US20130281851A1 - Heating/sensing catheter apparatus for minimally invasive applications - Google Patents

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.

Description

RELATED APPLICATION
• This application claims the benefit of provisional application No. 61/635,348, filed Apr. 19, 2012, the contents of which are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• This invention relates to medical catheter apparatus for minimally 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.
• 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.
• 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.
• 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 is 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.
• 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.
• 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 is 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.
• 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.
• 2. The Prior Art
• 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.
• 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 is such narrower and tortuous paths in the body, yet contributes minimal noise to the overall system.
SUMMARY OF THE INVENTION
• Accordingly, it is an object of the present invention to provide an improved microwave heating/sensing catheter apparatus for minimally invasive applications.
• 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.
• 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.
• Yet another object of the invention is to provide apparatus of this type whose antenna catheter has minimal insertion loss.
• Other objects will, in part, be obvious and will, in part, appear hereinafter.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• The invention description below refers to the accompanying drawings, in which:
• FIG. 1 is a diagrammatic view of heating/sensing catheter apparatus incorporating the invention;
• FIG. 2A is a sectional view with parts shown in elevation, on a larger scale, showing the cable/diplexer assembly of theFIG. 1 apparatus in greater detail;
• FIG. 2B is a sectional view on a larger scale taken alongline2B-2B ofFIG. 2A;
• FIG. 3 is a fragmentary sectional view showing a portion of a second cable/diplexer assembly embodiment for use in theFIG. 1 apparatus;
• FIG. 4 is a diagrammatic view of an assembly for testing theFIG. 3 cable/diplexer is assembly;
• FIG. 5 is a view similar toFIG. 1 of an apparatus embodiment with a disposable catheter cable and handle, and
• FIG. 6 is a similar view of still another apparatus embodiment.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
• Referring toFIG. 1 of the drawings, the present catheter apparatus comprises an antenna catheter shown generally at10 connected by acable12 to anexternal control unit14.Catheter10 includes a relatively long, e.g. 115 cm., veryflexible cable16 which includes acenter conductor18 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.
• In accordance with the invention,center conductor18 is formed as a thin-wall, e.g. 0.004 inch, tube of soft copper so that it is quite flexible and defines afluid pathway19 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 minimizes the current density thereon for a given cable diameter. This, in turn, minimizes the cable impedance and thus its insertion loss.
• The proximal end ofcable16 may connect to a passive diplexer indicated at22 which allowscatheter10 via antenna A to simultaneously emit electromagnetic energy of a first frequency while picking up thermal radiation of a second frequency. Thus, whencable16 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,catheter10 may be activated bycontrol unit14 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 enablingcontrol unit14 to display that temperature and control the heating process. Also as we shall see, thefluid pathway19 which extends from the catheter throughdiplexer22 and alongcable12 to a coolant source incontrol unit14 allows a coolant to be flowed alongcable16 to maintain thecenter conductor18 thereof at a relatively constant, low temperature. As we shall see,pathway19 may include a return path from the cable to the coolant source in the event that the coolant is recirculated.
• Referring now toFIGS. 2A and 2B, in addition to thehollow center conductor18,cable16 has a tubularouter conductor26 preferably made of metal braid so that it is electrically conductive and quite flexible. Theouter conductor26 may have an ID in the order of 0.042 inch and is shorter thanconductor18 so that a projectingdistal end segment18aofconductor18 forms antenna A. Ahollow cap28 of a dielectric material is provided at the distal or probe end of the catheter to cover antenna A and 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 ofouter conductor26 is covered by a layer orjacket34 of a suitable dielectric material.
• As usual with coaxial cables of this general type, the annular space betweenconductors18 and26 may be filled with a dielectric material. In this case, to is maximize the flexibility of the cable while dielectrically loading the cable, the insulation is composed of one or moredielectric strands40, e.g., Teflon® filament, wound around thecenter conductor18. A given cable may havemany strands40 or as few as one, depending on the characteristics desired for that cable. In addition to providing flexibility, the filament createsspaces41 between the filament turns that reduce the dielectric constant of the cable and give it a reduced impedance Z as follows:
• $Z_0=\frac{138}{\sqrt{\varepsilon }}\log 10\frac{D}{d}=30\mathrm{ohms}$
• where:
• D=outer conductor ID=0.042 in.
• d=center conductor OD=0.024 in.
• ∈=dielectric constant=1.25
• As will be described later, thefluid pathway19 may extend through ahole28ain thecap28 as shown inFIG. 2A so that a liquid coolant may be expelled from the catheter or the cap may be closed and a gaseous coolant recirculated back tocontrol unit14 via a return path constituted by thespaces41 between the dielectric strand(s)40.
• As shown inFIG. 2A,diplexer22 includes ahousing42 having anend wall42a. The proximal end ofcable16 passes through anopening44 in that wall and connects to one, i.e. the left,arm46aof a T-stub transmission line shown generally at46 which may be dielectrically loaded (not shown for clarity).Transmission line46 includes ahollow center conductor48 which receives and is connected to aprotruding end18bofcable conductor18. Thus,conductor48 continues thefluid pathway19 from the cable.Transmission line46 also has a T-shapedouter conductor52 whoseleft arm52ais surrounds and connects tocable conductor26 insidehousing42. The other, i.e. right,arm46boftransmission line46 extends to aninterior wall42bofhousing42 and thecenter conductor48 thereof passes through afeedthrough49 inwall42b. The spacing of the twoconductors48,52 of thetransmission line46 is maintained by a pair ofdielectric spacers54,54.
• The leg46cof the T-stub transmission line46, including a solid center conductor segment48cand an outer conductor segment52c, is connected by way of a low pass orband pass filter56 to acoaxial connector58 mounted to a side wall42cofhousing42. Thefilter56 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,filter56 is designed to pass the transmit frequency and block the receive frequency. Thus,transmission line46 helps to separate the different frequency signals to and from antenna A. More particularly, it forms a quarter wave stub (λ_T/4) while also providing a matched 90° bend for a transmitter (heating) signal applied toconnector58 as will be described.
• Preferably, a transformer indicated at62 is provided in theleft arm46aof the transmission line to step up the 30ohm cable16 impedance to 50 ohms in thetransmission line46 so that thediplexer22 can be tested, as will be described, using conventional connectors and test equipment designed for a 50 ohm cable. This impedance transformation may be implemented by stepping theouter conductor arm52a, e.g. in two steps as shown inFIG. 2A, or by stepping the inner conductor.
• Still referring toFIG. 2A, the housinginterior wall42balong with ahousing end wall42d, segments of thehousing side walls42cand42e, andtop wall42fand bottom wall42gform a waveguide indicated generally at64 which may be filled with adielectric material66 to minimize its size. The right end of the transmissionline center conductor48 extending throughfeedthrough49 is connected to a largerdiameter waveguide probe68 adjacent one narrower wall ofwaveguide64, while a waveguide-to-cable transition74 adjacent the opposite narrower wall projects into thewaveguide64 from aconnector76 mounted to the outside ofhousing end wall42dwhich 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 unit14 (FIG. 1). Thewaveguide64 constitutes a high-pass filter that passes the temperature sensing frequency, while blocking the heating frequency. It also provides a DC block, preventingcenter conductors18,48 from coupling directly to a patient. Thus, the combination of this filter and thetransmission line46 enables the diplexer to separate the two signals.
• Thewaveguide probe68 is unique in that it provides a coolant path as well as a microwave transition. More particularly,probe68 is formed with anaxial passage78 which is countersunk at78ato accept an end segment of a tube orconduit80 of a dielectric material.Tube80 extends to aconnector84 onhousing end wall42dwhere it may be connected to acomparable tube86 extending alongcable12 to controlunit14. Alternatively, of course,tubes80 and86 may be a single length of tubing. Thus,probe68 andtubes80,86 provide an extension of thepathway19 incable16. With the inclusion of aninjection port86aintube86, thediplexer22 can provide a path tocable16 for the injection of a contrast agent to track the position of the catheter via X-ray imaging during a treatment procedure. Theinjection port86awill also allow for the insertion of one or more thermocouples T (FIG. 2A) or other type of temperature sensor each having a lead T_Lto monitor the temperature of a coolant flowing along fluid ispathway19.
• As shown inFIG. 1, thecontrol unit14 includes a transmitter92 which delivers power at a microwave heating frequency, e.g. 2.45 GHz to theantenna catheter10 by way of acable component12aconnected toconnector58. RF heating may also be employed, e.g. at a frequency of 500 KHz. In either event, transmitter92 is controlled by aprocessor94 which receives instructions via control buttons on acontrol panel96 inunit14.Unit14 also includes aradiometer98 which receives the temperature-indicating signal fromantenna catheter10 via acable component12bconnected toconnector76. 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 todiplexer22 in an extension ofhousing42 as shown in phantom at98′ inFIG. 1 or incable12b. In either event, the signal fromradiometer98,98′ is conditioned by anamplifier102 and routed toprocessor94 which may process that signal to control adisplay104 which thereupon displays, in real time, the temperature of the fluid and/or tissue being probed bycatheter10. Of course, display104 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.
• Unit14 also includes acoolant source108 controlled byprocessor94 to deliver coolant viatube86 incable12 toantenna catheter10. 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 alongtube86 to thefluid pathway19 incenter conductors18,48. As the coolant flows along the cable, it maintains theconductors18 and48 at a substantially constant is relatively low temperature so that they have a relatively low loss regardless of the level of power delivered by transmitter92. Still,cable16 has a minimum outside diameter and is quite flexible due to its tubularinner conductor18, braidedouter conductor26 and intervening spiral dielectric winding strand(s)40. If the coolant is a liquid, thepathway19 may extend through ahole28aincap28 as shown inFIG. 2A and irrigate the probed body passage. If the coolant is a gas, the cap may be closed by blockinghole28a, and the coolant returned tosource108 along a return path provided by a passage from the interior ofcenter conductor18 to thespaces41 betweenstrands40 incable16 and pathways (not shown) alongdiplexer46 and cable12 (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 betweenouter conductor26 andjacket34 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.
• To use the catheter apparatus, a surgeon may insert the probe end ofcable16 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'sfluid pathway19 by way of theinjection port86aor the agent may be added to the coolant supplied bysource108. 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 inFIG. 1 such as the one disclosed in U.S. Pat. No. 6,210,367, the entire contents of which is hereby incorporated herein by reference. This allows the antenna A is to ablate tissue in a 360° pattern around the body passage and not just at a single contact point. Once the catheter is in place, theprocessor94, following instructions input atcontrol panel96, may causecoolant source108 to pump coolant throughtube86 to thepathway19 in the cable/diplexer assembly10 to maintain the cable'scenter conductor18 and the diplexer'scenter conductor48 at a selected relatively low temperature to prevent cable heating due to the power applied by transmitter92. Since thecoolant pathway19 in thecatheter10 is in the microwave receive path, receiver sensitivity is optimized.
• Processor94 also activates transmitter92 so that power is delivered viacable component12a,diplexer22 andcenter conductor18 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 viaconductor18,diplexer22 andcable component12btoradiometer98 incontrol unit14. That signal is detected by the radiometer and applied toprocessor94 to controldisplay104 which thereupon displays that temperature.Processor94 may also use that temperature signal to control transmitter92 to follow a selected heating profile or to maintain the targeted fluid and/or tissue at the desired temperature to achieve a desired result, e.g., warm blood, ablate tissue, denervate neural fibers, etc. All the while, the coolant influid pathway19 maintains the segments of thecenter conductor18 ofcable16 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.
• As noted above, the temperature sensors T monitor thecenter conductor18 temperature at various points along its length. The output(s) of the thermocouple(s) on lead(s) T_Lare applied toprocessor94 to enable the processor to controlcoolant source108 to keep the conductor at a selected temperature, which temperature may be displayed bydisplay104. Having the injection port82alocated close towaveguide probe50 allows insertion of thermocouples T, to measure both input and output coolant (conductor18) temperatures. The coolant also prevents overheating of the cable as a whole to prevent possible injury to the patient.
• Refer now toFIG. 3 which shows asecond cable embodiment16afor use in the cable/diplexer assembly10. The components ofcable16awhich are in common withcable16 carry the same identifying numerals. Thus,cable16acomprises acenter conductor18 defining afluid pathway19 and anouter conductor26 separated by a winding of dielectric strand(s)40.Cable16adiffers fromcable16 in that its distal end includes aconnection device110 in the form of a bead of a dielectric material. If a liquid coolant is to be used,device110 may be provided with one or more small diameter, e.g. 0.010 inch,radial passages112 which extend throughconductors18 and26 to connect thefluid pathway19 inconductor18 to the outside. Such holes filled with coolant do not significantly perturb the microwave transmissionline comprising cable16. On the other hand, if the coolant is a gas, it should not enter the blood stream. Therefore, in this event, thepassages112 are not present and a return passage may be provided indevice110 as shown in phantom at113 inFIG. 3 into thespaces41 in the cable to return the coolant tocoolant source108.
• Center conductor18 extends to the distal end ofbead110 and theouter conductor26 wraps around the bead and connects to theouter conductor114 of a smaller is diameter cable extension or probe indicated at116.Extension116 may be a short length of 30 ohm cable, thecenter conductor118 of which may be solid yet quite flexible. More particularly,extension116 includes a solidwire center conductor118 whose proximal end plugs into the distal end ofhollow center conductor18.Conductor118 extends to aconductive end cap120 spaced beyond the distal end ofouter conductor114 andconductors114 and118 are separated by adielectric material122 which may consist of wound strand(s) like strand(s)40. The length ofextension116 beyondouter conductor114 constitutes the antenna A.
• Cable16ahas all of the advantages ofcable16. In addition, its narrowerleading end extension116 is very flexible so that it can be navigated around especially sharp turns in a patient's vasculature and other body passages. Alternatively,extension116 may have the same diameter ascable16abut with anouter conductor124 formed with bellow-like convolutions124aas shown in phantom inFIG. 3 to maximize its flexibility.
• One advantage of this embodiment is that various different type extensions orprobes116 may be plugged into, or otherwise attached to, the end ofcable16a. These extensions may have various diameters and degrees of flexibility. For example, a given extension may have asolid center conductor118 and a relatively small outside diameter to form a monopole antenna A as shown in solid lines inFIG. 3. Another extension may have a larger diameter as indicated in phantom inFIG. 3 and/or a hollow center conductor to provide a pathway for a liquid coolant in lieu of thepassages112 inconnection device110. Yet another extension may define an antenna A in the is form of a helix as in the above U.S. Pat. No. 4,364,336.
• In addition, the ability of theextension116 inFIG. 3 to be formed separately fromcable16aallows the cable/diplexer assembly10 to be tested using standard 50 ohm connectors and test equipment. More particularly, a pair of theassemblies10 may be arranged back-to-back as shown inFIG. 4 with the distal ends of theircables16a, withoutextensions116, connected together electrically via acoaxial connector126. Allports58,76 of bothdiplexers22 are now at the standard 50 ohm impedance thus allowing the attachment of a standard 50ohm reflectometer130 to aconnector58. This enables simultaneous impedance measurements at both the transmitting and receiving frequencies, with or without coolant supplied viatubes80,86 and with or without power applied to aconnector76. After such testing, the cable/diplexer assemblies inFIG. 4 may be separated andcable extensions116 attached to the distal ends ofcables16aprior to use thereof.
• Thus, radiometric performance can be obtained with the transmitted power applied and radiometer measurements can be made with or without coolant flowing alongpathway19, 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.
• Providing catheter apparatus whose radiometer is external to the patient allows the option of making thecables16,16aanddiplexer46 as a disposable item.FIG. 5 illustrates an antenna catheter indicated at136 composed of two separate butconnectable parts136aand136b. Part136ais a barrel-like re-usable part which may contain aradiometer138 and anexternal cable140, comparable tocable12, for is connection to transmitter92,amplifier102 andcoolant source108 incontrol unit14. Part136aalso hasend contacts142awhich engagemating contacts142bofpart136bwhen the two parts interfit as shown inFIG. 5. Themating contacts142a,142bmay be part of a more or less conventional 50 ohm blind matecoaxial connector142. Also, there is a coolant line connection143 betweenparts136aand136b.
• Part136bis a sleeve-like disposable part which may encirclepart136aand be releasably locked thereto by any conventional locking means144, such as mating threads, bayonet connection, spring-loaded pin, etc.Part136bmay include thecatheter cable16 or16a,transformer62 anddiplexer22 along with a segment ofcoolant tube80 and perhapstube86. When assembled as shown,parts136a,136bmay function as a catheter handle forcable16 during a procedure. When the procedure is completed, these parts may be separated andpart136b, including itscable16, may be disposed of in proper fashion.
• Other partly disposable antenna catheters may be envisioned. For example, the disposable part may include only thecatheter cable16 and thetransformer62, the re-usable part having thediplexer46,radiometer98 and thecable140.
• 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 inFIG. 5. Of course, there is no size (diameter) constraint on any segment of the cable outside the body.
• Refer now toFIG. 6 which illustrates another antenna catheter apparatus is embodiment shown generally at150 composed of adisposable part150aand are-usable part150b. The proximal end ofcable16 is connected to part150awhich includes a T-shapedtransmission line152 whosearms152ahave a tubular inner conductor leading to acoolant connecter154 mounted to the side ofunit150a.Connector154 may be coupled to a tube similar totube86 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 line152 includes a branch orleg152bleading to a standard 50ohm port156amounted to the bottom ofpart150a.Port156ais adapted to be connected to amating 50ohm port156bmounted to the top ofpart150b.Part150bcontains atransmission line158 which connectsport156bto asimilar port160 mounted to the bottom ofpart150b. Also, acoaxial branch162 extends from adipole junction164 intransmission line158 to a waveguide-to-coaxial probe156 adjacent to one end of awaveguide168. A waveguide-to-coaxial port172 is present adjacent the opposite end of the waveguide.
• Theapparatus embodiment150 operates in more or less the same way asapparatus10. Whenport160 is connected to a transmitter andport172 is connected to a radiometer, thetransmission line158 functions as a low pass or band pass filter in the antenna transmit path and thewaveguide168 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 ofcable16, while at the same time matching the impedance ofcable16 to the impedance of the standard 50 ohmports160,172.Apparatus150 has an advantage overapparatus136 shown inFIG. 5 in that the coolant is not routed throughpart150bcontaining the diplexer per se. Thus, there is no need for a fluid connection like connection143 between thedisposable part150aand thereusable part150b. Yet, the coolant is still routed along most of the receive signal path from the antenna so as to obtain the advantages discussed above.
• It should be understood that while we have shown the high pass filter component of the diplexers inapparatus10 and150 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 theFIG. 6 apparatus embodiment, no such cooling passage would be required.
• It will thus be seen that the objects set forth above, among those made 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, fromcoolant source108 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 is the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
• 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.

Claims (34)

What is claimed is:

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 inclaim 1 wherein said receive path includes a first electrical filter.

3. The apparatus defined inclaim 2 wherein

said first filter comprises a waveguide with opposite ends, and

said inner conductor segment extends into the waveguide adjacent one end thereof forming a tubular probe therein that connects to a dielectric conduit extending out of the waveguide thereby continuing the coolant pathway, and

further including a waveguide-to-cable transition adjacent the other end of the waveguide and adapted for connection to a receiver.

4. The apparatus defined inclaim 3 wherein the transmission line is a T-shaped transmission line with a leg in said transmit path adapted for connection to a transmitter, said leg including a second electrical filter.

5. The apparatus defined inclaim 3 wherein the waveguide is loaded with a dielectric material.

6. The apparatus defined inclaim 3 wherein

the diplexer includes a housing containing the transmission line and waveguide, and

said conduit extends from the probe to the housing exterior and includes an injection port outside the housing.

7. The apparatus defined inclaim 1 wherein said first filter comprises a waveguide with opposite ends, and

said transmission line includes a branch extending into the waveguide adjacent one end thereof forming a probe therein, and

further including a waveguide-to-cable transition adjacent the other end of the waveguide and adapted for connection to a receiver.

8. The apparatus defined inclaim 1 and further including an impedance-matching transformer in series with the cable and the transmission line.

9. The apparatus defined inclaim 1 wherein the cable outer conductor comprises braided conductive strands.

10. The apparatus defined inclaim 1 wherein the cable insulating layer comprises a flexible winding of one or more dielectric strands having multiple fluid flow paths therebetween.

11. The apparatus defined inclaim 1 wherein said antenna comprises an extension of the center conductor beyond the outer conductor and the insulating layer.

12. The apparatus defined inclaim 11 wherein said extension is tubular and continues said fluid pathway to the outside.

13. The apparatus defined inclaim 1 wherein said antenna is connected to the center conductor via a connection device at the distal end of the cable.

14. The apparatus defined inclaim 13 wherein the connection device defines a fluid path between the interior of the center conductor and the outside.

15. The apparatus defined inclaim 13 wherein the connection device defines a fluid passage between the interior of the center conductor and said annular space so that said annular space can provide a coolant return path along the cable.

16. The apparatus defined inclaim 1 wherein the antenna is flexible.

17. The apparatus defined inclaim 1 and further including a stand-off device adjacent to the distal end of the cable for centering said antenna in a body passage.

18. The apparatus defined inclaim 1 and further including one or more temperature detectors positioned in said fluid pathway for monitoring coolant temperature at one or more locations therealong.

19. The apparatus defined inclaim 1 and further including a device for introducing an x-ray contrast agent into said center conductor.

20. The apparatus defined inclaim 1 and further including a microwave or RF transmitter connected to said transmit path.

21. The apparatus defined inclaim 1 and further including a coolant source connected to said second end of the tubular inner conductor of said transmission line segment.

22. 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 electrical insulating layer in an annular space between said conductors, said insulating layer being constituted by one or more windings of a dielectric material defining multiple flow paths along said annular space, and

23. The apparatus defined inclaim 22 and further including a connection device at the distal end of the cable connecting the interior of the center conductor to said annular space so that when a gaseous coolant is flowed into the proximal end of the cable, the coolant travels along the center conductor to the distal end of the cable and exhausts from the cable via said connection device and flow paths thereby cooling the center conductor.

24. The apparatus defined inclaim 23 wherein the connection device comprises a closed hollow end cap secured to the distal end of the cable and which connects the interior of the center conductor to said annular space.

25. The apparatus defined inclaim 24 wherein the center conductor extends into said cap to form an antenna.

26. The apparatus defined inclaim 23 wherein the connection device comprises a bead in the annular space at the distal end of the cable, said bead defining a passage between the interior of the center conductor and the annular space.

27. The apparatus defined inclaim 22 wherein the center conductor extends beyond the outer conductor at the distal end of the cable to form an antenna.

28. The apparatus defined inclaim 27 and further including a stand-off device adjacent to the distal end of the cable for centering the antenna in a body passage.

29. The apparatus defined inclaim 27 and further including a diplexer connected to the cable, said 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 being designed to isolate the signals on the two paths from one another.

30. The apparatus defined inclaim 29 and further including an impedance-matching transformer in series between the cable and the diplexer.

31. The apparatus defined inclaim 29 wherein said transmit path and said receive path are comprised of a T-shaped transmission line which is arranged and adapted to provide both a coolant path between a coolant source and said center conductor and an impedance matching transformer.

32. The apparatus defined inclaim 29 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.

33. The apparatus defined inclaim 22 wherein said outer conductor comprises braided conductive strands.

34. The apparatus defined inclaim 22 and further including one or more temperature sensors in said center conductor.

Images