focusing and the high power, laser beams are at present used to incise material. Thus, on the one hand, laser beams are used in the manufacture of components for electronics, in particular in the manufacture of integrated circuits. In medicine and particularly in ophthalmology they are used for heat coagulating the retina and disrupting a membrane such as a cataract.

If lasers with laser beams of long pulse duration are used (e.g. thermal lasers), the energy converted at the target point as heat also has an effect in the adjacent areas whereby a desirable heat coagulation of the incision walls is achieved, but undesirable material changes can occur outside the incision.

If lasers with very high power laser beams are used (e.g. solid-state lasers), rapid incisions can be made, however, the incision walls can be very unstable, particularly in soft materials, since the incision walls have not undergone any stabilization by heat. In particular in the case of materials containing much fluid, such as plant substances, human or animal tissue, fluid such as blood etc. -ⁱ ¬

penetrates into the incision when incising by means of a high power laser beam which does not coagulate, thus leading to problems, in particular, hindrances in the application of the laser. The thermal mode laser (Ion laser) converts its energy to heat with random molecular movement. However, in narrow closed space its heat becomes pressure in accordance with the law of the fourth power (pressure rises to the fourth power of the temperature: P = c.K4). The narrow spaces are provided by the energy conversion of the photodisruptive laser (ionizing laser) . The ensuing heat explosion disrupts tissue and supplies the force for the work that removes the tissue debris. Considering the entropy of this process with intensity factor that provides work and extensity factor that of random molecular movement which is heat, enough of the latter is provided to cook adjacent tissue and prevent bleeding. This is essential to provide favourable conditions to proceed with further ablation, proceeding with the formation of a shunt in depth. This is the object of the invention.

DISCLOSURE OF INVENTION The object of the invention is to provide a method for cutting with a sharply focused laser beam, with which fluid containing material can be cut with high efficiency.

A method of making incisions in material containing fluid, in accordance with the present inventivion comprises a laser beam from a laser source consisting of a photodisruptive first laser and a thermal second laser, directing the first and second laser beams confocally and simultaneously to form an incision in the material such that the rise of temperature in the area of the material, provided by the thermal laser, causes a 4% rise of pressure within the incision being formed. The thermal laser beam is relatively continuous and the photodisruptive laser beam is of a pulsating nature superimposed on the continuous exposure of the thermal laser beam.

A method for making incisions in human or animal tissue comprises a laser beam from a photodisruptive laser and another laser beam from a thermal (ion) laser whereby the two laser beams travel coaxially or on different pathways to engage on a common focal point which is the target. The photodisruptive pulses are superimposed in time over the continuous wave thermal laser or a pulsed thermal laser.

In particular with cuts in blood fluid containing animal or human tissue, the simultaneous application of different types of lasers is advantageous. The energy of the laser beam of the thermal laser is converted in the tissue into heat.

With low power, a coagulation of the tissue takes place by means of which the latter is coagulated in the incision area and a further escape of fluid is prevented. Because of its high energy output, the simultaneous pulsating beam of the photodisruptive laser brings about an ionization in the tissue whereby molecules and atoms are broken down. A plasma in the physical sense is produced in the incision. The plasma stores as intermediary the light energy of the laser beam and releases it again suddenly in the form of an effective vaporization.

This causes an explosion and thus a conversion into mechanical force whereby the tissue in the incision is torn apart. In this case, the conversion into mechanical energy is so efficient that the tissue around the area of the incision hardly heats up."

The laser beam of the thermal laser provides the heat coagulation in the incision by means of which the incision walls are stabilized and the entry of further fluid into the incision is prevented.

If the energy of the thermal laser beam is deposited with increased power in a small space, the tissue is disrupted and coagulated.

In a more specific embodiment of the present invention, the thermal laser is an argon laser while the ionizing laser or photodisruptive laser is a Nd:YAG laser. The Nd:YAG laser provides one millijoule into a short period of time of ten nanoseconds thus delivering 100 kilowatts that convert to destructive pressure stresses of 100 kilopascals. This action is confined in a small space providing high pressure, thereby causing tissue to become disrupted. The argon laser delivers with 1 watt, only 1 pascal of pressure after relatively lengthy exposure. Force is continuously added throughout the exposure time to gain momentum requiring a gradient from solid to gas, from hot to cold, so that work is accomplished in accordance with Carnot's principle, in order to provide expulsion of debris.

To express this by a specific example, the use of NdrYAG laser energy of one mJ that is delivered during 10 nsec m provides an example for realizing the creation of pressure:

One millijoule / 10 na

- —33 —8 nnoosseeccoonnddss:: 1100 mmJJ // 110 sec equals 5

10 W = 100 kW of power. If converted to Newton meters it equals 5

10 N x m / sec . Adjusting the N to pressure in pascals (N/m2 = Pa) , the high pressure of 100 kPa x m/sec is created. This must be conceived mainly as stress that acts as destructive force.

Argon laser energy of one Watt x 0.1 second exposure time provides:

1 W x 10^-1 sec = 10^_1 J;10^_1 J/10^_1 sec=l W = 1 N x m/sec.

The adjustment to pressure (Pa=N/m2) finalizes the equation to 1 Pa x m/sec = Pa x v. The pressure is noticeably diminished in comparison with the Nd:YAG laser while the speed is proportionately increased within this product that is governed by a constant.

At the end of the exposure time energy from the argon laser creates velocity of kinetic energy to direct molecular movement to clear debris through the open end of the trough. This working energy is only effective in the presence of an existing gradient from the solid-watery medium.

Pressure is not only created by the Nd:YAG laser but also by the argon laser if energy becomes trapped in small space (Pa = J /m.3 ) . In the open space of the trough, however, energy flows along the existing gradient.

Trapping energy in a short time or in a small space, creates pressure. Light converts fully to energy in a narrow trap and it is pressure that destroys and expands the enclosed space. The pressure and heat act in a synergistic manner in the closed space. 1% of temperature raises pressure by 4% .

This may be expressed as: 4P = dP/dK x K; becomes integrated P = c.K4; it equals N / m2 . K4 = c; if velocity m/sec = 1; N / m2 . K4 x m/sec = c; c becomes Sigma (Stefan-Boltzmann) = W / m.2 .K4. Converted back to mechanical energy it becomes N . m / sec . m2 . K4 = Pa . v/K4

A trough is created by the dual laser. The high wattage of the Nd:YAG laser creates a disruptive pressure. At the enclosed bottom end of the trough, the argon laser provided high temperature which is trapped in a small space thus creating pressure. Toward the open end, however, it becomes kinetic energy that moves matter along the gradient from solid to gas. This directs the excretion of debris as though it were a projectile within the barrel of a gun.

Thus, the dual laser, that is the Nd:YAG laser component deepens the ablation trough in the tissue while the argon laser component provides expulsion energy for the debris to clear the relatively wide lumen in the presence of a gradient. The application for the purpose of ablation of occular or other tissues, takes place by focus beamed from a remote position without contact with a probe. The appropriately proportioned combination of destructive pressure and kinetic energy provides the surgeon with a broadly useful cost-effective and generally available laser device.

The dual laser cuts deep sutures to abolish postoperative astigmatism. It achieves paracentesis for hyphema or pus which has been drained through a self-sterilizing opening. Large iridotomies in any colored iris are achieved with few applications of the dual laser despite foggy media. The heavily pigmented tissue of asian and black irides and their firm mesenchymal tissue presents no challenge for the dual laser. Its efficiency is always greatly aided by a cavitation bubble that provides a gradient to execute work.

This applies also to the formation of wide trabecular holes proven by reflux of blood from the canal of Schlemm through holes in the trabeculum into the anterior chamber. Its degree permits conclusion as to the size of the achieved shunt. Repeatable drainage points suffice for brief temporary success or lengthy control, for several months on the average . This dual laser procedure resembles in its achieved effect an ophthalmic procedure that is known as the Scheie procedure and which precludes the need for surgery or laser surgery by a laser probe.

BRIEF DESCRIPTION OF THE DRAWINGS An apparatus which would be typically used for conducting the dual laser procedure described above is shown in the attached drawings and is described as follows :

Figure 1 is a schematic arrangement of the device according to the invention of a thermal laser and a photodisruptive laser.

MODES FOR CARRYING OUT THE INVENTION

The device is arranged in a housing 1 and consists of a gas laser 2 and a solid-state laser 3, of which the laser beams 4,5 are reflected via a mirror arrangement 6 onto a common optical axis 7. For this purpose, the laser beam 4 of the gas laser 2 is deflected via a first mirror 6a to the optical axis 7 and reflected via a mirror 6b, arranged on the optical axis 7, in the optical axis toward the outlet 8. The laser beam 5 of the solid state laser 3 is likewise deflected via a first mirror 6c to the optical axis 7 and diverted via a mirror on the optical axis 6d toward the outlet 8. In this way, the beam of the solid state laser penetrates the mirror 6b which lies on the optical axis and which for this purpose is transparently silvered. To adjust the laser beams 4 and 5, the mirrors 6a to 6d are accordingly mounted in an adjustable way. The output beam 9 of the device according to the invention, can thus be the laser beam 4 of the gas laser 2 as well as the laser beam 5 of the solid state laser 3.

In the shown exemplified embodiment, the gas laser 2 is an argon laser which essentially consists of a somewhat rectangular toroidal tube filled with argon. This toroid can be arranged in three sections. The actual laser tube 10, which lies between two end tubes 11 with so-called Brewster windows and the tube section 13 surrounded by a coil

12 into which the energy required for the discharge is supplied. In this case, the tube section 13, to which the energy is supplied, has a considerably bigger diameter than the actual laser tube 10.

Via coils 14 the ion current is influenced magnetically in such a way that the ions are forced into a trajectory in the narrower tube and do not strike the walls. In this way the thermal load of the tube wall of the laser tube remains low.

On the one end tube 11, opposite the

Brewster window, a selection prism 15 is arranged with which the wave length of the laser beam 4, emerging through the output mirror 16, can be

adjusted within certain limits.

The coil 12 serves as high-frequency buncher which is fed by an amplifier 17. In this case, the high-frequency energy is then only transmitted to the HF buncher 12 if the controller 20 gives an appropriate signal to its control wire 21.

With the gas laser 2, to a large extent a continuous output beam 4 can be obtained which can have an output power of 2 W to 100 W. In the provided embodiment, the duration of the laser beam 4 is in the range of 0.1 sec.

The solid state laser 3 consists of a solid 18 in which neodymium is provided in an yttrium-aluminium oxide crystal lattice. Such a YAG laser consists of an internally silvered ellipsoid 19, in one axis of which the solid is arranged. In the other axis a flash lamp 22 is provided which is supplied with energy by a switching arrangement 23. The switching arrangement then always turns on the flash lamp 22 when the controller 20 gives an appropriate signal to the control wires 24.

With the flash discharge, light is pumped into the cylindrical solid 18, opposite the axial front ends of which there is in each case a mirror 25, 26. The mirror 26 is coated semi-transparently and lets through the laser beam 5 as soon as the beam reflected between the mirrors 25 and 26 has an energy level which makes possible the passage through the mirror 26. With the solid state laser output energies from 1 to 100 Ws can be generated. Since a solid essentially can only be used as pulse laser of very short pulse duration in the range of 1 ms, the resulting outputs are between 1 and 100 kW. In the exemplified embodiment, the laser beam 5 of the solid state laser has a pulse duration of 10 nanoseconds.

The device according to the invention, is put into operation via the controller 20. In this case, the control lights 30 and 31 respectively indicate the readiness of the lasers 2 and 3. The desired pulse duration of the laser beam can be set via the controllers 32 and 33. The controller 34 is used in this case to set the two lasers 2 and 3 simultaneously in operation. Finally, by means of the controller 35, a pause can be inserted between two successive sequences. Failure of one r the other laser is indicated by control lights 36 and 37. The employment of different laser types is advantageous in particular in incisions in fluid containing tissues such as animal or human tissue samples. The advantageous application of the device according to the invention in eye surgery should be emphasized. With the device, it is possible to carry out complicated incisions with minimal bleeding which can greatly hinder the repeated cutting by means of the solid state laser. In this case, the obtained strength of the incision walls is advantageous which is already achieved through a slight heat coagulation without thereby stimulating a healing process. Moreover, the implosion effect after the explosion, observed when the Nd:YAG laser is utilized at least twice, can be used advantageously.

By the implosion, excess heat-coagulated tissue is namely torn from the explosion cavity which advantageously enlarges the latter. The to-be-set power of the laser beam is important in this case. If too much tissue is torn out of the explosion cavity, it bleeds. If too little is torn out, it results in cicatrizing healing. Really ideal is the further tunneling by means of the YAG laser using a power which does not tear out heat-coagulatd scarred tissue completely, but for the most part, and enlarges the explosion cavity without causing the latter to collapse.

Claims

CLAIMS :

1. A method of making an incision in material containing fluid comprising providing a laser beam from a laser source consisting of a photo disruptive first laser and a thermal second laser, directing the first and second laser beams in a common optical axis simultaneously to form an incision in the material such that the rise of temperature in the area of the incision provided by the thermal laser causes a 4% rise of pressure within the incision being formed, the first and second laser beams are coaxial and confocal with the thermal laser beam being relatively continuous and the photodisruptive laser beam being of a pulsating nature superimposed on the continuous exposure of the thermal laser.