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BACKGROUND OF THE INVENTION
The present invention relates to a control system for an optical fiber
laser power delivery system wherein the system employs a tip assembly for
the optical fibers which provides a number of advantages for the delivery
system including control of beam focus and beam divergence, mechanical
protection for the optical fiber and in addition, functions as the source
of a condition responsive signal utilized in an associated laser
monitoring and control mechanism. While providing a response for a variety
of conditions, the tip assembly of the present invention responds to a
temperature parameter which is dependent upon a number of conditions
including optical fiber integrity, contamination at the discharge site, or
the like.
The tip assembly of the present invention employs a synthetic sapphire
shielding lens which, in addition to its desirable mechanical, optical and
focusing properties, has a light and temperature sensitive fluorescing
property useful in generating a signal utilized in a feedback control
system for the laser system. With a laser functioning at a given or known
power input level, the light and temperature sensitive fluorescing
property of the sapphire lens or window creates a signal indicative of
certain conditions existing at the tip of the optical fiber, including
laser power being transmitted and tip temperature. The improved tip
assembly accordingly has application not only as an optical fiber shield
but as a signal source for one control and monitor portion of the laser
system. The tip assembly of the present invention may be utilized in any
of a variety of systems utilizing laser power, with the tip assembly being
particularly well adapted for use in a laser enhanced transluminal
angioplasty catheter where it functions to mechanically protect the
optical fibers and also provide a feedback signal for use in monitoring
the output of the laser energy at the tip of the fiber and also the
temperature of the tip of the fiber.
The tip assembly and its associated control system provides a closed-loop
arrangement for monitoring and controlling the output of the laser, with
the closed-loop system having condition responsive signal generating means
disposed at the desired delivery or treatment site within predetermined
and/or preset limits. When utilized in angioplasty catheter applications,
the distal portion of the system, including the improved tip assembly of
the present invention, is preferably utilized as a component which may be
readily coupled into and de-coupled from the other portions of the system.
The tip assembly used in the combination of the present invention employs a
lens or window fabricated from synthetic sapphire or other suitable
substance, with the lens being positioned concentrically with and adjacent
to the distal tip end of an enclosed or sheathed optical fiber. The
synthetic sapphire lens or window device emits energy in the form of
fluorescent light in response to excitation with laser power, and also
when heated to an elevated temperature. Since the intensity of the signal
emitted by the sapphire lens in response to exposure to incident laser
power is temperature dependent, the power level of the laser energy being
transmitted through the fiber onto the tip and the temperature of the tip
may be determined. As indicated above, the thermal condition of the
sapphire lens in the tip provides an indication of the integrity of the
overall delivery system as well as an indication of any anomaly which may
exist in the tip area and/or the delivery system. The improved tip
assembly of the present invention further provides a means to deliver or
to transmit laser power to the required location, with the optical
properties of the synthetic sapphire lens being capable of determining the
focus or optical pattern of the fiber output, while simultaneously
providing a source for a signal useful in monitoring the condition of the
delivery system for the laser power, as well as the condition adjacent the
exterior of the tip as represented by the thermal response or the
temperature condition.
The monitor, control, and/or condition responsive feature of the present
invention is enabled by utilizing a lens responsive to laser power and
temperature for determining certain of the conditions existing within as
well as along the optical fiber delivery mechanism as well as to
conditions existing at or immediately adjacent the point at which
radiation in the form of a laser beam is being discharged from the tip. In
the assembly illustrated in the drawings, the inner surface or end of the
lens is fixedly disposed adjacent the optical fiber tip and the outer
surface or end is immersed in or otherwise subjected to the environment
into which the laser beam power output is delivered. Because of its
arrangement in the system, the condition responsive lens is ideally
situated and suited to function as a sensor responsive to certain
conditions, including laser power, or deliver system integrity and/or
conditions existing in the zone receiving the laser beam power. Each of
these conditions may be determined by an evaluation of the temperature of
the artificial sapphire lens body through its fluorescent behavior. In
addition to fluorescence of the lens as a function of laser light
intensity and lens temperature, other fluorescent signals may be generated
during operation of the laser, including, for example, signals generated
due to fluorescence of certain materials used in fabricating an
angioplasty catheter, as well as other signals obtained from materials or
matter receiving laser power, including the optical cable. The most
significant flourescent signal created during operation of the system is
that created by the fluorescent behavior of the lens body. The signal
emitted from the lens will be fed back through a portion of the laser beam
delivery system, filtered, and its amplitude determined electro-optically.
In other words, the amplitude of the flourescent signal obtained from the
lens will be determined electro-optically, and the value obtained is
compared to the value which is expected from the input to the laser. The
"window" is a range of values within performance tolerances. Deviation of
this signal from a window representative of an optimum signal value or
range of signal values will be indicative of one or more malfunctions
including, for example, unacceptable performance of the delivery system,
or the existence of contamination or accumulation of debris in the zone
receiving the beam energy. In operation, therefore, a sensed deviation
from a certain value or window of values will normally be utilized to
trigger the shut-off or interruption of flow of energy from the laser
unit. A value which falls below a certain range of output values may
indicate a malfunction in either the laser unit per se or in the
intermediate delivery system, and may be indicative of a broken optical
fiber, or fiber tip damage. Such an indication will be utilized to trigger
system shut-off or the interruption of flow of energy from the laser unit.
The lens forming a portion of the tip assembly performs a number of
functions in addition to the generation of a flourescent signal. For
example, the lens is utilized as a focusing element for the beam of laser
radiation exiting the fiber tip. This radiation is focused along a cone
which converges to a focal point. In this manner, the radiation from the
laser is normally dispersed in a pattern or profile representative of an
expanding or diverging cone beyond the focal point. In addition, the tip
assembly acts as a means to isolate or protect the fiber tip from debris
build-up or corrosion when the system is being utilized in an unclean or
harsh environment. When fabricated of metal or radiopaque material, it may
be utilized as a tip identifier in angioplasty procedures.
In one system employing features of the present invention, a lens system is
utilized which includes a synthetic sapphire lens body which functions as
a sensor emitting fluorescent radiation within a certain predetermined
wavelength when excited with coherent radiation from a laser source. The
amplitude of the emitted signal is sensitive to temperature, so that
system performance and delivery system integrity may be measured against
predetermined values for various known power input levels. The emitted
fluorescent radiation from this sensor has a wavelength which is
detectably different from that of the incident laser radiation. The
sensor, when at an appropriate operating temperature, such as within a
predetermined window of operating temperatures, and while transmitting or
passing a predetermined amount of laser power therethrough, emits a
fluorescent radiation signal having a magnitude, intensity or level
indicative of its temperature and the laser power. When the signal is
within predetermined desired upper and lower tolerance limits, as
determined by a comparision with a known and acceptable signal obtained
from the sensor when operating at its anticipated temperature and laser
power levels, the entire system is permitted to continue to function.
Since the fluorescent signal, as detected, may constitute the sum of a
number of such signals from components other than the tip, such as from
the catheter material or the fiber optical material, the ultimate signal
obtained will be the resultant or composite of a number of components or
inputs. Accordingly, when the temperature level of the synthetic sapphie
tip sensor is either above or below the anticipated or desired level, a
fluorescent signal (having a detectably different magnitude or level) will
be created which falls outside of the window. In other words, whenever a
uniform and predetermined amount of laser power is being delivered to the
sapphire tip, the fluorescent response is a function of the incident laser
power and the temperature of the sensor. When systems employing sensors of
the type described, have been calibrated, readings indicative of
departures from predetermined output power levels and predetermined tip
temperature levels may be detected. While the readings obtained may not
readily translate into indications of absolute temperature or the like, it
has been found that these readings do indicate proper operating
conditions, both on the fiber side of the tip and on the exterior. Once a
system has been properly calibrated, the flourescent response of the
synthetic sapphire tip may be utilized as a measure of proper overall
system operation.
Synthetic sapphire is an appropriate choice of lens material. The
wavelength of an output beam from an Argon ion laser will normally fall
within the absorption band of a chromium-doped synthetic sapphire body. It
will be appreciated that synthetic sapphires containing dopants other than
chromium, as well as certain other synthetic crystalline materials other
than sapphire may respond in a manner such that they may be useful in
systems of the present invention. However, it has been found that
synthetic sapphire, slightly doped with chromium ions within a relatively
low doping level, such as in the range of approximately 20 ppm provides a
fluorescing signal of a useful level when exposed to high intensity laser
light, such as that received from an Argon ion laser. This signal is
obtained without significant loss or degradation of the laser energy
passing through the synthetic sapphire. Impurities, other than the
intentionally added chromium ions, are selected or controlled at minimum
levels so that exceptionally low absorption and/or minimal interferring
fluorescent responses are obtained upon exposure to laser radiation within
the wavelength of the laser used.
The system of the present invention is designed for use with a laser beam
of moderate or long duration. In this connection, however, if output
pulses of known duration are employed, an indication of tip temperature
may be obtained by obtaining a measurement of the decay time of the
fluorescent output.
The power level of the output or response of the synthetic sapphire is
inversely proportional to its temperature. Such response is typical for
chromium-doped synthetic sapphire. Additionally, as the doping level of
chromium ions increases, at least up to a certain range or level, the
fluorescing activity also increases. It has been found that relatively low
doping levels, such as in the range of 20 ppm of chromium ions, provide
synthetic sapphires with a lens body having the desired fluorescent
response, with this response being obtained with a minimum of losses of
laser output power being transmitted through the sapphire.
While the terms "fluoresce" or "fluorescent" are used herein, it is to be
noted that these terms are being used in a comprehensive sense so as to
include generally the emission of light upon stimulation from another
light source, and wherein the wavelength of the emitted light of the
sensor element may or may not fall within the visible range for the human
eye. The emitted light is normally at a wavelength longer than that of the
stimulating light energy.
While the tip assembly and associated laser catheter monitor-control
apparatus of the present invention has general utility for various systems
employing laser beam energy, the tip assembly and its associated
monitor-control is particularly adapted for use in combination with laser
devices for a variety of medical end-uses, with one such end-use being in
combination with laser enhanced transluminal angioplasty catheter devices.
As is known, laser devices have been found useful in treatment of a number
of conditions, including treatment of some forms of arteriosclerosis.
Laser enhanced angioplasty catheter devices are useful for treatment of
certain types of obstructions or occlusions formed, created or otherwise
present in blood vessels such as those created and encountered due to
plaque build-up or the like. Exposure to laser beam energy is undertaken
in order to obtain either a partial removal, reduction and/or the
elimination of the obstruction by means of such exposure. In such systems
an optical fiber member is typically utilized for receiving, transmitting
or otherwise conducting a beam of laser energy from a generator onto a
remote output lens for precise delivery or discharge of the laser energy
from the lens and onto or against the plaque or other matter obstructing
or occluding a blood vessel. While the extent of exposure to laser beam
energy may be controlled by selecting and regulating the extent of on-time
of the laser, the power level involved, and/or the energy distribution at
the distal tip of the fiber, it is, nevertheless, desirable to monitor the
overall operation of the laser system so that any unusual variation in
output power, ambient or environmental conditions may be detected,
including either excessively high or unusually low power levels being
delivered to the tip. The system of the present invention provides a means
for determining the operating condition of the laser beam generator, its
transmission system, and its operating ambience, by precisely determining
the laser power output and the magnitude of the temperature change
existing at the output end, thereby providing a means for alerting the
user to the existence of certain operational anomalies. By way of example,
operational anomalies may occur if the generator is driven with an
unusually high or unusually low amount of input power, with another
operational anomaly occurring if one or more beam transmitting fibers
become cracked, fractured or displaced from the surface of the lens tip.
When utilized as a laser catheter monitor-control system in combination
with laser enhanced transluminal angioplasty catheter devices, the
apparatus of the present invention is useful in combination with those
certain laser catheter control and connecting apparatus disclosed and
claimed in co-pending applications Ser. No. 679,633, filed Dec. 10, 1984,
and Ser. No. 679,920, filed Dec. 10, 1984, each being assigned to the same
assignee as the present invention and reference may be made to the
disclosure contained therein.
The embodiment of the tip assembly and monitor-control system of the
present invention as illustrated herein is shown as functioning within a
laser enhanced transluminal angioplasty system, it being understood that
such a system is illustrated for purposes of explaining the fundamental
operational features of the system and not by way of limitation.
SUMMARY OF THE INVENTION
An improved fiber tip assembly and associated monitor-control system is
provided, with the arrangement being particularly adapted for use in a
laser enhanced transluminal angioplasty system or any other laser power
delivery system. The overall system comprises a laser beam generator, a
fiber optic laser beam transmission system, and a distal tip assembly
having a beam divergence and/or focusing optical element, with the optical
element being responsive to laser power transmission levels and to
temperature so as to function as the source of a signal indicative of
those conditions. The optical element is a form of synthetic sapphire
doped with chromium ions. These systems have been found particularly
adapted for use with the outputs of lasers such as Argon ion or Nd-YAG
lasers. Other lasers may, of course, be adapted for use in combination
with the arrangement of the present invention as well. Other doping
material can be used to adapt to different laser wavelengths. The light
transmission systems utilized with these lasers, particularly in medical
applications typically include light transmitting fibers normally referred
to as optical fibers, which terminate at the surface of the chromium
ion-doped synthetic sapphire lens or tip. Normally, the optical fibers are
disposed in substantial abutment with the surface of the lens. During
normal operation, the lens emits radiation of a wavelength and at a level
indicative of, or responsive to, the level of laser power transmitted
through the optical element, and also responsive to or indicative of their
thermal condition or temperature level. The emitted radiation has a level
or amplitude which may be detected, quantified and compared to a known
level indicative of normal operation. When operational anomalies exist
such as stressed fiber, contaminated distal tip, contaminated or damaged
fiber connector and broken fiber somewhere in the system, the detected
level of emitted radiation will be different from that expected or
anticipated. In other words, the chromium ion-doped synthetic sapphire tip
functions not only as a protective shield, but more importantly as a
source which emits fluorescent radiation when excited with laser beam or
other radiation within a certain bandwidth. The radiation so emitted has a
characteristic wavelength which is also detectably different from the
incident laser power and is emitted at a level which is inversely
proportional to the actual temperature of the lens.
Synthetic sapphire is the preferred material for the optical lens. Such
materials are, of course, commercially available, being fabricated as a
boule from aluminum oxide by a single crystal growing technique, such as,
for example, by the Czochralski Technique. The advantages of use of
synthetic doped sapphire in the present arrangement stems from their
optical properties, as well as their mechanical properties. Additional
advantages include their high temperature stability and durability as well
as their biochemical neutrality.
The fiber tip monitoring and protection assembly of the present invention
provides a means for continuous monitoring of the integrity and the
operational status of a fiber optic delivery system. The arrangement
provides for continuous evaluation of the level of laser power reaching
the tip, and further provides for constant indication of the temperature
condition at the tip end. The arrangement of the present invention
provides a means to interrupt, terminate, or otherwise discontinue
delivery of laser power to the tip when it is determined that the laser
power output at the distal tip is not within predetermined limits, or
alternatively that the temperature at the tip end is not within
predetermined limits.
Therefore, it is a primary object of the present invention to provide an
improved tip assembly and laser monitor-control system which utilizes a
shielding lens which emits fluorescent radiation when excited with
incident laser radiation transmitted through the lens, and wherein the
radiation so emitted has a wavelength which is detectably different from
the incident laser radiation, and wherein the output level of the emitted
radiation is dependent upon the power level of the incident radiation and
the temperature of the lens.
It is a further object of the present invention to provide an improved tip
assembly for an optical fiber laser beam delivery system employing a
chromium ion-doped synthetic sapphire lens element, and wherein means are
provided to control the operation of the laser system through detection of
fluorescent radiation emitted from the chromium ion-doped synthetic
sapphire lens, with the level of the emitted radiation being dependent
upon the incident power and lens body temperature, thereby providing an
indication of certain operational parameters within the system and within
the system ambience.
Other and further objects of the present invention will become apparent to
those skilled in the art upon a study of the following specification,
appended claims, and accopanying drawings.
IN THE DRAWINGS
FIG. 1 is a schematic diagram, partially in block form of the tip assembly
and associated monitor-control system of the present invention, showing
the arrangement embodied in a laser-enhanced transluminal angioplasty
catheter system;
FIG. 2 is a detail sectional view, taken through the diameter, of the tip
assembly and illustrating the configuration of the optical element
employed at the output end of the system, and illustrating the optical
element in a solid sphere configuration;
FIG. 3 is a view similar to FIG. 2, and illustrating the optical element in
the form of a double-dome as fabricated from a ball or rod stock;
FIG. 4 is a view similar to FIG. 2 illustrating the optical element in the
form of a single-dome;
FIG. 5 is a view similar to FIG. 2 and illustrating the optical element in
the form of a conically recessed sphere;
FIG. 6 is a view similar to FIG. 2 and illustrating the optical element in
the form of a sphere having a concave radial recess formed therein;
FIG. 7 is a view similar to FIG. 2 and illustrating the optical element in
the form of a reversed single dome; and
FIG. 8 is a view similar to FIG. 2 and illustrating the optical element in
the form of a negative lens.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With particular attention being directed to FIG. 1, the schematic block
diagram portion thereof and the remaining features depict a laser-enhanced
transluminal angioplasty catheter system embodying the tip assembly of the
present invention. This system, generally designated 10, comprises a
transluminal angioplasty catheter arrangement which is equipped or
provided with a means to deliver laser power. Optical fibers are utilized
for transmission of the laser energy, with a first optical fiber segment
11A being utilized to conduct laser power into control monitor 14, and
with a second optical fiber segment 11B being utilized to transmit laser
power from control monitor 14 to the output tip. The laser system
comprises a laser head 12 powered by power supply 13, with power supply 13
being controlled by control monitor 14 which is coupled to receive inputs
from laser output detector 15 and feedback signal detector 16. The power
output beam from laser head 12 is passed outwardly from the head and onto
electromechanical shutter 18, and thence onto beam splitter 19.
Electromechanical shutter 18 may be actuated from the control unit for
safety purposes as discussed hereinafter. Beam splitter 19 passes most of
the incoming radiation from laser head 12, with this transmitted radiation
then passing through focusing lens 21 and into the proximal end of the
optical fibers 20 disposed within segments 11A and 11B, and ultimately
exiting from tip 22. The items contained within the dotted line of FIG. 1
are those items which are normally contained within a fiber optic coupling
system enclosure either at or mounted on the head of the laser. Normally,
tip 22 will have an outer diameter less than the outer diameter of the
tube portion of segment 11B, but due to limitations of draftmanship, the
outer diameters are shown as being substantially equal in FIG. 1.
Control monitor 14 is interposed between focusing lens 21 and tip 22, and
optical fiber segments 11A and 11B are coupled to control monitor 14.
Segments 11A and 11B are coupled to control monitor 14 by means of
conventional optical fiber-to-fiber connectors. In other words, optical
fiber segment 11A transmits laser energy from focusing lens 21 into
control monitor 14, with a fiber-to-fiber connector designated at 23/23A
being utilized to couple the laser energy into the catheter portion of the
system, such as into optical fiber segment 11B.
Beam splitter 19 may be in the form of a dichroic beam splitter, and is
normally mounted with its surface at an angle of approximately 45.degree.
with respect to the axis of the incident beam, thus continuously sampling
the laser source, while permitting the majority of the laser power to be
transmitted therethrough. In addition to reflecting a portion of the
incident radiation, beam splitter 19 simultaneously functions to reflect
the feedback signal propagating from fluorescing sapphire 22 at a
distinguishable and characteristic wavelength In this fashion, therefore,
beam splitter 19 directs the energy sampled from the laser source onto
laser output detector 15, and furthermore directs the fluorescent feedback
signal to feedback signal detector 16 from the fluorescing sapphire 22. In
this arrangement, the fluorescent signal energy passes through the laser
catheter fiber 11B, into the connecting fiber 11A and through the focusing
lens 21-21 onto the beam splitter 19. The optical fibers 20 terminate at
tip assembly generally designated 22, after passing through optical
fiber-to-optical fiber connectors 23 and 23A, normally a butt-joint,
forming an optical connection between the connecting fiber 11A and the
catheter fiber 11B. Trailing segment 11B which is disposed between control
monitor 14 and tip assembly 22 is normally in the form of a disposable
catheter and typically in the form of a balloon catheter of the type shown
in applications Ser. Nos. 679,633 and 679,920, supra. When utilized as a
laser enhanced angioplasty device, the trailing segment 11B may be
detachably coupled to the system through the optical fiber connector pair
23 and 23A. Accordingly, optical fiber segment 11A represents a permanent
interconnecting fiber between control monitor 14 and the optical coupler
10 on or at the head of the laser housing the components contained within
the dotted line enclosure.
Beam splitter 19 directs or deflects a portion of the incoming laser beam
energy onto threshold detector 15, with such deflected energy passing
through attenuator 24, filter 25 and lens 26 before reaching laser output
detector 15. Laser output detector 15 is a typical electro-optical
detector having a comparator means to determine whether or not the
strength of the deflected portion of the beam is within normal operational
parameters. In this fashion, therefore, laser output detector 15 is
adapted to generate an electrical signal which is delivered to the control
monitor through the conductor system as at 27 in order to permit continued
operation of the system, or alternatively to interrupt such operation.
Detectors of the type employed in the system, such as laser output
detector 15 are readily commercially available. In operation, therefore,
when the strength of the deflected signal from the beam splitter 19 is not
within predetermined values, the system electronics in the control monitor
will function to close shutter 18, which effectively interrupts and/or
terminates system output.
With attention being directed to FIG. 2 of the drawings, and with continued
attention being directed to FIG. 1, tip assembly 22 comprises a spherical
lens 30 retained within a radiopaque metallic sleeve element 31, with
sleeve element 31 surrounding optical fiber 20 contained therewithin. This
metallic sleeve also serves as an identifier of the tip of the fiber under
fluoroscopy. Lens 30 functions as a window at the distal tip of the
optical fiber, and further functions as an emitting source of a light
signal of a different wavelength when excited by the laser power or
radiation. Metal sleeve 31 is preferably a fine metallic tube, but may
alternatively be fabricated from ceramic or glass, and is arranged to
enclose the far-tip of the polished optical fiber on one end, and an
optical element, capable of fluorescing, on the other end. Fiber 20 is
coated with a high strength buffer sleeve and a protective biologically
compatible buffer sleeve 36. The high strength buffer sleeve may be in the
form of a polyimide sheath 32, it being understood that other synthetic
resins with good high temperature properties may be used as well. A
conventional fiber-cladding film 33 is shown surrounding the core of fiber
20. An adhesive bond, preferably an epoxy adhesive, is applied so as to
wick-up under tube 31, thereby providing a sound and firm bond between
tube 31 and coating 32. In this fashion, a suitable bond is established
between metal sleeve 31 and the conventional biocompatible coating 36. A
commercially available biocompatible coating sold under the designation
"Tefzel", among others, may be employed as a material for coating 36. A
ceramic-to-metal seal zone is illustrated at 37, which is typically a high
quality ceramic-to-metal seal providing a hermetic bond or seal within the
confines of the tip assembly. While certain metals may be employed to form
the ceramic-to-metal bond, eutectic metal seals are normally employed and
are generally preferred. While those bonding materials typically
designated "ceramic-to-metal" seals are preferred, it is understood that
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