AU2255192A

AU2255192A - Lights-pumped high power medical system

Info

Publication number: AU2255192A
Application number: AU22551/92A
Authority: AU
Inventors: Shahriar Ghaffari
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-06-26
Filing date: 1992-06-26
Publication date: 1993-01-25
Anticipated expiration: 2012-06-26
Also published as: EP0591404A1; KR100289249B1; JPH06511594A; CA2112560A1; EP0591404A4; KR940701526A; AU673982B2; WO1993000551A1

Description

LIGHTS-PUMPED HIGH POWER MEDICAL SYSTEM

3 Field of the Invention

5 The present invention relates to a system for use in ό medical applications requiring light having high power

7 characteristics of lasers. More specifically, the present s invention provides a light source which is capable of

9 producing a beam of radiation having essentially the same o beam intensity and spot size as a beam of radiation 1 produced by a laser.

2 Background 3 Lasers have a number of optical properties which make them especially useful for a wide range of scientific, 5 industrial and medical applications. The two optical 6 characteristics most commonly associated with a beam of 7 laser radiation are "coherence" and "monochromaticity" of s the light beam. Other important characteristics of laser light are a high level of beam intensity and the ability to 0 focus the light beam into a very small spot size. Although ₁ the properties of coherence and monochromaticity are

2 essential to certain applications, many of the applications

3 for which lasers are used do not require these qualities, but, rather, only require beam intensity and wavelengths of

5 particular interest.

6 Laser systems are generally expensive to purchase and

7 operate and, thus, have not been available to many

8 potential users. Furthermore, in many of the applications

9 for which lasers are utilized, the expense of the system is ιo borne to obtain the optical beam qualities.- other than the 11 coherence and monochromaticity which are unique to lasers. 12 There is a need for an inexpensive optical system capable

13 of providing an intense beam which is capable of being

K focused into a small area, is A prior art lamp-based laser simulator is shown in

16 U.S. Patent No. 4,860,172 issued to Schlager et al. In the

17 system disclosed by Schlager, light from an omnidirectional

18 conventional light source is collected and focused with

19 conventional means into an optical coupling cone which is 0 intended to condense the conventionally focused beam for 1 launching into a fiber optic cable. 2 Although the stated goal of the '172 patent is to 3 provide a light source having many of the characteristics 4 of laser light, the optical parameters of the system 5 disclosed in the '172 patent are not capable of producing 6 laser-simulated light at an intensity suitable for most 7 medical applications. There are three parameters which ι must be optimized to produce light having a high intensity.

2 and small spot size using the optical components shown in

3 the '172 patent: 1) the gap spacing between the electrodes,

4 2) the magnification of the reflector, and 3) the

5 acceptance angle or numerical aperture of the optical

6 fiber. Larger lamp gap sizes tend to result in higher

7 power output. Large gap sizes, however, also tend to

8 result in larger spot sizes due to the magnification properties of the reflector. The acceptance angle of a 0 fiber optic dictates the maximum spot size on the cone at a 1 given entrance anc _ which can be completely coupled into 2 the fiber. Th*^* acceptance angle is related to the 3 numerical aperture of the optic fiber by the following 4 equation: 5 sin (acceptance angle) = numeric aperture. 6 There is a need, therefore, to match the gap size and the 7 magnification of the reflector to produce a beam which can s be accepted by the optical fiber for delivery to the 9 tissue. The system of the '172 patent attempts to optimize 0 the coupling of light into the fiber optic through the use i of a cone. More specifically, the '172 patent suggests 2 that light can be coupled into a fiber optic via a cone 3 which reduces the spot size. 4 Although the cone shown in the '172 patent will 5 produce a smaller spot size, the beam delivered power will 6 actually be reduced because of the inherent optical 7 properties of the coupling cone and the optical fiber. The 1 entrance of cone has an acceptance angle which determines

2 the first numerical aperture of the cone. Likewise, the

3 cone exit has an output numerical numerical aperture which

4 actually increases as the output beam spot size is reduced.

5 The increased numerical aperture of the cone exit will cause significant divergence in the exit beam. The

7 divergence of the beam from the cone exit results in an a optical loss because a significant portion of the energy 9 which exits from the cone may not meet the acceptance

10 criteria of the numerical aperture of the fiber optic. The ιι net result is a beam which does not have sufficient power

12 to provide the beam intensity needed for many medical

13 applications.

1 Summary of

2 the Invention

3 The present invention provides a system which utilizes a conventional light source to produce a narrowly focused s beam of radiation having intensity similar to that produced

6 by a laser. The system is broadly comprised of a

7 omnidirectional light source positioned in an optical

8 cavity comprising a first curved reflector and a second

9 reflector which can be either flat or curved. The optical o parameters of the light source and the reflectors are 1 matched to produce a narrowly focused beam of intense 2 radiation. The second mirrored surface has an aperture 3 therein which is placed at a point near the second focal 4 point of the first reflector. The light source is placed 5 at the first focal point of the reflector and the accepting 6 end of a fiber optic is placed at the second focal point of 7 the reflector. The aperture is positioned such that only s rays meeting predetermined geometrical exit criteria can 9 pass through the aperture and be accepted by the fiber 0 optic located at the second focal point. Those rays which i do not meet the exit criteria are reflected by the mirrored 2 surface toward the interior of the cavity. Some of the 3 reflected rays provide additional amplification of the 4 light produced by t_.e light sou ;e and the path of these 5 rays is altered such that they are eventually able to meet 6 the exit criteria and pass through the aperture. 7 The light produced by the system can be coupled into a fiber optic system for delivery to a target area. The dimension of the light source and the focal length of the reflectors in the optical cavity are chosen such that the focused beam can be easily accepted by a fiber optic having a numerical aperture approximately equal to the inverse of two times the "F/number" of the reflector.

1 Brief Description

2 of the Drawings

3 A better understanding of the present invention can be

4 obtained when the following detailed description of the

5 preferred embodiment is considered in conjunction with the

6 following drawings, in which:

7 FIG. 1 is an elevational side view of the optical a system of the present invention showing the light source 9 positioned in an optical cavity comprising a first curved ιo reflector and a second reflector. ιι FIG. la is an elevational side view of the optical

12 system of the present invention showing a curved second

13 reflector for redirecting light into the optical cavity.

14 FIG. 2 is an illustration of the geometry of the

15 focused light rays arriving at the second focal point of

16 the reflector.

17 FIG. 3 is an elevational side view of the optical

18 system of the present invention showing the electrode gap

19 in the light source.

20 FIG. 4 is a graphical illustration of a conventional

21 continuous wave power level and the pulsed power levels

22 employed in the system of the present invention.

23 FIG. 5 is an elevational view in cross section of the

24 optical delivery system of the present invention.

25 FIG. 6 is an illustration of a focussed beam of

26 radiation delivered by the system of the present invention. FIG. 7 is a graphical illustration of. the wavelengths ght produced by an arc lamp.

1 Detailed Description of

2 the Preferred Embodiment

3 Referring to FIG. 1, the optical system of the present

4 invention is shown in its preferred embodiment. The system

5 comprises a light source 10 which is mounted in an optical

6 cavity comprising a first curved reflector 12 and a second

7 reflector 14 which can be either curved or flat. Light β produced by the cavity is carried by a fiber optic 20 to a 9 delivery system 24, discussed in greater detail below. The o embodiment of the invention illustrated in FIG. 1 comprises 1 a second reflector 14 which is flat. The alternate 2 embodiment of the optical cavity, shown in FIG. la, 3 comprises a curved second reflector 14a. The light source 10 used in the present invention is a 5 conventional light source in the form of an arc lamp. The 6 arc lamp comprises a cathode 16 and an anode 18 which are 7 connected to an appropriate power source and mounted in a e quartz housing 19. The interior of the housing 19 is 9 filled with a gas or vapor which produces light when 0 excited by an electric current flowing between the cathode 1 16 and the anode 18. In the arc lamp used in the preferred 2 embodiment of the present invention is a Xenon-Mercury 3 vapor. 4 When the lamp is energized, the cathode 16 passes 5 electrons which are accelerated toward the anode 18. The 6 collision of the electrons with the Xenon or Mercury atoms 7 causes the electrons orbiting those atoms to move to a higher energy levels or "stimulated states." When the . excited electrons return to their normal energy levels, they emit photons which have a wavelength determined by the difference between the energy levels of the excited state and the normal state. FIG. 1 illustrates a plurality of light rays produced by the light source 10. The rays 22a-22b and 22a'-22b' originate at the theoretical center of the first focal point of the reflector 12 are all reflected toward the second focal point of the reflector 12 and can be coupled into the fiber optic 20 after passing through the aperture in the second reflector 14. Other rays originate at points between the cathode 16 and anode 18, as illustrated by rays 22c and 22c¹, respectively. These rays are also reflected by the reflector 12, but fail to pass through the aperture 13 in the second reflector 14 and, therefore, are reflected by the mirrored surface of the reflector 14 back toward the interior of the cavity, as discussed in greater detail below. Some rays, such as the one illustrated by reference numeral 22d are not reflected by the first reflector 12 and thus exit the reflector cavity. The light rays which are focussed at the second focal point can be accepted by the optical fiber 20, provided certain constraints are met. In general, the limiting factors are the size and acceptance angle of the optical fiber, the size of the gap of the light source 10 at the first focal point of the reflector 12 and the magnification of the reflector 12. As a general principle, the gap size of the light source is directly correlated with the amount of electromagnetic radiation produced with larger gap sizes producing greater power. The size of the gap, however, also has an impact on the ability to converge the light rays for efficient entry into the fiber optic. As discussed above, FIG. 1 includes an illustration of light rays produced from different portions of the gap between the cathode 14 and the anode 16 of the arc lamp used in the preferred embodiment of the invention. Since the rays originate from a band of points, rather than from the theoretical focal point of the reflector, the group of rays focused at the second focal point will also arrive in a band defined by the geometry of the reflector. This geometry of the arriving rays is shown in FIG. 2, which shows a band' of arriving rays passing through the aperture having a width of "D." In the case where the band width of the rays reflected by the curved reflector 12 and passing through the aperture corresponds to the acceptance angle of the fiber optic, there will be effective coupling into the fiber optic. However, in the case where the band width of the focussed rays exceeds the acceptance angle of the fiber optic, there will be inefficient coupling of the light into the fiber optic. The bands of incident rays illustrated by reference numerals 23 and 23' in FIG. 2 do not match the numerical aperture of the fiber optic and, therefore, would result in inefficient coupling. In the present invention, these rays are reflected by the mirrored inner surface of the second reflector 14 and, furthermore, the geometric parameters of the optical cavity prevent these rays from exiting until the criteria for efficient coupling have been met. If all of the surfaces in the cavity were perfectly reflective and had perfect geometry, the returned rays would be caught in a "reflective loop." However, a number of factors prevent this phenomenon. The rays which are returned by the reflector 14 are re-reflected by the first curved reflector 12 will be directed to the interior of the quartz housing of the arc lamp. Upon passing through the quartz, these rays will be refracted slightly. This will change the direction of the rays as illustrated in FIG. la, thus preventing them from being caught in a reflective loop. Moreover, the additional light returned from the reflective surface will add to the new light being generated in the arc gap between which will result in a certain degree of amplification of the light produced by the arc lamp. The amount of amplification is determined by the reflectivity of the reflectors and the absorption characteristics of the various media within the cavity. The reflective loop phenomenon can also be avoided by controlling the position of the second reflective surface with respect to the focal point of the first reflector. Also, a curved second reflector, such as that shown in FIG. la, can be used to minimize reflective loops, thus improving the output light generation efficiency. FIG. la is an illustration of an alternate embodiment of the present invention utilizing a curved reflector 14' having a mirrored inner surface. The curved reflector 14' includes an aperture 13' passing light rays meeting the acceptance criteria of the acceptance angle of the fiber optic 20. In this embodiment of the system, those rays which meet the exit criteria, e.g. ray 36, of the cavity are allowed to pass through the aperture 13 • . However, those rays, e.g. ray 38, will be reflected back into the interior of the cavity where they will be again reflected by the reflective surface of the elliptical reflector 12. In the present invention, the arc lamp 10 is pulsed to power levels several times higher than normally used for continuous wave (CW) operation of the lamp. This pulsed operation has the effect of creating very intense production of light. Referring to FIG. 3, a small sphere of plasma 15 production is shown at the tip of the cathode 16 of the arc lamp. This plasma is caused by very intense bombardment of electrons emerging from the tip of the cathode 18. This plasma region normally exists near the tip of the cathode when the lamp is operating in the CW mode. In the present invention, however, the pulsed operation of the lamp will cause the plasma region to temporarily expand to span the entire distance between the electrodes, as illustrated by the plasma region 15* shown 1 in FIG. 3.

2 FIG. 4 is a graphical illustration of the power levels

3 used in the present invention to create the pulsed plasma

4 effects discussed above. The power levels discussed herein

5 are for a Mercury-Xenon lamp; however, the principles of

6 pulsed operation can be applied to other types of lamps to

7 obtain similar results. The normal CW power level shown in

8 FIG. 4 is approximately 28 amps, 1000 watts of power

9 consumption. Using the pulsed method, however, the current 10 is increased to more than 50 amps for brief periods of ιι time, e.g., on the order of 1 to 10 milliseconds, resulting

12 in delivered electrical power in excess of 2,500 watts.

13 Indeed, it is possible to increase the power to even higher

14 levels for even shorter periods of time. For example, the

15 lamp is capable of sustaining 100 amps for periods of time

16 on the order of 100-500 microseconds. 7 The pulsed operation of the arc lamp used in the s present invention produces the intense plasma region 9 between the two electrodes, as discussed above, thus making 0 it possible to obtain beam intensities at very small spot i sizes which are very similar to those produced by 2 conventional lasers. 3 The various embodiments of the present invention, the 4 curved reflector 12 has an elliptical geometry. However, 5 other geometries known to those skilled in the art can- be 6 used. For example, a parabolic reflector with an 7 appropriate lens system could be used to obtain focussing properties similar to that obtained with v._e elliptical reflector used in the preferred embodiment. The magnification of the elliptical reflector 12 is determined by the distance between the focal points and the size of the ellipse. The light source 10 is placed at one of the first focal point of the reflector and an optical fiber 20 is placed at a second focal point of the reflector. The delivery system of the present invention, shown in FIG. 5, is comprised of two lenses configured in a 4-f arrangement. The delivery system comprises a housing 40 with an optic terminator 42 secured in one end thereof. The terminator delivers light from the fiber optic 20 to a first diverginc lens 44 to produce a collimated light beam. The collimated light beam is passed through an appropriate filter 46, discussed in greater detail below, and is received by a converging lens 48 for focussing the light radiation on the tissue to be treated. The filter is placed in the light path to control the wavelengths being delivered to the ablation or coagulation site. In order to reduce the tolerances on the filters, the position of the filter is chosen in the delivery system between the two lenses. The ' filtering operation may be chosen by sliding a filter into a slot in the delivery system. Two grated index GRIN fiber lenses can replace the normal lenses as presented, as long as both of them have good transmission in the ϋV and visible wavelengths. A conical tip 50, discussed in greater detail below, assists in the precise delivery of the light to a ι desired location on the tissue.

2 The advantage of a 4-f configuration is that the fiber

3 optic output light is focussed into a smaller spot at a

4 given wavelength. In the present invention, the advantage

5 of using this lens arrangement is that the UV wavelengths

6 are focussed into a small spot closer to the 2Nd lens than

7 the visible wavelengths (due to Chromatic aberrations) . a The conical tip 50 is used as a guide to indicate the

9 best focussing point for optimized cutting action. FIG. 6 ιo is an illustration of the concentric cones of radiation ιι which result from the light being focused by the 4-f lense

12 system. The UV light creates an ablation sight which is

13 shown touching the surface of the tissue in FIG. 6. The

14 visible wavelengths are focussed to just below the ablation

15 plane of the delivery system which cause coagulation of the

1 underlying blood vessels before the ablation front reaches 7 these layers. 8 Typical spectra for Mercury and Xenon lamps are shown in FIG 7. The Mercury lamp has several peaks in UV and 0 visible ranges as opposed to the Xenon lamp which has a more 1 continuous spectrum. Mercury-Xenon lamps have 2 characteristics very similar to the Mercury with a small 3 additional Xenon baseline. 4 The Mercury lamp spectrum peaks at 404, 430, 546 and 5 579 are very close to the peaks of the absorption 6 characteristic of blood. Tissue, on the other hand, has low 7 absorption characteristic in the visible, increasing in ι excess of 100 cm^-1 in the UV wavelengths below 320 nm.

2 Presently, Excimer lasers at 351 and 308 nm have shown very

3 good cutting action with minimal damage to the surrounding

4 tissue about the ablation site. The minimum thermal damage

5 is partially due to the short pulse widths and photo- ablation effects of the UV Excimer wavelengths.

7 If only an Excimer laser is used for tissue cutting, β the tissue will bleed since the blood vessels are not 9 coagulated to stop the blood flow. Blood coagulation could 0 be promoted by using a dye laser tuned at the wavelength of 1 high blood absorption, but with much lower tissue absorption 2 in which the target of coagulation is the blood and not the normal tissue. Consequently, an optimized scalpel may be 4 based on using multiple wavelengths such as UV for cutting 5 and wavelengths around 420, 546 and 577 where the relative 6 blood absorption is higher than other wavelengths. The 7 Mercury lamp (or Mercury Xenon lamp) has the proper 8 characteristic to match the needed multi-spectral 9 characteristics as discussed above. 0 The system of the present invention can be operated in 1 a pulsed mode, as discussed above, to produce ablation of a 2 site using pulse durations on the order of a few 3 milliseconds. The short pulse width results in minimal 4 thermal damage to the tissue. 5 The present invention may be used for cutting tissue if 6 all available wavelengths are focussed at the tip of the 7 delivery system. In order to cauterize or coagulate blood. the wavelengths in the visible range and of particular interest the peaks of 546 and 577 nm can be delivered to the tip with other wavelengths being filtered out by inserting an appropriate filter into the delivery system. Several different wavelengths of lasers from argon (488 and 514 nm) and YAG (1064 nm) and C02 (10,600 nm) have been used for tissue welding. The main goal in tissue welding is to heat the junction of the two sections of tissue (held against each other) to reach temperatures just below their coagulation point resulting in melting of the collagen of tissue together. The melting of the collagen promotes better and faster tissue healing of the junction. The present invention is capable of generating a beam having wavelength components which can penetrate into tissue to depths of several millimeters. Consequently, if the system is configured to operate in a continuous wave mode, rather than pulsed mode, the continuous low level light can produce sufficient heating of tissue to allow the present invention to be used for tissue welding as well. A temperature monitoring system can be incorporated in the delivery system to provide more accurate tissue heat generation thereby avoiding over-exposure of the tissue while allowing more homogeneous welding process. In normal surgery, it is usually important to use a cutting device to penetrate into the tissue or body. The present invention can be used to ablate tissue and cut through different layers of skin. The delivery system is placed against the ablation site and the light source is activated to produce high power pulses of light. The generated light causes tissue ablation and the operator can move the delivery system along the desired cutting pattern on the skin. A complete penetration through skin normally requires several passes of tissue removal with a careful inspection of the ablation site. The present invention also can be used to cauterize blood quickly. The cauterizing filter is place in the optical path and the system is activated while the delivery system is pointed toward the bleeding site. This technique can be used to coagulate blood vessels under skin in depths down to 0.6 millimeters as well. When the operation is completed the cut size is closed using a few conventional sutures. The system can then be configured to operate in the welding mode whereby a continuous low level light is produced. Upon activation, the delivery system produces mild heating of the closed cut area as it is moved along the cut path. The rate of movement and the heat generated can be calibrated by either a heat sensing feedback system or the experience of the operator. Normal junction temperatures in the 60-85 °C produces the desired effect. Althougr. the present invention has been described in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein but, on the contrary, it is intended to include such modifications, alternatives and equivalents as may - reasonably be included with the scope of the invention as defined by the appended claims.

Claims

I Claim: 1. A system for producing an intense beam of light having a small spot size for delivery to a portion of tissue, comprising: a radiation source; a first reflector means having first and second focal points, said radiation source being placed at said first focal point, said first reflector means being operable to direct beams from said radiation source toward said second focal point; optical means for limiting radiation received at said second focal point to a specific numerical aperture; an optical receptacle at said second focal point, said optical receptacle having a numerical aperture to accept beams of said radiation passed by said means for limiting said radiation received at said second focal point; and means for delivering radiation from said receptacle to a portion of tissue.
2. The system of claim 1, wherein said means for producing radiation comprises a conventional light source.
3. The system of claim 2, wherein said light source is an arc lamp having first and second electrodes with a gap therebetween.
4. The system of claim 3, wherein said light source is provided with pulsed power to cause intense pulses of light to be produced between said electrodes.
5. The system of claim 4, wherein said power is pulsed for a period of between one and ten milliseconds.
6. The system of claim 5, wherein said means for limiting radiation received at said second focal point comprises a reflective surface having an aperture therein, said aperture allowing rays meeting a predetermined numerical aperture criteria to be passed therethrough, with rays not meeting said numerical aperture criteria being redirected toward said first reflector.
7. The system of claim 6, wherein said means for delivering said radiation comprises a fiber optic.
8. The system of claim 7, wherein said means for delivering said radiation further comprises means operably coupled to said fiber optic to receive radiation passed therethrough and to focus said radiation on a portion of said tissue.
9. The system of claim 8, wherein said means for delivering said radiation further comprises filtering means for controlling the wavelength of radiation focussed on said tissue.
10. The system of claim 9, wherein said arc lamp comprises a Mercury-Xenon vapor, said radiation produced by said lamp comprising light at wavelengths corresponding to ultraviolet, visible and infrared.