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BACKGROUND OF THE INVENTION
The technical field of this invention is surgery and, in particular, method
and materials for joining living tissues and promoting the healing of
small biological structures.
The conventional approach to joining tissue segments following surgery,
injury or the like, has been to employ mechanical sutures or staples.
While these techniques are often successful, there are a number of
limitations inherent in such mechanical approaches. First, the practice of
suturing or stapling tissue segments together is limited by the eyesight
and the dexterity of the surgeon which can present a severe constraint
when anastomosing tiny biological structures. Second, when delicate
biological tissues or organs are sutured, even minimal scarring can affect
the function of the structure. Finally, suturing can be less than
satisfactory, even when properly performed, because of the gaps which are
left between the stitches, the inherent weakness of the joint, or the
possibility of progressive structural weakening over time.
Various researchers have proposed the use of laser energy to fuse
biological tissues together. For example, Yahr et al. in an article in
Surgical Forum, pp. 224-226 (1964), described an attempt at laser
anastomosis of small arterial segments with a neodymium laser. However,
the neodymium laser used by Yahr et al. operated at a wavelength of about
1.06 micrometers was not efficiently absorbed by the tissue, requiring
large amounts of energy to effect fusion, while also affecting too large
of a tissue volume.
Further research on laser fusion involving various alternative laser
sources, such as the carbon dioxide laser emitting laser light at about
10.6 micrometers, the argon laser emitting light at about 0.50
micrometers, and the ruby laser emitting light at about 0.70 micrometers,
continued to encounter problems. In particular, the output of carbon
dioxide lasers was found to be heavily absorbed by water and typically
penetrated into water-laden tissue only to a depth to about 20
micrometers. This penetration depth and the resulting bond induced by
carbon dioxide laser fusion was too shallow to provide durable bonding in
a physiological environment.
Argon and other visible light laser also produced less than satisfactory
effects. The output of argon lasers and the like was found to be heavily
absorbed by blood and subject to substantial scattering within the tissue.
These effects combined to create a narrow therapeutic "window" between a
proper amount of energy necessary for laser fusion and that which induces
tissue carbonization, particularly in pigmented tissues and tissues that
have a high degree of vascularization. Moreover, argon lasers have been
particularly cumbersome devices, requiring large amounts of electricity
and cooling water.
Recently, the development of new solid state laser sources have made
prospects brighter for efficient, compact laser fusion systems suitable
for clinical use. Such systems typically employ rare earth-doped yttrium
aluminum garnet (YAG) or yttrium lithium fluoride (YLF) or
yttrium-scadium-golilinium-garnet (YSGG) lasers. See, for example, U.S.
Pat. Nos. 4,672,969 and 4,854,320 issued to Dew, disclosing the use of a
neodymium-doped YAG laser to induce laser fusion of biological materials
and to obtain deeper tissue penetration. However, even with such solid
state laser sources, the problems of scattering and damage to adjacent
tissue remain. The Dew patents disclose the use of computer look-up tables
to control the laser dose based on empirical data.
The absorptive properties of biological structures differ considerably from
one tissue type to another, as well as from individual to individual,
making dosage look-up tables often unreliable. There exists a need for
better methods and materials for accurately controlling the formation of
anastomotic bonds which avoid thermal damage and achieve optimal results.
In particular, non-mechanical suture materials which can take advantage of
laser or other high energy light sources to join biological materials
together or otherwise make repairs to delicate body tissues would satisfy
a long-felt need in the art.
SUMMARY OF THE INVENTION
Materials and methods for photoreactive suturing of biological tissue are
disclosed. The suture material includes a structure adapted for
positioning at an anastomotic site and has at least a portion of the
structure formed by a photoreactive crosslinking agent, such that upon
irradiation of the structure the crosslinking agent adheres to the
biological material. In one embodiment, the suture material can also
include a high tensile strength element which is coated with a laser
activatable crosslinking agent or glue. The suture methods can be
practiced manually, or with various apparatus, such as endoscopes,
catheters or hand-held instruments.
The present invention can employ various "biological glue" materials as
crosslinking agents in either solid, liquid, gel or powder form to form a
bond to tissue segments and thereby hold them together while natural
healing processes occur. The crosslinking agents should be biocompatible
and are preferably biodegradable over time in vivo. Examples of such
crosslinking agents include collagen, elastin, fibrin, albumin and various
other photoreactive polymeric materials.
Various strength enhancing agents can also be incorporated into the suture
structure to provide additional tensile support along and across the
anastomosis. Such high tensile strength elements can be formed from
pre-crosslinked segments of the same material that forms the photoreactive
crosslinking agent, or they can be formed from strips or fibers of other
natural or synthetic biodegradable materials such as cotton or polyesters,
to enhance the strength of the bond.
The present invention permits the creation of anastomoses of biological
structures with the optimal use of appropriate laser energy, minimizing
the total energy delivered to the site while obtaining maximum bond
strength and integrity. The terms "anastomosis" and "anastomotic site" are
used herein to broadly encompass the joinder of biological structures,
including, for example, incision and wound healing, repair of blood
vessels and other tubular structures, sealing of fissures, nerve repairs,
reconstructive procedures, and the like.
The present invention is preferably practiced in conjunction with a high
energy light source, such as laser, for delivery of a beam of radiation to
an anastomotic site, and can also employ a reflectance sensor for
measuring light reflected from the site and a controller for monitoring
changes in the reflectance of the light from the site and controlling the
laser in response to the reflectance changes.
In one embodiment, the laser radiation is delivered through a hand-held
instrument via an optical fiber. The instrument can also include one or
more additional fibers for the delivery of illumination light or radiation
from a laser diode (which can be broadband or white light or radiation
from a laser diode) which is reflected and monitored by the reflectance
sensor. Reflectance changes during the course of the suturing operation at
one or more wavelengths can be monitored (or compared) to provide an
indication of the degree of tissue crosslinking and determine when an
optimal state of fusion has occurred.
In the present invention, reflective feedback is used to monitor the state
of crosslinking of the suture material with the biological material, as
well as the degree of fusion or coagulation of the biological structures
so as to allow an optimal dose by either manipulation of the energy level
or exposure time, or by controlling the sweep of energy across an exposure
path. Reflectance changes can also be employed by a control means in the
present invention to adjust or terminate laser operation.
Various light sources can be employed, including gas, liquid and solid
state laser media. Because the present invention permits the user to
carefully monitor the energy dosage, solid state lasers can be utilized
instead of the more conventional (and cumbersome) gas lasers. Such solid
state laser include optically-pumped (e.g., lamp or diode pumped) laser
crystals, diode lasers, and diode pumped optical fibers. Tunable laser
sources can also be used to practical advantage in the present invention.
In some applications, high intensity flash lamps can also be employed in
lieu of a laser source. Since the feedback control systems disclosed
herein eliminate (or reduce) the need for look-up tables, a tunable laser
source can be used to full advantage by matching the laser output
wavelength with the absorptive and/or dimensional characteristics of the
biological structures to be repaired or otherwise joined. In one
embodiment of the invention, the laser source can be tuned over at least a
portion of a wavelength range from about 1.4 micrometers to about 2.5
micrometers to match particular tissue profiles.
In another aspect of the invention, a real-time display means is disclosed
which can be incorporated into a surgical microscope or goggles worn by
the clinician during the procedure to provide a visual display of the
state of tissue coagulation simultaneously with the viewing of the
surgical site. The display can reveal reflectance values at one or more
specific wavelengths (preferably, chosen for their sensitivity to the
onset and optimal state of tissue crosslinking), as well as display a
warning of the onset of tissue carbonization.
In one method, according to the invention, a technique for photoreactive
suturing of biological structures is disclosed in which laser energy is
applied to join together two or more tissue segments via a suture
structure that includes a photoreactive crosslinking agent, while the
reflectance of light from the irradiated site is monitored. Changes in
scattering due to crosslinking of the tissue and crosslinking agent will
cause reflectance changes. The reflectance can be monitored in real-time
to determine the optimal exposure duration or aid as visual feedback in
the timing used in sweeping the energy across the anastomosis during the
suturing procedure.
The method can further be enhanced by employing a suturing material which
incorporates high tensile strength elements, and/or by coating the entire
anastomotic site with a biological glue. The reinforcing strips provide
load support across and along the repair line, and preferably are also
bonded by the crosslinking agent to the tissue, itself, providing superior
bond strength.
The depth of penetration of the laser energy can be controlled in one
embodiment by tuning a mid-infrared laser along a range of wavelengths
from about 1.4 micrometers to about 2.5 micrometers to adjust the
penetration to match the desired weld depth. Tuning can be accomplished,
for example, by mechanical or electro-optical variation in the orientation
of a birefringent crystal disposed in the laser beam path.
This allows the clinician to select a weld depth appropriate to the size
and type of structures to be welded. This feature of the invention can be
particularly advantageous with delicate biological structures where
accuracy is needed to crosslink only what is necessary for temporary
strength, while avoiding thermal denaturing of critical structures that
cannot function once scarred. In most instances, the patient's body will
metabolize the suture material over time simultaneous with (or following)
the natural healing of the repair site by physiological processes.
The invention will next be described in connection with certain illustrated
embodiments; however, it should be clear by those skilled in the art that
various modifications, additions and subtractions can be made without
departing from the spirit or scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of a photoreactive suturing system
according to the present invention;
FIG. 2 is a perspective view of a clinical system embodying the principles
of the invention;
FIG. 3 is a schematic illustration of a suture material incorporating a
high tensile strength element according to the invention;
FIG. 4 is a schematic illustration of another suture material according to
the invention;
FIG. 5 is a schematic illustration of a yet another suture material
according to the invention;
FIG. 6 is a schematic illustration of a further suture material according
to the invention;
FIG. 7 is a schematic illustration of a suture material and detachable
carrier according to the invention;
FIG. 8 is a schematic illustration of a tubular suture material according
to the invention;
FIG. 9 is a schematic illustration of a staple-like suture material
according to the invention;
FIG. 10 is a more detailed schematic diagram of a laser source useful in
the system of FIG. 1;
FIG. 11 is a partial, cross-sectional view of a laser beam delivery
handpiece according to the invention;
FIG. 12 is a front view of the laser delivery handpiece of FIG. 11;
FIG. 13 is front view of a surgical instrument incorporating both a suture
means and a laser means according to the invention;
FIG. 14 is a more detailed schematic diagram of reflectance monitor for use
in the present invention; and
FIG. 15 is a schematic illustration of a clinical eyepiece view showing a
"heads-up" display of reflectance measurements according to the invention.
DETAILED DESCRIPTION
In FIG. 1, a schematic block diagram of a photoreactive suturing system 10
is shown, including a laser 12, power supply 14, controller 16 and
photoreactive suturing material 36. The system can further include a
beamshaping/delivery assembly 20, illumination source 22, reflectance
monitor 18, display 24 and tuner 26. In use, the output of laser 12 is
delivered, preferably via beamshaping/delivery assembly 20, to an
anastomotic site 30 to fuse the suture material 36 on opposite sides of a
fissure or cleavage line 32 in a biological material. As the laser beam
irradiates exposure zone 34, a crosslinking reaction occurs to fuse the
suture material and the biological tissue in the vicinity of the site 30.
The degree of crosslinking can be determined by the reflectance monitor
18, which provides electrical signals to controller 16 in order to control
the procedure. The reflectance monitor 18 preferably receives light
reflected by the site from a broadband or white light illumination source
22. In addition to controlling the laser operation automatically, the
reflectance monitor 18 and/or controller 16 can also provide signals to a
display 24 to provide visual (and/or audio) feedback to the clinical user,
thereby permitting manual control. Tuner 26 can also be employed by the
user (or automatically controlled by controller 16) to adjust the
wavelength of the annealing radiation beam.
FIG. 2 provides further schematic illustration of the photoreactive suture
system 10 in use. The electrical and optical components of the system can
be housed in a system cabinet 60 suitable for use in an operating room or
other clinical environment. The laser output is delivered to the patient
by an optical fiber cable 62 (which can include multiple optical fibers as
detailed below) and a handpiece 64. The system is preferably used in
conjunction with a surgical microscope (or goggles) 66 which are adapted
to provide a "heads-up" display to the user. Display signals from the
system cabinet 60 are transmitted to the microscope (or goggles) 66 by
cable 68. The laser output can also be delivered to a remote site via an
arthroscope, endoscope or catheter and the display features of such an
instrument can be similarly adapted to provide the user with data on
progress of the crosslinking reaction.
The suture materials of the present invention can take various forms. In
the simplest embodiment, the suture material comprises a strip or strand
of a photoreactive crosslinking agent, such a collagen fibers, which can
be sewn or draped upon a fissure or incision and then crosslinked to the
tissue to provide closure. Once in place, the suture material is
irradiated with laser or other high intensity light energy to fuse the
suture to the anastomotic site.
Alternatively, as shown in FIG. 3, the suture material 36 can include a
high tensile strength core element 40 and an outer cross-linkable agent 38
which are likewise used to sew or drape the anastomotic site prior to
irradiation and fusion.
In another embodiment, as shown in FIG. 4, a suture material 36A can be
employed which is fabricated in a zig-zag strip form and applied directly
upon the incision or fissure 32 to close the opening. Again, suture
material 36A can include a high tensile strength core element 40 and an
outer cross-linkable agent 38.
In further embodiments 36B and 36C, shown in FIGS. 5 and 6, respectively,
the suture material can be fabricated as a patch with a high strength
element 40 incorporated into the structure, and also including a
crosslinking agent 38 to join the suture material to the underlying tissue
and thereby effect closure of the anastomotic site 32. In the embodiments
of FIGS. 5 and 6, the high strength element 40 can be fabricated, for
example, from the same material as the bonding agent 38, but
pre-crosslinked to provide the addition resistance to tearing or shearing
forces as the wound heals.
The present invention can employ various materials as crosslinking agents
in either solid, liquid, gel or powder form to form a bond to tissue
segments and thereby hold them together while natural healing processes
occur. The crosslinking agents should be biocompatible and are preferably
biodegradable over time in vivo. Examples of such crosslinking agents
include collagen, elastin, fibrin, albumin and various other photoreactive
polymeric materials.
Various strength enhancing agents can also be incorporated into the suture
structure to provide additional tensile support along and across the
anastomosis. Such high tensile strength elements can be formed from
pre-crosslinked segments of the same material that forms the photoreactive
crosslinking agent, or they can be formed from strips or fibers of other
natural or synthetic biodegradable materials such as polyesters, to
enhance the strength of the bond.
In FIG. 7, a detachable carrier 37 is shown for use in applying a zig-zag
type strip of crosslinking agent 36 to an anastomotic site 32. In one
preferred embodiment, the detachable carrier 37 is substantially
transparent to photo-irradiation and can be detached from said
crosslinking agent 36 following the bonding of the agent to the biological
material.
In FIG. 8, a tubular suture material 36 is shown for repairing a torn blood
vessel 31 or other body tube or lumen. The suture material 36 preferably
includes a crosslinking agent 38 and reinforcing elements which can be
braided, woven or simply matted fibers 40. In use, the suture material is
either fitted over the severed lumen (in the case of a tube-shaped suture
material) or wrapped around the severed biological structure (e.g., with a
strip-like suture material), and then irradiated to crosslink the
materials together. In some applications, the tubular suture material 36
of FIG. 8 can be designed to shrink as the crosslinking reaction occurs
and thereby more tightly wrap the anastomotic site. In such procedures, it
may also be preferable to first dispose a stent 33 or similar support
within the lumen to prevent collapse.
In FIG. 9, a staple structure 37 is shown incorporating a crosslinking
agent 36 on each prong such that the staple can be applied to close a
wound and then fused in place by application of laser radiation to the
crosslinking agent 36. Alternatively, the entire staple can be formed from
a crosslinking agent and then irradiated (e.g., such that the exposed
prongs are melted into tissue-bonding balls) to fuse the staple in place.
(A similar approach can be taken to "knot," or otherwise secure
conventionally sewn sutures when a crosslinking agent comprises, or forms
part of, the suture thread; in such an application, the surgeon would put
the stitches in place and then irradiate the site in order to bond the
suture thread to tissue or itself and thereby increase the strength of the
closure.)
The present invention can be practiced with a wide variety of laser
sources, including both gas and solid state lasers, operating in either
continuous wave ("c.w.") or pulsed modes. More specifically, the laser
sources can be carbon monoxide, carbon dioxide, argon lasers or various
excimer lasers utilizing mixtures of halogen and noble gases, such as
argon-flouride, krypton-fluoride, xenon-chloride and xenon-fluoride.
Additionally, the laser can be a solid state laser employing a rare,
earth-doped Yttrium Aluminum Garnet (YAG) or Yttrium Lithium Fluoride
(YLF) or a Yttrium-Scandium-Gadolinium-Garnet (YSGG) laser.
In one preferred embodiment, the laser source is a rare, earth-doped, solid
state laser, such as a holmium-doped, erbium-doped or thulium-doped solid
state laser of the YAG, YLF or YSGG type which can be operated in a low
wattage c.w. or pulsed mode with an output wavelength in the range of
about 1.4 to about 2.5 micrometers and a power density of about 0.1
watt/mm.sup.2 to about 1.0 watt/mm.sup.2. Such laser sources are disclosed
in U.S. Pat. No. 4,917,084 issued on Apr. 17, 1990, to the present
inventor and incorporated herein by reference.
The absorption of laser energy from such solid state laser sources by
biological tissues is relatively high in relation to the absorption of
such energy by water, thereby providing an absorption length in the
subject's body of about 100 microns or more. Thus, it is possible to
operate satisfactorily even with 10-20 micrometers of blood between the
handpiece tip and the anastomotic site.
FIG. 10 is a schematic illustration of laser source 12, including a
solid-state laser crystal 41, vacuum chamber 42 and diode pump source 44.
The laser crystal 41 is preferably surrounded by a cooling quartz or
fused-silica jacket 46 having inlet pipe 48 and an outlet pipe 50 for
circulation of liquid nitrogen or other cryogenic coolant. The laser
cavity can be formed by input crystal face coating 52 and
partially-reflective output mirror 54.
Generally, the laser crystal 41 is excited by optical pumping, that being,
irradiation of the crystal with light from the laser diode 44. (The diode
44 can be cooled by a pumped coolant or employ a heatsink). Both ends of
the laser crystal 41 are preferably polished flat. The input face of the
crystal 41 is preferably finished with a coating 52 for high transmittance
at the pump wavelength and high reflectance of the output wavelength. The
other end of the crystal 41 preferably includes an antireflective coating
50 for high transmittal of the output wavelength. The entire cavity of the
reflector preferably is evacuated to provide thermal insulation and avoid
moisture condensation.
For further details on the construction of cryogenic, solid-state lasers,
see, for example, an article by Barnes et al., Vol. 190, Society of the
Photo-Optical Instrumentation Engineers, pp. 297-304 (1979), NASA/JPL
Technical Brief No. NPO-17282/6780 by Hemmati (June, 1988) and
above-referenced U.S. Pat. No. 4,917,084, all of which are herein
incorporated by reference.
Also shown in FIG. 10 is a tuning element 26 which can include, for
example, a birefringent crystal 28 disposed along the beam path 58 at a
slight offset from Brewster's angle. The crystal 28 can be tuned
electro-optically by application of a voltage, as shown schematically in
the figure. Alternatively, the laser wavelength can be tuned mechanically
by tilting or rotating the crystal 28 relative to the beam path using
techniques well known in the art.
In FIG., 11 a partial, cross-sectional side view of a handpiece 64 is
shown, including a casing 70 adapted for gripping by the clinical user and
multiple lumens disposed therein. With further reference to FIG. 12 as
well, the handpiece serves to deliver laser irradiation suitable for
biological tissue fusion via a central optical fiber 72 connected to laser
source, as well as one or more additional illumination fibers 74 for the
delivery of illumination light and the transmittal of reflected light. The
surgical laser delivery fiber 72 is preferable a low, hydroxyl ion content
silica fiber. As shown in FIG. 12, the handpiece 64 can deliver
illumination light via fibers 74. In one embodiment, these fibers 74 can
also be used to collect reflective light and deliver it to a controller.
Alternatively, some of the fibers 74 can be devoted entirely to collection
of reflected light. The handpiece 64 can further include one or more lens
elements 76, as well as a transparent protective cover element or terminal
lens 82.
FIG. 13 shows an apparatus 81 for remote application of sutures according
to the invention. The apparatus 81 can be incorporated into a catheter,
endoscope or arthroscope and disposed adjacent to a remote anastomotic
site. As shown, apparatus 81 includes a suture means 85 and a laser means
83. The suture port 85 delivers a photoreactive suture material to the
anastomotic site, the suture material comprising a structure with at least
a portion of the structure formed by a crosslinking agent such that upon
irradiation of said suture means the crosslinking agent adheres to the
biological material and thereby provides closure at said anastomotic site.
The laser means 83 provides the necessary light energy in the form of
laser radiation to effect crosslinking of the suture material at the
anastomotic site. The apparatus 81 can also include a viewing port 87, an
illumination port 89 and a reflectance sensing port 91 to provide a
display and monitoring of the crosslinking process, as described in more
detail below.
FIG. 14 is a more detailed schematic diagram of a reflectance monitor 18,
including a coupling port 90 for coupling with one or more fibers 76 to
receive reflectance signals from the handpiece of FIG. 4 or the apparatus
of FIG. 13. The reflectance monitor 18 can further include a focusing lens
92 and first and second beam splitting elements 94 and 96, which serve to
divide the reflected light into 3 (or more) different beams for
processing.
As shown in FIG. 14, a first beam is transmitted to a first optical filter
98 to detector 102 (providing, for example, measurement of reflected light
at wavelengths shorter than 0.7 micrometers). A second portion of the
reflected light signal is transmitted by beam splitter 96 through a second
optical filter 100 to detector 104 (e.g., providing measurement of light
at wavelengths shorter than 1.1 micrometers). Finally, a third portion of
the reflected light is transmitted to photodetector 106 (e.g., for
measurement of reflected light at wavelengths greater than 1.6
micrometers). Each of the detector elements 102, 104, and 106 generate
electrical signals in response to the intensity of light at particular
wavelengths.
The detector elements 102, 104 and 106 preferably include synchronous
demodulation circuitry and are used in conjunction with a modulated
illumination source to suppress any artifacts caused by stray light or the
ambient environment. (It should be apparent that other optical
arrangements can be employed to obtain multiple wavelength analysis,
including the use, for example, of dichroic elements, either as
beamsplitters or in conjunction with such beamsplitters, to effectively
pass particular wavelengths to specific detector elements. It should also
be apparent that more than three discreet wavelengths can be measured,
depending upon the particular application.) The signals from the detector
elements can then be transmitted to a controller and/or a display element
(as shown in FIG. 1).
In the controller, signals from the reflectance monitor are analyzed (as
detailed below) to determine the degree of crosslinking which is occurring
in the suture material and/or in the biological tissue exposed to the
laser radiation. Such analysis can generate control signals which will
progressively reduce the laser output energy over time as a particular
site experiences cumulative exposure. The control signals can further
provide for an automatic shut-off of the laser when the optimal state of
crosslinking has been exceeded and/or the onset of carbonization is
occurring.
As shown in FIG. 15, the data from the reflectance monitor can also be
provided directly to the clinician. In FIG. 15, a simulated view from an
eyepiece 110 is shown in which the field of view 112 includes a fissure or
cleavage line 114 dividing separate bodies at an anastomotic site. Also
shown within the field of view is the suture material 36, a fusion track
116 which has been formed by laser radiation, and a present exposure zone
118. Also displayed within the eyepiece 110 is a "heads-up" display of the
reflectance values for the reflectance monitor of FIG. 14, including
illuminated warning lights 122 which serve to indicate the reflectance
intensity at particular wavelengths or other optical data indicative of
the degree of crosslinking and/or tissue fusion.
In use, the apparatus of the present invention can be employed to analyze
the degree of crosslinking by comparing the reflectance ratios of a site
at two or more wavelengths. Preferably, intensity readings for three or
more wavelength ranges are employed in order to accurately assess the
degree of crosslinking and to ensure that the optimal state is not
exceeded. The particular wavelengths to be monitored will, of course, vary
with the particular tissue undergoing treatment. Although the tissue type,
(e.g., blood-containing tissue or that which is relatively blood-free)
will vary, the general principles of the invention, as disclosed herein,
can be readily applied by those skilled in the art to diverse procedures
in which the fusion of biological materials is desired.
For example, it is known that carbonization of many tissue types is
accompanied by a decrease in visible light reflectance and an increase in
infrared reflectance. Thus, the analyzing circuitry of the controller can
be constructed to provide a warning (or automatically shut off the laser
radiation) when darkening in the visible wavelengths occurs or when the
ratio of visible to infrared values falls below a predefined level.
Moreover, when the material to be joined (e.g., aortic tissue) is
relatively unpigmented, reliance on changes in the reflectance of visible
light can be inaccurate, but infrared reflectance changes (e.g., above 1.1
micrometers) can reliably indicate the degree of crosslinking. (Lack of
change in the visible reflectance is one of the reasons that tissues of
this type are difficult to crosslink, as no change in the target's visible
properties are observed until the tissue is overexposed to laser energy.)
Consequently, the analyzing circuitry can monitor infrared reflectance
changes (e.g., greater than about 1.0 micrometers) as an indicator of
proper crosslinking.
Finally, the reflectance sensor can also be used as a proximity monitor to
ensue that the laser is in fact disposed at a proper distance from the
anastomic site. By measuring total reflectance (over the entire
visible-infrared range or a portion thereof), a sudden drop in the
reflectance value will typically be related to incorrect placement of the
handpiece. Thus, the analyzing circuitry can sense the changes in
reflectance and generate a warning to the user (or automatically shut off
the system) until proper placement is achieved.
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