Laser beam surgical system

A laser beam surgical system provided with a cannula insertable into a body passage leading to a surgical site. The cannula includes a rotatable inner tube whose inlet section has two input ports, one being in line with the tube axis and being coupled to a white light source, the other being at right angles to the axis and being coupled to a carbon dioxide laser projecting a collimated beam. Supported at a 45.degree. angle within the inlet section is a pellicle that is permeable to the beam of white light impinging thereon and reflective to the laser beam whereby both are directed toward an outlet section at the other end of the tube. Supported within the outlet section at a 45.degree. angle with respect to the tube axis is a normally planar reflective membrane which directs both beams through a lateral output port toward the surgical site which is illuminated by the white light. The geometric center of the membrane is coupled at its rear to a controllable actuator which forces the membrane to assume a concave form acting optically to bring the laser beam to a focus at a target surface on the surgical site.

BACKGROUND OF INVENTION 
1. Field of Invention: 
This invention relates generally to laser beam systems for carrying out 
surgical procedures, and more particularly to a system using a carbon 
dioxide laser whose collimated laser beam is conducted through a cannula 
to an outlet section where the beam is directed by a reflective deformable 
membrane toward the surgical site, the membrane being controllable to 
assume a concave form which optically focuses the beam at a target surface 
on the site. 
2. Status of the Art: 
Throughout the course of modern surgery, the desideratum has always been 
for a technique by which one can execute the surgical procedure of 
interest in a manner optimizing operating room time and surgical effect 
while minimizing tissue trauma and bleeding as well as the period during 
which the patient is under anesthesia. 
With the advent of miniaturized arthroscopic instruments, orthopaedic 
surgeons are now able to perform delicate operations in a relatively short 
time that were not heretofore feasible. An arthroscope is a cannula whose 
diameter is small enough to enter interstices between the bones in a joint 
to create a body entry which is small compared to that normally required 
in a cold knife procedure. By using a miniature rotary cutter that slides 
into the cannula, the surgeon is able to debride tissue fragments that are 
responsible for joint deterioration, disease and arthritis. 
The present invention deals with a system in which a laser beam projected 
through an arthroscope functions as a non-mechanical surgical tool. The 
use of laser energy in medicine is now commonplace. Laser beams are used, 
for example, in skin treatment, in eye repair and in surgery. The main 
concern of the present invention is with surgical applications in which a 
high power laser beam functions to both cut and cauterize and must 
therefore be focused onto the surgical target. 
Ordinary light is non-coherent and is made up of random and discontinuous 
wavelengths and phases of varying amplitude. The principle characteristic 
of a laser beam lies in its coherence, which means that corresponding 
points in its wavelength are in phase. In surgical applications, lasers in 
current use are the Nd:YAG, the CO.sub.2 and the Argon laser. In practice, 
the laser may be pulsed or continuous. 
Laser light is usually more intense, more monochromatic and more highly 
collimated than light from ordinary sources such as tungsten-filament 
lamps. The intensity of laser light can be extremely high. Thus power 
densities of over 1000 MW/cm.sup.2 are obtainable to produce a beam 
capable of cutting through and vaporizing solid materials. Lasers fall 
into four basic categories: solid state-optically pumped; liquid dye; 
semi-conductor; and gas. Together, these four laser types cover the 
spectral region extending from ultraviolet to infrared. 
The present invention will be described chiefly in the context of knee 
surgery, for meniscectomies and synovectomies are among the most 
frequently encountered surgical problems for which arthroscopic surgery is 
the appropriate solution. It will, however, be recognized that the 
surgical applications are by no means limited to these procedures, and 
that the invention is useful wherever the need exists to direct a focused 
CO.sub.2 laser beam toward a surgical site in a path other than 
line-of-sight. The invention is also useful in those industrial 
applications which require a steerable and focusable laser beam. 
Though standard arthroscopic techniques employing miniature surgical 
cutting tools yield good results, they have been hampered by difficulties 
encountered in tool miniaturization and in site designation during the 
surgical procedure. Due to size constraints the accuracy with which 
miniature tools can be manipulated and placed has imposed practical limits 
on arthroscopic surgery. 
A carbon dioxide laser has distinct advantages over other types as an 
effective surgical tool, for it cuts a visible and extremely clean line 
with very little backscatter, and it is capable of applying enormous 
amounts of energy onto a tissue site, thereby vaporizing the tissue into 
its gas constituents and leaving no biological residue. Because a CO.sub.2 
laser beam can vaporize any biological target such as cancer cells, it 
creates an absolutely sterile wound site devoid of biological 
contaminants. Moreover, the CO.sub.2 laser lends itself to a precise level 
of control and can therefore be set to cut through one cell layer at a 
time in almost any cell substrate, or to burn through several millimeters 
of hard tissue, whichever procedure is indicated. 
Despite its marked advantages over other types of lasers, the use of a 
CO.sub.2 laser beam has hitherto been unavailable in arthroscopic surgery, 
for a CO.sub.2 beam cannot be conducted through a fiber optic conduit. A 
CO.sub.2 laser beam has a wavelength of 10.6 micrometers which lies in the 
infrared region of the spectrum and is therefore too long to be 
transmitted through existing fiber optic light conduits. As a consequence, 
the CO.sub.2 laser in the field of surgery has heretofore been limited to 
those applications which do not make use of a fiber optic conduit for 
conducting the laser beam. 
In arthroscopic surgery, the usual practice is to employ a cannula having a 
3-5 millimeter diameter. If one seeks therefore to integrate a CO.sub.2 
laser with an arthroscope to perform surgery on a joint such as the knee, 
the requirements of the surgical procedure then dictate that the laser 
beam be orientable and be capable of travelling around corners. Beam 
steering expedients such as motorized lenses and rotating mirrors are not 
only expensive, but they are difficult to incorporate in a small bore 
arthroscopic cannula. As a consequence, use has not previously been made 
of a CO.sub.2 laser in knee surgery. 
In arthroscopic surgery, the object is to remove tissue particles from 
joints (meniscectomies and synovectomies--i.e., removing tendril-like 
particles of the meniscus and synovia). In other types of surgery such as 
in prosthetic hip, shoulder and knee implants, the aim of the procedure is 
to debride and polish particular areas of bone or tissue to create a 
socket whereby the prosthesis can then be driven into a precisely 
contoured socket. 
In order to carry out orthopaedic surgery in soft or hard tissue with a 
laser beam, the operating surgeon must know just where cutting is taking 
place. The surgeon does not have a scalpel in his hand as a cutting tool; 
hence it is only by visual observation that he can sense his laser 
incisions, not by tactile sensation. Nd:YAG and Argon types of lasers make 
it difficult for surgeons to accurately evaluate the parameters of their 
incisions, for these have a short wavelength and exhibit backscatter 
characteristics. Backscatter or distal tissue penetration, is a phenomenon 
experienced when a laser beam having a short wavelength impinges on a 
visible target surface, the beam penetrating the target to a depth beyond 
that which can be visually observed. This penetration in depth heats and 
volatilizes the tissue in the backscatter region underlying the exposed 
target surface which is the only visible area of impact. This region 
assumes a non-linear geometric form that is a function of the type of 
cells and tissue which border one another in the region subject to 
backscatter effects. 
An Argon laser is centered at about 0.512 micrometers in the wavelength 
spectrum, while that of an Nd:YAG laser is centered at about 0.532 
micrometers. These shorter wavelengths are comparable to ultraviolet or 
blue-green light at the upper end of the light spectrum, as opposed to 
infrared radiation at the lower end. As a consequence, an Nd:YAG or an 
Argon laser beam will penetrate flesh, tissue and water, the beam 
transferring its energy to pigmented tissues beyond the surface of beam 
impingement. Because of the backscatter experienced with Nd:YAG and Argon 
laser beams, this gives rise to deleterious tissue destruction. 
In contradistinction, a CO.sub.2 laser generates a long wavelength beam 
having a 10.6 micrometer wavelength which lies in the infrared portion of 
the light spectrum. The energy of a CO.sub.2 laser beam is fully absorbed 
by water and therefore by cells composed mostly of water. As a 
consequence, those cells in the target surface which are directly exposed 
to a focused CO.sub.2 laser beam are the only ones destroyed, for there is 
virtually no backscatter. The energy transmitted to the focal point is 
almost entirely absorbed by the water in the local cells, and the energy 
penetrating the region beyond this point is at a very low and innocuous 
level. 
As noted previously, in arthroscopic surgery, the usual practice is to use 
a cannula having a 3-5 millimeter diameter. If one attempts to integrate a 
CO.sub.2 laser with an arthroscope to perform surgery in joints such as 
the knee, the requirements of the procedure dictate a steering action by 
which one is able to direct the laser beam around corners toward the site 
of interest. While a flexible fiber optic conduit is capable of directing 
light conducted therethrough in any desired direction, a conduit of this 
type is not useable with a long wavelength CO.sub.2 laser beam. And though 
it is possible to steer a CO.sub.2 laser beam with rotating mirrors and 
motorized lenses, these expensive expedients are difficult to incorporate 
in a small bore cannula. 
3. Prior Art: 
The patent to Swope discloses a photo-coagulation technique in which the 
beam from a gas laser is directed by an optical system created by a series 
of mirrors to the site to be treated. In the Kawaski U.S. Pat. No. 
4,174,154, a condenser lens and a series of mirrors is used in conjunction 
with a CO.sub.2 laser beam to direct the beam to a desired site. In the 
CO.sub.2 laser beam endoscope shown in the Worster U.S. Pat. Nos. 
4,211,229 and 4,141,362, a lens system is used to bring the beam to a 
focus. The Frank U.S. Pat. No. 4,313,431 makes use of fiber optics in an 
endoscope to conduct a laser beam. 
The U.S. Pat. No. to Bredemeier 3,796,220 shows a stereo laser endoscope 
using a CO.sub.2 laser which is focused by means of a lens and a 
reflecting mirror to provide a fixed focus system, the lens being so 
chosen as to focus the laser beam on a point lying in the focal plane of a 
microscope. 
SUMMARY OF INVENTION 
In view of the foregoing, the main object of this invention is to provide a 
surgical system which makes use of a carbon dioxide laser whose beam is 
conducted through a small bore cannula in an arrangement wherein the 
focused beam is steerable to impinge onto the site of interest. 
More particularly, an object of this invention is to provide an 
arthroscopic system of the above type capable of generating a wide beam 
divergence angle close to the tissue in a deep cavity remote from the 
terminal lens whereby the action of the focused laser beam is concentrated 
at the surgical target and the tissue underlying the target is unaffected 
thereby. 
Also an object of the invention is to provide in a carbon dioxide laser 
beam surgical system precise focal length control in real time as well as 
real time position control in the X, Y and Z axes. 
Yet another object of the invention is to provide a surgeon with a fully 
integrated, accurate and easily controllable CO.sub.2 laser system. 
Briefly stated, these objects are attained in a laser beam surgical system 
provided with a cannula insertable into a body passage leading to a 
surgical site. The cannula includes a rotatable inner tube whose inlet 
section has two input ports, one being in line with the tube axis and 
being coupled to a white light source, the other being at right angles to 
the axis and being coupled to a carbon dioxide laser projecting a 
collimated beam. Supported at a 45.degree. angle within the inlet section 
is a pellicle that is permeable to the beam of white light impinging 
thereon and reflective to the laser beam whereby both are directed toward 
an outlet section at the other end of the tube. Supported within the 
outlet section at a 45.degree. angle with respect to the tube axis is a 
normally planar reflective membrane which directs both beams through a 
lateral output port toward the surgical site which is illuminated by the 
white light. The geometric center of the membrane is coupled at its rear 
to a controllable actuator which forces the membrane to assume a concave 
form acting optically to bring the laser beam to a focus at a target 
surface on the surgical site.

DETAILED DESCRIPTION OF INVENTION 
Operational Modes: 
All lasers, regardless of type, function in one of two operational modes. 
The simplest, which is the axial or Fabry-Perot mode, operates in integral 
multiples of 2 pi phase changes. A second modal permutation is the TEM or 
Transverse Electromagnetic Mode. TEM modes are reproducible cyclic phase 
fronts which are self-propagating in any cavity in which they can 
reproduce in one complete round trip in that cavity. 
Each of these modes is partitioned into several geometric orders. These are 
designated TEM.sub.pq (`p` and `q` designate the orthagonal nodes). We 
shall concern ourselves only with lasers that operate in the TEM.sub.pq 
modes. TEM lasers generate many different wavefront geometries. In 
surgical procedures only two of these geometries are significant. One is 
the TEM.sub.00 and the other is the TEM.sub.10 * geometry. 
A TEM.sub.00 mode laser generates a typically Gaussian wavefront. Since its 
energy distribution is Gaussian, when impacting tissue sites, it creates a 
uniform cross-sectional heating front. Its output description can be 
likened to the Fabry-Perot oscillation because the phasing characteristics 
are virtually identical outside of the laser's oscillation cavity. The 
Gaussian energy front of the TEM.sub.00 laser is useful because the focus 
of the laser contains 0.865 of the total power contained in the beam 
envelope. 
The laser generates a light wave front with its energy peak at the axial 
dead center of the beam. Since the center of the beam is where the energy 
is concentrated, the periphery, measured radially from the dead center to 
the circumference, is at a slightly lower energy level as the edge of the 
focal point is approached. Because the beams are focused and the foci are 
small in size (3.0, 1.0, 0.1 millimeters and smaller), the energy density 
as a practical matter can be assumed to be uniform across the 
cross-section of the prime focus. Only when the laser power is reduced to 
a low level or the laser is modified to project a wide beam does the 
effect become noticeable. 
The other mode used in some surgical procedures it the TEM.sub.10 * mode. 
This is commonly called the donut mode in that the cross-sectional map of 
its energy distribution resembles a donut. It occurs because the nodes of 
the phasefront propagated in the laser cavity rotate with real time. Since 
the energy is concentrated at the circumferences of the focal spot, the 
beam will destroy the tissue at the edge of the prime focus, thereby 
leaving the tissue in the center of the ring intact. This type of 
wavefront can be useful because of the laser's controllable heat transfer 
as well as its backscatter characteristics. 
The TEM.sub.10 * phenomenon allows a surgeon to choose a target and destroy 
tissue on the periphery of a healthy central mass. Because of the 
differential phasefronts and the unusual geometry of the energy envelope, 
the TEM.sub.10 * laser has a limited number of uses. This is not to 
downgrade its useability, but in most conventional surgeries the surgeon 
must have close control over a beam of predictably uniform power 
distribution. Therefore the use of TEM.sub.10 * lasers is limited to 
highly specialized surgical situations. 
Energy: 
The basic unit of power used with all lasers is the joule. Power can be 
varied by modulating the laser beam's amplitude; hence surgical lasers 
include means to control the power input into the lasing system and 
therefore the intensity of the energy output. 
Time or duration is the second power-related variable in a laser beam 
system. Duration is the length of time the energy remains over the subject 
tissue. It is inherently variable in all lasers in that the on-off control 
for the laser is via a foot switch used by the surgeon, or it is 
preprogrammed into a pulse train network which can be initiated or 
reinitiated at the surgeon's option. 
The critical variable in a system according to the invention is that of 
beam area. This is directly related to spot size and therefore to focal 
length, cutting zone depth, and focal control. This variable is of primary 
concern, for it is dependent completely on the terminal optics of the 
laser's lens system. Such a lens system is attachable to any laser 
generator and therefore influences with the greatest degree of variability 
the amount of energy that can be transferred to the tissue. 
As previously indicated, the TEM.sub.00 mode laser operates with a Gaussian 
wavefront that concentrates 89.5% of the energy at the focus of the beam. 
This then makes it possible to change the total energy E.sub.t by altering 
the area A of the beamfront (spot size). By reducing the value of A by 
making the area smaller, the energy density is enhanced and therefore 
E.sub.t is caused to increase. Conversely, making the value of A larger 
diminishes the energy density and decreases E.sub.t accordingly. 
The total energy value E.sub.t is critical in surgery because in certain 
circumstances one may not wish to vaporize tissue but only to coagulate 
it. Coagulation is a moderate heating of the tissues such that the 
collagen fibers depolymerize and repolymerize, thereby becoming sticky and 
inducing hemostatic coagulation. When cutting, the tissue is vaporized or 
blown apart by the high temperature and shock of the impact of the laser 
beam wavefront on the tissue. Since cutting requires more energy than 
coagulation, coagulation therefore calls for more control over the value 
of E.sub.t. 
Ultimate flexibility of control hinges on the control of the value of A, 
the area or spot size. It is the most difficult parameter to control 
because of the paradox of lens convergence angle versus focal length. The 
critical variable for the laser cutting or coagulation of tissue is the 
energy density applied to that tissue. 
Beam Angle: 
In arthroscopy and in other types of internal surgery where the surgical 
entry wound is a small hole rather than a large scalpel cut, the focal 
characteristics of the laser are critical, for these determine the 
dimensions of the cutting zone. As noted previously, both Argon and Nd:YAG 
lasers have high levels of backscatter, creating deep zones of distal 
tissue destruction that cannot be seen from the surface. 
With the CO.sub.2 laser, this is not the case, for the area of impact is 
the only area of tissue destroyed. Since a CO.sub.2 laser can have a very 
hot focus and as it is equipped with a long focal length narrow beam 
divergence angle lens, it can cut through a great depth of tissue in a 
very short time. 
In areas where the tissue is very thin or where the tissue fragment to be 
excised, as in a meniscectomy, is immediately in front of healthy tissue, 
great care must be exercised in controlling the depth of cut. This 
constraint, from a surgical and anatomical point of view, which requires 
the destruction only of targetted tissue and not tissue distal to the 
point of impact, makes the beam divergence angle of the CO.sub.2 laser a 
critical factor. 
To better appreciate this problem, let us consider an elementary lens. A 
typical thin convex lens has a specified focal length (f.sub.o =prime 
focus). This is the point in space where the rays of light transmitted 
through the lens converge and represents the point of maximum light 
intensity. This means that all of the parallel rays which enter the lens 
from one side emerge from it, forming a sterian (solid angle .theta.) to 
converge at one point. Any point displaced from the focus along the axis 
of the lens has a lower energy density due to the larger zone of 
dispersion of the light rays. 
The focal point is finite, hence, the rays of light which travel in 
straight lines away from the lens at specified angles from the lens' 
surface not only converge at the focal point but diverge beyond it. The 
beam widens and therefore diverges past the focal point at the same angle 
at which it converges to the focal point (angle .theta.'). The angle of 
convergence is then equal to the angle of divergence (.theta.=.theta.'). 
This phenomenon, which makes it possible for the surgeon to cut with the 
laser, also hampers his ability to use the laser at long distances from 
the target. 
If one uses a laser with a long focal length optical system (a long 
distance between the lens and the focal point), the beam's "cutting zone" 
is large and therefore deep. If one uses a laser with a short focal length 
optical system (short distance between the lens and the focal point), the 
cutting zone is small. 
When the angle of convergence is large, the angle of divergence is likewise 
large and the laser's energy is only concentrated close to the focal 
point. Any point displaced from the focal point, either side on or off 
axis, is at a much lower power density. Thus, short focal length lenses 
have a large angle of convergence and a concomitantly large angle of 
divergence and therefore have a very narrow cutting zone. When the angle 
of convergence is small, the resultant angle of divergence is also small. 
And because these angles are small, they concentrate the heat energy of 
the laser in a small area for a longer linear distance. 
Thus long focal length lenses (100 millimeters or more) have very narrow 
angles of convergence and therefore very narrow angles of divergence, 
creating a long distance about the focus on axis where the beam is 
sufficiently concentrated to perform cutting operations. When a particular 
case requires a very narrow cutting angle, the surgeon also has the 
greatest depth of cut. This comes automatically because of the necessity 
for a long focal length lens. When a lens with a wide beam divergence 
angle is used, the terminal lens has to get very close to the surgical 
target. This rule imposes a restriction on the surgeon which in many cases 
is contrary to the requirements for accomplishing necessary surgical 
tasks. 
The distance from the terminal lens (objective) to the prime focus is 
critical because of the relationship between focal length and working 
distance of the laser. Infrared-transparent lenses which are currently 
available are made of zinc selenide, gallium arsenide, zinc sulfide and 
other metals. These have a short focal length (wide divergence angles, 
hence close operating range) and must be large in diameter in order to 
achieve acceptable quantum efficiency. Their large physical diameter 
coupled with their wide beam divergence angle critically limits their use 
at any distance from the surgical target and precludes their use in a 
cannula. 
However, one of the advantages of using a lens with wide beam divergence is 
that once the prime focal point is set and the target lased, the beam 
disperses so fast that in a very short distance (0.5 to 2.0 millimeters 
away) the energy density is low enough that the beam will not cut or 
critically heat distal tissue. This is an advantage where surgical 
procedures are required to remove one or two cells or a single layer of 
cells at a shallow depth. 
The cannula, which must be from 20-40 centimeters long in order to reach 
into a cavity, would require that the lens be mounted at its terminus. 
This construction would require extremely complex sub-miniature linkages 
to control the prime focus of the lens. In addition, the lens would be 
subject to clouding, abrasion, direct tissue contact and contamination. 
The lens' primary constituents, zinc and selenium, are toxic metals. Beam 
position control would be difficult too because positioning would only be 
possible by moving the entire cannula assembly. This technique lends 
itself neither to precision control or to speed. It would seem therefore 
that the surgical requirements for laser arthroscopy and the cutting 
characteristics of the laser and its optical control system are working at 
cross purposes. 
Anatomical Factors: 
In knee surgery, two things are required from a laser. First, the surgeon 
must be able to deliver the laser beam onto the target, and second, the 
laser beam must cut the target and nothing more. Knee tissue, like most 
body tissue, is convoluted and three-dimensionally contoured. Unwanted 
damage of peripheral tissue can cause complications and anatomical 
difficulties. In order to avoid this problem the surgeon must have a 
carefully focused laser beam, a clear target and the means to deliver the 
beam accurately to the target. 
Focus of the laser beam without regard to divergence and convergence angle 
(length of the cutting zone) can cause serious problems. Since the focal 
point does not account for or indicate convergence or divergence angle 
(only cross-sectional area on the target), it is possible that a 
non-optimal (wrong focal length) lens might be used. 
A 1.0 cm diameter, 400 millimeter (f.sub.o) lens will focus a laser beam at 
an included angle of 1.degree.30', providing cutting energy density levels 
for 5 centimeters on both sides of the prime focus with a 2.0 mm spot. 
This means that when the beam is focused on a target and the laser is 
fired, the first pulse of the laser beam vaporizes the target and the 
second pulse can travel through the now vaporized target's space and, 
because of its small divergence angle, impact tissue distal to the target, 
destroying that tissue. 
The requirement for a long focal length lens is based on the need to get 
the beam through a long arthroscope onto a deep or remote target. The 
inability of the CO.sub.2 laser to be used with fiber optic light guides 
has rendered it impossible to use in arthroscopic surgical situations 
because of the length of the arthroscopes, most of which are in the order 
of 20-40 centimeters in length. This is too long to incorporate lenses of 
useful focal lengths and acceptable quantum efficiencies in their bodies. 
If one attaches a beam splitter and viewing head to an arthroscope having a 
20 centimeter length and assumes that the target will be one centimeter 
from the arthroscope's terminus, one then has a 35-40 centimeter distance 
between the laser's parallel light output and the arthroscope's cutting 
aperture. This distance demands a lens which has a focal length of 300 to 
400 millimeters. Given a lens with a beam convergence and divergence angle 
of 2.0 to 0.5 degrees yields a cutting zone depth from 10-25 centimeters 
(.+-.12.5 centimeters on either side of the prime focus). 
Under these circumstances, once the meniscus fragments are blown away, 
there remains the possibility of the laser beam cutting 5 to 12 
centimeters deeper into the tissue and perhaps out the other side of the 
knee or sufficiently far to damage healthy tissue distal to the target. 
This limitation is the problem which blocks the use of the CO.sub.2 laser 
in standard arthroscopic hardware with conventional lens systems. Since 
the surgical anatomy of knees and other joints is irregular and 
multi-geometric, the ability to control the focal point and the depth of 
the cutting zone of the laser is of critical importance. 
A large convergence angle (short focal length) lens demands that the 
terminal lens be very close to the target area. Since the laser cannula 
can only be 3-5 millimeters in diameter, this size constraint puts an 
extreme burden on the lens designer and restricts the quantum efficiency 
of the lenses. He does not have 300 to 700 millimeters of focal distance 
with which to design a lens which can be held outside of the body and 
therefore is large enough to efficiently focus the laser light on a 
distant target. The technical difficulties surrounding the making of a 
small diameter, high angle of convergence quantumly-efficient lens are 
therefore considerable. 
A laser beam system having a long focal length and therefore a shallow 
convergence angle is a definite hazard, but it fulfills the optical path 
length requirements for the arthroscope. A short focal length, high 
convergence angle beam is a definite advantage, but cannot be used at the 
end of a 40 centimeter optical path. The difficulties created by this 
situation are such as to call for some solution other than that of a 
conventional lens formulation. The solution provided by the present 
invention is a system having the characteristics of small diameter optics 
as well as the ability to generate a high convergence angle light beam in 
a small diameter with a variable focal point. It has to allow for 
adjustment in the depth of cut at the same time the focal point area is 
adjusted to preserve the ability of the surgeon to control tissue 
destruction caused by the laser beam at the specific focal point. 
In addition to the mechanical requirement of this type of surgical 
procedure, secondary surgical effects (consequential tissue trauma) must 
be minimized. Such trauma is caused in part by the movement of the 
arthroscope and of the associated implements through large angles and the 
subsequent stretching and tearing of tissue immediately in contact with 
them. An instrument in accordance with the invention is designed so that 
relatively little physical displacement is necessary once the single 
cannula is inserted into the joint. This, in turn, minimizes tissue trauma 
while providing the surgeon with all of the required beam maneuverability. 
In a laser cutting system, the angles indicative of the degrees of 
displacement that the instruments must transverse for the surgeon to reach 
the appropriate areas of the tissue to be lased are rather large. The 
insertion points are not necessarily at the vertices of the angles and the 
trauma caused to the skin, musculature, and vascular micro-structure is 
substantial. To add to the problem, when standard arthroscopic instruments 
are used, additional punctures must be made for effluent irrigation, 
affluent irrigation, and for the mechanical cutting system (arthroscopic 
cutter or scissors) to do the actual tissue removal. This can require as 
many as three large punctures. 
A laser steering cannula in accordance with the invention virtually 
eliminates all of the angular displacement by using rotational angular 
changes to reach the surgical target. Hence, with the present system there 
is only one large puncture, a minimum of tissue trauma, and disturbance to 
the vascular micro-structure. 
Inflation Media Requirements: 
In standard arthroscopic surgical procedures, liquid is used to inflate the 
knee or whatever joint is involved, for the joint parts need to be 
separated. In the case of the knee, one must separate the tibia from the 
femur and the paletta so that the synovia and meniscus can be viewed and 
operated on. 
To be effective in this context, the inflation medium must be biologically 
inert, and it must not give rise to any distentum or turgor of the tissues 
or any emboli. Nor should the medium readily diffuse into peripheral 
tissue or blood. The inflation medium should be easy to apply to the 
patient and be free of unwanted side effects such as drying of the tissue, 
for this may result in peripheral vascular or cell damage. Finally, the 
medium should lend itself to easy control by the surgeon and be economical 
to use. 
During the typical arthroscopic procedure, normal physiological saline is 
injected under pressure into the knee through a needle. Physiological 
saline is used because it is the standard inexpensive, 
biologically-neutral and absorbable material which is available. In 
addition, by circulating a flow of saline, debris and particles of 
resected tissue can be removed with little difficulty. 
Surgeons, by means of television cameras, are now able to look into the 
knee through arthroscopes and to view what is going on when the liquid 
circulates around the surgical site. The surgeon can observe on a video 
screen the debridement characteristics of the liquid upon the surgical 
premises. Since lasers have not heretofore been useable in arthroscopes 
for the reasons previously explained, the inflation medium has never been 
of consequence. 
With the present invention which makes it possible to use the CO.sub.2 
laser through an arthroscope, physiological saline can no longer be used 
as an inflation medium. The reason is that physiological saline is water 
with 0.8% salt content, and the 10.6 micrometer wavelength of CO.sub.2 
laser light is fully absorbed by the water. Thus, if physiological saline 
was used as the inflation medium in an arthroscopic laser surgical 
procedure, all of the CO.sub.2 laser's energy would be converted to heat 
by the water. As a consequence, the water will possibly boil, thereby 
generating tissue burning steam. It is therefore evident that a 
water-based liquid medium for inflating the knee is interdicted in a 
CO.sub.2 laser arthroscopic procedure. Thus the logical choice for the 
inflation medium is a gas. 
The two gases that have been regularly used in surgical procedures are 
diatomic nitrogen and carbon dioxide. These gases have properties that 
make them useful in surgical procedures, for they are fairly stable at 
normal operating temperatures and pressures, they are readily available 
and economical, and they have minimum toxicity to exposed tissue. 
Moreover, these gases displace water readily, have fairly high boiling 
points, and do not freeze at lowered body temperatures. However, these 
gases exhibit serious disadvantages when used in conjunction with CO.sub.2 
lasers which rule out their use as an inflation medium. 
Diatomic nitrogen is stable at low temperatures but at elevated 
temperatures it tends to combine with hydrogen and oxygen to form nitric 
acid and nitrogen compounds which include nitrous oxide, nitric oxide, 
etc., all of which are injurious to protoplasm. Nitric acid resulting from 
the reaction of nitrogen gas with hydrogen and oxygen at high temperatures 
is destructive to all tissue, especially nerve tissue (which is most 
susceptible because of its protein makeup). 
In a normal surgical procedure, the use of a CO.sub.2 laser to vaporize or 
destroy tissue creates an impact site temperature well in excess of 
1000.degree. Celsius. This temperature is high enough to destablize almost 
any nitrogen-bearing compound. These include hydrocyanidic acid, cyanide, 
nitric acid, nitrogen dioxide, and nitrous oxide. None of these compounds 
are desirable in vivo or at an operative site. To further add to the 
medical risk is the possibility that these compounds might become trapped 
inside a body cavity. The potential of biological damage and 
post-operative complication is high with nitrogen gas chemistry should it 
be used as the inflation medium with a CO.sub.2 laser. Nitrogen gas is 
therefore not an acceptable inflation medium for use with the CO.sub.2 
laser. 
Carbon dioxide, which is also in common use in surgical procedures, does 
not possess quite so many of the undesirable characteristics of nitrogen 
at elevated temperatures. However, at the laser's impact site, carbon 
dioxide will disassociate into its constituent molecules. These, in the 
presence of the protein and amine-based compounds of which our bodies are 
made, can generate hydrocyanic acid and cyanide gas. 
Carbon dioxide has another characteristic which makes it even less 
acceptable for use with the CO.sub.2 laser. This characteristic is the 
ability of carbon dioxide to trap heat, for it is an excellent thermal 
insulator. The 10.6 micrometer (far infrared) wavelength generated by the 
laser is almost completely contained by carbon dioxide gas. This 
phenomenon will impede the surgeon's ability to keep the wound site cool 
and hence the ability to protect peripheral tissue damage from thermal 
exposure. 
The requirements for an inflation medium in arthroscopic surgery clearly 
point to the choice of a gas that is thermally stable, chemically inert, 
and of low solubility so that it will not dissolve into tissues rapidly. 
We have found that helium and argon satisfy these requirements. They are 
both inert monoatomic gases, they share equivalence sports in the periodic 
chart, they do not react electrically and both gases are good conductors 
of heat. 
Though helium has a high osmotic permeability coefficient because its atom 
is even smaller than a molecule of hydrogen, it does not readily dissolve 
into tissue at low pressures. Argon, on the other hand, is a substantially 
larger atom. It does not have the permeability coefficient of helium, but 
it does have a tendency to dissolve into fluids and tissues of the body. 
However, neither of these gases will give rise to chemical and 
electrochemical effects when excited by high temperatures. 
From strictly thermal considerations, either helium or argon could be the 
medium of choice for inflation for arthroscopic laser procedures. Both He 
and Ar have the ability to absorb the heat generated by the CO.sub.2 laser 
and will facilitate cooling and thereby limit the transfer of heat to 
peripheral tissue in the surgical area. 
When considering argon and helium gases as media, it must be noted that the 
specific heat of helium is 1.24 and that of argon is 0.124. This 
difference indicates that helium absorbs much more heat than does argon; 
therefore, the ability of helium to cool the laser target area and 
maintain the peripheral tissue temperature is an order of magnitude 
greater than that of argon. In addition, the entropy S.degree. of helium 
is less than argon. The value for helium is 30.13, while argon is 36.983. 
These differences are substantial and the practical application of the 
entropic differentials and of energy transfer per unit per degree Kelvin 
are not insignificant in the context of the present invention. 
Helium is much more soluble in blood and therefore does not present the 
problem of the blood retaining quantities of it and becoming saturated 
under elevated pressures because it gasses out as fast as it dissolved. It 
does not generate the potential of forming micro-emboli at surgical 
working pressures. 
Since the body is an isothermic system with built-in regulators, we can 
assume that temperature functions and the effect of the heat absorbed by 
the inflation gas when it expands, in relation to the total thermal mass 
of the body, is negligible. This means that the influence of the body heat 
on the solubility of the gases of the blood in terms of a differential 
driven process can be ignored. Helium is much less soluble in blood than 
is argon. 
It is clear therefore that for use in conjunction with CO.sub.2 laser 
surgery, helium gas is the preferred inflation medium. Because of its high 
specific heat, helium has the ability to absorb and transfer heat away 
from the laser impact target to the atmosphere. Helium is inert at all 
temperatures, it is easy to handle, and can safely be used in the 
operating room from the standpoint of both chemical reactivity and 
ionization hazards. 
Helium Delivery System: 
Delivery methods for helium are not complex, but there are several 
considerations that must be taken into account. One of these stems from a 
phenomenon associated with the laser beam's impact on tissue, called "beam 
masking". The material at the impact site is literally blown apart into 
its constituent elements. Should the target be a solid material such as 
bone (calcium phosphate), the surface of the bone will be vaporized and 
thereby broken down into elemental compounds, and the sub-surface layers 
will be fractured and fragmented by the shock wave caused by the laser's 
impact. 
Particles will dislodge and be scattered in a means similar to the impact 
of a high explosive projectile on the ground. These particles and dense 
gases create a smokescreen which can totally block the laser beam. When 
this occurs, the procedure must be stopped. If the target continues to be 
lased, the gas and obstructing media continue to heat up, adding heat to 
the wound site and raising the mean temperature of the peripheral tissue 
to an unacceptable leve1. 
In order to ensure that the CO.sub.2 laser's beam path stays clear (minimum 
beam masking), the inflation medium should be conducted through the 
cannula of the laser arthroscope device. This will provide a constant 
stream of gas pumped through the laser tube to keep the laser clear of 
scattered debris, dense gas, blood products, and materials which might 
otherwise lodge in the tube or cloud the beam path, impairing the laser 
focusing device and the delivery of the laser beam. 
FIG. 1 schematically shows a laser arthroscope 10 in accordance with the 
invention operating in conjunction with a CO.sub.2 laser 11. Supplied to 
arthroscope 10 is an inflation medium derived from a helium supply 
cylinder 12. The helium from the cylinder is fed to the cannula of the 
arthroscope through a helium manifold 13 and a line 14 extending from the 
manifold through a regulator 15, an anti-backflow valve 16, and a 
start/stop switch 17 which interlocks with the laser. 
The gas delivery and circulation system is preferable controlled by 
regulating the output or the low pressure side. This serves to keep a 
steady circulation of uncontaminated gas through the wound site so that 
materials resulting from the high temperature decomposition of organic 
products do not build up; hence heat generated by the laser is removed. 
To this end, a purging tube 18 is provided which is coupled to manifold 13 
through alternate paths at a junction 19, one being through a low-pressure 
regulator 20, a switch 21, and an anti-backflow valve 22, the other being 
through a high-pressure regulator 23, a foot-operated on/off switch 24, 
and an anti-backflow valve 25. 
The system shown in FIG. 2 makes it possible to remove the gas easily from 
the surgical site and opposite of the area of surgical interest. As has 
been stated, it is necessary to keep a constant flow of helium at a 
constant pressure through the laser cannula and across the surgical 
target. This allows both tissue cooling and provides an inert target 
envelope which further reduces the probability of poisonous compounds 
being formed as byproducts of the high temperature vaporization beam. 
To effect gas removal, evacuation cannula 26 is placed immediately behind 
(or to the side of) the surgical site so as to create a "draft" across the 
surgical target. This technique ensures proper flow of gas around the 
surgical site which will facilitate proper cooling and keep the area swept 
clean of interfering clouds. The draft effect of the gas helps to suck 
away and debride surgical rubble and particles from the wound site, 
allowing the surgeon a continuously clear view of the target. 
In the arrangement shown in FIG. 2, evacuation cannula 26 is coupled to a 
collection container and smoke filter 27 which is coupled to a vacumn pump 
28 through a vacumn safety valve 29 and a source select switch 30 which is 
linked to the atmosphere through an anti-backflow valve 31. 
Vacumn pump 28 provides negative pressure at the output rather than simply 
venting the helium to the atmosphere. If the gas is simply vented to the 
atmosphere, control over the inflation (distention level) of the knee is 
limited, for one is not then able to control back pressure. Effluent 
pumping makes it possible to accurately balance the helium input against 
the output and to accommodate another helium jet directed toward specific 
contaminants or to provide additional cooling of sensitive tissue. 
The Laser Beam System: 
Shown in FIG. 3 is a laser beam system in accordance with the invention for 
performing a surgical procedure in which a laser beam is focused on a 
target at a surgical site. The system includes an elongated cannula 
constituted by an outer tube 32 and an inner tube 33 coaxially supported 
for rotation within the outer tube by upper and lower annular bearings 34 
and 35. Thus one can turn the inner tube relative to the fixed outer tube 
to direct the beam as required. The lower end of the inner tube is closed 
by a flat plate, as is the lower end of the outer tube, a thrust bearing 
36 being interposed between the end plates. The cannula is insertable into 
a body passage leading to the surgical site. 
Attached to the upper end of the inner tube 33 and projecting beyond the 
outer tube 32 is an inlet section 37. Inlet section 37 is provided with a 
first input port 38 which is colinear with the longitudinal axis of the 
inner tube 33, and a second or lateral input port 39 at right angles 
thereto. Supported within the inlet section 37 is a semi-transparent 
mirror or pellicle 40 which is at a 45.degree. angle with respect to input 
ports 38 and 39. The pellicle is optically permeable to white light and 
reflective with respect to infrared energy. 
Coupled to input port 38 is a white light source 41 whose rays are 
collimated to produce an illumination beam which passes through pellicle 
40 which is transparent thereto. The light beam is directed down the inner 
cannula tube 33 and serves to illuminate the surgical site for direct 
visualization or for television viewing as will be later explained. 
Coupled to the lateral input port 39 is a carbon dioxide laser 42 whose 
10.6 micrometer beam which lies in the infrared region, is reflected by 
pellicle 40 and directed thereby down inner tube 33 concurrently with the 
white light. Also introduced into lateral input port 39 is an inflation 
gas derived from a controlled helium source generally represented by block 
43, the helium flowing through the inner tube 30 into the surgical site. 
The lower end of the inner cannula tube 33 terminates in an outlet section 
44 which is disposed within the lower end of the outer tube 32. Outlet 
section 44 is provided with a lateral output port 45 at right angles to 
the longitudinal axes of inner tube 33. Mounted within outlet section 44 
at a 45.degree. angle with respect to this axis is a deformable membrane 
46 which is normally planar and is peripherally supported by an 
elastometric coupling 47 within an annular mounting ring 48. Thus the 
deformation of the membrane is not distorted at its periphery. The angular 
position of the membrane with respect to the axis of inner tube 33 creates 
a right triangular conic section which when viewed at a position normal to 
the plane thereof results in an ellipse, as shown separately in FIG. 4. 
Attached to the geometric center of the elliptical membrane on the rear 
side thereof between the two foci and coplanar with its surface is a rigid 
drive pin 49. The pin is thermo-compression welded or otherwise fixedly 
secured to membrane 46. This pin allows forces to be exerted on the 
deformable membrane by an actuator 50 adapted to deflect it geometrically. 
These deflecting forces give rise to stress vectors and so alter the 
curvature and contour of the membrane as to define a concave aspheric 
mirror having optical properties making it possible to focus the laser 
beam impinging thereon. 
The membrane may be made of an aluminized polyester sheet such as mylar, or 
of polished titanium, and acts to reflect close to 100% of the 10.6 
micrometer wavelength light generated by the CO.sub.2 laser. The light is 
focused by the concave membrane mirror at a point whose distance from the 
mirror's surface is inversely proportional to the displacement of the 
membrane. Thus when the membrane is planar, the laser beam projected 
through the cannula strikes the membrane and is reflected in a parallel 
beam. Since the light source is a laser, all incident rays are exactly 
parallel and coherent; therefore all reflected rays will be parallel. This 
parallel beam has the same area as that of the beam in the cannula and 
does not concentrate the light to a sufficiently high energy density to 
cut tissue. 
The actuator 50 may be an electromagnetic or other electrically-operated 
mechanism capable of displacing the pin. When the pin is extended axially 
by activator 50 and thereby pushed toward deformable membrane 46, its 
contour is rendered convex. This shape disperses the light as a second 
order function of the distance of displacement and completely diffuses the 
beam to cause it to cover a very large area, thereby reducing its energy 
density and inhibiting the laser's ability to even so much as heat tissue. 
Conversely, when the pin is pulled down by actuator 50 so that it shapes 
the reflective membrane into a concave form, it then focuses the laser 
beam to a point. Since the membrane is designed to only assume the form of 
a quasi-parabolic section, the resultant focus is a single point. 
This parabolic shape takes parallel rays and converges them to a point or 
the focus of the parabola. The focal distance from the apex (or the bottom 
of the parabola's trough) is a function of the parabola. By changing the 
quasi-parabola's contour, one can change the point at which the light is 
brought to a focus. This makes it possible to change the focal point of 
the laser beam by changing the shape of the parabola. 
In order to obtain proper deformation of the membrane to form a 
quasi-parabola, we must arrange for proper deflection of the membrane 
mirror material. Since the quasi-parabolic shape is non-linear, it follows 
that the stresses that deflect the membrane must also be non-linear. But 
stress in a uniform material is a linear quantity having magnitude and 
direction. This raises the question as to how one can generate a 
non-linear stress to form the desired non-linear shape. Since we cannot 
alter the stress vector, we must control the cross-section of the stressed 
material so as to reproduce the function that we require. 
Ordinarily when one uses an annularly-shaped membrane of uniform thickness 
and stresses it at its center, the resultant profile shape is a second or 
third order parabola. This is due to the build-up of stresses in the 
material. This shape is not acceptable, since that function gives us a 
close focal point, not a single focal point. This would, in effect, focus 
the beam into the mirror, making it useless for surgery. 
In order to circumvent the problem of parabolic deflection it is necessary 
to create a condition in the material which will force the stresses to 
build up in directions and at magnitudes which create a quasi-parabolic 
curve when the pin is pulled, as shown schematically in FIG. 5. Because 
the membrane 46 is located in its geometric center in a direction at right 
angles to its suspension plane and with a high displacement load, this 
places the focus on both the optical and geometric axis and in the 
aperture. 
The best way to accomplish this end is to contour the thickness of the 
membrane as shown in FIG. 6 so that the stress concentrations build up 
properly as they proceed radially from the center to the circumference. 
This will accommodate the decreasing material strength and distribute the 
stresses in a non-linear fashion across the surface of the mirror. Thus 
the membrane is thinnest at its center and becomes increasingly thick as 
one moves away from the center. 
The tailoring and control of the cross-sectional profile of the mirror 
makes it possible to create non-uniform stresses in a material of uniform 
elastic modulus. Because of this we can use the non-linear deflection of 
the reflective membrane to create both on axis focal points and off axis 
focal points. Thus steering can be accomplished in off axis, off aperture 
focal points. 
Since the membrane mirror shape generated by the laser focusing and 
steering device is aspheric, it has the characteristics of both parabolic 
and hyperbolic mirrors. The system is therefore unique because of its 
ability to generate both exceedingly sharp focal points as well as a short 
length of focal loci. The short length focal loci or line of focus can be 
controlled accurately in both depth and width. This makes it possible for 
the laser to bore a very neat cylindrical hole, thereby developing a 
uniform zone of tissue destruction and a minimum of peripheral tissue 
damage. 
Because the membrane mirror operates on the principle of elastic 
deformation, it affords a large measure of engineering freedom as to the 
materials one can choose to implement its structure. Thin polished 
titanium is a preferred membrane material because of its high yield 
strength and its exceptional hardness which can be brought to a high 
optical finish. For some specific applications, an elastomeric polymer 
such as silicone rubber or neoprene rubber may be better suited. These can 
be molded cheaply into almost any cross-section and then treated with 
vapor-deposited aluminum for high reflectance. 
The angular deflection of the deformable membrane and therefore the depth 
of the quasi-parabola and its conical aspheric shape, control the focal 
point of the laser beam. Because the inner tube of the cannula is mounted 
co-axially within the outer tube thereof, we not only can change the focal 
length, but we can also steer it by biasing the stresses on the pin off 
the axial centerline of the membrane. 
To this end one may use an actuator 50 for drive pin 49 in the form of a 
piezoelectric actuator 50P as shown in FIG. 7 which can be electrically 
excited to displace the pin in either the X or Y direction whereby the 
beam reflected by the membrane can be displaced both in the X and Y axes. 
In addition, the inner tube 33 can be rotated within the outer tube 32 
about the axis of the cannula to allow coverage of a fairly large arc 
sector. This makes it possible to control the beam in a three axis 
coordinate system with a high degree of precision. In practice, the 
piezoelectric actuator may be controlled by signal commands originating in 
a remote computer. 
Because the helium-inflation medium is fed to the surgical site through the 
inner tube of the cannula, the gas is thereby channelled to concentrate at 
the laser's target site. This provides the ability to use the minimum 
amount of purging gas and to achieve the optimum effect. 
Visualization: 
As shown in FIG. 8, to facilitate television viewing light source 41 is 
arranged to direct its rays through a diffuser plate 51 and a lens 52 onto 
a beam splitter mirror 53 which is at 45.degree. relative to the axis of 
the inner tube 33 of the cannula. Mirror 53 acts to reflect the light beam 
into the cannula through lenses 54 and 55 to be directed at the outlet 
section by the focusing membrane 46 onto the surgical target T which is 
illuminated thereby. The illuminated image of the target which passes 
through beam splitter mirror 53 is viewed by a TV camera through a TV 
lens. 
The pellicle 40 which is reflective to the infrared light from laser 42 but 
transparent to white light, acts to send both the white light and the 
laser cutting beam down the cannula. Since both the white light and laser 
beams are focused by the same membrane mirror 46 (terminal device), the 
area or target point T that is in focus optically for visual siting and 
inspection is the same area or target point that is in focus for the 
laser-cutting beam. 
This arrangement does away with the need for a second cannula opening close 
to the surgical site to make direct visualization or video observation 
possible, for the entire system is integrated with TV and direct 
visualization optics. 
A highly significant advantage of this arrangement is that all of the 
beams--the visualization beam (light returning from the target to the eye 
of the observer or television camera), the illumination beam (the light 
that is transmitted through the beam splitter 53 which floods the target 
area with illumination), the coherent laser cutting beam (the CO.sub.2 
surgical cutting beam), as well as a HeNe pilot beam--all converge at the 
same point which is the focus generated by the deformation of the membrane 
mirror 46. As a consequence, the surgeon, visualizing the surgical target 
through the focusing system, is able to perceive exactly what is the 
target of the laser, this being seen in the dead center of the visible 
image and in precise focus. There is no focal differential between the 
white light and the infrared laser beams. 
Conventional lenses that are transparent to a 10.6 micrometer infrared 
CO.sub.2 cutting beam are opaque to visible light, whereas lenses that are 
transparent to visible light will absorb the 10.6 micrometer cutting beam. 
The absence of either type of lens in the cannula passage makes it 
possible for all of the beams to be bundled and allows them to fulfill 
their respective functions together. This is only possible by using a 
membrane mirror in accordance with the invention, for this mirror, unlike 
a lens, treats all light wavelengths in the same manner. The membrane 
mirror deflects light through reflection, not refraction, and the angles 
of reflection are not related either to the refractive index or to the 
dielectric constant of the material from which the mirror is made. There 
is no focal point shift as the wavelength of the light reflected by the 
mirror changes. 
This characteristic which causes all beams passing through the cannula to 
focus at the same point, permits multiple wavelength broadband light to be 
coaxially superimposed on the laser, and permits visualization return and 
illumination beams. Thus Nd:YAG and Argon beams may be combined with a 
CO.sub.2 beam to facilitate broader surgical utility of the laser system. 
When the unit is assembled, it must be bore sited so that the helium-neon 
pilot beam, the CO.sub.2 laser cutting beam, the white light illumination 
beam, and the visualization return beam are all exactly coaxial. All of 
these beams can then be treated as one bundle of light that is exactly 
parallel from its origin to its terminus (focus). 
When using a television camera as the mapping device for a 
computer-controlled system, the television's raster scan generates the X 
and Y coordinates of the tissue in relation to the beam (and vice versa). 
Because of the coherent laser and white light reflection characteristics 
of the mirror, the focal point will be the depth. The amount of control 
used to deflect the membrane mirror can then be translated into a value 
which can be translated into a Z coordinate, thus giving the computer a 
three-dimensional, triaxial representation of the surgical field. 
Though the illumination light is focused by the deformable membrane mirror, 
it is different from the laser beam because it is inherently diffuse. 
Since it is not coherent, it will diffuse over an area larger than the 
target area (surgical field). Thus the target area will be generally 
illuminated while the laser beam is focused at its dead center. 
The steering membrane mirror affords ultimate control over the laser's 
focal characteristics by making practical the use of a wide beam angle 
source at long distances from the laser generator. The pragmatic benefit 
of this device is that a short focal length lens is put in close proximity 
to the tissue area of surgical interest. And though it mechanically acts 
like a long focal length lens, it has none of its disadvantages. 
Because of the non-linear mirror and focal characteristics of this laser 
steering device, it is readily adaptable to the emerging technology of 
EXCIMER laser ablative surgery. Its optical characteristics make it 
possible to focus an EXCIMER laser without the need for a molybdenum mask 
to confine the beam. The elimination of the mask gives the surgeon more 
latitude in shaping and controlling the ablation while reducing the cost. 
Computer Control: 
The key to extending the use of this system is that the membrane mirror is 
the control point of a powerful laser beam energy source which may now be 
precisely directed. It therefore becomes feasible with the use of computer 
control to carry out procedures which have heretofore been too delicate, 
risky or tedious to attempt manually. 
Because of the tremor of the human hand, the surgeon cannot hold a scalpel 
on a line with an excursion of less than .+-. half a millimeter. A laser 
beam's focal point can be smaller than 0.01 millimeter. Computer control 
allows maneuver of the membrane mirror within several ten thousandths of 
an inch, making precision control feasible. Indeed, control can be so 
accurate that the laser may be used to remove single cells or a layer of 
cells less than a tenth of a micrometer thick. 
Among the uses of a system with this degree of accuracy and resolution are 
ultrafine vessel anastomosis, microscopic neurolysis and tenodesis, 
microscopic duct and vascular work, microscopic excision of carcinomas, 
microscopic neurosurgery, as well as other neurological repair 
applications. These procedures can be carried out by using various types 
of cannulated delivery systems similar to the arthroscope and laparoscope. 
With the computer controlling the direction, power density, focal length, 
spot size and pulse rate of the laser, the imprecision inevitably 
attending human control can be virtually eliminated. 
A further extension of this technology is to couple the 
computer-manipulated laser with a television video camera scanning the 
target site. By using the computer to recognize and interpret the video 
algorithm (picture), this would allow manipulation of the laser cutting 
instrument at high speed through and around a set of bounded coordina. 
Those coordina could be defined by the presence of certain chemical dyes 
of selected color, pre-programmed cell topology, or programmed coordinate 
positioning. 
Thus, cancer cells can be stained for identification and the computer's 
video interface then used to rapidly and accurately destroy, on a 
selective basis, only those cells that are identified. This would allow 
cancerous tissue to be excised without inflicting damage on healthy 
tissue, and it would reduce the possibility of leaving a few cancerous 
cells behind to cause a recurrent tumor in the patient. And it would at 
the same time reduce the surgical risk to the patient. 
The use of a computer as the control station for the laser focusing mirror 
would allow the surgeon to prepare simulation and testing programs using 
software models with the computer to run test scenarios before the laser 
is actually used on the patient. These test scenarios could be run on 
inert models or run on the patient in vivo by using the helium-neon pilot 
steering beam of the CO.sub.2 laser, before the actual cutting beam is 
turned on. 
This would give the surgeon an immediate, direct outline of how the 
procedure is to be executed on the patient. In this way the surgeon could 
conduct a pre-evaluation and first test whether or not the program covered 
all the necessary points. When the surgeon is satisfied by this test 
procedure that the program is complete, he may then run the program and 
permit the computer to perform the surgery under his direction and 
control. 
Software modeling can save a great deal of time in the operating room and 
give surgeons the ability to stay current and in practice so that they do 
not lose their "touch" with the laser. Such computer simulations using the 
laser focusing mirror are also useful in medical education. 
While there has been shown and described a preferred embodiment of LASER 
BEAM SURGICAL SYSTEM in accordance with the invention, it will be 
appreciated that many changes and modifications may be made therein 
without, however, departing from the essential spirit thereof.