U.S. patent application number 15/309193 was filed with the patent office on 2017-03-23 for system for tissue ablation using pulsed laser.
The applicant listed for this patent is EXIMO MEDICAL LTD.. Invention is credited to Ilan BEN OREN, Oren Meshulam STERN, Yoel ZABAR.
Application Number | 20170079718 15/309193 |
Document ID | / |
Family ID | 54553515 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170079718 |
Kind Code |
A1 |
ZABAR; Yoel ; et
al. |
March 23, 2017 |
SYSTEM FOR TISSUE ABLATION USING PULSED LASER
Abstract
Systems for enabling delivery of very high peak power laser
pulses through optical fibers for use in ablation procedures
preferably in contact mode. Such lasers advantageously emit at 355
nm wavelength. Other systems enable selective removal of undesired
tissue within a blood vessel, while minimizing the risk of damaging
the blood vessel itself, based on the use of the ablative
properties of short laser pulses of 320 to 400 nm laser wavelength,
with selected parameters of the mechanical walls of the tubes
constituting the catheter, of the laser fluence and of the force
that is applied by the catheter on the tissues. Additionally, a
novel method of calibrating such catheters is disclosed, which also
enables real time monitoring of the ablation process. Additionally,
novel methods of protecting the fibers exit facets are
disclosed.
Inventors: |
ZABAR; Yoel; (Nes Ziona,
IL) ; STERN; Oren Meshulam; (Shilo, IL) ; BEN
OREN; Ilan; (Modiin, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EXIMO MEDICAL LTD. |
Rehovot |
|
IL |
|
|
Family ID: |
54553515 |
Appl. No.: |
15/309193 |
Filed: |
May 18, 2015 |
PCT Filed: |
May 18, 2015 |
PCT NO: |
PCT/IL2015/050529 |
371 Date: |
November 6, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61994904 |
May 18, 2014 |
|
|
|
62006389 |
Jun 2, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 2005/0602 20130101;
A61B 2018/2211 20130101; G02B 6/4296 20130101; A61B 2017/320044
20130101; H01S 3/109 20130101; A61B 2018/00559 20130101; A61B
18/245 20130101; A61B 2017/00274 20130101; A61B 2018/00785
20130101; A61N 2005/0609 20130101; A61B 2018/00505 20130101; A61B
2018/00577 20130101; A61B 2017/00778 20130101; A61B 2018/00488
20130101; A61N 2005/0661 20130101; A61N 2005/067 20130101; H01S
3/11 20130101; H01S 3/1643 20130101; A61B 2018/00345 20130101; G02B
6/04 20130101; A61B 2018/00494 20130101; H01S 3/1611 20130101; A61B
2018/00601 20130101; A61B 2218/002 20130101; A61N 2005/061
20130101; A61N 2005/0611 20130101; A61N 2005/063 20130101 |
International
Class: |
A61B 18/24 20060101
A61B018/24; G02B 6/42 20060101 G02B006/42; G02B 6/04 20060101
G02B006/04 |
Claims
1.-13. (canceled)
14. A device for selective cutting within blood vessels, wherein
said device comprises: a pulsed laser coupled to a plurality of
optical fibers, such that a flux of energy is emitted from said
fibers, and tubes acting as boundaries to said plurality of fibers,
each of said tubes having a blunt distal edge in the same axial
plane as the output end of said plurality of fibers, such that when
a distal force is applied to said device, said blunt distal edges
push through atheromatous material in said blood vessel in the
region where said flux of energy is emitted from said fibers, and
wherein the ratio of the total core area from which said flux of
energy is emitted to the total distal tip area of said device is at
least 25%, and wherein the wavelength of said pulsed laser is
between 320 nm and 420 nm.
15. The device according to claim 14, wherein said ratio is in the
range of 30% to 40%.
16. The device according to claim 14, wherein said laser is a third
harmonic Nd:YAG laser emitting at 355 nm.
17. The device according to claim 14, wherein said flux is at least
50 mJ/mm.sup.2.
18. The device according to claim 14, wherein said flux is in the
range of 50 to 80 mJ/mm.sup.2.
19. The device according claim 14, wherein said flux is in the
range of 65 to 80 mJ/mm.sup.2.
20. The device according to claim 14, wherein said plurality of
fibers is a bundle of fibers.
21. The device according to claim 20, wherein the overall width of
each of said tubes and said fibers is less than 400 .mu.m and more
than 200 .mu.m.
22. The device according to claim 14, wherein dyes or substrates
are used to enhance absorption at desired wavelengths.
23. The device according to claim 22, wherein the said dye is
tetracycline and the desired wavelength is 355 nm.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of pulsed high
power lasers and the problem of delivering their output through
optical fibers and especially for use in tissue ablation with the
energy transmitted through those fibers.
BACKGROUND OF THE INVENTION
[0002] Delivery of high pulsed laser power through optical fibers
is widely used for ablation of tissue or other targets. For such
ablation procedures, ultra-violet (UV) light has many advantages,
as it is well absorbed by biological matter and organic compounds.
Rather than burning or cutting material, the UV laser adds enough
energy to disrupt the molecular bonds of the surface tissue, which
effectively disintegrates into the air in a tightly controlled
manner through ablation rather than burning. The laser energy is
also strongly absorbed and leads to sharp local elevation of
temperature and results in generation of strong mechanical forces
leading to photo-acoustic and photo-thermal ablation. Thus lasers
emitting in the ultraviolet have the useful property that they can
remove exceptionally fine layers of surface material with almost no
heating or change to the remainder of the surrounding material
which is left intact. Excimer lasers emitting at 308 nm (XeCl) are
commonly used. However, such lasers are bulky, require careful
maintenance and frequent calibration, and the beam quality is poor
and may not be stable. Third harmonic, Q-switched Nd:YAG lasers
emitting at 355 nm have also been used for such UV ablation
procedures.
[0003] In order to obtain effective tissue ablation, fluencies
above a certain threshold are required, and high peak power pulses,
of the order of 50 mJ/mm.sup.2 in pulses of down to the 10 nsec
range are generally desired. The delivery of such fluences is very
challenging for the optical fibers, and can lead to damage at the
entrance or exit facets of the fiber, or in the bulk of the fiber
by selective heating, plasma generation, self-focussing or the
generation of cracks at the exit facet. In order to overcome the
challenge of this kind of damage, methods have been proposed in the
prior art of taking the high quality beam emitting by the laser,
and of homogenizing the beam before input to the fiber, to
eliminate "hot spots". Some such methods that have been proposed
include:
[0004] (i) The laser is coupled to the optical fiber using a
diffractive optical element (DOE) and a coupling lens. The DOE
homogenizes the beam spatial energy density and eliminates "hot
spots" of the laser. The DOE can form different shapes, including a
square, a circle, rectangular, as adapted to the different shapes
of the input plane of a bundle of fibers. Different coupling lenses
and different distances between the DOE and the coupling lens have
been used, in order to obtain different spot sizes.
[0005] (ii) A micro-lens array is used to achieve a homogenized
spot. More than one array can also be used in order to achieve
better homogeneity and to avoid hot spots due to beamlet
interference. The size and shape of the spot can be manipulated by
varying the pitch size and the coupling lens focal length. Such a
micro-lens array homogenizer for executing the coupling of high
peak power laser pulses into optical fibers, has been described in
an article by T. Schmidt-Uhlig et al, entitled "New Simplified
Coupling Scheme for the Delivery of 20MW Nd:YAG Laser Pulses by
Large Core Optical Fibers", published in Applied Physics B, Lasers
and Optics, Vol. 72, pages 183-186 (2001).
[0006] (iii) Use of a multimode fiber in order to homogenize the
beam energy density. A positive lens is used to couple the laser
beam into the homogenizer fiber, and a second positive lens is used
to image the homogenizer fiber output into the fiber delivering the
beam to the ablation target. A convenient option is to use a fused
silica fiber, which is more suitable for high power
transmission.
[0007] (iv) The use of pairs of pulses to achieve effective removal
of tissue from a surgical site, in which the first pulse
"conditions" the tissue which can then be more easily removed by a
second, often longer pulse. This arrangement enables ablation to
the accomplished with less damage to the fiber than if an
equivalent single pulse were to be used. Such a method is described
in U.S. Pat. No. 5,312,396 for "Pulsed Laser System for the
Surgical Removal of Tissue" to M. S. Feld et al.
[0008] Additionally, a similar procedure using multiple pulses is
described in the article by D. Albagli et al entitled "Time
dependence of laser-induced surface breakdown in fused silica at
355 nm in the nanosecond regime", published in SPIE Vo. 1441, Laser
induced Damage in Optical Materials, 1990. Using first and second
pulses of the pair at two different wavelengths may also be
advantageously used.
[0009] In an alternative approach, the pulse length of the laser
has been extended to more than 100 nsec in order to improve the
damage threshold of the fibers, or has been split into at least two
pulses with a 100 to 200 nsec delay between them, but this comes at
the expense of the ablation efficiency of hard tissues, such us
highly calcified lesions as described in the article by Rod S.
Taylor et al entitled "Dependence of the XeCl laser cut rate of
plaque on the degree of calcification, laser fluence, and optical
pulse duration" published in "Lasers in Surgery and Medicine"
Volume 10, Issue 5, pages 414-419, 1990.
[0010] However, all of the above mentioned methods have
disadvantages, particularly in terms of the limited improvement in
energy density carrying capacity that can be achieved for the
optical fiber setup used, and/or the system energy throughput,
and/or damage to the fiber tip when in contact with tissue.
[0011] There therefore exists a need for a method and apparatus for
performing ablative surgical methods using fiber optical delivery
of the ablation energy, which overcomes at least some of the
disadvantages of prior art systems and methods.
[0012] In addition to the need for new systems for enabling the
ablation process, there is a growing need for the specific
procedure of removing pacemaker and defibrillator leads in
patients, due to such reasons as lead fracture or abrasion of the
insulation causing shorting and infections. Approximately 5 million
leads are implanted worldwide and it is estimated that 4-7% will
have to be removed at some time during the patient's lifetime. It
is estimated that over 100,000 leads were extracted in the US and
Europe in 2010.
[0013] In Lead Extraction procedures, known hereinafter as LE, the
most critical point in the procedure is reached when the lead at a
bend in the vein has to be debulked. When the electrode separation
procedure is performed, there is a risk of perforation of the vein
by the catheter, and in severe cases, this can even result in death
of the patient. Rates of 1% death cases or even higher are reported
using active dilators.
[0014] Laser ablation and mechanical based cutters are widely used
solutions for atherectomy procedures in order to open or partially
open blockages inside blood vessels. One of the methods of reducing
the danger of the vessel wall perforation is by using a system
having parameters which preferentially cut or ablate the atheroma
tissue over the wall of the blood vessel. If the cutting or
ablating effect is significantly more effective on the atheroma
material than on the artery or vein wall material, and the
procedure is executed under conditions which fall safely below the
threshold at which damage may be caused to the vessel wall, there
will be less likelihood that the artery or vein wall will be cut
during the debulking procedure. In the prior art, in an article
entitled "Preferential Light Absorption in Atheromas in
Vitro--Implications For Laser Angioplasty" by M. R. Prince et al,
published in Journal of Clinical Investigation Vol. 78(1): pages
295-302, July 1986, it has been shown that atheromas indeed absorb
more than the normal aorta between 420 and 530 nm. However, this
was not found to be so in the UV, where at the widely used 308 nm
wavelength, the absorption by the aorta is higher than that of
atheroma. However, since use of the 420-530 nm range, with its
advantageous ablation selectivity, has an inherent disadvantage in
the potential thermal damage caused by the larger energies needed
for efficient ablation and deeper penetration, it is preferable to
use a method for selective ablation which uses laser radiation
within the UV region.
[0015] However, it has also been found, as described in the article
entitled "Laser Ablation of Atherosclerotic Blood Vessel Tissue
Under Various Irradiation Conditions" by R. O Esenaliev et al,
published in IEEE Transactions on Biomedical Engineering. Vol. 36,
no. 12. Pages 1188 to 1194 (December 1989), that for wavelengths in
the UV (355 nm and 266 nm), no difference in the optical
attenuation coefficients to short pulses, has been found between
the normal wall and fibrous plaque areas of atherosclerotic blood
vessels. Therefore, other prior art methods, such as shown in the
article entitled "Selective Absorption of Ultraviolet Laser Energy
by Human Atherosclerotic Plaque Treated with Tetracycline" by D.
Murphy-Chutorian et al, published in the American Journal of
Cardiology, Vol. 55, pages 1293-1297,1985, have suggested the use
of sensitizers such as tetracycline, to increase the absorption in
the plaque. Tetracycline binds strongly to the plaque and has
strong absorption in the UV. The problem with such methods for use
in clinical treatments is that tetracycline is an antibiotic, and
needs additional regulation and tests to ensure absence of side
effects.
[0016] There therefore also exists a need for a method and
apparatus for safely performing lead extraction, using fiber
optical delivery of the ablation energy, which overcomes at least
some of the disadvantages of prior art systems and methods.
Similarly, there is a need for atherectomy tools for debulking of
atheroma in blood vessels that reduce the risk of vessel
perforation or dissection and debulking of enlarged glands in
Benign Prostatic Hyperplasia (BPH) while reducing the risk of
capsule injury.
[0017] Laser catheters should be calibrated prior to the operation
in order to verify the fluence and the repetition rate of the laser
energy that is emitted from the catheters.
[0018] The prior art deals with methods of calibration of catheters
in which the catheter is pulled out of its packaging, coupled to
the laser system, the distal tip is held by a housing in front of a
detector, the laser is operated and the energy is measured by the
detector as described in U.S. patent Ser. No. 11/946,376 for "Laser
catheter calibrator" to Tom Dadisman.
[0019] Since the catheters are sterilized before use, this method
can involve risk of moving the distal tip of the catheter out of
the sterilized area in the operation room.
[0020] There therefore also exists a need for a method and
apparatus for internal calibration of the laser system and for
detecting a failure of the system and/or the catheter.
[0021] The disclosures of each of the publications mentioned in
this section and in other sections of the specification, are hereby
incorporated by reference, each in its entirety.
SUMMARY
[0022] The present disclosure describes new exemplary systems for
enabling the coupling and transmission of very high energy pulses
having a very short pulse width, preferably from a solid state Q
Switched laser emitting in UV, into optical fibers for use in
ablation procedures, which enable substantially higher energy
pulses to be transmitted than in the systems described in the prior
art. In prior art systems, a laser having as high a quality output
as possible is generally used, in keeping with the mantra that in
order to achieve high coupling efficiency and better beam quality
without "hot spots", a laser having the mode closest to a single
mode output should be used, generally as close as possible to a
diffraction limited, Gaussian mode. This is the accepted logic in
the use of laser beams for cutting or spot ablation, as indicated
for instance in the above-mentioned U.S. Pat. No. 5,312,396, where
it is stated, in extolling their suitability for the purpose, that
the Nd:YAG lasers used "have good beam quality". Similarly, in the
above referenced article by T. Schmidt-Uhlig et al, it is stated
that the pulses of the Q-switched frequency doubled Nd:YAG laser
used in their system had "a nearly guassian (sic) temporal and
spatial profile". The same design philosophy applies through most
of the prior art high pulse energy, fiber-delivered surgical
ablation systems. Similarly, the article by B. Richou et al
entitled "Delivery of 10-MW Nd:YAG laser pulses by large-core
optical fibers: dependence of the laser-intensity profile on beam
propagation" published in Applied Optics Vol. 36, No. 7 (1997),
reported higher (230 mJ) transmission of a pulsed Nd:YAG
near-Gaussain beam compared to a flat-hat beam (130 mJ). The
individual fibers used in the fiber bundles of the systems of the
present application generally have core diameters of less than 200
microns, and preferably less than 100 microns, wherein the energy
transmitted is in the order of 1-2 mJ with pulse length of 10 ns
cannot lead to self-focusing.
[0023] However, the system design used in the present application,
uses the fact that it is precisely because of the high quality mode
structure of such lasers that the serious problems of coupling and
transmission through the optical fiber arise, even when dealing
with fibers with small diameter such as 100 micron core fibers.
[0024] The presently described system differs from these prior art
systems in that a source laser outputting multiple transverse modes
is used, thereby having a highly multimode output. The cavity
should also advantageously be a stable resonator cavity. Such a
laser a priori outputs a beam with low spatial coherence, and
therefore reduces the prevalence to damage in the bulk of the fiber
due to interference phenomena. Such a laser outputs a beam which is
significantly closer to having a uniform beam profile, known as a
top-hat configuration, than the prior art, high quality lasers
generally used in such systems. In order to improve the immunity
from fiber damage even more, prior art homogenization, beam
manipulation methods can also advantageously be applied to such a
flat-topped beam, with accordingly improved performance. The
transmission of such pulses down the fibers results in a higher
damage threshold than when using high quality laser pulses, and it
has been found possible to transmit pulses having higher energy
density, than those of prior art systems, before fiber damage sets
in. It is believed that this phenomenon is related to the absence
of meaningful interaction between discrete parts of the beam across
its profile, which could generate hot spots or interference.
However, it is to be understood that the invention is claimed
independently of the real reason for its physical operation. It
should be noted that since the catheters of the present disclosure
utilize a bundle of fibers, and the energy of the individual laser
pulses is transmitted through a bundle of fibers and not a single
fiber, references to single fibers within this disclosure is
generally intended to mean a single fiber out of the bundle of
fibers, and is not intended to mean transmission through solely a
single fiber.
[0025] The mode quality of a laser output beam can be characterized
by the beam size and beam divergence. The smaller the divergence
for a beam of given size and wavelength, the higher the beam
quality. One parameter used for characterizing the beam mode
quality is the M.sup.2 parameter. The M.sup.2 parameter of the beam
mode output by the laser is used in the present application to
characterize the beam properties for achievement of very high pulse
energy densities for such pulses in the nanosecond range. It is to
be understood however that use of the M.sup.2 parameter is only one
way of characterizing beam quality, and the invention of the
present disclosure is not intended to be limited by use of this
measure.
[0026] The M.sup.2 parameter is related to the ratio of the output
beam size and the beam divergence by the following
relationship:
M 2 = D .theta. .pi. 4 .pi. ( 1 ) ##EQU00001##
[0027] where D=the beam diameter, [0028] .lamda.=the wavelength of
the laser beam, and [0029] .theta.=the full angle beam divergence
in radians.
[0030] A pure diffraction-limited beam would have an M.sup.2
parameter of 1, while practical, high-efficiency, commercial lasers
for use in surgical or precision industrial applications generally
have an M.sup.2 parameter in the low single digit range.
[0031] The M.sup.2 parameter can also be defined for a beam at any
point along its optical path, by inserting a focussing lens at that
point and measuring the size of the focal spot obtained.
Intuitively, the tighter the focal spot, the better the mode
quality of the beam at that point, and the lower the M.sup.2
parameter. The M.sup.2 parameter in that case is given by the
following relationship:
M 2 = D d .pi. 4 f .lamda. ( 2 ) ##EQU00002## [0032] where D is now
the beam diameter at the point of insertion of the lens, [0033] f
is the focal length of the lens used, and [0034] d is the size of
the focal spot obtained.
[0035] It is to be understood throughout this disclosure that the
M.sup.2 parameter used is calculated according to the appropriate
one of these formula, depending on whether the measurement relates
to the laser output beam, or to a beam downstream in the optical
path.
[0036] The systems and methods described in the present disclosure
differ from those described in the prior art in that the laser used
for transmission down the fiber and for ablation at the treatment
site is selected to have a highly multimode beam output, preferably
a third harmonic Nd:YAG laser, such that the M.sup.2 parameter of
the output beam should be at least of the order of a few tens,
typically at least 30, and optimally up to 70 or even more, such as
greater than 100. The M.sup.2 of the laser may be greater than 10,
but the M.sup.2 of the system, including the optics is greater than
70 and preferably more than 200. Such beams therefore behave in a
very distinct manner from those described in the prior art, and
allow transmission of pulses having pulse energy densities at least
twice as much, and even more, than the pulses available from prior
art ablation systems using high beam quality lasers. Additional
optical means may be added, such as a micro-lens array, to further
increase M.sup.2 and to increase pulse energy density transmitted
reliably for a large number of pulses through fibers typically with
100 micron core or less.
[0037] Details of typical performance of such systems are to be
found hereinbelow in the Detailed Description section.
[0038] The present disclosure furthermore describes new exemplary
systems for enabling selective removal of undesired tissue within a
blood vessel, while minimizing the risk of damaging the blood
vessel itself, based on the use of the ablative properties of short
laser pulses of 320-400 nm laser wavelength, with selected
parameters of the mechanical walls of the tubes constituting the
catheter, of the laser fluence and of the force that is applied by
the catheter on the tissues. As stated hereinabove, It was
previously believed that the selectivity characteristics of a given
tissue without the existence of sensitizers could not be determined
using UV radiation, since normal aorta and atheromatous tissues
share numerous common molecules whose absorption bands are all in
the UV region, whether at 355 nm or at 308 nm. Although the
dissociation energy of many organic molecular bonds is typically
higher than the photon energy of the 355 nm wavelength (3.5 eV),
this does not apply to the 308 nm excimer laser wavelength, whose
photon energy is higher (4 eV). Thus, it is believed that the
dominant ablation mechanisms at the 355 nm wavelength is
photomechanical. In contrast, at the shorter, 308 nm wavelength of
the excimer laser, and obviously at even shorter wavelengths,
photochemical processes, in which chemical bonds are dissociated by
the laser radiation, are more relevant. Because of this difference
in the interaction mechanism with the target tissue, this selection
of wavelength, together with the other selected parameters, is
believed to have a central influence on the success of the
presently described catheters. Thus, by using the correctly
selected parameters, ablation of the blood vessel walls is far less
likely to occur than for the atheroma, because the blood vessel
walls have greater elasticity than the atheroma, and therefore
withstand the photomechanical mechanisms operating on them much
better than the atheroma, which is more readily broken up by such
photomechanical influences.
[0039] It is also possible that in addition to the operated
wavelength aspects, since shock waves plays a major role in the
photomechanical ablation mechanism, a reduction in the pulse
duration (i.e. higher peak power) may lead to an increased
efficiency of the process.
[0040] However it is to be emphasized that the present application
relates to the catheters described therein, regardless of the
physical mechanisms on which the success of their operation is
based, and the application is not intended to be limited by any
proposals regarding possible mechanisms by which the catheters
fulfill their function.
[0041] According to one exemplary catheter system of the present
disclosure, a third harmonic Nd:YAG laser outputting at 355 nm is
coupled to a hybrid catheter, which incorporates a bundle of
optical fibers receiving the laser illumination, and at least one
blunt-ended tubular structure whose distal edge is located on an
essentially single surface with the output facets of the optical
fibers, to interact with the atheromatous tissue within the blood
vessel. Different configurations are available for LE use and for
debulking or opening blood vessels where substantial deposits of
atheromatous material is found such as in Peripheral Artery Disease
(PAD). In the LE case, a thin annular bundle of fibers is required,
with cylindrical walls bounding it on the inner and outer sides of
the annulus. The cylindrical walls constitute the blunt-ended
tubular structure. On the other hand, In PAD, for removal of
deposits across the whole cross-section of a blood vessel, the
bundle of fibers essentially covers the whole of the cross section
of the catheter, usually with a thin opening in the center of the
bundle for a guide wire, but in this case too, the cylindrical
walls of the bundle region constitute the blunt ended tubular
structure. Throughout this disclosure, these blunt ended tubular
structures are termed "blunt mechanical blades".
[0042] Using the LE case as an example, the catheter operates, once
within the blood vessel and in contact with the intravascular
deposit, by using the laser pulses to ablate a thin layer of the
tissue, typically only a few tens of microns deep, making a thin,
shallow slit to enable the continued penetration of the blunt
mechanical blade in response to the pressure applied distally on
the catheter. The blade or blades are therefore constructed to be
too blunt to initiate dissection, but with enough of an edge to
create the slit to enable deeper catheter penetration into the
tissue. The borders of the tissue being ablated, which possesses a
transient zone, are mechanically weakened due to the trauma, which
facilitates dissection by the blunt blade. The width of the blades,
and the ratio of the total area of the cores of the fibers within
the fiber optical bundle, from which the ablation energy is
emitted, relative to the total cross-sectional area of the tip of
the catheter, not including the empty central area, are important
parameters which also characterize the catheters of the present
disclosure.
[0043] The force applied distally on the catheter is an additional
parameter whose level is adjusted to ensure that the catheter
advances through the atheromatous tissue at a rate commensurate
with the rate of laser ablation and mechanical peeling of the
hybrid catheter action. The larger the diameter of the catheter,
the larger the force that needs to be applied.
[0044] The present disclosure furthermore describes new exemplary
systems to enable reliable operation of the catheter in a mode of
contact with the tissue.
[0045] In some embodiments a thin sapphire window or similar is
added at the distal end of the fibers. In some embodiments the
window is coated with an AR coating.
[0046] In other embodiments, the fiber ends at the distal tip are
coated with a hard coating. Coating the catheter tip may provide
additional performance enhancement. One possible material is
diamond. Diamond Like Coatings (DLC) are commonly used in
industrial applications where hard, strong, and smooth surfaces are
required, for example, to protect from mechanical wear. One of the
means to obtain such coatings is through Chemical Vapor Deposition
(CVD). Cutting tools are often coated to improve durability. DLC
has excellent biocompatibility as it is commonly employed in joint
replacements and coronary artery stents.
[0047] A diamond coated catheter may have the following advantages.
First, the coating hardness may protect the fiber tips from damage
due to contact with hard biological media and from the resulting
shockwaves from laser ablation. Second, the smoothness (low
friction) and simultaneous nano-roughness may be advantageous to
allow progression of the catheter and/or enhanced material removal
by scraping. Third, the high thermal conductivity may help to
distribute heat from absorption of the laser pulses in the
tissue.
[0048] DLC's are generally not thought suitable for visible
wavelengths due to their high absorption. However, when considering
the optimal layer thickness required for maximum UV light (355 nm)
transmission, a DLC coating with an index of 2.4 would only need to
be about 74 nm thick when applied to fused silica in order to
obtain a minimum reflection of 3.7%. Absorption of the material
should be minimal with such a low thickness. Furthermore,
transparent diamond coating can used such as described in the
article of E. Pace et al entitled: "Fast stable visible-blind and
highly sensitive CVD diamond UV photodetectors for laboratory and
space applications" published in "Diamond and Related Materials",
Volume 9, Issues 3-6, Pages 987-993 (April-May 2000). Several
manufacturers have applied DLC coatings to glass, including, for
example, Jenoptik and Reynard Corporation which produces Clear DLC
with enhanced visible light transmission.
[0049] Another limitation of use of CLD is the high index of
refraction which leads to very high "Fresnel Loses". A potential
way to deal with those loses is to add an AR coating, but this is
problematic in the current embodiment due to a number of
reasons:
[0050] The AR coating can't withstand very high power at the fiber
tip. In addition, it needs to be made from biocompatible materials
to allow close contact with tissue. Furthermore, the AR coating is
subject to mechanical abrasion when in contact with tissue.
[0051] Thus, according to the present invention, a diamond layer is
used as an AR film wherein its thickness is selected to reduce
reflection loses in order to save energy and avoid back reflection
into the fiber that can damage it. The thickness can be determined
according to the rules used in antireflection coatings such as
quarter wavelength, 5/4 wavelength or other combinations according
to the angle of emitted light (NA). The thickness can also be
determined in such a way that a 355 nn wavelength will be
transmitted while another wavelength in the visible are will be
reflected. For example, the hard coating at the exit facet can be
such that transmits the 355 nm out of the catheter by using a
thickness of 9/4 wavelength wherein the wavelength is 355 nm (and
corrected according to the refraction index) so that the same layer
will be 3/2 of the wavelength at 532 nm (and corrected according to
the refraction index) and result in effective back reflection from
the fiber end facet for calibration of energy delivered by the
system, wherein the 532 nm and 355 nm are generated by the same
laser and transmitted through the same coupling optics and
catheter. This enables effective calibration before the procedure
and serve as on-line calibration and quality control of the
catheter throughout the procedure. By mode of example, if the index
of refraction is 2.4, a layer with the thickness of 332.8 nm is
equivalent to 9/4 wavelengths of 355 nm (in vacuum) and to 1.5
wavelengths of 532 nm (in vacuum). Other embodiments are possible
that are optimized for the incident of laser rays transmitted
through the fiber that can get up NA of 0.22.
[0052] In other implementations, the laser pulse is split into at
least two pulses with a delay between pulses of less than 15 nsec
delay in order to protect the distal facets of the fibers without
significant impact on ablation efficiency. Details of such system
can be found below in the detailed description section.
[0053] In alternative implementations means to facilitate the
flushing of the tip with saline throughout the procedure are
described. Details of typical performance of such systems are to be
found hereinbelow in the Detailed Description section.
[0054] The present disclosure furthermore describes new exemplary
systems to enable effective and convenient apparatus for
calibration of laser system delivering energy through the fibers.
Details of typical performance of such systems are to be found
hereinbelow in the Detailed Description section.
[0055] There is thus provided in accordance with an exemplary
implementation of the devices described in this disclosure, a laser
device for ablating a region within a luminar vessel, comprising a
pulsed laser, and at least one optical fiber coupled to said laser
by means of a coupling optic, wherein the laser has a multimode
output such that its M.sup.2 parameter is larger than 30. The
M.sup.2 parameter may be larger than 70 or even 100.
[0056] According to another implementation of such devices, there
is provided a laser device for ablating a region within a luminar
vessel, or other lumens in the body, comprising a pulsed laser
emitting in the ultra violet region of the spectrum, and at least
one optical fiber coupled to said laser by means of a coupling
optic, wherein the laser beam has a multimode profile as measured
by the spot size of the beam focused by a lens of known focal
length, such that the beam has an M.sup.2 parameter of at least 30.
The M.sup.2 parameter may be larger than 70 or even 100.
[0057] In either of these two implementations, the at least one
optical fiber may have a core of less than 200 microns diameter.
Additionally, the coupling optics may comprise any one or more of a
micro lens array, a diffractive optical element, a holographic
diffuser, a light pipe rod, and a large core optical fiber. In some
implementations, M.sup.2 parameter of the laser may be larger than
10 or alternatively greater than 30 but the M.sup.2 of the laser
together with the above mentioned elements is larger than 70 and
preferably greater than 200.
[0058] The pulsed laser may advantageously be a Nd:YAG, solid state
laser, the laser wavelength may be 355 nm, the laser pulse width
may be less than 15 nsec and the pulse laser repetition rate may be
greater than 10 Hz. In the latter case, the laser is such that a
fluence of at least 60 mJ/mm.sup.2 can be delivered through the
optical fiber for more than one minute. According to further
implementations, the fluence delivered through the optical fiber
for more than one minute may be at least 200 mJ/mm.sup.2 or even
300 mJ/mm.sup.2.
[0059] There is thus provided in accordance with an exemplary
implementation of the devices described in this disclosure, a
device for selective cutting within blood vessels, wherein the
device comprises:
[0060] (i) a pulsed laser emitting in the wavelength range of 320
to 400 nm, and being coupled to a plurality of optical fibers, such
that a flux of energy is emitted from the fibers, and
[0061] (ii) tubes acting as boundaries to the plurality of fibers,
each of the tubes having a blunt distal edge in the same axial
plane as the output end of the plurality of fibers, such that when
a distal force is applied to the device, the blunt distal edges
push through atheromatous material in the blood vessel in the
region where the flux of energy is emitted from the fibers,
[0062] wherein the ratio of the total core area from which the flux
of energy is emitted to the total distal tip area of the device is
at least 25%.
[0063] In such a device, the ratio may be in the range of 30% to
40%. Additionally, the laser may advantageously be a third harmonic
Nd:YAG laser emitting at 355 nm.
[0064] In any of the above described devices, the flux may be at
least 50 mJ/mm2 or it may be in the range of 50 to 80 mJ/mm2, or
even in the range of 65 to 80 mJ/mm2.
[0065] Additionally, the plurality of fibers of the above described
device may be a bundle of fibers. In such a case, the overall width
of each of the tubes and the fibers should be less than 400 .mu.m
and more than 200 .mu.m.
[0066] Furthermore, according to yet more implementations of such
devices, dyes or substrates may be used to enhance absorption at
desired wavelengths. The dye may be tetracycline and the desired
wavelength 355 nm.
[0067] Another example implementation can involve a system for
ablating a region of a tissue, comprising:
[0068] (i) a laser emitting a beam of laser pulses, the beam being
coupled by means of coupling optics to at least one optical fiber,
such that a flux of energy is emitted from the at least one fiber,
the at least one fiber having an input facet and an output
facet,
[0069] (ii) a beam splitter disposed between the laser and the at
least one fiber, such that the beam can pass undeflected through
the beam polarizer to the at least one fiber, for transmission to
the region of tissue, and
[0070] (iii) a detector disposed at the beam splitter in a position
normal to the direction at which the beam passed undeflected
through the beam splitter,
[0071] wherein the detector receives a predetermined fraction of
the beam reflected from at least one of the input facet and the
output facet of the at least one optical fiber, such that the flux
of energy passing through the at least one optical fiber can be
determined.
[0072] Such a system may further comprise
[0073] (i) a linear polarizer disposed in the optical path of the
beam, such that the beam has a predetermined linear polarization
before impinging on the beam splitter, and
[0074] (ii) a quarter wave plate disposed between the beam splitter
and the input facet of the at least one fiber, such that the
predetermined fraction of the beam reflected from at least one of
the input facets and the output facets has a linear polarization
orthogonal to that of the beam inputting the at least one fiber,
such that the beam splitter directs the predetermined fraction
towards the detector.
[0075] In either of the latter two cases, one of the input and
output facets may have an anti-reflective coating, such that the
predetermined fraction of the reflected beam is limited to that
facet which is uncoated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0076] The present invention will be understood and appreciated
more fully from the following detailed description, taken in
conjunction with the drawings in which:
[0077] FIG. 1 illustrates schematically an exemplary laser ablation
system using a multimode laser, which enables the transmission of
very high energy density pulses through optical fibers of an
ablation catheter;
[0078] FIG. 2 illustrates schematically a further exemplary
implementation of the system shown in FIG. 1, in which splitting of
the laser beam is used in order to enable transmission of the pulse
train through the fiber in the form of double pulses temporally
separated and avoid damage at the output facets of the optical
fibers;
[0079] FIGS. 3A and 3B are respectively a schematic end view and a
cross sectional side view of an exemplary annular hybrid catheter
which can selectively ablate atheromatous tissue over the tissue of
the wall of blood vessels, such that lead extraction or PAD
procedures can be more safely performed;
[0080] FIGS. 4A and 4B are respectively a schematic end view and a
cross sectional side view of an exemplary hybrid catheter which can
selectively ablate plaque from atherosclerotic blood vessels more
safely; and
[0081] FIG. 5A illustrates schematically an arrangement for
calibrating the hybrid catheters described in FIGS. 1 to 4B during
their operation, and to detect malfunction of the system in real
time.
[0082] FIG. 5B illustrates schematically end view of exemplary
spatial filter for the calibration system described in FIG. 5A.
[0083] FIGS. 6A, 6B and 6C are respectively a schematic end view
and a cross sectional side view of an exemplary catheters with
capillaries for flushing the distal tip of the catheter.
DETAILED DESCRIPTION
[0084] Reference is now made to FIG. 1, which illustrates
schematically an exemplary laser ablation system, of the type
described in the present disclosure, incorporating a solid state
laser source 10 emitting in the ultra-violet, and having a
multi-mode output, as exemplified by the beam profile
representation 15 adjacent to the output beam. The representation
is only for illustrative purposes to show the multi-mode output as
being very distant from a Gaussian beam, and is not intended to
limit the application in any way. The laser beam output should have
an M.sup.2 parameter of at least 30, and more advantageously at
least 70, though lasers having a beam output with an M.sup.2
parameter of over 100 can provide even better performance in the
exemplary ablation system of FIG. 1. For optimum performance, short
pulse widths are used, preferably less than 10 nanoseconds, and the
laser should supply pulses that can provide an energy density of at
least 50 mJ/mm.sup.2 through the fiber. For stability and
compactness, a solid state laser is used, such as a Nd:YAG,
operating at its third harmonic 355 nm.
[0085] Although the laser 10 emits a well-mixed multimode beam, the
laser beam is input to a beam homogenizing and/or coherence
manipulation unit 14, in order to mix the multiple modes of the
output beam 11 even more, such that the fiber has an even higher
damage threshold than would be obtained with the multimode output
from the laser alone. This unit 14 can be any one or more of a
homogenizing plate, a diffractive optical element, a holographic
element, a micro-lens array, or a homogenizer optical fiber bent to
ensure additional mode mixing during propagation of the pulses down
it. A coupling lens 12 is then used for coupling the laser beam
into the optical fiber bundle 13. Although the individual fibers
could have a core size of less than 200 microns, the optical fiber
bundle includes a large number of these individual fibers, and is
thus substantially larger than the diameter of the individual
fibers, such that there are no special optical difficulty in
coupling such a multimode beam into such small fibers. Although
only one coupling lens 12 is shown in FIG. 1, it is to be
understood that the system could incorporate two coupling
lenses--one to couple the raw laser beam into a homogenizer fiber,
for instance, and the other to couple the output of the treated
beam into the fiber bundle of the catheter. In some embodiments
combination of such optical elements enable delivery of high
fluencies through fibers of 100 micron or less a laser beam with
M.sup.2 greater than 10 may also be used.
[0086] Reference is now made to FIG. 2, which illustrates
schematically a further exemplary implementation of the system
shown in FIG. 1, in which polarization splitting of the laser beam
is used in order to enable transmission of the pulse train down the
fiber in the form of double pulses temporally separated,
particularly reducing the danger of damage to the output facet of
each of the fibers when in contact with tissue. These output
facets, where the fibers are in contact with the tissue being
ablated, are subject to particularly harsh conditions. When the
system described in FIG. 1 is implemented and the fibers are in
contact with tissue the likelihood of facet damage is greater at
the output facets than at the input facets of the fibers, and
therefore this implementation will be most effective to protect the
output facets from damage, it is to be understood that it is also
useful for protecting both the input facet, and the fiber bulk
itself.
[0087] The beam from the highly multimode laser 10, is transmitted
through a half wave plate 27 and then to a polarization beam
splitter 28 in order to split the laser beam into two component
parts--S-polarized and P-polarized. In the example shown in FIG. 2,
the S-polarization is deflected through 90.degree. while the
P-polarization passes through the cubic beam splitter without
deflection. The S polarization is conveyed on an optical path
longer than that of the P polarization, and after reflection
through 180.degree., accomplished by means of two full reflector
mirrors, the S- and the P-polarization beams are recombined by
means of a second polarization beam splitter 29, ready for coupling
by means of the coupling lens 12 into the fibers 13 of the
catheter. By adjusting the optical path difference along which the
P- and S-polarizations travel, it is possible to control the
temporal delay between the two beams, such that the input is made
up of double pulses, separated by the selected time delay, and the
use of such a double pulse laser energy enables the avoidance of
fiber damage, not only at the entrance facet of the optical fiber,
but also on the problematic output facet of the optical fiber, in
contact mode with the ablated material. The time delay has to be
selected such that the double pulses are not separated by more than
the relaxation time of the vascular material being treated, such
that ablating efficiency is not lost. For 10 ns pulses, a time
delay between pulses of the order of 10 ns is regarded as being
acceptable. The success of this double pulse mode depends also on
the knowledge that the ablation efficiency is not a linear function
of peak power of the laser pulse, such that division of the power
into two pulses does not degrade the ablation effect by the same
factor of two. Additionally, a lens (not shown in FIG. 2) could be
disposed in the longer optical paths in order to image the beam
waist in such a manner that the waists of the two beams traversing
the two different optical paths are both located at the fiber input
facet. This is necessary in order to compensate for the extra beam
divergence which the beam in the longer optical path undergoes. As
an alternative to the configuration shown in FIG. 2, it is possible
to use thin film polarizers (TFP) to split and combine the two
beams.
[0088] Furthermore, the laser beam may split into more than two
channels, to even further reduce the potential damage level of the
fibers. Additionally, different wavelengths emitted by a laser,
such as the second and third harmonics, or the fundamental and
third harmonic of the Nd:YAG laser, can be split and combined
again. It is also possible to use multiple lasers with a
synchronized delay between the pulses.
[0089] Reference is now made to FIGS. 3A and 3B and to FIGS. 4A and
4B which show schematically further implementations of hybrid
ablation catheters of the present disclosure, which illustrate how
the catheters can be used to selectively ablate atheromatous
material from the blood vessels, while reducing the danger of
perforating the blood vessel wall. The structures of the hybrid
catheters shown in these drawings have the common feature that
besides the fiber bundles emitting the ablating laser pulses, the
blunt distal ends of the tubular elements enclosing the fiber
bundles are also constructed such that they contribute to the
operation of the catheters. As explained in the summary section of
this disclosure, the distal ends of the tubular structures are
specifically constructed having non-sharp ends, called hereinbelow
blunt mechanical blades, so that they do not unintentionally
dissect the blood vessel walls.
[0090] Referring first to FIGS. 3A and 3B, they show respectively a
schematic end view and a cross sectional side view of an exemplary
annular hybrid catheter which can selectively ablate atheromatous
tissue substantially more readily than the walls of blood vessels,
such that lead extraction can be more safely performed. The laser
energy is transmitted to the distal end of the catheter through a
bundle of optical fibers 30 embedded within an adhesive matrix, in
the form of an annulus having a large central clear area 33. The
annulus of optical fibers 30 is bounded on its inner side by a thin
tube 31, which constitutes the inner blunt mechanical blade, and on
its outer side by another thin tube 32, which constitutes the outer
blunt mechanical blade. The distance between the innermost edge of
the inner tube 31 and the outermost edge of the outer tube 32 is
known as the effective wall thickness 34 of the catheter, or the
distal tip. In use, the catheter is inserted into the blood vessel
over the lead to be extracted, such that the lead is situated in
the central annular area 33. The laser pulse energy is applied to
the fiber bundle 30, typically in the ultraviolet region of 320 to
400 nm, and having a fluence of 50 to 80 mJ/mm.sup.2, accompanied
by a force applied distally to the catheter, enables the catheter
to proceed in a distal direction debulking the lead from the walls
of the blood vessel, without damaging the walls of the blood
vessel, as explained in the summary section hereinabove. The
important parameter for the success of this process is based on the
trade-off between two energetic processes taking place at the
tissue interaction plane at the tip of the catheter. On the one
hand, the total area of the fiber cores emitting the laser pulses,
known as the active emitting area, is providing the ablating energy
in order to degrade the atheromatous material, while the mechanical
force exerted distally on the catheter, which pushes and peels off
the degraded material mechanically, operates through what is termed
the distal tip area, which includes all of the mechanical parts of
the distal face of the catheter, including the inner and outer
blunt mechanical blade areas, and the mechanical area of the fiber
adhesive matrix, but not the hollow central area. The wall
thickness or distal tip 34 of such catheters is typically in the
range of 200 to 400 .mu.m, such that the ratio of the fiber core
area to the distal tip area of the catheter is between 25% and 50%.
The most effective ratio is in the range of 30% to 40%. The distal
force applied to the catheter may be in the region of 0.5 kg and
even up to 2 kg.
[0091] FIGS. 4A and 4B now show in end view and in cross sectional
side views, an exemplary hybrid catheter which can selectively
ablate plaque from atherosclerotic blood vessels more safely, such
as for use in PAD treatment. This type of catheter differs from
that shown in FIGS. 3A and 3B in that the fiber optical bundle 40
fills the majority of the central region of the catheter, leaving
only a small central opening 43 inside the inner tube 41, typically
left so that the catheter can ride on a guide wire. The effective
wall thickness 44 of this hybrid catheter is the distance between
the outer surface of the outer tube 42 and the inner wall of the
inner tube 41, and is typically in the range of 400 to 1,200 .mu.m.
As in the case of the LE catheter, the ratio of the fiber core area
to the distal tip area of the catheter is between 25% and 50%.
Because of the nature of the PAD treatment, more care is required
in pushing the catheter through for instance a curved blood vessel,
such that the force may be smaller, but at least 100 gm.
[0092] Reference is now made to FIG. 5A, which illustrates
schematically an arrangement for calibrating the hybrid catheters
described in this disclosure. Calibration is necessary prior to the
operation in order to verify the fluence and the repetition rate of
the laser energy that is emitted from the catheters.
[0093] In the prior art, methods of calibration of catheters have
been described in which the catheter is coupled to the laser
system, while the distal tip is held by a housing in front of a
detector, and the transmitted energy is measured by the detector
while the laser is operated. Since the catheters are sterilized
before use, this method can involve the risk of moving the distal
tip of the catheter out of the sterilized area in the operation
room.
[0094] The system shown in FIG. 5A differs from prior art methods
in that it enables the internal calibration of the catheter, while
it is in use, and also enables detection of a failure of the system
while it is operating.
[0095] The incident beam from the laser 50 is directed through a
beam polarizer 51, which outputs the beam as P-polarized, as marked
in FIG. 5A. After traversing the coupling lens 52, the P-polarized
beam is input to a polarizing beam splitter 53, from which it
emerges undeflected. The P-polarized beam is then input through a
quarter wave plate 54, which converts its polarization to circular.
This circularly polarized beam then enters the fiber 55, passing
therethrough by total internal reflections (TIR), and the majority
of the energy is emitted from the output facet at the distal end of
the fiber, for use in the ablation procedure 59. However a small
percentage of the energy is reflected back towards the entrance of
the fiber due to Fresnel reflection from the output facet.
Additionally, any Fresnel reflection 56 from the front facet is
also reflected back. This small reflected fraction of the input
beam now passes back through the quarter wave plate 54, where it is
converted from circular into S-polarization, such that when it
enters the polarizing beam splitter 53, it is deflected along a
path 57 approximately normal to its entrance axis towards the
detector 58. Since the percentage reflection from the front and
rear facets is known, the detector is able to determine, from a
measurement of this reflected power, the energy emitted from the
fiber output to the ablation application. The measurement of the
detector output is thus a real-time monitor of the laser energy
being used in the ablation procedure.
[0096] If the entrance facet is coated with an anti-reflective
coating, the power measured by the detector 58 is that due only to
reflection from the output facet, such that differentiation can be
made between reflections from these two facets.
[0097] An alternative to the use of an anti-reflective coating on
the entrance facet in order to differentiate between the front and
the rear facet reflections, it is possible to use a spatial filter
disposed between the front facet and the polarizing beam splitter,
in order to filter out the reflection from the input facet, which
has a smaller divergence angle than the reflection from the output
facet, since the numerical aperture of the output reflection is
significantly larger. The spatial filter may conveniently be a thin
film polarizer (TFP) as illustrated in FIG. 5B, wherein The TFP 60
is coated at its peripheral edges 61, such that those edges
diverged the reflected beam from the output facet to the detector
58, while the central region 62 of the TFP 60 is uncoated and
therefore the smaller divergence reflection from the input facet
passes through that central uncoated window, and does not reach the
detector.
[0098] According to another exemplary implementation, a cap may be
placed over the distal tip of the catheter, with the inside of the
cap is coated with reflective coating in order to enhance the
signal that is reflected from the distal facets of the fibers.
[0099] The cap may be coated with a fluorescent material that
changes the wavelength of the output reflected beam, and by use of
an optical filter, its separation from the entrance facet
reflection is achieved. The cap may be sterilized together with the
catheter.
[0100] Alternatively, The cap may also be covered with material,
polyamide for example, that gives a vocal indication when energy
above specified level strikes it. Alternatively, the cup can be
covered with material that changes it color when exposed to the
radiation of the laser.
[0101] The above-described calibration procedure can be performed
while the fiber is rolled up inside its packaging, keeping the bend
radius of the fiber known and constant, so that the percent of
energy reflected back from the output facet does not change.
[0102] In some other embodiments, the entrance facet is not coated,
and the detector will measure both the energy reflected from the
input and output facets.
[0103] In some embodiments, the system can be internally
calibrated, without connecting the catheter, wherein there is a lid
that is moved aside when the catheter is connected, and is closed
when the catheter is moved out. This lid is mirror coated at the
side that is pointing to the laser, and the energy reflected from
this mirror coating is folded by the polarized beam splitter and
can be measured in the detector.
[0104] The described method of calibrating such catheters also
enables real time monitoring of the ablation process, by measuring
the reflected energy in the system detector during the procedure
and informing the user about energy degradation due to fiber
damage.
[0105] Reference is now made to FIGS. 6A to 6C. When UV laser
catheters are used for debulking tissues inside the vessels, the
distal tip of the fibers may be damaged due to the shock wave that
is created because of the high absorption in the blood and in the
contrast media. In order to protect the distal tip of the catheter,
saline is injected through a guiding sheath in normal procedures.
Alternatively, the saline can be injected through the inner lumen
of the catheter, but this restricts the physician because of the
need to choose smaller guidewire than possible.
[0106] Reference is now made to FIG. 6A wherein the distal end of
laser catheter 63 is illustrated. Hollowed capillaries 65 may be
incorporated between the optical fibers 66 and allow the flow of
the saline to the point of contact of the distal tip of the
catheter 63 and the ablated tissue. The hollowed capillaries 65 may
extend from the handle to the distal tip of the catheter 63, and
the saline is injected through the proximal side of the hollowed
capillaries 65.
[0107] Reference is now made to FIG. 6B. In order to allow free
flow of saline without the restriction of the capillaries forces, a
large hollowed capillary 67 may be connected to the small and short
hollowed capillaries 65 that are placed at the distal tip of the
catheter 63. Another embodiment is illustrated in FIG. 6C. The
Saline in injected in the space wherein the optical fibers 66 are
located, between the inner tube 69 and the outer tube 68. The small
capillaries 65 are located at the distal tip of the catheter, in
between the glue 72, the inner blade 71 and the outer blade 70.
Thus the capillaries 65 enable dripping of the Saline through the
distal tip of the catheter.
[0108] While the present invention uses example from blood vessels,
the utility is relevant for other medical indications requiring
controlled resection of tissue such as Barrett's esophagus, flat
polyps' removal in the intestine or in urology and gynecology
applications such as debulking in BPH.
[0109] It is appreciated by persons skilled in the art that the
present invention is not limited by what has been particularly
shown and described hereinabove. Rather the scope of the present
invention includes both combinations and subcombinations of various
features described hereinabove as well as variations and
modifications thereto which would occur to a person of skill in the
art upon reading the above description and which are not in the
prior art.
* * * * *