U.S. patent application number 14/032315 was filed with the patent office on 2014-01-16 for heating/sensing catheter apparatus for minimally invasive application.
This patent application is currently assigned to Meridian Medical Systems, LLC. The applicant listed for this patent is Meridian Medical Systems, LLC. Invention is credited to Robert C. Allison.
Application Number | 20140018697 14/032315 |
Document ID | / |
Family ID | 48190594 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140018697 |
Kind Code |
A1 |
Allison; Robert C. |
January 16, 2014 |
HEATING/SENSING CATHETER APPARATUS FOR MINIMALLY INVASIVE
APPLICATION
Abstract
Catheter apparatus comprises a coaxial cable having proximal and
distal ends. The cable includes a hollow center conductor, an outer
conductor and an electrically insulating layer between the
conductors. An antenna is at the distal end of the cable, and a
diplexer is connected to the cable, the diplexer including a
transmit path for connecting the antenna to a transmitter which
transmits first frequency signals and a receive path for connecting
the antenna to a receiver which detects second frequency signals
the diplexer isolating the signals on the two paths from one
another. A transmission line connects the cable to the diplexer,
the transmission line having a segment with a tubular inner
conductor one end of which is connected to the center conductor and
a second end of which is adapted for connection to a coolant
source, the center and inner conductors forming a continuous
coolant pathway.
Inventors: |
Allison; Robert C.; (Rancho
Palos Verdes, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Meridian Medical Systems, LLC |
Portland |
ME |
US |
|
|
Assignee: |
Meridian Medical Systems,
LLC
Portland
ME
|
Family ID: |
48190594 |
Appl. No.: |
14/032315 |
Filed: |
September 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14017812 |
Sep 4, 2013 |
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14032315 |
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13709434 |
Dec 10, 2012 |
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14017812 |
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61635348 |
Apr 19, 2012 |
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Current U.S.
Class: |
600/549 |
Current CPC
Class: |
A61B 5/01 20130101; A61B
2018/00791 20130101; A61B 2018/00029 20130101; A61B 2018/00577
20130101; A61B 18/18 20130101; A61N 5/025 20130101; A61B 18/1815
20130101; A61N 1/403 20130101; A61N 5/045 20130101; A61B 2018/1861
20130101; A61B 2018/00011 20130101 |
Class at
Publication: |
600/549 |
International
Class: |
A61B 5/01 20060101
A61B005/01 |
Claims
1. Catheter apparatus comprising an elongated flexible coaxial
cable having proximal and distal ends, said cable including a
hollow center conductor, an outer conductor and an electrically
insulating layer in an annular space between said conductors; an
antenna at the distal end of the cable; a diplexer including a
transmit path for connecting the antenna to a transmitter which
transmits signals of a first frequency and a receive path for
connecting the antenna to a receiver which detects signals of a
second frequency, said diplexer isolating the signals on the two
paths from one another; a transmission line connecting the cable to
the diplexer, said transmission line including a segment with a
tubular inner conductor one end of which is connected to the center
conductor of the cable and a second end of which is adapted for
connection to a coolant source, said center conductor and said
inner conductor forming a continuous coolant pathway.
2. The apparatus defined in claim 1 wherein said receive path
includes a first electrical filter.
3. The apparatus defined in claim 1 and further including an
impedance-matching transformer in series with the cable and the
transmission line.
4. The apparatus defined in claim 1 wherein the cable outer
conductor comprises braided conductive strands.
5. The apparatus defined in claim 1 wherein the cable insulating
layer comprises a flexible winding of one or more dielectric
strands having multiple fluid flow paths therebetween.
6. The apparatus defined in claim 1 wherein said antenna comprises
an extension of the center conductor beyond the outer conductor and
the insulating layer.
7. The apparatus defined in claim 6 wherein said extension is
tubular and continues said fluid pathway to the outside.
8. The apparatus defined in claim 1 wherein said antenna is
connected to the center conductor via a connection device at the
distal end of the cable.
9. The apparatus defined in claim 8 wherein the connection device
defines a fluid path between the interior of the center conductor
and the outside.
10. The apparatus defined in claim 1 wherein the antenna is
flexible.
11. The apparatus defined in claim 1 and further including a
stand-off device adjacent to the distal end of the cable for
centering said antenna in a body passage.
12. The apparatus defined in claim 1 and further including one or
more temperature detectors positioned in said fluid pathway for
monitoring coolant temperature at one or more locations
therealong.
13. The apparatus defined in claim 1 and further including a
microwave or RF transmitter connected to said transmit path.
14. The apparatus defined in claim 1 and further including a
coolant source connected to said second end of the tubular inner
conductor of said transmission line segment.
15. The apparatus defined in claim 1 wherein said cable and said
diplexer are formed as a unitary disposable first part designed for
connection both electrically and mechanically to a mating reusable
second part containing microwave receiver.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of patent application
Ser. No. 14/017,812 filed on Sep. 4, 2013 entitled HEATING/SENSING
CATHETER APPARATUS FOR MINIMALLY INVASIVE APPLICATIONS (Cesari and
McKenna LLP Docket No. 102015-0053C1), which is a continuation of
patent application Ser. No. 13/709,434, filed on Dec. 10, 2012,
having the same title (Cesari and McKenna LLP Docket No.
102015-0053U), which claims priority to Provisional Patent
Application Ser. No. 61/635,348 filed on Apr. 19, 2012 entitled
INTEGRATED MICROWAVE CATHETER AND CABLE (Cesari and McKenna LLP
Docket No. 10215-0053R).
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to medical catheter apparatus for
minimally is invasive applications. It relates especially to
catheter apparatus which utilizes electromagnetic radiation to
simultaneously controllably heat, and detect the temperature of,
fluid or tissue in a human or animal body. The apparatus includes
an antenna catheter which is essentially a long flexible cable
having a distal end or probe containing an antenna. In order to
perform its function, the catheter must be small in diameter and
flexible so that it can be threaded along blood vessels and other
natural passages in the body to position the antenna at a selected
target site.
[0004] By placing the catheter probe at the region of interest in
the body, one may warm blood and/or ablate tissue to treat tumors,
cardiac arrhythmias, renal disease, benign prosthetic hyperplasia
(BPH) and the like.
[0005] The proximal end of the catheter cable may be connected to
an external control unit which includes a transmitter for
transmitting electromagnetic energy via the cable to the antenna in
the catheter tip in order to heat fluid or tissue, and a receiver
which detects thermal emissions picked up by the antenna reflecting
the temperature of that fluid or tissue. The receiver outputs a
corresponding temperature signal to control a display which
displays that temperature. The same signal may also be used to
control the transmitter to maintain a selected heating profile.
[0006] For apparatus detecting thermal emissions in the microwave
range which is of primary interest here, the receiver is usually a
radiometer. Every component of a radiometer generates noise power
that contributes to the overall noise of the system. Therefore, the
total radiometer output signal contains not only noise received by
the antenna, but also noise generated within the apparatus itself.
Such variations within the apparatus can produce output signal
fluctuations that are sometimes greater than the useful signal
level to be measured. To overcome these gain variations, Dicke
developed the common load comparison radiometer which utilizes a
switch, aka a Dicke switch, to alternately connect the antenna,
(picking up the unknown thermal radiation) and a reference
temperature (which may be a stable noise source or a temperature
sensor within the catheter). This configuration greatly reduces the
effects of short-term gain fluctuations in the radiometer. More
particularly, the switch provides a mechanism to allow both the
reference and the unknown signals to pass through the apparatus
essentially at the same time relative to the expected gain drift in
the radiometer's amplifiers such that any drifting gain will be
applied equally to both the antenna and reference signals.
[0007] Since the radiometer input is switched at a constant rate by
the Dicke switch between the antenna and the constant-temperature
load, the switch-demodulated RF signal should, therefore, be
inserted at a point prior to RF amplification in the radiometer and
as close to the antenna as possible. Any component or transmission
line located between the unknown temperature being detected by the
antenna and the Dicke switch can introduce an error. One such error
source is the relatively long cable which connects the antenna in
the catheter tip to the external radiometer.
[0008] In other words, the temperature of that cable contributes to
the temperature measurement. The cable temperature is usually not
known and varies along the length of the cable. That portion of the
cable within the body will be at body temperature, whereas the
segment of the cable outside the body will be at room temperature.
All of these parameters may vary with the flexing of the cable and
the depth of its insertion into the body. Also, when the apparatus
includes a transmitter to heat fluid or tissue, some of the
transmitter power (about 30 watts) is absorbed by the cable causing
the cable to be heated. If the loss in the cable is, say, 3 dB
(which could easily be the case), one half of the antenna noise
power may come from the desired tissue or fluid volume being
examined at the target site and the rest results from the cable.
Thus, all errors common to both measurements, i.e., the unknown
temperature and the reference temperature, are cancelled in a
Dicke-type radiometer. However, any changes or errors between the
unknown and the Dicke switch affect only the unknown temperature
measurement and are thus not common to both measurement paths.
[0009] Accordingly, to achieve accurate temperature measurement, it
is highly desirable to minimize the losses between the antenna and
the radiometer in order to improve the performance and reliability
of the overall apparatus.
THE PRIOR ART
[0010] One way to minimize such losses and unwanted noise is to
minimize the distance between the antenna and the radiometer by
locating the radiometer in the catheter, thus essentially
eliminating the cable in the receive path as described in U.S. Pat.
No. 7,769,469. However, that solution rigidifies the catheter probe
and places a lower limit on its diameter making it more difficult
to thread the catheter along narrower blood vessels in the body and
around sharp turns in such vessels and in other body passages. It
also requires that wires extend along the cable to the
radiometer.
[0011] Thus, there is a need for a microwave heating/sensing
catheter apparatus of this general type whose catheter is small and
flexible enough to be navigated along such narrower and tortuous
paths in the body, yet contributes minimal noise to the overall
system.
SUMMARY OF THE INVENTION
[0012] Accordingly, it is an object of the present invention to
provide an improved microwave heating/sensing catheter apparatus
for minimally invasive applications.
[0013] Another object of the invention is to provide apparatus of
this type whose antenna catheter is quite flexible and has a
minimum diameter so that it can be navigated along small blood
vessels and other irregular passages in a human or animal body.
[0014] A further object of the invention is to provide such
apparatus having a reduced sensitivity to unwanted noise so that
the apparatus can have an external radiometer.
[0015] Yet another object of the invention is to provide apparatus
of this type whose antenna catheter has minimal insertion loss.
[0016] Other objects will, in part, be obvious and will, in part,
appear hereinafter.
[0017] The invention accordingly comprises the features of
construction, combination of elements and arrangement of parts
which will be exemplified in the constructions hereinafter set
forth, and the scope of the invention will be indicated in the
claims.
[0018] In general, my catheter apparatus comprises an antenna
catheter for is insertion into a natural body passage, e.g., the
vasculature, cardio-renal system, gastrointestinal tract, etc. of a
human or animal body. When the catheter is to be threaded along
narrow blood vessels, the catheter, especially its leading end
portion, or probe should have a small diameter and be very
flexible. Therefore, a diplexer and radiometer cannot be
incorporated into the catheter probe as disclosed in the above
patent. Rather, the antenna in the probe is connected to a
transmitter and a Dicke-type radiometer located in an external
control unit by a special, very low-loss flexible cable to be
described later.
[0019] On the other hand, when the particular application does not
demand such small size and flexibility, the radiometer and/or
diplexer may be located anywhere along the cable either inside or
outside the body or even in the probe.
[0020] When the transmitter is operative, it delivers
electromagnetic energy of a first frequency via the cable to the
antenna which radiates energy into the adjacent body tissue and/or
fluid to heat same. That same antenna also picks up thermal
emissions of a higher frequency from that tissue and/or fluid and
delivers a corresponding signal via the cable to the radiometer
which thereupon outputs a temperature signal indicative of the
temperature of the heated tissue and/or fluid. Thus, the apparatus
may be used to heat a fluid, e.g. blood, following a selected
heating profile, and to heat or ablate tissue to treat tumors, BPH
and various renal and cardio-renal diseases by modulating or
denervating neurofibers.
[0021] To enable the catheter to heat (transmit) and detect
temperature (radiometrically sense) simultaneously, a passive
diplexer is provided at the proximal end is of the cable, the cable
and diplexer forming a unique assembly which also allows for
cooling of the cable. That is, to minimize component insertion
loss, the cable/diplexer assembly provides a reduced cable
impedance as well as a fluid path for a coolant delivered from the
control unit to the catheter.
[0022] Even when the catheter is to be introduced into larger body
passages and thus may include an internal diplexer and radiometer
as described in the above patent, it is desirable that the catheter
apparatus include this special cable to prevent excessive heating
of the cable by the transmitter.
[0023] As will be described in more detail later, the cable has a
hollow center conductor and a relatively low cable impedance, e.g.
30 ohms, compared to the usual 50 ohms. Lowering the cable
impedance lowers its insertion loss because, for a given cable
outside diameter, the cable's center conductor may be larger, thus
increasing its conducting surface area and lowering the current
density in that conductor. The hollow center conductor also
provides a passage for the aforementioned coolant. The cable's
center conductor is surrounded by insulation in the form of one or
more filament strands wrapped around the center conductor. These
strand(s) improve cable flexibility, while creating spaces that
reduce the cable's dielectric constant and thus its insertion loss.
These spaces may also provide a return path for a gaseous coolant
whose temperature may be controlled to maintain the center
conductor at a constant, safe temperature regardless of the level
of applied power to the antenna in the catheter thereby to enhance
the radiometric sensing capability of the apparatus.
[0024] As we shall see, the distal or probe end of the cable may be
designed to is allow a gaseous coolant to be re-circulated through
the catheter or to allow a liquid coolant to be expelled therefrom
into a blood vessel or other body passage, e.g. for irrigation.
Also, the catheter antenna per se may be attachable to the distal
end of the cable to enable the cable to be terminated by
different-type antennas. The attachable antenna also allows the
cable/diplexer assembly with its lower-impedance cable to be tested
by replacing the antenna with a second cable/diplexer assembly and
using a standard 50 ohm reflectometer and standard 50 ohm
connectors as will be described later.
[0025] Thus, the present catheter apparatus with its unique
cable/diplexer assembly has a minimum sensitivity to unwanted
noise, yet its catheter is able to be navigated along, and around
turns in, small blood vessels and other body passages. Therefore,
it should find wide application in the non-invasive treatment by
heating and ablation of many serious human and animal diseases and
abnormalities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention description below refers to the accompanying
drawings, in which:
[0027] FIG. 1 is a diagrammatic view of heating/sensing catheter
apparatus incorporating the invention;
[0028] FIG. 2A is a sectional view with parts shown in elevation,
on a larger scale, showing the cable/diplexer assembly of the FIG.
1 apparatus in greater detail;
[0029] FIG. 2B is a sectional view on a larger scale taken along
line 2B-2B of FIG. 2A;
[0030] FIG. 3 is a fragmentary sectional view showing a portion of
a second cable/diplexer assembly embodiment for use in the FIG. 1
apparatus;
[0031] FIG. 4 is a diagrammatic view of an assembly for testing the
FIG. 3 cable/diplexer is assembly;
[0032] FIG. 5 is a view similar to FIG. 1 of an apparatus
embodiment with a disposable catheter cable and handle, and
[0033] FIG. 6 is a similar view of still another apparatus
embodiment.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0034] Referring to FIG. 1 of the drawings, the present catheter
apparatus comprises an antenna catheter shown generally at 10
connected by a cable 12 to an external control unit 14. Catheter 10
includes a relatively long, e.g. 115 cm., very flexible cable 16
which includes a center conductor 18 extending the entire length of
the cable and forming an antenna A at the distal or probe end of
the cable. The illustrated antenna A is a monopole, but it may have
other forms such as a helix as in U.S. Pat. No. 5,364,336, whose
contents hereby is incorporated herein by reference.
[0035] In accordance with the invention, center conductor 18 is
formed as a thin-wall, e.g. 0.004 inch, tube of soft copper so that
it is quite flexible and defines a fluid pathway 19 which extends
the entire length of the cable. For example, that center conductor
may have an OD of 0.024 inch. The larger diameter, hollow center
conductor is minimizes the current density thereon for a given
cable diameter. This, in turn, minimizes the cable impedance and
thus its insertion loss.
[0036] The proximal end of cable 16 may connect to a passive
diplexer indicated at 22 which allows catheter 10 via antenna A to
simultaneously emit electromagnetic energy of a first frequency
while picking up thermal radiation of a second frequency. Thus,
when cable 16 is navigated along a blood vessel or other body
passage or within a catheter guide to position antenna A at a
selected target site in a body, catheter 10 may be activated by
control unit 14 to heat fluid and/or tissue at the target site to
accomplish the desired objective, while at the same time sensing
the temperature of the heated fluid and/or tissue thereby enabling
control unit 14 to display that temperature and control the heating
process. Also as we shall see, the fluid pathway 19 which extends
from the catheter through diplexer 22 and along cable 12 to a
coolant source in control unit 14 allows a coolant to be flowed
along cable 16 to maintain the center conductor 18 thereof at a
relatively constant, low temperature. As we shall see, pathway 19
may include a return path from the cable to the coolant source in
the event that the coolant is recirculated.
[0037] Referring now to FIGS. 2A and 2B, in addition to the hollow
center conductor 18, cable 16 has a tubular outer conductor 26
preferably made of metal braid so that it is electrically
conductive and quite flexible. The outer conductor 26 may have an
ID in the order of 0.042 inch and is shorter than conductor 18 so
that a projecting distal end segment 18a of conductor 18 forms
antenna A. A hollow cap 28 of a dielectric material is provided at
the distal or probe end of the catheter to cover antenna A and is
provide the probe with a rounded tip. The cap interior, if closed,
connects the interior of the center conductor to the annular space
between the two conductors. Preferably, the entire length of outer
conductor 26 is covered by a layer or jacket 34 of a suitable
dielectric material.
[0038] As usual with coaxial cables of this general type, the
annular space between conductors 18 and 26 may be filled with a
dielectric material. In this case, to maximize the flexibility of
the cable while dielectrically loading the cable, the insulation is
composed of one or more dielectric strands 40, e.g., Teflon.RTM.
filament, wound around the center conductor 18. A given cable may
have many strands 40 or as few as one, depending on the
characteristics desired for that cable. In addition to providing
flexibility, the filament creates spaces 41 between the filament
turns that reduce the dielectric constant of the cable and give it
a reduced impedance Z as follows:
Z 0 = 138 log 10 D d = 30 ohms ##EQU00001##
[0039] where:
[0040] D=outer conductor ID=0.042 in.
[0041] d=center conductor OD=0.024 in.
[0042] .di-elect cons.=dielectric constant=1.25
[0043] As will be described later, the fluid pathway 19 may extend
through a hole 28a in the cap 28 as shown in FIG. 2A so that a
liquid coolant may be expelled from the catheter or the cap may be
closed and a gaseous coolant recirculated back to control unit 14
via a return path constituted by the spaces 41 between the
dielectric strand(s) 40.
[0044] As shown in FIG. 2A, diplexer 22 includes a housing 42
having an end wall 42a. The proximal end of cable 16 passes through
an opening 44 in that wall and is connects to one, i.e. the left,
arm 46a of a T-stub transmission line shown generally at 46 which
may be dielectrically loaded (not shown for clarity). Transmission
line 46 includes a hollow center conductor 48 which receives and is
connected to a protruding end 18b of cable conductor 18. Thus,
conductor 48 continues the fluid pathway 19 from the cable.
Transmission line 46 also has a T-shaped outer conductor 52 whose
left arm 52a surrounds and connects to cable conductor 26 inside
housing 42. The other, i.e. right, arm 46b of transmission line 46
extends to an interior wall 42b of housing 42 and the center
conductor 48 thereof passes through a feedthrough 49 in wall 42b.
The spacing of the two conductors 48, 52 of the transmission line
46 is maintained by a pair of dielectric spacers 54, 54.
[0045] The leg 46c of the T-stub transmission line 46, including a
solid center conductor segment 48c and an outer conductor segment
52c, is connected by way of a low pass or band pass filter 56 to a
coaxial connector 58 mounted to a side wall 42c of housing 42. The
filter 56 may be a conventional printed circuit or a short length
of coax (tube filter) which is cut off at the receive frequency. In
any event, filter 56 is designed to pass the transmit frequency and
block the receive frequency. Thus, transmission line 46 helps to
separate the different frequency signals to and from antenna A.
More particularly, it forms a quarter wave stub (.lamda..sub.T/4)
while also providing a matched 90.degree. bend for a transmitter
(heating) signal applied to connector 58 as will be described.
[0046] Preferably, a transformer indicated at 62 is provided in the
left arm 46a of the transmission line to step up the 30 ohm cable
16 impedance to 50 ohms in the transmission line 46 so that the
diplexer 22 can be tested, as will be described, using is
conventional connectors and test equipment designed for a 50 ohm
cable. This impedance transformation may be implemented by stepping
the outer conductor arm 52a, e.g. in two steps as shown in FIG. 2A,
or by stepping the inner conductor.
[0047] Still referring to FIG. 2A, the housing interior wall 42b
along with a housing end wall 42d, segments of the housing side
walls 42c and 42e, and top wall 42f and bottom wall 42g form a
waveguide indicated generally at 64 which may be filled with a
dielectric material 66 to minimize its size. The right end of the
transmission line center conductor 48 extending through feedthrough
49 is connected to a larger diameter waveguide probe 68 adjacent
one narrower wall of waveguide 64, while a waveguide-to-cable
transition 74 adjacent the opposite narrower wall projects into the
waveguide 64 from a connector 76 mounted to the outside of housing
end wall 42d which constitutes a broader wall of the waveguide. As
will be seen, that connector may couple the temperature sensing
signal from antenna A to a radiometer in control unit 14 (FIG. 1).
The waveguide 64 constitutes a high-pass filter that passes the
temperature sensing frequency, while blocking the heating
frequency. It also provides a DC block, preventing center
conductors 18, 48 from coupling directly to a patient. Thus, the
combination of this filter and the transmission line 46 enables the
diplexer to separate the two signals.
[0048] The waveguide probe 68 is unique in that it provides a
coolant path as well as a microwave transition. More particularly,
probe 68 is formed with an axial passage 78 which is countersunk at
78a to accept an end segment of a tube or conduit 80 of a
dielectric material. Tube 80 extends to a connector 84 on housing
end wall 42d where it may be connected to a comparable tube 86
extending along cable 12 to control unit 14. Alternatively, of
course, tubes 80 and 86 may be a single length of tubing. Thus, is
probe 68 and tubes 80, 86 provide an extension of the pathway 19 in
cable 16. With the inclusion of an injection port 86a in tube 86,
the diplexer 22 can provide a path to cable 16 for the injection of
a contrast agent to track the position of the catheter via X-ray
imaging during a treatment procedure. The injection port 86a will
also allow for the insertion of one or more thermocouples T (FIG.
2A) or other type of temperature sensor each having a lead T.sub.L
to monitor the temperature of a coolant flowing along fluid pathway
19.
[0049] As shown in FIG. 1, the control unit 14 includes a
transmitter 92 which delivers power at a microwave heating
frequency, e.g. 2.45 GHz to the antenna catheter 10 by way of a
cable component 12a connected to connector 58. RF heating may also
be employed, e.g. at a frequency of 500 KHz. In either event,
transmitter 92 is controlled by a processor 94 which receives
instructions via control buttons on a control panel 96 in unit 14.
Unit 14 also includes a radiometer 98 which receives the
temperature-indicating signal from antenna catheter 10 via a cable
component 12b connected to connector 76. The radiometer may have a
center frequency of, say, 4 GHz. In order to minimize cable losses
between antenna A and the radiometer, the radiometer may be located
close to diplexer 22 in an extension of housing 42 as shown in
phantom at 98' in FIG. 1 or in cable 12b. In either event, the
signal from radiometer 98, 98' is conditioned by an amplifier 102
and routed to processor 94 which may process that signal to control
a display 104 which thereupon displays, in real time, the
temperature of the fluid and/or tissue being probed by catheter 10.
Of course, display 104 can also display other parameters related to
the proper operation of the apparatus such as transmitter output
power, reflected power, catheter cable temperature, elapsed time,
etc.
[0050] Unit 14 also includes a coolant source 108 controlled by
processor 94 to deliver coolant via tube 86 in cable 12 to antenna
catheter 10. For some applications, the coolant may be a liquid,
e.g. 0.9% saline, in others, the coolant may be a de-watered gas
which has the same microwave characteristics as air, e.g. nitrous
oxide. The coolant flows along tube 86 to the fluid pathway 19 in
center conductors 18, 48. As the coolant flows along the cable, it
maintains the conductors 18 and 48 at a substantially constant
relatively low temperature so that they have a relatively low loss
regardless of the level of power delivered by transmitter 92.
Still, cable 16 has a minimum outside diameter and is quite
flexible due to its tubular inner conductor 18, braided outer
conductor 26 and intervening spiral dielectric winding strand(s)
40. If the coolant is a liquid, the pathway 19 may extend through a
hole 28a in cap 28 as shown in FIG. 2A and irrigate the probed body
passage. If the coolant is a gas, the cap may be closed by blocking
hole 28a, and the coolant returned to source 108 along a return
path provided by a passage from the interior of center conductor 18
to the spaces 41 between strands 40 in cable 16 and pathways (not
shown) along diplexer 46 and cable 12 (FIG. 1). If a liquid coolant
is to be returned along the cable and not expelled into the probed
body passage, that may be done via a conduit extending between
outer conductor 26 and jacket 34 or between the jacket and the
catheter introducer or guide (not shown) placed in the blood vessel
or other body passage prior to insertion of the catheter.
[0051] To use the catheter apparatus, a surgeon may insert the
probe end of cable 16 into a patient's vasculature or other body
passage using a conventional introducer. To facilitate navigating
the cable to position its antenna A at a selected target site, a
contrast agent may be injected, as needed, into the cable's fluid
pathway 19 by way of the is injection port 86a or the agent may be
added to the coolant supplied by source 108. In either event, the
position of the catheter probe may be tracked using a fluoroscope
or other X-ray apparatus to position the cable's antenna A at the
target site. If desired, the catheter may include a stand off or
centering device of a dielectric material shown in phantom at S in
FIG. 1 such as the one disclosed in patent U.S. Pat. No. 6,210,367,
the entire contents of which is hereby incorporated herein by
reference. This allows the antenna A to ablate tissue in a
360.degree. pattern around the body passage and not just at a
single contact point. Once the catheter is in place, the processor
94, following instructions input at control panel 96, may cause
coolant source 108 to pump coolant through tube 86 to the pathway
19 in the cable/diplexer assembly 10 to maintain the cable's center
conductor 18 and the diplexer's center conductor 48 at a selected
relatively low temperature to prevent cable heating due to the
power applied by transmitter 92. Since the coolant pathway 19 in
the catheter 10 is in the microwave receive path, receiver
sensitivity is optimized.
[0052] Processor 94 also activates transmitter 92 so that power is
delivered via cable component 12a, diplexer 22 and center conductor
18 to antenna A at the probe end of the cable. Antenna A radiates
electromagnetic energy at a first frequency, e.g. 2.45 GHz, into
the adjacent fluid and/or tissue thereby heating same. At the same
time, antenna A picks up thermal emission of a second frequency,
e.g. 4 GHz, from that fluid and/or tissue and delivers a
corresponding signal via conductor 18, diplexer 22 and cable
component 12b to radiometer 98 in control unit 14. That signal is
detected by the radiometer and applied to processor 94 to control
display 104 which thereupon displays that temperature. Processor 94
may also use that temperature signal to control transmitter 92 to
follow a selected heating profile or to maintain the targeted fluid
and/or tissue at the is desired temperature to achieve a desired
result, e.g., warm blood, ablate tissue, denervate neural fibers,
etc. All the while, the coolant in fluid pathway 19 maintains the
segments of the center conductor 18 of cable 16 both inside and
outside the patient at a substantially constant temperature so that
the insertion loss of the cable remains low-loss constant
throughout the procedure.
[0053] As noted above, the temperature sensors T monitor the center
conductor 18 temperature at various points along its length. The
output(s) of the thermocouple(s) on lead(s) T.sub.L are applied to
processor 94 to enable the processor to control coolant source 108
to keep the conductor at a selected temperature, which temperature
may be displayed by display 104. Having the injection port 82a
located close to waveguide probe 50 allows insertion of
thermocouples T, to measure both input and output coolant
(conductor 18) temperatures. The coolant also prevents overheating
of the cable as a whole to prevent possible injury to the
patient.
[0054] Refer now to FIG. 3 which shows a second cable embodiment
16a for use in the cable/diplexer assembly 10. The components of
cable 16a which are in common with cable 16 carry the same
identifying numerals. Thus, cable 16a comprises a center conductor
18 defining a fluid pathway 19 and an outer conductor 26 separated
by a winding of dielectric strand(s) 40. Cable 16a differs from
cable 16 in that its distal end includes a connection device 110 in
the form of a bead of a dielectric material. If a liquid coolant is
to be used, device 110 may be provided with one or more small
diameter, e.g. 0.010 inch, radial passages 112 which extend through
conductors 18 and 26 to connect the fluid pathway 19 in conductor
18 to the outside. Such holes filled with coolant do not
significantly perturb the microwave transmission line comprising
cable 16. On the other hand, if the coolant is a gas, it should not
enter the blood stream. Therefore, in this event, the passages 112
are not present and a return passage may be provided in device 110
as shown in phantom at 113 in FIG. 3 into the spaces 41 in the
cable to return the coolant to coolant source 108.
[0055] Center conductor 18 extends to the distal end of bead 110
and the outer conductor 26 wraps around the bead and connects to
the outer conductor 114 of a smaller diameter cable extension or
probe indicated at 116. Extension 116 may be a short length of 30
ohm cable, the center conductor 118 of which may be solid yet quite
flexible. More particularly, extension 116 includes a solid wire
center conductor 118 whose proximal end plugs into the distal end
of hollow center conductor 18. Conductor 118 extends to a
conductive end cap 120 spaced beyond the distal end of outer
conductor 114 and conductors 114 and 118 are separated by a
dielectric material 122 which may consist of wound strand(s) like
strand(s) 40. The length of extension 116 beyond outer conductor
114 constitutes the antenna A.
[0056] Cable 16a has all of the advantages of cable 16. In
addition, its narrower leading end extension 116 is very flexible
so that it can be navigated around especially sharp turns in a
patient's vasculature and other body passages. Alternatively,
extension 116 may have the same diameter as cable 16a but with an
outer conductor 124 formed with bellow-like convolutions 124a as
shown in phantom in FIG. 3 to maximize its flexibility.
[0057] One advantage of this embodiment is that various different
type extensions or probes 116 may be plugged into, or otherwise
attached to, the end of cable 16a. These extensions may have
various diameters and degrees of flexibility. For example, a given
extension may have a solid center conductor 118 and a relatively
small outside diameter to form a monopole antenna A as shown in
solid lines in FIG. 3. Another extension may have a larger diameter
as indicated in phantom in FIG. 3 and/or a hollow center conductor
to provide a pathway for a liquid coolant in lieu of the passages
112 in connection device 110. Yet another extension may define an
antenna A in the form of a helix as in the above patent U.S. Pat.
No. 4,364,336.
[0058] In addition, the ability of the extension 116 in FIG. 3 to
be formed separately from cable 16a allows the cable/diplexer
assembly 10 to be tested using standard 50 ohm connectors and test
equipment. More particularly, a pair of the assemblies 10 may be
arranged back-to-back as shown in FIG. 4 with the distal ends of
their cables 16a, without extensions 116, connected together
electrically via a coaxial connector 126. All ports 58, 76 of both
diplexers 22 are now at the standard 50 ohm impedance thus allowing
the attachment of a standard 50 ohm reflectometer 130 to a
connector 58. This enables simultaneous impedance measurements at
both the transmitting and receiving frequencies, with or without
coolant supplied via tubes 80, 86 and with or without power applied
to a connector 76. After such testing, the cable/diplexer
assemblies in FIG. 4 may be separated and cable extensions 116
attached to the distal ends of cables 16a prior to use thereof.
[0059] Thus, radiometric performance can be obtained with the
transmitted power applied and radiometer measurements can be made
with or without coolant flowing along pathway 19, and the flow rate
and temperature of the coolant can be monitored. Most importantly,
all test measurements can be made with commercially available 50
ohm microwave test equipment and connectors.
[0060] Providing catheter apparatus whose radiometer is external to
the patient allows the option of making the cables 16, 16a and
diplexer 46 as a disposable item. FIG. 5 illustrates an antenna
catheter indicated at 136 composed of two separate but connectable
parts 136a and 136b. Part 136a is a barrel-like re-usable part
which may contain a radiometer 138 and an external cable 140,
comparable to cable 12, for connection to transmitter 92, amplifier
102 and coolant source 108 in control unit 14. Part 136a also has
end contacts 142a which engage mating contacts 142b of part 136b
when the two parts interfit as shown in FIG. 5. The mating contacts
142a, 142b may be part of a more or less conventional 50 ohm blind
mate coaxial connector 142. Also, there is a coolant line
connection 143 between parts 136a and 136b.
[0061] Part 136b is a sleeve-like disposable part which may
encircle part 136a and be releasably locked thereto by any
conventional locking means 144, such as mating threads, bayonet
connection, spring-loaded pin, etc. Part 136b may include the
catheter cable 16 or 16a, transformer 62 and diplexer 22 along with
a segment of coolant tube 80 and perhaps tube 86. When assembled as
shown, parts 136a, 136b may function as a catheter handle for cable
16 during a procedure. When the procedure is completed, these parts
may be separated and part 136b, including its cable 16, may be
disposed of in proper fashion.
[0062] Other partly disposable antenna catheters may be envisioned.
For example, the disposable part may include only the catheter
cable 16 and the transformer 62, the re-usable part having the
diplexer 46, radiometer 98 and the cable 140.
[0063] Also as mentioned above, the radiometer and/or diplexer may
be incorporated into the cable at any point along its length either
inside or outside the body; see U.S. Pat. No. 7,197,356 and U.S.
Pat. No. 7,769,469, the contents of which are hereby incorporated
herein by reference. Also, the radiometer need not be integrated
with the diplexer as in FIG. 5. Of course, there is no size
(diameter) constraint on any segment of the cable outside the
body.
[0064] Refer now to FIG. 6 which illustrates another antenna
catheter apparatus embodiment shown generally at 150 composed of a
disposable part 150a and a re-usable part 150b. The proximal end of
cable 16 is connected to part 150a which includes a T-shaped
transmission line 152 whose arms 152a have a tubular inner
conductor leading to a coolant connecter 154 mounted to the side of
unit 150a. Connector 154 may be coupled to a tube similar to tube
86 leading to a coolant source and having a port for the
introduction of a contrast agent, thermocouple, etc. as described
above. As before, the transmission line serves both as a coolant
path and a transformer, i.e. 30/50 ohms. Transmission line 152
includes a branch or leg 152b leading to a standard 50 ohm port
156a mounted to the bottom of part 150a. Port 156a is adapted to be
connected to a mating 50 ohm port 156b mounted to the top of part
150b. Part 150b contains a transmission line 158 which connects
port 156b to a similar port 160 mounted to the bottom of part 150b.
Also, a coaxial branch 162 extends from a dipole junction 164 in
transmission line 158 to a waveguide-to-coaxial probe 156 adjacent
to one end of a waveguide 168. A waveguide-to-coaxial port 172 is
present adjacent the opposite end of the waveguide.
[0065] The apparatus embodiment 150 operates in more or less the
same way as apparatus 10. When port 160 is connected to a
transmitter and port 172 is connected to a radiometer, the
transmission line 158 functions as a low pass or band pass filter
in the antenna transmit path and the waveguide 168 functions as a
high pass, low loss filter in the receive path thereby separating
the signals to and from the antenna at the distal end of cable 16,
while at the same time matching the impedance of cable 16 to the
impedance of the standard 50 ohm ports 160, 172. Apparatus 150 has
an advantage over apparatus 136 shown in FIG. 5 in that the coolant
is not routed through part 150b containing the diplexer per se.
Thus, there is no need for a fluid connection like connection 143
between the disposable part 150a and the reusable part 150b. Yet,
the coolant is still routed along most of the receive signal path
from the antenna so as to obtain the advantages discussed
above.
[0066] It should be understood that while we have shown the high
pass filter component of the diplexers in apparatus 10 and 150 as
being a waveguide, it may just as well be a more or less
conventional printed transmission line structure e.g. stripline,
suspended substrate, microstrip, etc. For example, a high pass
filter of the suspended substrate type may include a metal
enclosure having a rectangular cross-section and containing a
printed circuit board spanning the narrow walls of the enclosure,
the board bearing metalized strips on opposite faces of the board
which are centered in the enclosure. The circuit board may be
formed with a coolant path extending along the board between the
metal strips where there is no microwave field so that the coolant
does not adversely affect the operation of the diplexer. Of course,
if that type of filter should be used in the FIG. 6 apparatus
embodiment, no such cooling passage would be required.
[0067] It will thus be seen that the objects set forth above, among
those made is apparent from the preceding description, are
efficiently attained. Also, certain changes may be made in the
above constructions without departing from the scope of the
invention. For example, in a given application, instead of ablating
tissue using electromagnetic energy as described above, a cryogenic
fluid, e.g. nitrous oxide, from coolant source 108 may be
circulated through the catheter to cause tissue ablation or renal
denervation by freezing the tissue; the temperature measurement
process using the antenna catheter remains the same. Therefore, it
is intended that all matter contained in the above description or
shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
[0068] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the
invention described herein.
* * * * *