Laser balloon catheter

A laser balloon catheter intended primarily for coronary angioplasty includes a flexible tube having an inflatable balloon secured to its distal end, a central shaft within the balloon for carrying a guide wire, an optical fiber for carrying laser radiation through the flexible tube into the balloon, and a tip assembly in the balloon for directing laser radiation outwardly through a major portion of the balloon surface while limiting shadowing by the central shaft. The tip assembly preferably includes a tip portion of the optical fiber contained within a transparent, heat-formable tube and formed into a spiral shape around the central shaft by the heat-formable tube. The optical fiber tip portion is tapered so that it directs laser radiation outwardly over its length. Deuterium oxide is preferably used for inflation of the balloon because of its very low attenuation of laser radiation in the wavelength range of interest. The disclosed laser balloon catheter is capable of delivering 30-40 watts of laser radiation to a surrounding artery for times on the order of 30 seconds without excessive heating of the balloon assembly.

FIELD OF THE INVENTION 
This invention relates to laser balloon catheters and to methods for the 
manufacture and use of laser balloon catheters and, more particularly, to 
laser balloon catheters intended for use with a guide wire and capable of 
providing a high level of laser output power through the balloon wall into 
surrounding tissue. The laser balloon catheter of present invention is 
intended primarily for coronary angioplasty, but is not limited to such 
use. 
BACKGROUND OF THE INVENTION 
Balloon angioplasty has been utilized for a number of years to treat 
coronary arteries narrowed by plaque deposits. A catheter having an 
inflatable balloon secured to its distal end is advanced through an artery 
to a narrowed region. The balloon is then inflated with a fluid from an 
external source, causing the narrowed region of the artery to be expanded. 
The balloon is then deflated and withdrawn. A serious problem associated 
with balloon angioplasty has been the occurrence in up to 30% of the cases 
of so-called restenosis, either immediately after the procedure or within 
about six months. Immediate restenosis, also known as abrupt reclosure, 
results from flaps or segments of plaque and plaque-ridden tissue which 
are formed during balloon angioplasty and which can block the artery. Such 
blockage of the artery requires emergency surgery and often results in 
death. Furthermore, a surgical team is required to stand by during the 
balloon angioplasty procedure. Restenosis at a later time results from 
causes that are not totally known. Thrombus formation is believed to play 
an important part. Often repeat balloon angioplasty or surgery is 
required, and another episode of restenosis may occur. 
A technique which has shown great promise for overcoming the problem of 
restenosis is the simultaneous application of heat and pressure to a 
plaque-narrowed region of an artery. The technique is described by John F. 
Hiehle, Jr. et al in "Nd-YAG Laser Fusion of Human Atheromatous 
Plaque-Arterial Wall Separations in Vitro," American Journal of 
Cardiology, Vol. 56, Dec. 1, 1985, pp. 953-957. In accordance with this 
technique, a catheter having an inflatable balloon at its distal end is 
advanced to a narrowed region of an artery and the balloon is inflated, as 
in the case of balloon angioplasty. However, in distinction to balloon 
angioplasty, sufficient heat is applied through the wall of the balloon to 
fuse the surrounding tissue and thereby eliminate the flaps which can 
later block the artery. One advantageous means of heating the surrounding 
tissue is by directing laser radiation through an optical fiber carried by 
the catheter and terminating within the balloon. The laser radiation is 
then directed through the balloon wall to cause heating of the surrounding 
tissue. 
Although the laser balloon catheter has been proposed in principle, there 
are numerous problems and difficulties in constructing a practical 
catheter suitable for human use. The balloon containing the device for 
diffusing laser radiation and the deflated catheter containing the optical 
fiber must be extremely flexible and small in diameter (on the order of 
1.0 to 1.5 millimeters) in order to permit navigation of the catheter 
through an artery to the desired site. The laser balloon catheter is 
preferably compatible with a guide wire which is used to guide the 
catheter through the artery to the desired location. Where the guide wire 
passes through the balloon, shadowing of the laser radiation pattern by 
the guide wire must be avoided. 
Another critical factor is the technique used for heating the surrounding 
tissue and the associated power level. It has been found desirable to 
apply radiation which penetrates the surrounding plaque and plaque-ridden 
tissue and the artery wall and heats that region by radiant heating, in 
distinction to conductive heating by the balloon. Furthermore, it has been 
found desirable to apply such radiation at a power level on the order of 
30-40 watts for times of on the order of thirty seconds. With such high 
power levels, it is extremely critical to efficiently transfer the input 
laser radiation through the fluid which inflates the balloon and through 
the balloon wall with minimum heat dissipation within the balloon. 
Other techniques involving the application of heat in a coronary artery 
include the so-called "hot tip" as disclosed in U.S. Pat. No. 4,646,737 
issued Mar. 3, 1987 to Hussein et al and U.S. Pat. No. 4,662,368 issued 
May 5, 1987 to Hussein et al, wherein a thermally conductive tip located 
at the end of a catheter is heated by laser radiation and conducts heat to 
the surrounding region as it is pushed through a narrowed artery. The hot 
tip reaches temperatures on the order of several hundred degrees Celsius 
in order to produce the necessary conductive heating as it is pushed 
through the artery. The hot tip is unable to expand the artery beyond the 
conductive tip diameter, which must be limited for passage through the 
artery. Another heating technique wherein a microwave-radiating antenna is 
located within an inflatable balloon is disclosed in U.S. Pat. No. 
4,643,186 issued Feb. 17, 1987 to Rosen et al. A coaxial transmission line 
is carried through a catheter and connects to the antenna. 
An endoscopic device wherein low power, narrow beam laser radiation is 
directed through a balloon wall is disclosed in U.S. Pat. No. 4,470,407 
issued Sept. 11, 1984 to Hussein. The problem of providing relatively 
uniform heating of tissue surrounding a balloon at high power levels and 
without shadowing is not addressed by the Hussein patent. 
Prior art techniques have been disclosed for directing laser radiation 
outwardly from the tip of an optical fiber. A tapered optical fiber 
surrounded with a diffusing medium for laser radiation treatment of tumors 
is disclosed in U.K. Patent Application No. 2,154,761 published Sept. 11, 
1985. An optical fiber surrounded with a scattering medium for producing a 
cylindrical pattern of light at the tip of an optical fiber is disclosed 
in U.S. Pat. No. 4,660,925 issued Apr. 28, 1987 to McCaughan, Jr. A 
technique for roughening the surface of an optical fiber tip to cause wide 
angle radiation of laser energy is disclosed by H. Fujii et al, "Light 
Scattering Properties of A Rough-ended Optical Fiber," Optics and Laser 
Technology, February 1984, pp. 40-44. None of the prior art techniques 
provide the combination of small diameter, flexibility, power handling 
capability and compatibility with a guide wire necessary for a laser 
balloon catheter. 
It is a general object of the present invention to provide an improved 
laser balloon catheter. 
It is a further object of the present invention to provide a laser balloon 
catheter suitable for use in coronary angioplasty. 
It is another object of the present invention to provide a laser balloon 
catheter capable of delivering and surviving a high power output. 
It is another object of the present invention to provide a laser balloon 
catheter which can be utilized with a guide wire for advancing the 
catheter through an artery. 
It is another object of the present invention to provide a laser balloon 
catheter which produces substantially uniform heating of tissue 
surrounding the balloon. 
It is still another object of the present invention to provide a method for 
manufacturing a laser balloon catheter. 
It is yet another object of the present invention to provide a laser 
balloon catheter which is small in diameter and flexible so that it is 
easily advanced through an artery. 
It is yet another object of the present invention to provide a laser 
balloon catheter wherein heat dissipation of laser radiation within the 
balloon is limited to allow heating deep into an artery wall without 
excessive total energy. 
It is a further object of the present invention to provide a laser balloon 
catheter wherein a relatively high proportion of the input laser radiation 
is delivered through the balloon wall to the surrounding tissue. 
SUMMARY OF THE INVENTION 
According to the present invention, these and other objects and advantages 
are achieved in a laser balloon catheter comprising an elongated flexible 
tube having a distal end and a proximal en, an inflatable balloon secured 
to the flexible tube at or near the distal end thereof, means for 
inflating and deflating the balloon, a central shaft disposed within the 
balloon and coupled to the flexible tube, an optical fiber for carrying 
laser radiation through the flexible tube into the balloon, and tip 
assembly means in the balloon and coupled to the optical fiber for 
directing laser radiation outwardly through a major portion of the balloon 
area while limiting shadowing by the central shaft. 
Preferably, the tip assembly means includes a tip portion of the optical 
fiber which is tapered to a smaller diameter at the distal end thereof and 
shaping means for retaining the tip portion of the optical fiber in a 
shape having at least one turn around the central shaft. The tip portion 
of the optical fiber preferably has a generally spiral shape. In a 
preferred embodiment, the shaping means includes a heat-formable tube 
containing the tip portion of the optical fiber and a material located 
between the heat-formable tube and the tip of the optical fiber selected 
to match the indices of refraction of the heat-formable tube and the tip 
portion. The spiral tip portion of the optical fiber is flexible and emits 
laser radiation outwardly over its length while limiting shadowing by the 
central shaft. 
Preferably, the central shaft, which is typically used for carrying a guide 
wire, includes an inner tube, a concentric outer tube and a spring coil 
between the inner and outer tubes. The spring coil prevents the central 
shaft from collapsing when the balloon is inflated. The central shaft 
includes a laser radiation-reflecting outer surface such as white vinyl or 
a thin layer of gold disposed on the outer tube. 
In another important aspect of the invention, a laser balloon catheter is 
inflated with a liquid which attenuates laser radiation at the wavelength 
of interest less than saline in order to limit heat dissipation within the 
balloon and to increase output power. Preferably, the liquid has an 
attenuation of less than about 0.16/cm at a preferred laser wavelength of 
1.06 micrometer. In a preferred embodiment, the balloon is inflated with 
deuterium oxide for reduced absorption of laser radiation in comparison 
with conventional inflation fluids such as saline or water. The deuterium 
oxide absorbs a negligible amount of energy at the preferred laser 
wavelength of 1.06 micrometer. Deuterium oxide can be advantageously used 
in any laser balloon catheter to reduce energy absorption and is not 
limited to the laser balloon catheter described herein. The deuterium 
oxide is biologically safe and is preferably utilized in conjunction with 
a transparent PET balloon. 
According to other features of the invention, a dye responsive to laser 
radiation of a predetermined first wavelength for emitting radiation at a 
predetermined second wavelength, and a dye solvent, can be mixed in the 
inflation fluid. The inflation fluid can contain a contrast agent to 
facilitate location of the balloon during use. A material with thermally 
sensitive optical properties can also be mixed in the inflation fluid for 
monitoring the temperature of the balloon along the optical fiber. An 
inwardly-facing reflector can be provided on a portion of the balloon to 
control the heating pattern produced by the laser radiation. 
According to another aspect of the present invention, there is provided a 
method of operating a laser balloon catheter comprising the steps of 
advancing a catheter having an inflatable balloon secured at or near its 
distal end and having an optical fiber terminating within the balloon 
through a body passage to a desired treatment location, inflating the 
balloon with a low attenuation liquid such as deuterium oxide and 
directing laser radiation through the optical fiber into the balloon such 
that the radiation passes through the low attenuation liquid and the 
balloon for treatment. 
According to still another aspect of the present invention, there is 
provided a method of making an optical fiber tip assembly for emitting 
laser radiation outwardly therefrom along its length comprising the steps 
of providing an optical fiber having a tapered tip portion, inserting the 
tapered tip portion into a transparent tube and filling the space between 
the transparent tube and the tapered tip portion with a material that is 
selected to match the indices of refraction of the transparent tube and 
the tip portion. Preferably, the transparent tube is heat-formable and the 
method further includes the step of preforming the transparent tube to a 
desired shape. The step of filling the space between the transparent tube 
and the tip portion preferably includes the steps of immersing a silicon 
tube in freon to cause expansion thereof, slipping the expanded silicon 
tube over the transparent tube, permitting the silicon tube to contract to 
its normal size and injecting the material from a syringe through the 
silicon tube into the transparent tube. 
According to still another aspect of the invention, there is provided a 
method of making a laser balloon catheter comprising the steps of forming 
a spiral tip assembly at one end of an optical fiber, providing a flexible 
tube having a distal end and a proximal end and having at least two lumens 
therethrough, attaching a central shaft for carrying a guide wire to the 
distal end of the flexible tube so that a passage through the central 
shaft is aligned with one of the lumens, inserting the optical fiber 
through another of the lumens so that the spiral tip assembly is disposed 
at the distal end of the flexible tube around the central shaft, and 
sealing an inflatable balloon to the distal end of the flexible tube 
around the spiral tip assembly and the central shaft. 
In another embodiment of the tip assembly, a transverse optical waveguide 
surrounds the optical fiber and the central shaft. The transverse 
waveguide directs a portion of the laser radiation around the central 
shaft and limits shadowing. 
In yet another embodiment of the tip assembly, one or more optical fibers 
are stressed at multiple points by pressing them against a spring coil in 
the central shaft. The regions of stress emit laser radiation outwardly.

DETAILED DESCRIPTION OF THE INVENTION 
A laser balloon catheter in accordance with a preferred embodiment of the 
invention is shown in FIGS. 1-5. An elongated flexible tube 10 has a laser 
balloon assembly 12 at its distal end and connectors 14, 16, 18 and 20 at 
its proximal end. The flexible tube 10 preferably includes three lumens 
21, 22 and 23 (FIG. 4). The laser balloon assembly 12 includes an optical 
fiber tip assembly 24 (FIG. 2) for emitting laser radiation, a central 
shaft 26 adapted for carrying a guide wire 28 (shown in phantom in FIG. 4) 
and for carrying a fluid to the treatment region and a balloon 30 which is 
inflated and deflated from the proximal end of the flexible tube 10. 
An optical fiber 32 extends from connector 20 through lumen 23 of the 
flexible tube 10 and terminates in optical fiber tip assembly 24. 
Connector 20 is coupled to the output of a laser. The guide wire 28 is 
introduced into the catheter through connector 16 and passes through lumen 
22 of flexible tube 10 and through central shaft 26, which is coupled to 
lumen 22. A source of pressurized fluid is coupled through connector 14 
and lumen 21 to the interior of balloon 30. Means for evacuating the 
balloon are also coupled through connector 14 and lumen 21 to the interior 
of balloon 30. Connector 18 is a vent port coupled to the balloon via 
lumen 23. 
As shown in FIGS. 3 and 5, the optical fiber tip assembly 24 includes a tip 
portion 36, a transparent tube 38 surrounding the tip portion 36 and a 
transparent epoxy 40 that fills the space between transparent tube 38 and 
tip portion 36. The tip portion 36 is preferably a continuation of optical 
fiber 32. 
Tip portion 36 is tapered over a distance T in order to cause laser 
radiation to be directed outwardly in a transverse or radial direction 
relative to the catheter axis. It is known in the art that a tapered 
optical fiber causes light to be gradually directed outwardly since the 
critical angle for reflected rays is gradually exceeded. In a preferred 
embodiment, an optical fiber type SG822 from Spectran Corporation, having 
a 150 micrometer outer diameter and a 100 micrometer core diameter, is 
tapered over a tip portion length of about 2 centimeters. The fiber is 
tapered from full diameter at the proximal end of the tip portion 36 to 
essentially zero diameter, or a few micrometers diameter, at the distal 
end. 
Tapering of the optical fiber tip portion 36 is accomplished using 
hydrofluoric acid as an etchant. The fiber 32 is placed in the etching 
solution and is withdrawn at a controlled rate under computer control. In 
a preferred embodiment, a uniform taper is obtained by withdrawing the 
fiber from the etching solution at a constant rate. In other embodiments, 
the taper is nonuniform in order to control the axial light intensity 
distribution. The light intensity emitted by the fiber is relatively high 
in a region with a high rate of taper and is relatively low in a region 
with a low rate of taper. For example, the rate of taper can be greatest 
near the proximal end 35 of tip portion 36, as shown in FIG. 9, so that 
the emitted light intensity is increased near the proximal end of the 
balloon. Alternatively, the rate of taper can be greatest near the distal 
end 37 of the tip portion 36, as shown in FIG. 8, thereby increasing the 
light intensity at the distal end of the balloon. In general, the axial 
light intensity distribution is tailored by controlling the rate of 
optical fiber taper. 
Another important feature of the optical fiber tip assembly 24 is that it 
preferably has a spiral or helical configuration extending around central 
shaft 26 so that shadowing by central shaft 26 is minimized. While the tip 
assembly 24 can have any convenient shape, it should have at least one 
full turn around central shaft 26 in order to minimize shadowing. The 
gradually-curving spiral shape avoids sharp turns which are likely to 
break the optical fiber 32. In a preferred embodiment, the tip assembly 24 
makes two full turns around the shaft 26 over a distance of about 2 
centimeters. 
Presently available optical fibers cannot be formed to retain the desired 
spiral shape. In addition, it is desirable that the tip portion 36 be 
relatively free to move and flex within the balloon in order to facilitate 
passage of the catheter through an artery. The transparent tube 38 
performs the functions of shaping the tip portion 36 of the optical fiber 
to the desired spiral shape and also acts as a replacement for the 
protective optical fiber buffer which was removed during the tapering 
process. It has been found that the tapered tip portion 36 must have a 
relatively smooth surface to prevent fiber breakage. Although optical 
fibers with roughened surfaces have been used as diffusion tips, such 
roughened fibers have been found likely to break in a catheter application 
requiring flexibility. The transparent tube 38 is preferably a 
heat-formable tube and, most preferably, is polyethyleneterephthalate 
(PET). The PET tube is formed by wrapping it around a mandrel in the 
desired spiral shape and heating it to a temperature of about 200.degree. 
C. After cooling, the PET tube retains the spiral shape. 
The tapered tip portion 36 of the optical fiber is then inserted into the 
spiral transparent tube 38, and the space between the tube 38 and tip 
portion 36 is filled with an optically transparent material selected to 
match the indices of refraction of tube 38 and tip portion 36. Preferably, 
an optically transparent epoxy such as Environ/Tex Lite is utilized. In a 
preferred technique for injecting the epoxy 40 into the tube 38, a length 
of silicon tubing, smaller in diameter than tube 38, is dipped in freon. 
The freon causes the silicon tube to swell, permitting it to be slipped 
over one end of transparent tube 38. After removal from the freon, the 
silicon tube shrinks and forms a tight fit over the PET tube 38. The other 
end of the silicon tube is attached to a syringe containing the epoxy. 
Upon operation of the syringe, the epoxy is injected through the silicon 
tube into the PET tube 38 and is allowed to cure. The silicon tube is then 
removed from the end of the transparent tube 38. 
The central shaft 26 provides a passage for guide wire 28. The proximal end 
of central shaft 26 is coupled to lumen 22 of flexible tube 10. The 
central shaft 26 must be relatively incompressible to prevent its collapse 
when the balloon 30 is inflated. In a preferred embodiment shown in FIGS. 
3 and 5, the central shaft 26 includes an inner vinyl tube 46 having a 
passage 48 for guide wire 28, an outer vinyl tube 50 concentric with tube 
46 and a spring coil 52 located between tubes 48 and 50. The spring coil 
52 is preferably 0.001 in..times.0.003 in. stainless steel wire frequently 
used in guide wire catheters. The assembly comprising tubes 48 and 50 and 
spring coil 52 is heated to a temperature of about 150.degree. so as to 
cause elastic flow of the vinyl tubes 48, 50 between the turns of the 
spring coil 52. The spring coil 52 prevents the shaft 26 from collapsing 
on guide wire 28 when balloon 30 is inflated. 
The outer surface of vinyl tube 50 should have high reflectivity at the 
selected laser wavelength in order to prevent absorption of laser 
radiation and heating of central shaft 26. The use of a white vinyl tube 
50 provides the necessary reflectivity over a broad band of wavelengths. 
In another preferred embodiment as shown in FIGS. 6 and 7, a thin layer of 
gold leaf 53 is applied to the outer surface of vinyl tube 50 for improved 
reflectivity. The gold leaf 53 can have a spiral configuration around the 
vinyl tube 50 which matches the spiral shape and is located adjacent to 
optical fiber tip assembly 24. Thus, the portion of central shaft 26 
adjacent to tip assembly 24 has a highly reflective gold surface. 
Alternatively, the entire shaft 26 can be coated with gold. An advantage 
of the gold surface is that it is radiopaque and can be used for x-ray 
location of the balloon assembly 12. 
The central shaft 26 is further provided with a pair of spaced-apart 
radiopaque markers 54. The markers 54, which can be platinum bands around 
shaft 26, can be seen in an x-ray so that the balloon assembly 12 can be 
precisely located during use. The shaft 26 is further provided with one or 
more openings 56 near its distal end for introduction of a fluid into the 
treatment region via connector 16. 
The inflatable balloon 30 has a generally tubular shape. It is sealed at 
one end at or near the distal end of flexible tube 10 and is sealed at its 
other end to central shaft 26 as shown in FIG. 2. The balloon 30 is 
optically transparent at the selected wavelength of the laser radiation. 
Preferably, a PET balloon is utilized. PET has a number of characteristics 
which make it a suitable balloon material. These characteristics include 
good optical transparency and a thin wall to reduce the overall catheter 
cross section and also to reduce heat absorption. In addition, PET does 
not deform at elevated temperatures and does not stick to the tissue being 
treated. In one embodiment, a balloon which inflates to 3 millimeters is 
used. It will be understood that the inflated diameter of the balloon is 
selected in accordance with the cross-sectional area of the body passage 
being treated. 
In a preferred embodiment, a 40 watt neodymium YAG continuous laser is used 
as the source of laser radiation. This laser has an output wavelength of 
1.06 micrometer. Typical treatment times are on the order of 30 seconds. 
The 1.06 micrometer wavelength has been selected for its ability to 
penetrate the plaque and plaque-ridden tissue and the artery wall and to 
cause deep heating of such tissue, rather than to simply heat the tissue 
surface. Thus, heating of the tissue surrounding balloon 30 is by 
radiation as contrasted with conductive heating from a hot element. One 
object of the present laser balloon catheter configuration is to reduce 
heat dissipation within balloon 30. 
A relatively high level of laser power is required to be transferred 
through the optical fiber 32 and the laser balloon assembly 12. 
Accordingly, it is important to minimize absorption of laser radiation 
within the laser balloon assembly 12 in order to minimize melting, burning 
and other detrimental effects of the high power levels. In accordance with 
an important aspect of the present invention, the balloon 30 is inflated 
with a liquid having an attenuation at the laser wavelength of interest 
less than that of commonly-used saline. Preferably, the balloon inflation 
liquid has an attenuation less than about 0.16/cm at a wavelength of 1.06 
micrometer. It has been found that the heat dissipation within the balloon 
assembly 12 can be substantially reduced by utilizing deuterium oxide 
(D.sub.2 O) as the fluid for inflation of the balloon 30. Deuterium oxide 
has substantially lower absorption at the 1.06 micrometer wavelength of 
interest than prior art inflation fluids such as saline or water. A 3 
millimeter diameter laser balloon catheter filled with deuterium oxide 
transmits approximately 90% of the input laser radiation at 1.06 
micrometer, whereas the same catheter filled with water transmits 
approximately 80% of the laser radiation. Relatively low absorption is 
characteristic of deuterium oxide at wavelengths in the range between 0.9 
and 1.8 micrometers. As a result, heat dissipation within the balloon 30 
is reduced by a factor of one-half by using deuterium oxide for inflation. 
Additional advantages of deuterium oxide as the balloon inflation fluid 
include the ability to use a larger diameter balloon without exceeding a 
prescribed power dissipation limit and more light output for a given laser 
input. Furthermore and importantly, deuterium oxide is biologically safe 
for use in the human body. It will be understood by those skilled in the 
art that the use of deuterium oxide for balloon inflation is not limited 
to the laser balloon catheter structures described herein, but can be 
utilized in any inflatable balloon wherein it is desired to transmit 
radiation in the above-identified wavelength range. 
In order to assemble the laser balloon catheter of the present invention, 
the optical fiber tip assembly 24 and the central shaft 26 are fabricated 
as described hereinabove. The central shaft 26 is heat bonded to the end 
of flexible tube 10 so that passage 48 is aligned with lumen 22. Next, 
optical fiber 32 is fed through lumen 23 of flexible tube 10 starting at 
the distal end thereof so that the spiral tip assembly 24 surrounds 
central shaft 26. The distal end 38a of transparent tube 38 is bonded to 
shaft 26 with cynoacrylate in order to fix their relative positions. 
Otherwise, the tip assembly 24 and shaft 26 may contact each other along 
their lengths but are not attached. This configuration maintains the 
flexibility of the central shaft 26 and tip assembly 24. The spiral tip 
assembly 24 has more flexibility and less risk of breakage than a straight 
segment of optical fiber. The balloon 30 is sealed at its proximal end to 
the flexible tube 10 and is sealed at its distal end to the central shaft 
26. 
The interior of the balloon 30 is in fluid communication with lumen 21 of 
flexible tube 10 for inflation and deflation and with lumen 23 for 
venting. The use of lumen 21 in conjunction with vent lumen 23 permits the 
catheter to be purged of air bubbles. Connectors 14, 16, 18 and 20 are 
installed at the proximal end of flexible tube 10 in conventional manner. 
In use, the laser balloon catheter of the present invention and an 
associated guide wire 28 are advanced through an artery to a desired 
treatment location, typically, a narrowed region of a coronary artery. It 
will be understood that in some applications, a guide wire will not be 
necessary and that the laser balloon catheter of the present invention can 
be utilized without a guide wire. The precise location of the balloon 
assembly is determined by identifying markers 54 on an x-ray. The balloon 
30 is then inflated by filling it with deuterium oxide carried through 
lumen 21 of flexible tube 10. After balloon inflation, the laser is 
energized, causing laser radiation to be carried through optical fiber 32 
and tip assembly 24 into the balloon. The laser radiation passes through 
transparent balloon 30 and irradiates the tissue surrounding balloon 30 
with a substantially uniform heating pattern. The heating causes the 
surrounding plaque and plaque-ridden tissue to be fused to the artery 
walls so that flaps and segments are not formed. Although the clinical 
aspects of the treatment are outside the scope of the present invention, 
it will be understood that an enlarged passage is formed in the artery 
with the walls of the passage being fused into a generally cylindrical and 
continuous configuration. The laser radiation is applied for a time on the 
order of about thirty seconds. After laser radiation has been completed, 
the region is allowed to cool and the balloon 30 is evacuated through 
lumen 21 and the catheter is removed. 
It will be understood that numerous variations and features can be 
incorporated into the laser balloon catheter of the present invention. For 
example, various materials can be mixed with the fluid utilized to inflate 
the balloon 30. As described above, deuterium oxide is the preferred 
inflation fluid, but water or saline can be used in applications requiring 
moderate or low power levels. Also, any other fluid having sufficiently 
low attenuation and suitable biological compatibility can be utilized. 
Radiopaque iodine-based contrast media can be mixed with the fluid used 
for inflation of the balloon. The contrast media permits the size, shape 
and location of the inflated balloon to be determined by x-ray. 
In another variation, materials having optical properties that change with 
temperature can be mixed with the inflation fluid. An example of such 
material is liquid crystals. A color change can be sensed through the 
optical fiber for monitoring of the balloon temperature. If the balloon 
temperature exceeds a predetermined limit, the laser beam can be turned 
off. 
In yet another variation, a laser dye material such as rhodamine is mixed 
with the fluid used to inflate the balloon. The laser dye material absorbs 
radiation at the wavelength of the laser source and emits radiation at a 
different wavelength. Alternatively, the laser dye can be mixed with the 
epoxy 40 in the space between the tip portion 36 of the optical fiber and 
the transparent PET tube 38. In either case, the laser dye material 
changes the wavelength of the laser output wavelength to another desired 
wavelength more suitable for treatment. 
The laser balloon catheter of the present invention has been described 
primarily in connection with coronary angioplasty. It will be understood 
by those skilled in the art that the laser balloon catheter, with 
appropriate scaling of dimensions when necessary, can be utilized in any 
body passage requiring the simultaneous application of heat and pressure. 
One example of such an application is the treatment of cancer in various 
body passages. When a larger diameter balloon is required, a double 
balloon arrangement can be utilized. As shown in FIG. 13, an inner balloon 
66 of relatively small diameter is filled with deuterium oxide or water, 
and a concentric outer balloon 68 of larger diameter is inflated with air. 
It may be desirable under some circumstances to heat a sector or portion 
of a body passage rather than providing uniform heat. In such a case, an 
inwardly-facing reflecting layer 70 is applied to a portion of the balloon 
surface as shown in FIG. 10. Where the reflecting layer 70 is present, the 
laser radiation is reflected through the opposite balloon wall. In this 
manner, a desired radial heating pattern can be accomplished. 
According to another embodiment of the present invention, a transverse 
waveguiding technique is utilized to provide substantially uniform laser 
radiation output from the balloon when a guide wire is used. In this 
embodiment, the tip portion of the optical fiber can be straight, can have 
a spiral shape as described above or can have some other convenient shape. 
A transverse waveguide 80 surrounds both the optical fiber tip assembly 24 
and the central shaft 26 as shown in FIG. 11. The transverse waveguide 80 
can, for example, be a partially transmissive tube with a scattering 
material on its inner surface. Laser radiation emitted by the optical 
fiber tip assembly 24 impinges on the interior surface of the transverse 
waveguide 80. A fraction of the incident laser radiation passes through 
the transverse waveguide 80 and another fraction is guided in a 
circumferential direction around the central shaft and optical fiber tip 
assembly 24. Eventually, all of the incident laser radiation passes 
through the transverse waveguide with a generally uniform radial pattern, 
thereby avoiding shadowing by the central shaft 26. 
According to yet another embodiment of the present invention, a technique 
utilizing microbending of one or more optical fibers within the balloon 
provides laser radiation outwardly through the wall of the balloon. It is 
known that optical fibers emit light outwardly at points of stress and 
bending. In the present embodiment, optical fibers 90, 92, 94 are oriented 
more or less parallel to the spring coil 52 within the balloon 30 and are 
pressed against it, as shown in FIG. 12, by an optically transparent, heat 
shrinkable tube 96. At each turn of spring coil 52, a stress is applied to 
each of the optical fibers 90, 92, 94, and laser radiation is emitted at 
each stress point 90a, 92a, 94a. More or fewer optical fibers can be 
utilized. Furthermore, some, all or none of the optical fibers 90, 92, 94 
can be selectively energized at a given instant of time to control the 
laser radiation pattern and timing. 
While there has been shown and described what is at present considered the 
preferred embodiments of the present invention, it will be obvious to 
those skilled in the art that various changes and modifications may be 
made therein without departing from the scope of the invention as defined 
by the appended claims.