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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to conducting laser energy from a laser energy
source along a course that includes curves of small radius.
In many circumstances in various industrial and medical applications,
matter to be cut or welded or otherwise altered or removed is located at a
site that is inaccessible or difficult to reach.
Many sites within the body of an animal such as a human patient are
difficult to reach for performing surgery, because they are surrounded by
hard tissues such as bone or because they are surrounded by delicate
tissues which can be damaged. Sites within the thorax, such as the heart
and the blood vessels near it, for example, are enclosed by bone
structures, and sites within the cranium, such as arteries supplying the
brain, for example, are surrounded by delicate brain tissue as well as by
bone. The coronary arteries and the arteries of the brain can become
occluded for example by atheromatous plaque formations or by thrombi or
emboli, with serious consequences for the patient.
One approach to providing a supply of blood to the heart when a coronary
artery is occluded is bypass surgery, that is, coronary artery bypass. The
patient's thorax is opened, and a substitute conduit for supplying blood
to the heart is provided by engrafting a substitute vessel between a point
upstream from the occlusion, such as the aorta, and a point in the
coronary artery downstream from the occlusion. Coronary bypass surgery is
an involved and delicate procedure, entailing significant risk and expense
to the patient. Many patients are unable to benefit from bypass surgery.
In an alternative approach to relieving an occlusion of an artery, drugs
are administered to cause the vessels to dilate. Not all patients can use
such drugs, however, and the results are generally only temporary, as the
occluding process can continue, eventually blocking even the dilated
vessel.
In still other approaches, generally termed percutaneous translumenal
angioplasty, an instrument for dilating the occluded artery is introduced,
generally by means of a catheter, through an opening in the skin and
through an opening in the wall of a large artery such as the brachial
artery or the femoral artery, and passed within the arterial lumens to the
site of the occlusion. In balloon angioplasty, for example, a fine guide
wire is first passed to the site of the occlusion through the lumens of
major arteries, observed by radiography as it progresses; then a catheter
having a balloon near its tip is passed over the wire to the site, also
within the arterial lumens; and finally the balloon is inflated at the
site of the occlusion to stretch the walls of the artery and open the
lumen. The results of balloon angioplasty can also be temporary, as the
occluding process in 30-40% of patients can continue at the site until the
vessel is again blocked. Moreover, the procedure carries risks of
perforation or acute occlusion of the arteries by the instrument, and the
flow of blood through the vessel being treated is interrupted for a time
during the procedure. Only selected patients can benefit from balloon
angioplasty, leaving many patients with no viable treatment, including
patients having atheromas involving long segments of vessels, or having
diffuse distal artery disease, or having arteries too tortuous to permit
passage of guidewires.
In a variety of industrial and medical applications, useful results can be
obtained by directing laser energy at a site. For example, various
materials melt or vaporize upon absorption of laser energy, and parts
constructed of such materials can in effect be cut or welded to achieve a
desired result. Laser energy can be used in surgery for alteration or
removal of tissues or obstructions or deposits by directing the energy at
the matter to be altered or removed.
In a surgical technique known as laser angioplasty, conventional light
guides using fiber optics have been employed for directing laser energy
onto arterial plaque formations to ablate the plaque and remove the
occlusion. Individual optically conducting fibers are typically made of
fused silica or quartz, and are generally fairly inflexible unless they
are very thin. A thin fiber flexible enough to pass through a course
having curves of small radius, such as through arterial lumens from the
femoral or the brachial artery to a coronary artery, typically projects a
beam of laser energy of very small effective diameter, capable of
producing only a very small opening in the occlusion; moreover the energy
is attenuated over relatively small distances as it passes within a thin
fiber. Small diameter fibers can tend to mechanically perforate vessels
when directed against the vessel wall as they are passed within the vessel
toward the site.
In order to bring a sufficient quantity of energy from the laser to the
plaque, light guides proposed for use in laser angioplasty usually include
a number of very thin fibers, each typically about 100 to 200 microns in
diameter, bundled together or bound in a tubular matrix about a central
lumen, forming a catheter. Laser energy emerging from a small number of
fibers bundled together in known such catheters produces lumens of
suboptimal diameter which can require subsequent enlargement by, for
example, balloon dilation. Such devices do not remove an adequate quantity
of matter from the lesion, and their uses are generally limited to
providing access for subsequent conventional balloon angioplasty.
Moreover, although individual fibers of such small dimensions are flexible
enough to negotiate curves of fairly small radius, a bundle of even a few
such fibers is much less flexible, and use of laser angioplasty has as a
practical matter been limited to the larger, straighter blood vessels such
as, for example, the large arteries of the leg, in which the laser energy
is conducted by the light guide over only relatively short distances on a
relatively straight course. Coupling mechanisms for directing laser energy
from the source into the individual fibers in a light guide made up of
multiple small fibers can be complex, including lenses and mechanisms by
which the individual fibers can be addressed serially by the source beam.
Improper launch of the laser energy into such a light guide can destroy
the fibers, ruining the instrument and endangering the patient.
More flexible light guides can be provided by filling a flexible tube with
a liquid material whose refractive index is less than that of the tube
wall material. H. F. Eastgate, U.S. Pat. No. 4,045,119, describes a liquid
core light guide, having a plug at each end of the tube to seal the liquid
in, for transmitting laser energy at high power from a laser source such
as a pulsed laser to an area of application.
The presence of blood near the distal end of such instruments can prevent
laser light from reaching its appropriate target, such as for example
arterial plaque or a blood clot. Moreover, absorption of laser energy by
blood or blood components can result in generation of heat or formation of
detonations, which can damage adjacent vessel walls.
SUMMARY OF THE INVENTION
We have discovered that laser energy can be efficiently conducted along a
course that includes curves of small radius and directed onto a target at
a remote site by launching laser energy into a liquid-filled flexible tube
that is at least partially open at the end nearest the site (i.e. the
distal end of the tube) so as to permit a portion of the liquid to flow
out from that end toward the target.
In general, in one aspect, the invention features a method for conducting
laser energy to a site, including the steps of bringing the distal end of
a flexible tube near the site, filling the tube with a liquid that can
include a radiographic contrast medium, and directing laser energy from a
laser energy source into the proximal end of the tube, whereby a portion
of the laser energy emerges from the distal end of the tube at the site.
In some embodiments the tube is provided with means for limiting the flow
liquid out from the tube at the distal end.
In another aspect, the invention features a method for conducting laser
energy to a site, such as into a site of the body of an animal, including
the steps of bringing the distal end of a flexible tube near the site,
providing a flow of a liquid into the tube, and directing laser energy
from a laser energy source into the proximal end of the tube, whereby a
portion of the laser energy emerges from the distal end of the tube at the
site.
In preferred embodiments, a portion of the liquid is permitted to flow out
from the distal end of the tube toward the site; the step of bringing the
distal end of the tube near the site includes passing it into the body of
the animal by way of an opening in the animal, or by direct surgical
approach, and includes passing it through the lumen of a passage within
the body of the animal, such as through the lumen of a blood vessel of the
animal. The site includes a mineral deposit, an atheromatous plaque, an
atheroembolus, a thrombus, or a blood clot; the site is located in a body
space such as in an artery, in a vein, in a ureter, in a common bile duct,
in the trachea, in a bronchus, or in the gastrointestinal tract. The step
of providing a flow of a liquid into the tube includes passing the liquid
from a source of liquid into the tube by way of a port in the tube wall;
the method further includes the step of continuing to pass the liquid into
the tube after the tube has been filled with the liquid whereby a portion
of the liquid passes out from the distal end of the tube.
Causing the liquid to flow from a source of liquid in a controlled manner
through the tube and distally out from the tube during the treatment can
produce a column of liquid between the distal end of the tube and the
target, effectively permitting a continuous guide for the laser energy for
a short distance beyond the distal end of the tube. A variety of body
fluids, such as, for example, blood or urine, have indices of refraction
sufficiently low with respect to the liquid in the tube to provide such a
light guide effect beyond the distal end of the tube. Moreover, matter
that may interfere with the laser treatment, including substances normally
present at the site, such as blood in the case where the site is within a
blood vessel, or substances produced at the site as debris during the
treatment, can be continually flushed away without interrupting the
procedure by the flow of liquid out from the distal end of the tube.
In another aspect, the invention features a method for removing an
obstruction from a blood vessel in an animal, comprising bringing the
distal end of a flexible tube near the obstruction, filling the tube with
a liquid by passing the liquid into the tube, continuing to pass the
liquid into the tube after the tube has been filled with liquid, so that a
portion of the liquid passes out from the tube at the distal end, and
directing laser energy from a source into the proximal end of the tube,
whereby a portion of the laser energy emerges from the distal end of the
tube and strikes the obstruction. Where the obstruction includes an
atheromatous plaque, the method can be one for treating atherosclerosis;
where the obstruction includes a thrombus, the method can be one for
treating thrombosis or thromboembolism.
The method does not require completely restricting the flow of blood
through the vessel being treated, so the procedure can be carried out
without haste. Moreover, the flushing action of the liquid flowing out
from the tube toward the target can enhance laser energy delivery by
removing blood, which can absorb wavelengths of laser energy that can be
useful for removal of plaque or thrombus.
In another aspect, the invention features apparatus for delivering laser
energy to a site, including a liquid, a flexible tube having an opening in
one end, arranged and adapted to be brought near the site, through which
the liquid can pass, means for providing a flow of the liquid into the
tube, and a source of laser energy operationally associated with another
end of the tube, wherein the tube and the liquid contained within it can
cooperate to conduct laser energy from the source and to emit a portion of
the laser energy from the second end of the tube.
In preferred embodiments, at least a portion of the tube is adapted to be
bent without substantial change in cross-sectional shape or without
kinking into a curve having a radius of curvature as small as 20 mm, more
preferably as small as 10 mm; The tube includes a wall having a refractive
index n.sub.w, one surface of the wall describing the lumenal surface of
the tube, and the liquid has a refractive index n.sub.f, wherein n.sub.f
is greater than n.sub.w ; the values of n.sub.f and n.sub.w are such that
the ratio
r.sub.f,w =(n.sub.f)/(n.sub.w)
is greater than 1.0, more preferably greater than about 1.05, still more
preferably greater than about 1.1; the value of n.sub.f is about 1.46, or
at least about 1.46; the value of n.sub.w is about 1.33, or at least about
1.33; the liquid includes a radiographic contrast medium; the liquid is
biocompatible; a support layer surrounds the wall; the wall is made of a
polymer, preferably a fluorinated polymer, such as tetrefluoroethylene
hexafluoropropylene (FEP) or polypentadecafluorooctylacrylate elastomer. A
cap is affixed to the first end of the tube; the cap is arranged and
adapted to substantially restrict movement of the liquid out from the tube
by way of the first end; the cap is configured to provide a smooth and
rounded proximal surface; the cap has a bore through it substantially
aligned with the axis of the tube, preferably of a diameter sufficiently
to permit passage of a guidewire through it, preferably sufficiently small
to restrict the flow of the liquid through it, preferably about 500
micrometers, or at least about 500 micrometers; the cap is made of quartz,
or of sapphire; the cap has a reflective surface arranged and adapted to
direct the laser energy in a direction away from the axis of the tube; The
lumen of the tube has a transverse dimension between about 1 mm and 3 mm;
the lumen has a substantially circular cross-sectional shape; it has a
diameter between about 1 mm and 3 mm. The apparatus further includes a
coupler at a the second end of the tube for conducting energy from the
source of laser energy to the liquid-containing tube; the coupler
comprises a window, a lens, or an optical fiber (preferably inserted into
the lumen of the tube); the coupler is made of quartz or fused silica; the
means for providing a flow of the liquid into the tube includes a conduit
for conducting the liquid between the source and the tube; the tube
includes a port intermediate its first and second ends for passing the
liquid between the source and the tube; the means for providing a flow of
the liquid into the tube further includes a filter to prevent bubbles from
moving into the tube.
In other embodiments, the tube wall includes a reflective layer, one
surface of which describes the lumenal surface of the wall; preferably the
reflective layer is of a reflective polymer or metallized material, such
as a material including aluminum or silver, coextruded with or bonded to
the lumenal surface of the tubing material.
The liquid-core light guide according to the invention can be made
sufficiently flexible to negotiate the small curves commonly incountered
in finer arteries such as the coronary arteries, while projecting an
effective beam sufficiently broad to remove an occlusion. The tubing for
the light guide itself can be simply and inexpensively made by, for
example, a continuous extrusion or coextrusion process, and cut for length
as required for each particular use. Advancing the light guide through
arterial or venous lumens can be facilitated by initially advancing a
guidewire along the course to be followed and then advancing the light
guide over the guidewire to the target location, Alternatively, a guiding
catheter can be emplaced at the origin of the obstructed artery and the
light guide can be advanced within the lumen of the guiding catheter. The
laser energy source can be coupled to the light guide in a straightforward
fashion, presenting few launch complications. The laser energy can be
launched directly from the laser through a focusing lens to the light
guide or alternatively it can be launched initially into a conventional
fiber inserted into the lumen of the light guide at the proximal end.
The liquid and the tube can be made from biocompatible materials. Using a
radiographic contrast medium as a liquid permits continuous fluoroscopic
imaging of progress throughout the procedure without interruption.
Moreover, a light guide containing a radiographic contrast medium can be
used with fluoroscopic monitoring to deliver laser energy with precision
in nonmedical applications where the site to be treated is accessible only
by way of a tortuous pathway, such as, for example, in repair or
reconstruction of internal parts of hydraulic apparatus in which the
hydraulic fluid is a hazardous material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Drawings
FIG. 1 is a somewhat diagrammatic view of portions of a liquid core light
guide according to the invention, partially cut away along the long axis
of the tube.
FIG. 2 is a section thru the light guide of FIG. 1 at 2--2.
FIG. 3 is a somewhat diagrammatic view of the proximal portion of a liquid
core light guide, cut away along the long axis of the tube, showing a
liquid port and conduit for passing liquid into the tube.
FIGS. 4 through 7 and 9 are somewhat diagrammatic views of the distal
portion of a liquid core light guide, cut away along the long axis of the
tube, showing end caps in various configurations.
FIG. 8 is a section thru the distal portion of a liquid core light guide of
FIG. 7 at 8--8.
FIG. 10 is a somewhat diagrammatic view of portions of an alternate liquid
core light guide of the invention, partially cut away along the long axis
of the tube.
FIG. 11 is a section thru the light guide of FIG. 7 at 8--8.
FIG. 12 partially cut away through the long axis of the tube, showing a
window for coupling a source of laser energy to the light guide.
FIG. 13 partially cut away through the long axis of the tube, showing an
alternate laser coupler employing an optical fiber.
FIG. 14 is a somewhat diagrammatic view of the proximal portion of an
alternative liquid core light guide of the invention, cut away along the
long axis of the tube, having a reflective lumenal surface.
FIG. 15 is a somewhat diagrammatic view of the distal portion of a liquid
core light guide of the invention, cut away along the long axis of the
tube, in combination with a balloon dilation device.
FIG. 16 is a somewhat diagrammatic view of the distal portion of a liquid
core light guide of the invention, cut away along the long axis of the
tube, showing a light diffusion balloon.
Structure and Operation
FIGS. 1 and 2 are views of a liquid core light guide of the invention. The
light guide includes a tube, shown generally at 10, whose wall 16 encloses
a lumen 24 which is filled with a liquid 26. The inner surface of wall 16
defines lumenal surface 22 of tube 10.
Laser energy can be directed from a source of laser energy (not shown in
FIGS. 1 and 2) into proximal end 14 of liquid filled tube 10, as indicated
generally by arrow I. The energy passes within the liquid filled tube
toward distal end 12. The energy is attenuated as it passes away from the
source, so that a portion of it emerges from proximal end 12, as indicated
generally by arrow O. The proportion of the energy introduced to the
proximal end that emerges from the distal end of the liquid-filled light
guide depends upon the dimensions and physical characteristics of the
liquid and the tube wall, and on the extent to which the tube follows a
curving course.
Referring now to FIG. 3, port 62 through wall 16 is provided near proximal
tube end 14, and one end of conduit 64 is coupled to point 62. Fluid can
be introduced at the other end of conduit 64 as indicated by arrow F from
a source of liquid such as a syringe or a pump, such as, for example, a
peristaltic pump (not shown in FIG. 3), into-tube 10 through conduit 64
via port 62. Similarly a conventional guide wire (not shown in FIG. 3) can
be introduced into tube 10 through conduit 14 via port 62.
The materials for wall 16 and for liquid 26 are selected in part to provide
a high degree of internal reflection at the lumenal surface; that is, wall
16 and liquid 26 are each transparent to the laser energy to be conducted
through the light guide, and the index of refraction n.sub.w of wall 16 is
greater than the index of refraction n.sub.f of liquid 26.
Further, the material for wall 16 is selected in part to provide structural
strength as well as flexibility so that the liquid-filled light guide can
be bent through curves of small radius without kinking or substantially
distorting the cross-sectional geometry of the tube.
Preferably wall 16 is made of a fluorinated ethylenepropylene, such as is
available commercially for example as "FEP Teflon.RTM.", and the liquid is
a radiographic contrast medium, such as is available commercially for
example as "Renographin 76 .RTM.". FEP Teflon.RTM. has a refractive index
about 1.33, and Renographin 76.RTM. has a refractive index about 1.46; the
ratio of their refractive indices is thus about 1.1, providing for
substantially total internal reflection even at fairly steep angles of
incidence. Preferably the lumenal surface of the tube is smooth, as
irregularities in the surface can introduce unsatisfactory irregularities
in angles of incidence. Preferably the tube has a circular cross-sectional
shape, and the inner diameter (i.e. the diameter of the lumen of the tube)
is about 1-3 mm according to the diameter of the arterial lumen to be
opened. Preferably the thickness of the wall 16 is at least about two
times the wavelength of the transmitted light. Such a tube, 110 cm long,
with a wall of FEP Teflon.RTM. and containing Renographin 76.RTM., can
transmit from the distal end about 60% of laser energy at 480 nm, launched
through a refractive index-matched lens or window into the distal end from
a laser.
Alternatively, the laser energy can be launched into a conventional quartz
fiber from the laser, and the quartz fiber can be inserted into the distal
end of the tube. However, proximal portions of the tube which contain such
a fiber are thereby rendered much less flexible, and it is advantageous in
applications where great flexibility is required particularly in a distal
portion of the light guide not to insert the fiber so far that the distal
end of the fiber reaches into the preferably flexible distal region of the
light guide.
Such a tube of such composition can have a "memory"; that is, the tube can
be preformed to conform to a particular desired curvature, so that, while
it can be straightened or flexed, it will t | | |
