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Claims  |
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What is claimed:
1. Apparatus for the automatically controlled application of optical energy
in the reconstruction of biological tissue to cause the formation of a
proteinaceous framework from denatured protein in the vicinity of the
biological tissue, the framework approximating the biological tissue to be
reconstructed, said apparatus comprising:
an optical energy source for producing a beam of optical energy;
guide means for directing said beam of optical energy to a spot on a
biological tissue to be reconstructed, said guide means having a
distalmost end remote from said optical energy source and from which said
optical energy is emitted;
data conversion means, responsive to a user input signal representative of
a characteristic of the tissue, for generating an output signal
representative of corresponding appropriate settings of control parameters
of said beam to cause the amount of optical energy delivered by said
source to said tissue to be within a tissue nondestructive range bounded
by a minimum rate at which the tissue forms a collagenous substance and a
maximum rate at which water in the tissue would boil; and
means operatively connected to said optical energy source and to said data
conversion means, and responsive to said output signal, for controlling
said beam in accordance with said beam parameter settings; whereby
proteinaceous components of the tissue are denatured.
2. Apparatus as in claim 1, wherein said means for controlling parameters
of said beam comprises means for setting the power output of said optical
energy source.
3. Apparatus as in claim 2, wherein said means for setting the power output
of said optical energy source comprises electronic circuitry having an
input terminal, an output terminal connected to said optical energy
source, and a data processing device for delivering a power output setting
signal at said output terminal in response to receipt of said input signal
at said input terminal.
4. Apparatus as in claim 3, wherein said data processing device comprises a
computer memory device for storing data relating to power output settings
for various tissue types and thicknesses.
5. Apparatus as in claim 4, wherein said optical energy source comprises a
laser, and wherein said means for setting the power output of said optical
power source further comprises current control setting circuitry connected
between said output terminal and said laser.
6. Apparatus as in claim 5, wherein said data processing device further
comprises means for delivering a power output signal in digital form at
said output terminal, wherein said current control setting circuitry
comprises a digital-to-analog signal converter connected to convert said
digital form output signal to a corresponding analog signal, a
voltage-to-frequency converter connected to convert said analog voltage
signal to a corresponding frequency signal, and a frequency-to-voltage
converter connected to receive isolated inputs from said
voltage-to-frequency converter and to deliver a laser power source setting
signal to said laser.
7. Apparatus as in claim 2, wherein said means for controlling parameters
of said beam further comprises means for controlling the time of emission
of said beam from said distalmost end of said guide means.
8. Apparatus as in claim 7, wherein said means for limiting the time
duration of said beam comprises a switch; a shutter interposed between
said optical energy source and said distalmost end of said guide means,
and which is movable in response to operation of said switch from a normal
beam blocking position to a beam passing position; and a timer limiting
the time during which said shutter can remain in said beam passing
position in response to said switch.
9. Apparatus as in claim 8, wherein said timer comprises a data processing
device connected to said switch for counting the number of clock pulses
elapsed since activation of said switch, and means for deactivating said
switch to close said shutter when the number of clock pulses counted
reaches a number preestablished according to said tissue representative
input signal.
10. Apparatus as in claim 7, wherein said means for controlling parameters
of said beam further comprises means for establishing the diameter of said
beam at said spot.
11. Apparatus as in claim 10, wherein said means for controlling the
diameter of said beam at said spot comprises means for determining the
working distance between said distalmost end and the tissue.
12. Apparatus as in claim 11, wherein said working distance determining
means comprises means for displaying working distance determined according
to said tissue representative input signal, and a sliding scale positioned
at said distalmost end for lateral movement parallel to said emitted beam.
13. Apparatus as in claim 1, wherein said optical energy source has a
wavelength between approximately 1.2 and 1.4 micrometers.
14. Apparatus as in claim 13, further comprising marker means for producing
a beam of visible optical energy coincident with said emitted beam of
optical energy, whereby a region which is desired to be illuminated by
said beam of optical energy can be identified.
15. Apparatus as in claim 1, wherein said optical energy source is a Nd:YAG
laser operated at a secondary wavelength of 1.32 micrometers.
16. Apparatus as in claim 15, further comprising an auxiliary optical
energy source that produces an auxiliary beam of optical energy which has
a wavelength which is substantially absorbed in biological tissue.
17. Apparatus as in claim 16, wherein said auxiliary optical energy source
comprises a helium neon laser.
18. Apparatus for the automatically controlled application of optical
energy in the reconstruction of biological tissue to cause the formation
of a proteinaceous framework from denatured protein in the vicinity of the
biological tissue, the framework approximating the biological tissue to be
reconstructed, said apparatus comprising:
a laser optical energy source for producing a beam of optical energy having
a wavelength between approximately 1.2 and 1.4 micrometers;
an optical fiber guide for directing said beam of optical energy to a spot
on a biological tissue to be reconstructed, said guide means having a
distalmost end remote from said optical energy source and from which said
optical energy is emitted; and
means operatively connected to said optical energy source, and responsive
to a user input signal representative of a characteristic of the tissue,
for generating corresponding appropriate settings for the output power,
exposure time and spot diameter of said beam, and for controlling the beam
in accordance therewith, to cause the amount of optical energy delivered
by said source to said tissue to be within a tissue nondestructive range
bounded by a minimum rate at which the tissue forms a collagenous
substance and a maximum rate at which water in the tissue would boil;
whereby proteinaceous components of the tissue are denatured.
19. Apparatus as in claim 18, wherein said means for controlling said
output power, exposure time and spot diameter parameters comprises
computer means, responsive to input signals representative of tissue type
and thickness, for determining and setting appropriate values of said
parameters based on stored information on previously established
relationships between tissue characteristics and acceptable values for
said beam parameters.
20. A method for the automatically controlled application of optical energy
in the reconstruction of biological tissue to cause the formation of a
proteinaceous framework from denatured protein in the vicinity of the
biological tissue, the framework approximating the biological tissue to be
reconstructed, said method comprising the steps of:
entering an input signal into a computer representative of a characteristic
of tissue to be reconstructed;
using said computer to determine suitable parameters, based on stored data,
of an optical energy beam to be delivered to the tissue site at an energy
level within a tissue nondestructive range bounded by a minimum rate at
which the tissue forms a collagenous substance and a maximum rate at which
water in the tissue would boil, whereby proteinaceous components of the
tissue are denatured; and
using said parameters to control the power, exposure time and diameter of
emission of an optical energy beam from an optical energy source to the
tissue, thereby maintaining the energy delivered by said beam to the
tissue at said energy level. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates generally to methods and apparatus for closing
wounds and more particularly, to a method and apparatus for applying
optical energy to biological tissue whereby the tissue is converted to a
collagenous, denatured protein substance which joins severed tissues and
closes wounds.
Historically, suturing has been the accepted technique for rejoining
severed tissues and closing wounds. Suturing has been achieved with a
surgical needle and suturing thread, and more recently, with a variety of
polymeric or metallic staples. The intended function of sutures is to hold
the edges of the wounds against one another during healing so as to reduce
discomfort, pain, scarring, and the time required for healing.
It is a problem with known suturing systems that since they are applied
intermittently along a wound, they permit gaps in the wound between
sutures to remain open thereby accepting dirt and bacteria. Moreover, in
addition to producing a relatively high risk of infection and tissue
rejection, such gaps between sutures are eventually filled in by keloid,
which results in disfiguration and scarring. In addition, inflammation
often results from the foreign body presence of the suture material.
It is an additional disadvantage of conventional sutures that they may slip
in an axial direction thereby permitting relative motion between the
tissues which are desired to be joined, and may loosen before the healing
process has advanced sufficiently to maintain a tight closure of a wound.
Thus, sutures must frequently be removed and replaced, thereby requiring
multiple visits to a physician. There is a need, therefore, for a wound
closure system which is uniform throughout the length of a wound.
A variety of cauterization and cryogenic techniques have been developed to
reduce the flow of blood in an open wound, or a surgically-induced
incision. Generally cauterization is achieved by using intense heat to
sear and seal the open ends of the tissues, such as vessels and
capillaries. In known cauterization systems, heat is generated by
resistance heating of a metallic probe which is subsequently applied to
the tissue to be cauterized. Alternatively, undesired blood flow is
discontinued by applying a cryogenic temperature which freezes the tissue.
More recently, the medical field has utilized high intensity optical
energy generated by one or more lasers to achieve cauterization which
limits blood flow. In such known laser systems, the optical energy is
applied in sufficient quantity to sear or burn the vessels. Laser
cauterization is illustratively described in U.S. Pat. No. 4,122,853 to
Michael R. Smith. These techniques, however, destroy the surrounding
tissue leading to longer healing times, infection, and scarring.
Recent advances in the state of the art have produced cauterization with
the use of ultrasonic energy which is converted to mechanical vibrations
through a knife. Such a rapidly vibrating knife simultaneously cuts and
closes off severed vessels. A system of the ultrasonic vibrational type is
described in U.S. Pat. No. 3,794,040 which issued to Balamuth. In the
known system, ultrasonic energy is applied to create heating of the
vessels desired to be cauterized above room temperature, but below a
temperature at which such vessel would sear. The heat thus produced causes
hemostasis, by denaturing of the proteins in the tissue to form a
collagenous substance which performs as a glue to achieve the closure or
bond. This technique, however, has not gained widespread use for delicate
surgery because it requires bringing a vibrating probe into contact with
the tissue to be affected. Morever, ultrasonic energy is nonpreferentially
absorbed and affects all of the surrounding tissue.
Optical energy generated by lasers has been applied in recent times to
various medical and surgical purposes because the monochromatic and
coherent nature of the light generated by lasers has been shown to have
absorbency characteristics which vary with the nature of the illuminated
tissue. Thus, for a given tissue type, the laser light may propagate
through the tissue, substantially unattenuated, or may be almost entirely
absorbed. Of course, the extent to which the tissue is heated, and
ultimately destroyed, depends on the extent to which it absorbs the
optical energy. It is generally preferred that the laser light be
essentially transmissive in tissues which are desired not to be affected,
and absorbed by the tissues which are to be affected. For example, when
using lasers in fields which are wet with blood or water, it is desired
that the optical energy not be absorbed by the water or blood, thereby
permitting the laser energy to be directed specifically to the tissues
desired to be affected. Such selective absorption also permits substantial
time saving during an operation by obviating the need for cleaning and
drying the operating field.
It is a further known advantage of a laser system that the optical energy
can be delivered to the tissues desired to be operated upon in a precise
location and at predeterminable energy levels. The precision with which
the laser energy can be directed is enhanced by its ability to be guided
by known thin optical fibers which permit the optical energy to be
utilized within a body without requiring large incisions or to be inserted
into the body through an endoscope. The optical fibers which conduct the
laser-generated optical energy for performing the operation can be
combined with other optical fibers which conduct light in the visible
range, and further optical fibers which are of the image-transmissive type
such that a surgeon may view and control an operation which is occurring
within a body.
Ruby and argon lasers which are known to emit energy in the visible portion
of the electromagnetic spectrum have been used successfully; particularly
in the field of ophthalmology to reattach retinas to the underlying
choroidea and to treat glaucoma by perforating anterior portions of the
eye to relieve intraocular pressure. The ruby laser energy has a
wavelength of 0.694 micrometers and, thus, appears red. The argon laser
emits energy at 0.488 and 0.515 micrometers, thus, appearing blue-green.
The ruby and argon laser beams are minimally absorbed by water, such as
tissue water, but are intensely absorbed by the blood chromagen
hemoglobin. Thus, the ruby and argon laser energy is poorly absorbed by
nonpigmented tissue such as the cornea, lens, and vitreous humor of th
eye, but is preferentially absorbed by the pigmented retina where it can
then exert a thermal effect.
Another type of laser currently in surgical use is the carbon dioxide
(CO.sub.2) gas laser which emits a beam which is intensely absorbed by
water. The wavelength of the CO.sub.2 laser is 10.6 micrometers and
therefore lies in the invisible, far infrared region of the
electro-magnetic spectrum. Reference to FIG. 1A shows that the absorption
of energy by water in this part of the spectrum is so great that it is
absorbed independently of tissue color by all soft tissues having a high
water content. Thus, the CO.sub.2 laser makes an excellent surgical
scalpel and vaporizer. Since it is so completely absorbed, its depth of
penetration is shallow and can be precisely controlled with respect to the
surface of the tissue being operated upon. The CO.sub. 2 laser is
frequently used for neurological surgery where it is used to vaporize or
coagulate neural tissue with minimal thermal damage to underlying tissues.
The fourth commonly used type of laser is the neodymium doped
yttrium-aluminum-garnet (Nd:YAG) laser. The Nd:YAG laser has a predominate
mode of operation at a wavelength of 1.06 micrometers in the near infrared
region of the electromagnetic spectrum. As discussed in copending
application Ser. No. 539,527, the Nd:YAG emission at 1.06 micrometers
wavelength is absorbed to a greater extent by blood than by water making
it useful for coagulating large bleeding vessels. The Nd:YAG at 1.06
micrometers laser energy has, for example, been transmitted through
endoscopes to treat a variety of gastrointestinal bleeding lesions, such
as esophogeal varices, peptic ulcers, and arteriovenous anomolies.
It is characteristic of all of these known uses of laser energy that the
tissue thus exposed is destroyed by searing, charring, or vaporization. It
is therefore an object of this invention to utilize laser energy either to
heal or reconstruct tissue, rather than to destroy tissue.
It is also an object of this invention to replace surgical sutures or
staples in wound closures by a technique which creates an immediate seal
of the severed tissue, is faster, requires minimal surgical manipulation
of tissue, reduces possibility of infection, and minimizes scarring.
It is another object of this invention to use the body's own tissue
elements to form a seal or a bond between severed elements of tissue.
It is still another object to use electro-optical energy to form a
collagenous bonding tissue which is similar in composition to the tissue
from which it is produced.
It is yet a further object of the invention to provide wound closure and
reconstruction, inter alia, of the following tissues: skin, nerve fiber,
vascular tissues, reproductive tissue structures such as vas deferens or
fallopian tubes, gastrointestinal tract, eye tissues, and tendons.
It is also a further object of the invention to provide the wound closure
and reconstruction of the above-identified tissues quickly, with little or
no scarring, and with minimal risk of infection.
It is a still further object of the invention to use laser energy having a
low absorbance in a bloody or wet field to increase the utility of the
laser within the normal operating fields.
It is still another object of the invention to utilize a laser energy which
is not preferentially absorbed by either blood or water, thereby enabling
a low temperature thermal effect to be produced upon a desired tissue with
deeper penetration and with substantially reduced risk of damaging
neighboring tissues.
It is also another object of the invention to provide a laser apparatus
which is automated and portable for effecting closure of wounds and
reconstruction of tissues.
SUMMARY OF THE INVENTION
The foregoing and other objects are achieved by this invention which
provides a method and apparatus for the controlled application of optical
energy to convert biological tissue into a collagenous substance for
facilitating healing and wound closure. In accordance with the invention,
responsive to an input signal representative of a characteristic of the
tissue for which closure is sought, the parameters of a generated beam of
optical energy guided to the area of the intended juncture are controlled
to cause the amount of optical energy delivered to the tissue in the
vicinity of the wound to be within a tissue nondestructive range that
causes the tissue to be converted to a denatured proteinaceous collagenous
substance which forms a biological glue that closes the wound.
The intensity of the optical energy is controlled such that the rate at
which such optical energy is absorbed by the tissue in the vicinity of the
wound and converted into thermal energy is within a tissue nondestructive
range bounded by a minimum absorption rate at which the tissue is
converted to a collagenous substance and a maximum absorption rate above
which the water contained in the tissue wound boil.
In accordance with the invention, a beam of optical energy is produced by a
source, illustratively a laser, having a wavelength selected such that the
optical energy is propagated without substantial attenuation through water
and/or blood, but is absorbed in the biological tissue desired to be
repaired. Such substantially unattenuated transmission through water and
blood simplifies surgical procedures by obviating the need for operation
in a dry, clean field. The arrangement is further provided with a guide,
such as a flexible optical fiber, for directing the beam of optical energy
to the wound in the tissue. Moreover, the arrangement is provided with
means for controlling the parameters of the beam so that the delivered
energy is controlled to remain at a level above which the tissue in the
vicinity of the wound is converted to the collagenous substance, but below
a level at which water in the tissue being repaired would boil.
In an embodiment of the invention, described in greater detail below, the
optical energy source is constituted by a Nd:YAG laser which is tuned or
is tunable to 1.32 microns. Beam intensity control is provided by
circuitry that regulates the laser power source. The flexible optical
fiber is provided with a shutter and timer on a foot or hand operated
switch to regulate exposure time. The optical fiber is provided with a
hand-piece that includes a sliding scale which sets beam spot size at the
tissue by establishing the working distance between the beam emitting end
of the hand-piece and the tissue being operated on. In response to input
information on tissue type and thickness, a microprocessor establishes the
parameters for the beam intensity control circuitry, shutter timer and
hand-piece scale required to achieve the proper energy level for tissue
welding.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention have been chosen for purposes of illustration
and description, with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic view of a laser surgical system for use in accordance
with the invention;
FIG. 2 is a side sectional view of the hand-piece of FIG. 1;
FIG. 3 is a block and schematic diagram of microprocessor control circuitry
usable in the system of FIG. 1; and
FIGS. 4a-4c are a flow diagram of a software program for use by the
microprocessor of FIG. 3.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Biological tissue comprises cell layers in a protein framework for tensile
strength. All proteins are amino acids which have side chains which are
dissolvable either in water or fat. Naturation is a process wherein the
amino acids fold over, always in the same configuration for each protein
type, when the protein leaves the interior of a cell and is confronted
with tissue water. In such case, the hydrophobic portion of a side chain
folds to the interior of the molecule. The proteinaceous components of the
tissue can be unfolded or denatured by the application of heat.
As stated in copending application Ser. No. 539,527, it has been discovered
that application of optical energy to biological tissue, in a
nondestructive amount sufficient to generate enough heat to denature the
proteinaceous components, can be used to cause the body's own tissues to
substantially reproduce the prior tissue structure at a wound or severed
tissue site. In particular, energy from an optical energy source, such as
a laser, can be applied to bring the temperature of biological tissue
somewhere above room temperature, but below the boiling point of water;
preferably above 45 degrees centigrade and particularly to about 60-70
degrees centigrade. Collagen, a major source of protein in the body, is
denatured by application of such energy in such a way as to go into
solution and form a "biological glue" to seal a lesion, anastomize a
severed vessel, or reconstruct damaged tissue. When the source of heat is
removed, the proteins begin to re-nature and form an approximate
replication of the prior tissue structure. As the body heals, the
so-called "biological glue" will be reabsorbed and replaced by natural
tissue.
The application of heat, to form a collagenous seal to immediately close a
lesion or anastomize a severed vessel accelerates healing time, leaves
little or no scarring, preserves the tissue, and avoids inflammation
and/or infection caused by the inclusion of foreign suture material in a
wound.
Optical energy of a particular wavelength is converted to heat in tissue
which absorbs energy at that wavelength. As detailed in copending Ser. No.
539,527, it was discovered that optical energy having a wavelength of 1.2
to 1.4 micrometers is relatively unattentuated in both water and blood
and, so, is particularly advantageous for use as an optical energy source
for the formation of a "biological glue" in order to effect repair of
gastrointestinal tract tissue, close skin wounds (whether originating
accidentally, intentionally or through biological processes), and repair
and reconstruct tissue such as reproductive tissue, tendons, and vascular
tissue, provided the intensity, exposure time and spot size of the beam at
its point of incidence on the tissue are controlled to keep the energy
absorption by the tissue within the desirable range. A suitable wavelength
is obtainable using a commercially available Nd:YAG laser configured to
generate optical energy at a wavelength of about 1.32 micrometers.
FIG. 1 illustrates a surgical system for achieving tissue welding in
accordance with the invention. The system has a source of optical energy,
laser 20, which is preferably of the Nd:YAG crystalline variety wherein an
yttrium-aluminum-garnet (YAG) rod is doped with neodymium (Nd) ions as the
active light-producing element. Such a laser 20 includes a resonant cavity
for amplifying the emitted light and pumping means, such as a dc Krypton
arc lamp, for supplying energy to create a population inversion of the
normal energy state of Nd ions. The population inversion results in the
stimulated emission of light according to well-known known laser
principles.
Absent any tuning of the laser cavity, Nd:YAG lasers will emit light at a
fundamental dominant wavelength of 1.06 micrometers. Such lasers also emit
light at a secondary wavelength of approximately 1.32 micrometers. Proper
utilization of this secondary mode in laser operation requires the
dominant emission, which has a greater amplitude than the secondary
emission, to be suppressed. Typically, peak power output at this secondary
emission level is 20-30% of the continuous wave peak power output at the
dominant level. It is the secondary wavelength that is utilized in the
method and apparatus of the invention.
As readily understood by persons skilled in the art, laser 20 includes a
power supply circuit for activating the pumping arc lamp and cooling means
for cooling the laser. A suitable Nd:YAG laser for use in this invention
is produced by Control Laser Corporation, Orlando, Fla. 32809.
A lens 21 is provided to focus the emerging coherent light beam from laser
20 into an optical fiber 22. Lens 21 may comprise a system of lenses.
Optical fiber 22 can be of any known type, which efficiently transmits the
desired wavelength. Optical fiber 22 provides a flexible conduit for
guiding the optical energy from the laser into a hand-piece or wand 23
which is manipulable by the physician. A shutter 24 is located,
preferably, between laser 20 and lens 21. Hand-piece 23 contains a shutter
switch 25 which controls release of the laser energy and which may be
actuated by either the hand or the foot of the operator. A timer 26 is
provided to control the shutter and, thereby, the duration of energy
exposure. Hand-piece 23 may include a lens (not shown) for focusing or
defocusing the beam.
Advantageously, hand-piece 23 includes means to enable the physician to set
the working distance between the tissue to be irradiated and the
distalmost end of the optical fiber or lens. In an illustrative
embodiment, as shown in FIG. 2, a sliding scale 27 which cooperates with a
protective case 28 on the end of optical fiber 22 controls the working
distance, and hence, the diameter of the beam spot. As shown in FIG. 2,
the divergence of the beam is used to control the beam diameter as the
distance between the distalmost end of the fiber 22 and the tissue is
increased or decreased.
For a given suitable optical wavelength and mode or beam geometry, the
following electro-optical parameters require proper adjustment for each
type of tissue: output power, time exposure and beam spot size. In
particular, the thermal effects on the tissue can be controlled by proper
selection of the electro-optical parameters. Power density measures the
energy concentration of the applied light beam and is typically expressed
in watts per square centimeter area of the applied beam spot. Power
density is directly related to the amount of heat that will be produced at
a given absorptivity. Radiant exposure, expressed in joules per square
centimeter, is a measure of the power density multiplied by the exposure
time. If the wavelength of the applied beam is poorly absorbed, more heat
can be generated by increasing the time of tissue exposure to the applied
beam. Laser output power and beam spot size selections affect the power
density; overall radiant exposure is affected by power density and time
exposure selections.
Suitable means for control of the power output of laser 20 is provided by a
control unit 40, described further with reference to FIG. 3, below.
Optical output power detector 41 is provided for initial calibration of
the beam of laser 20 at start-up and a second detector 42, which always
receives a portion of the beam of laser 20 by means of a beam splitter 43,
is provided for continuous monitoring and feedback adjustment of the laser
20 output. The power delivered to the tissue surface should be maintained
under 10 watts for purposes of tissue reconstruction by laser 20 as
described herein. The object is to deliver a specific amount of energy per
volume of tissue. For a given spot size, which is related to the volume of
tissue exposed, there are many combinations of power output and time
exposure which will deliver equivalent amounts of energy. To-wit, power
delivered to the tissue typically ranges between 1 and 4 watts; although
power delivered could go as high as 10 watts if the time exposure were
reduced commensurately.
In the lowest order transmission mode, TEM.sub.oo specifically, a more
concentrated beam results which can be used for cutting purposes at higher
power output or for achieving very small beam spot size for tissue
reconstruction. In the alternative, multimode transmission can be used for
tissue reconstruction, but the beam spot size can not be as finely focused
as the TEM.sub.oo mode. However, if the beam is defocused, less power is
delivered per unit area.
As will be understood, the selection of the various electro-optical
parameters for each tissue type is made as a result of skill and
experience; but is determinable without undue experimentation by one of
ordinary skill in the art.
In a particularly advantageous embodiment, data relating to appropriate
settings of electro-optical parameters for various tissue types can be
coded on a computer memory device, such as floppy disc or programmable
read-only memory computer chip. The functions of control unit 40 and timer
26 can be computer controlled to adjust automatically the power level, and
time exposure and display the proper spot size upon input of tissue type
and the operating conditions by the physician or surgeon.
The system of FIG. 1 also includes a marker laser 30, illustratively a
low-power helium-neon laser, which is coaligned with the infrared beam of
laser 20. Laser 30, however, can be of any type which emits radiation in
the visible range of the electromagnetic spectrum. The power rating of the
helium-neon marker laser 30 is between 1-5 Watts. Marker laser 30 can be
arranged so that its focal point coincides with that of the main operating
laser 20 by any known technique.
As an optional feature, in order to permit the use of the laser apparatus
of FIG. 1 on very thin tissue or tissue upon which only surface heating is
desired, such as epineurium of nerve tissue, an auxiliary source of
optical energy 50 can be incorporated into the apparatus to emit radiation
having a wavelength which is intensely absorbed by biological tissue. A
carbon dioxide laser, of any known type, would be a suitable auxiliary
source. Source 50 is also preferably arranged so as to have its output
beam coincide with the beam from marker laser 30.
I should be further pointed out that provision can be made for permitting
selection of the 1.06 micrometer wavelength of the Nd:YAG laser 20 by
means which are well known in the art for the purposes of tissue
coagulation and wound hemostasis, as desired.
FIG. 3 shows suitable circuitry for implementation of the functions of the
control unit 40 and timer 26 which utilizes a microprocessor 50, such as
provided in an IBM PC/AT computer, for controlling parameters of the
optical beam so as to deliver the appropriate amount of energy to the
tissue reconstruction site. In response to input by the physician of the
applicable tissue type and thickness, the computer 50 accesses a data base
stored in a memory device to establish appropriate settings for power
level, time exposure and spot size.
Optical output power is controlled by delivery of a signal from the
microprocessor to the conventional current control circuitry for the power
supply of the laser 20. A digital-to-analog converter 62 is connected to
receive a digital current control signal from the microprocessor 50. The
analog output of the converter 62 is amplified by an amplifier 64 and then
converted to a frequency signal by a voltage-to-frequency converter 65.
The output of the converter 65 is used via an isolating circuit 66 to
drive a frequency-to-voltage converter 67 to deliver a signal from a power
source 68 and voltage regulators 69, 70 through an amplifier 71 to the
power control input of the laser 20 (e.g. the current control circuitry
for a Control Laser Model 512 power supply). The isolation between the
computer 50 and the laser 20 is provided for protective purposes and may
be achieved through use of an optocoupler.
Verification of power setting accuracy is accomplished initially by
requiring that the wand 23 end of the optical fiber 22 be inserted in the
calibration port of power detector 41 located in a system console (not
shown).
The power detector 41 may take the form of a coherent power detector, such
as a thermal calorimeter. Following determination by the computer 50 of
the correct power setting for the laser 20 for a particular tissue type
and thickness, at first fire-up of the lamp the hand-piece or wand 23 is
inserted in a receptacle on the control unit console. Initial firing of
the laser is prevented unless the hand-piece 23 is in the receptacle. The
output of the detector 41 is amplified by an amplifier 72 and converted in
an analog-to-digital converter 73 for input to the microprocessor 50. The
microprocessor 50 then performs a calibration subroutine to adjust the
digital output to the converter 62 and thus to the laser power source,
until the desired optical power output is read at the power detector 41.
If the intensity of the beam output is too low, the value of the digital
signal to converter 62 is incremented; if the output is too high, it is
decremented. The microprocessor 50 will then clear the system for
operation outside of the receptacle under control of the shutter switches
25 and timer 26.
Subsequent beam output adjustment is undertaken by microprocessor 50, in
accordance with well-known principles, by which a small amount of the
optical output is diverted by the beam splitter 43 (FIG. 1) for
measurement by the detector 42, which suitably takes the form of a
photodiode connected through an amplifier 74 and an analog-to-digital
converter 75 to deliver a power level input to the microprocessor 50. The
photodiode 42 circuit provides a continuous feedback loop through the
microprocessor 50 for power output vertification.
As already indicated, a shutter switch 25 (FIG. 1) is provided control to
emission of the beam toward the tissue. For control of the total energy
applied, the computer 50 also serves the function of a timer 26 (FIG. 1)
to limit the total time for which shutter 24 permits the beam from laser
20 to reach the tissue on any one shot. The shutter 24 is arranged to
normally be in a beam blocking position. The switch 25 is connected to the
computer 50 with the aid of an amplifier 76, as shown in FIG. 3, and
programming is provided so that a counter is set up to increment for each
clock pulse received during the time that shutter 24 is open. When the
count indicates that the total specified exposure time set by computer 52
is reached the shutter will be closed and blocked from reopening until a
certain counter reset time delay has passed. This ensures that each
passage of beam energy from the laser 20 will have the required energy. It
will be appreciated that other arrangements for the timer 26 shutter
control circuitry are possible and that, in particular, the function by
programming in microprocessor 50 can be replaced by hardwired timer
circuitry, if desired.
For the ill | | |
