U.S. patent application number 11/879278 was filed with the patent office on 2008-05-22 for air-core microwave ablation antennas.
This patent application is currently assigned to Micrablate. Invention is credited to Christopher Lee Brace, Paul F. Laeseke, Fred T. Lee, Daniel Warren van der Weide.
Application Number | 20080119921 11/879278 |
Document ID | / |
Family ID | 37495102 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080119921 |
Kind Code |
A1 |
Brace; Christopher Lee ; et
al. |
May 22, 2008 |
Air-core microwave ablation antennas
Abstract
A method and device delivers microwave power to an antenna
through a coaxial cable utilizing air or other gases as its
dielectric core. The cable includes supports made of low-loss
materials to keep the inner conductor centered in the cable, and
defining spaces therebetween for the air or gas. Channels in the
supports allow the air or gas to circulate in the cable. The gas
may be chilled or cooled to provide an addition level of heat
dissipation. The device enables delivery of large amounts of power
to tissue without undue heating of the feed cable or peripheral
tissues, and without increasing the diameter of the feeding cable
or antenna, keeping the antenna safe for percutaneous use.
Inventors: |
Brace; Christopher Lee;
(Madison, WI) ; van der Weide; Daniel Warren;
(Madison, WI) ; Laeseke; Paul F.; (Madison,
WI) ; Lee; Fred T.; (Madison, WI) |
Correspondence
Address: |
Casimir Jones, S.C.
440 Science Drive, Suite 203
Madison
WI
53711
US
|
Assignee: |
Micrablate
Middleton
WI
|
Family ID: |
37495102 |
Appl. No.: |
11/879278 |
Filed: |
July 17, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11236985 |
Sep 28, 2005 |
7244254 |
|
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11879278 |
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|
10834802 |
Apr 29, 2004 |
7101369 |
|
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11236985 |
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60679722 |
May 10, 2005 |
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60684065 |
May 24, 2005 |
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60690370 |
Jun 14, 2005 |
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60702393 |
Jul 25, 2005 |
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60707797 |
Aug 12, 2005 |
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60710276 |
Aug 22, 2005 |
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60710815 |
Aug 24, 2005 |
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Current U.S.
Class: |
607/156 |
Current CPC
Class: |
A61B 18/1815 20130101;
A61B 2018/00023 20130101; A61B 2018/00017 20130101; A61N 1/06
20130101; A61B 18/18 20130101 |
Class at
Publication: |
607/156 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Claims
1. A device for delivery of microwave power to an antenna,
comprising: a coaxial cable having air or other gas as the
dielectric core; and discrete supports integrated into the
cable.
2. The device of claim 1, further comprising flow channels in each
support.
3. A device for combined delivery of microwave power to an antenna
and cooling of the device, comprising: a co-axial cable having air
or other gas as the dielectric core; and discrete supports
integrated into the cable.
4. The device of claim 3, further comprising flow channels in
supports.
5. The device of claim 3, further comprising a hollow tube center
conductor.
6. A method for delivery of microwave power to an antenna,
comprising the steps of: defining spaces in a co-axial cable
attached to the antenna; circulating gas between the spaces in the
co-axial cable; and supplying power to the co-axial cable.
7. The method of claim 6 wherein the co-axial cable has a hollow
tube center conductor.
Description
CLAIM OF PRIORITY
[0001] This application is a Continuation-In-Part of co-pending
U.S. Non-Provisional Patent Application entitled "Triaxial Antenna
for Microwave Tissue Ablation" filed Apr. 29, 2004 and assigned
U.S. application Ser. No. 10/834,802, the entire disclosure of
which is hereby herein incorporated by reference.
[0002] This application further claims priority to U.S. Provisional
Patent Applications entitled "Segmented Catheter for Tissue
Ablation" filed May 10, 2005 and assigned U.S. application Ser. No.
60/679,722; "Microwave Surgical Device" filed May 24, 2005 and
assigned U.S. application Ser. No. 60/684,065; "Microwave Tissue
Resection Tool" filed Jun. 24, 2005 and assigned U.S. application
Ser. No. 60/690,370; "Cannula Cooling and Positioning Device" filed
Jul. 25, 2005 and assigned U.S. application Ser. No. 60/702,393;
"Intralumenal Microwave Device" filed Aug. 12, 2005 and assigned
U.S. application Ser. No. 60/707,797; "Air-Core Microwave Ablation
Antennas" filed Aug. 22, 2005 and assigned U.S. application Ser.
No. 60/710,276; and "Microwave Device for Vascular Ablation" filed
Aug. 24, 2005 and assigned U.S. application Ser. No. 60/710,815;
the entire disclosures of each and all of these applications are
hereby herein incorporated by reference.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0003] This application is related to co-pending U.S.
Non-Provisional Patent Application entitled "Triaxial Antenna for
Microwave Tissue Ablation" filed Apr. 29, 2004 and assigned U.S.
application Ser. No. 10/834,802; and to U.S. Provisional Patent
Applications entitled "Segmented Catheter for Tissue Ablation"
filed May 10, 2005 and assigned U.S. application Ser. No.
60/679,722; "Microwave Surgical Device" filed May 24, 2005 and
assigned U.S. application Ser. No. 60/684,065; "Microwave Tissue
Resection Tool" filed Jun. 24, 2005 and assigned U.S. application
Ser. No. 60/690,370; "Cannula Cooling and Positioning Device" filed
Jul. 25, 2005 and assigned U.S. application Ser. No. 60/702,393;
"Intralumenal Microwave Device" filed Aug. 12, 2005 and assigned
U.S. application Ser. No. 60/707,797; "Air-Core Microwave Ablation
Antennas" filed Aug. 22, 2005 and assigned U.S. application Ser.
No. 60/710,276; and "Microwave Device for Vascular Ablation" filed
Aug. 24, 2005 and assigned U.S. application Ser. No. 60/710,815;
the entire disclosures of each and all of these applications are
hereby herein incorporated by reference.
FIELD OF INVENTION
[0004] The present disclosure relates generally to the field of
tissue resection, coagulation, and hemostasis, and delivery of
microwave energy to tissue. Specifically, the present disclosure
relates to a method and device for the delivery of microwave power
to an antenna through a coaxial cable utilizing air or other gases
as its dielectric core.
BACKGROUND
[0005] Use of energy to ablate, resect or otherwise cause necrosis
in diseased tissue has proven beneficial both to human and to
animal health. Microwave ablation and hyperthermia are
well-established techniques to heat tumors to the point of
necrosis. Larger zones of necrosis and shorter treatment times may
be realized by applying larger powers to the antenna. Antennas used
to deliver energy at microwave frequencies (300 MHz-300 GHz) to
tissue typically require a coaxial cable to feed energy to the
antenna. A coaxial antenna is an antenna created from a coaxial
transmission line--an electromagnetic structure whereby an inner
conductor wire, a dielectric core and outer conductor wire share a
common axis. Current coaxial antenna designs use a polymer [e.g.,
polytetrafluoroethylene (PTFE)] as the dielectric core. Small cable
and antenna diameters are required to ensure the procedure is
minimally-invasive and safe.
[0006] Limitations of the above techniques center on the power
rating and diameter of the coaxial cable used to feed the antenna,
as well as microwave losses inside the coaxial cable dielectric
core. An approximately exponential relationship between cable
diameter and power rating exists; that is, as cable diameter
decreases, the amount of power that cable may handle without
failure decreases exponentially. Losses inside the coaxial cable
dielectric core cause heat to be generated when large microwave
powers are applied. This causes undue heating of the feeding cable,
which causes unwanted necrosis of tissue near the feed cable and is
undesirable for patient safety. Thus, the antenna input power is
limited by the amount of power the feeding cable may handle without
failure and by peripheral heating caused by the feed cable. This,
in turn, limits the size of the zone of necrosis obtained in a
given time. For this reason, current microwave ablation and
hyperthermia antennas are limited in their ability to be operated
at high powers and still be safe for percutaneous use.
[0007] Therefore, there is a need for a method and device for the
delivery of microwave power to tissue which overcomes the above
identified disadvantages and limitations of, and which represents
an improvement over current coaxial antenna designs. The present
disclosure fulfills this need.
SUMMARY
[0008] This present disclosure relates to a method and device for
the delivery of microwave (e.g. approximately 300 MHz and higher
frequencies) power to an antenna through a coaxial cable having air
or other gases (CO.sub.2, argon, helium, etc.) as the dielectric
core. The device uses small mechanical supports made of low-loss
materials (e.g., PTFE) to keep the inner conductor centered in the
cable. The device enables delivery of large amounts of power to
tissue without undue heating of the feed cable or peripheral
tissues. This is accomplished without increasing the diameter of
the feeding cable or antenna, which keeps the antenna safe for
percutaneous use.
[0009] The supports and antenna may contain holes or channels to
allow passage of circulating gases. The advantage of using gases
for this purpose is that they have a low viscosity (to pass easily
through the support and antenna channels), a very low conductivity,
and the circulating gas can help cool the antenna. Circulation may
be achieved from an external pump or compressor operatively
connected with the cable. The gases may be chilled or cooled before
entering the cable to provide an addition level of heat
dissipation.
[0010] Accordingly, it is one of the objects of the present
disclosure to provide a method and device for the delivery of
microwave power to tissue.
[0011] It is a further object of the present invention to provide
an improved co-axial cable for delivery of microwave energy to an
antenna.
[0012] It is another object of the present invention to provide a
coaxial cable utilizing air or other gases as its dielectric
core.
[0013] Numerous other advantages and features of the disclosure
will become readily apparent from the following detailed
description, from the claims and from the accompanying drawings in
which like numerals are employed to designate like parts throughout
the same.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A fuller understanding of the foregoing may be had by
reference to the accompanying drawings wherein:
[0015] FIG. 1 is a longitudinal, cross-sectional view of the
co-axial cable of the preferred embodiment of the present
disclosure, showing the arrangement of the supports within the
coaxial structure.
[0016] FIG. 2 is an enlarged longitudinal, cross-sectional view of
a portion of the co-axial cable of the preferred embodiment of the
present disclosure, and illustrating an alternate embodiment of the
supports having channels therethrough.
[0017] FIG. 3 is an enlarged axial, cross-sectional view the
co-axial cable of the preferred embodiment of the present
disclosure, and illustrating one embodiment of the arrangement of
the channels in the supports.
[0018] FIG. 4 is a longitudinal, cross-sectional view of an
alternate embodiment of the present disclosure.
DESCRIPTION OF DISCLOSED EMBODIMENT(S)
[0019] While the invention is susceptible of embodiment in many
different forms, there is shown in the drawings and will be
described herein in detail one or more embodiments of the present
disclosure. It should be understood, however, that the present
disclosure is to be considered an exemplification of the principles
of the invention, and the embodiment(s) illustrated is/are not
intended to limit the spirit and scope of the invention and/or the
claims herein.
[0020] With reference to the drawings, the co-axial cable of the
preferred embodiment of the present disclosure is shown. It should
be understood that the cable can be of any suitable length, and the
drawings figures are not intended to limit the length of the cable
to the specific length illustrated or any specific length. Instead,
it should be understood that only a representative portion or
section of cable is illustrated.
[0021] FIG. 1 illustrates a semi-rigid coaxial cable, preferably
constructed of copper or silver, utilizing air or other gas as the
dielectric. The cable's inner conductor 2 is held with respect to
the outer conductor 1 by supports 4 of length L2, separated by a
distance L1. The length L2 is sufficiently short (.about.1 mm) to
be much less than the wavelength inside the cable. L1 is as long as
possible (.about.5-10 cm) to keep the inner conductor 2 centered
with respect to the outer conductor 1. The gas dielectric 3 fills
the space between each support. The cable can be chosen from
commercially-available standards, but will be designed with a
characteristic impedance of about 50 .OMEGA..
[0022] It should be understood that the cable is connectorized or
fixed to another feed cable on the proximal end 5, for connection
with a power supply. It should also be understood that an antenna
is connected or fixed to the distal end 6 of the cable in any
suitable manner.
[0023] Referring now to FIG. 2, an alternate embodiment of the
supports 4 is illustrated. As can be seen, one or more channels 7
are provided in the supports 4, allowing for the air or gas 3 to
flow between the spaces existing between each support 4. The
number, pattern and size of the channels may be varied with gas
flow requirements, gas viscosity or heating rate.
[0024] FIG. 3 illustrates one example of the arrangement of
channels 7 in the support 4. As can be seen in the embodiment
illustrated in FIG. 3, six channels are generally equally spaced
around the inner conductor 2, allowing for the circulation of air
or other gas within the feed cable. As should be understood, an
external pump or compressor can be operatively connected with the
cable to circulate the air or gas. The air or gases may be chilled
or cooled before entering the cable, or otherwise during
circulation, to provide an addition level of heat dissipation.
[0025] FIG. 4 is a longitudinal, cross-sectional view of another
embodiment of the present disclosure, depicting a hollow center
conductor with holes or channels for both introduction and exhaust
of cooling gasses. The return flow of cooling gasses is through the
interstitial space between center conductor and co-axial outer
conductor. Also indicated are the distal and proximal joints
between solid center conductors and the hollow center
conductor.
[0026] As can be seen in FIG. 4, outer conductor 12 houses a
dielectric core 13 for flow of air or other gasses, and further
houses a center conductor 14, which is a hollow tube to conduct
cooling gas along its length from one or more holes or channels at
its proximal end 15 along its length to one or more holes or
channels where the gas exits at its distal end 16. This exit 16
could also function as a venturi to allow for expansion of the gas
as it changes pressure, further enhancing the cooling via the
Joule-Thompson effect at the distal end of the co-axial cable. The
gas is returned to the distal end through the core 13, and it exits
through one or more holes or channels in the outer conductor 17. A
non-conducting plug or support 18 at the distal end serves to
support the center conductor, prevent the flow of cooling gas to
the antenna at the distal end 20, and supports the joint between
the antenna and the hollow-tube center conductor. A shaped and
ported non-conducting plug or support 19 at the proximal end serves
to introduce cooling gasses at 15, support the center conductor,
prevent the flow of cooling gas to the solid center conductor at
the proximal end 21, and support the joint between the solid center
conductor and the hollow-tube center conductor.
[0027] It is to be understood that the embodiment(s) herein
described is/are merely illustrative of the principles of the
present invention. Various modifications may be made by those
skilled in the art without departing from the spirit or scope of
the claims which follow. For example, other applications of the
co-axial cable disclosed herein are contemplated.
* * * * *