Abstract:
Microwave antenna assemblies incorporating a high-strength antenna coupler are described herein. The microwave antenna has a radiating portion connected by a feedline to a power generating source, e.g., a generator. Proximal and distal radiating portions of the antenna assembly are separated by a microwave antenna coupler. In embodiments, the described antenna coupler includes a dielectric member and at least one discrete coupling member. The coupling member isolates coupling forces, such as tension and torque, from the dielectric member, which may prevent cracking and reduce the incidence of mechanical failure of the dielectric. The coupling member may be formed from high strength materials, such as stainless steel, allowing greater coupling forces to be achieved when compared to couplers using only dielectric materials. The coupling member may additionally include reinforcing members which extend into the dielectric member for increased strength.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority to U.S. Provisional Application Ser. No. 61/045,678 entitled “HIGH-STRENGTH MICROWAVE ANTENNA COUPLING” filed Apr. 17, 2008 by Arnold V. DeCarlo, which is incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates generally to microwave surgical devices having a microwave antenna which may be inserted directly into tissue for diagnosis and treatment of diseases. More particularly, the present disclosure is directed to an insulated coupler for coupling the distal and proximal elements of a microwave antenna. 
         [0004]    2. Background of Related Art 
         [0005]    In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures (which are slightly lower than temperatures normally injurious to healthy cells). These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Other procedures utilizing electromagnetic radiation to heat tissue also include ablation and coagulation of the tissue. Such microwave ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate and coagulate the targeted tissue to denature or kill the tissue. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such microwave therapy is typically used in the treatment of tissue and organs such as the prostate, heart, and liver. 
         [0006]    One non-invasive procedure generally involves the treatment of tissue (e.g., a tumor) underlying the skin via the use of microwave energy. The microwave energy is able to non-invasively penetrate the skin to reach the underlying tissue. However, this non-invasive procedure may result in the unwanted heating of healthy tissue. Thus, the non-invasive use of microwave energy requires a great deal of control. 
         [0007]    Presently, there are several types of microwave probes in use, e.g., monopole, dipole, and helical. One type is a monopole antenna probe, which consists of a single, elongated microwave conductor exposed at the end of the probe. The probe is typically surrounded by a dielectric sleeve. The second type of microwave probe commonly used is a dipole antenna, which consists of a coaxial construction having an inner conductor and an outer conductor with a dielectric junction separating a portion of the inner conductor, which may be coupled to a portion corresponding to a first dipole radiating portion, and a portion of the outer conductor which may be coupled to a second dipole radiating portion. The dipole radiating portions may be configured such that one radiating portion is located proximally of the dielectric junction, and the other portion is located distally of the dielectric junction. In the monopole and dipole antenna probe, microwave energy generally radiates perpendicularly from the axis of the conductor. 
         [0008]    The typical microwave antenna has a long, thin inner conductor which extends along the axis of the probe and is surrounded by a dielectric material and is further surrounded by an outer conductor around the dielectric material such that the outer conductor also extends along the axis of the probe. In another variation of the probe, which provides for effective outward radiation of energy or heating, a portion or portions of the outer conductor can be selectively removed. This type of construction is typically referred to as a “leaky waveguide” or “leaky coaxial” antenna. Another variation on the microwave probe involves having the tip formed in a uniform spiral pattern, such as a helix, to provide the necessary configuration for effective radiation. This variation can be used to direct energy in a particular direction, e.g., perpendicular to the axis, in a forward direction (i.e., towards the distal end of the antenna), or a combination thereof. 
         [0009]    Invasive procedures and devices have been developed in which a microwave antenna probe may be either inserted directly into a point of treatment via a normal body orifice or percutaneously inserted. Such invasive procedures and devices potentially provide better temperature control of the tissue being treated. Because of the small difference between the temperature required for denaturing malignant cells and the temperature injurious to healthy cells, a known heating pattern and predictable temperature control is important so that heating is confined to the tissue to be treated. For instance, hyperthermia treatment at the threshold temperature of about 41.5° C. generally has little effect on most malignant growth of cells. However, at slightly elevated temperatures above the approximate range of 43° C. to 45° C., thermal damage to most types of normal cells is routinely observed. Accordingly, great care must be taken not to exceed these temperatures in healthy tissue. 
         [0010]    However, many types of malignancies are difficult to reach and treat using non-invasive techniques or by using invasive antenna probes designed to be inserted into a normal body orifice, i.e., an easily accessible body opening. These types of conventional probes may be more flexible and may also avoid the need to separately sterilize the probe; however, they are structurally weak and typically require the use of an introducer or catheter to gain access to within the body. Moreover, the addition of introducers and catheters necessarily increase the diameter of the incision or access opening into the body thereby making the use of such probes more invasive and further increasing the probability of any complications that may arise. 
         [0011]    Structurally stronger invasive probes exist and are typically long, narrow, needle-like antenna probes which may be inserted directly into the body tissue to directly access a site of a tumor or other malignancy. Such rigid probes generally have small diameters that aid not only in ease of use but also reduce the resulting trauma to the patient. A convenience of rigid antenna probes capable of direct insertion into tissue is that the probes may also allow for alternate additional uses given different situations. However, such rigid, needle-like probes may experience difficulties in failing to provide uniform patterns of radiated energy; and may fail to provide uniform heating axially along and radially around an effective length of the probe. Accordingly, it may be difficult to otherwise control and direct the heating pattern when using such probes. 
         [0012]    Additionally, a dielectric junction used to separate portions of a rigid probe may be subjected to bending, compression, and rotational forces during manufacture, and during use. These forces may lead to failure of the junction, particularly where the dielectric junction includes an integrally formed coupling member, such as a threaded or ribbed section. Such threads or ribs often have edges which may cause stress concentrations induced by manufacturing or operational forces, causing mechanical or electrical failure of the dielectric junction. This effect is exacerbated by the structural properties of suitable dielectric materials, such as porcelain or other ceramic materials, which tend to be brittle. 
       SUMMARY 
       [0013]    The present disclosure provides a high-strength microwave antenna coupler assembly and methods of use therefor, e.g., in microwave antenna assemblies used in tissue ablation applications. In some variations, the microwave antenna assembly has proximal and distal radiating portions. The coupler assembly may be a junction member that couples the proximal and distal radiation sections. At least a portion of the coupler assembly may be disposed between the proximal and distal radiating portions. The distal end of the distal radiating portion may have a tapered end which terminates at a tip configured to allow for the direct insertion into tissue with minimal resistance. An inner and an outer conductor extend through the proximal radiating portion, with the inner conductor disposed within the outer conductor. The inner conductor may extend through a channel disposed longitudinally in the coupler assembly. The inner conductor may further extend at least partially into the distal radiating portion The microwave antenna assembly may also be connected to a source of microwave energy. 
         [0014]    The coupler includes a dielectric member and at least one discrete coupling member that is joined with the dielectric member. In embodiments, the dielectric member and the coupling member are formed from dissimilar materials. Additionally or alternatively, the dielectric member and the coupling member may be formed from similar or the same materials. 
         [0015]    At least two benefits may be realized by dissociating the dielectric member from the coupling member as described herein. First, by providing a coupling member that is discrete from the dielectric member, the coupling member may be able to absorb stresses imposed thereupon, rather than transmit such stress into the dialectic member. Second, the disclosed arrangement permits the use of materials that are better-suited to their function, for example, the dielectric member may be formed of porcelain while the coupling member may be formed of stainless steel. Continuing with the present example, porcelain may be well suited as a dielectric member because of its excellent insulative properties, yet may be poorly suited as a coupling member due to its brittleness. Conversely, stainless steel may be well-suited as a coupling member because of its toughness and strength, yet is electrically conductive therefore unsuitable as a dielectric. The present disclosure provides a coupler that advantageously combines the benefits of these materials without the drawbacks of either material. 
         [0016]    The dielectric member may be formed from any suitable non-conductive material, such as glass, porcelain, ceramic, or polymer material. The coupling member may be formed from any suitable material, such as stainless steel, that is configured to operably engage the proximal and distal radiating portion of the antenna assembly to the coupler. The coupling portion may be configured as a threaded sleeve for screw mounting of the radiating portions to the coupler. The coupling member may be rigidly joined to the dielectric member, or it may be loosely joined in a “floating” configuration. 
         [0017]    In embodiments, the insulating member may have longitudinal symmetry, having a radial thickness that is non-uniform about the longitudinal axis. The insulating member may include a central portion radius similar to the radius of the outer conductor, a sleeve portion having a radius configured to engage the inner diameter of the coupling member, and an end portion having a radius configured to retain the coupling member. The transitions between differing radii may be stepped (discontinuous), or may be tapered (continuous). The end portion may include a bevel to facilitate placement of the coupling member onto the insulating member during manufacturing. 
         [0018]    The sleeve portion may include at least one longitudinal rib that is configured to engage a corresponding slot in the threaded coupling member. In this arrangement, the rib may serve to limit or prevent movement of the coupling member with respect to the insulating member arising from, for example, torque applied to the coupling member during antenna assembly. 
         [0019]    Alternatively, the coupling portion may be configured for frictionally mounting the radiating portions to the coupler. For instance, the coupling portion may include ribs, projections, depressions, and/or textures configured to facilitate the frictional or interference coupling of the radiating portion(s) of the antenna assembly to the coupler. 
         [0020]    In embodiments, the coupling portion may include a generally cylindrical reinforcing collar which extends into a corresponding cylindrical recess provided by the insulating member. The reinforcing collar may add strength to thinner regions of the insulating member, and may additionally distribute stresses to thicker regions of the insulating member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which: 
           [0022]      FIG. 1  shows a representative diagram of a variation of a microwave antenna assembly; 
           [0023]      FIG. 2A  shows an exploded, cross-sectional view of a representative variation of a microwave antenna assembly; 
           [0024]      FIG. 2B  shows a cross-sectional view of a representative variation of a microwave antenna assembly; 
           [0025]      FIG. 3  shows a prior-art antenna coupler; 
           [0026]      FIG. 4  shows a cross-sectional view of an embodiment of an antenna coupler insulating member in accordance with the present disclosure; 
           [0027]      FIG. 5  shows a cross-sectional view of an embodiment of an antenna coupler in accordance with the present disclosure incorporating the insulating member of  FIG. 4 ; 
           [0028]      FIG. 6  shows an oblique view of the antenna coupler insulating member of  FIG. 4  in accordance with the present disclosure; 
           [0029]      FIG. 7  shows an oblique view of the an antenna coupler of  FIG. 5  in accordance with the present disclosure; 
           [0030]      FIG. 8A  shows an oblique view of a threaded coupling member in accordance with the present disclosure; 
           [0031]      FIG. 8B  shows a side view of the threaded coupling member of  FIG. 8A  in accordance with the present disclosure; 
           [0032]      FIG. 9  shows a cross-sectional view of an embodiment of an antenna coupler in accordance with the present disclosure mated to distal and proximal radiating portions of a microwave antenna assembly; 
           [0033]      FIG. 10  shows a cross-sectional view of another embodiment of an antenna coupler insulating member in accordance with the present disclosure; 
           [0034]      FIG. 11A  shows an oblique view of an embodiment of the antenna coupler insulating member of  FIG. 10  in accordance with the present disclosure; 
           [0035]      FIG. 11B  shows an oblique view of a split coupling member in accordance with the present disclosure; 
           [0036]      FIG. 12A  shows a side view of yet another embodiment of an antenna coupler insulating member in accordance with the present disclosure; 
           [0037]      FIG. 12B  shows an end view of the antenna coupler insulating member of  FIG. 12A  in accordance with the present disclosure; 
           [0038]      FIG. 13  is an exploded, top view of yet another embodiment of an antenna coupler in accordance with the present disclosure incorporating the antenna coupler insulating member of  FIG. 12A ; 
           [0039]      FIG. 14  is a top view of the antenna coupler of  FIG. 13  in accordance with the present disclosure; 
           [0040]      FIG. 15  is an oblique view of the antenna coupler of  FIG. 13  in accordance with the present disclosure; 
           [0041]      FIG. 16  is an oblique, cutaway view of the antenna coupler of  FIG. 13  in accordance with the present disclosure; 
           [0042]      FIG. 17  is an oblique, cutaway view of the antenna coupler of  FIG. 13  mated to distal and proximal radiating portions of a microwave antenna assembly in accordance with the present disclosure; 
           [0043]      FIG. 18  is an oblique view of yet another antenna coupler in accordance with the present disclosure; 
           [0044]      FIG. 19  shows an oblique view of a threaded coupling member having a reinforcing collar in accordance with the present disclosure; 
           [0045]      FIG. 20  is an oblique, cutaway view of the antenna coupler of  FIG. 18  incorporating the threaded coupling member of  FIG. 19  in accordance with the present disclosure; and 
           [0046]      FIG. 21  is an oblique, cutaway view of the antenna coupler of  FIG. 18  mated to distal and proximal radiating portions of a microwave antenna assembly in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    Particular embodiments of the present disclosure will be described herein with reference to the accompanying drawings. As shown in the drawings and as described throughout the following description, and as is traditional when referring to relative positioning on an object, the term “proximal” refers to the end of the apparatus that is closer to the user and the term “distal” refers to the end of the apparatus that is further from the user. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
         [0048]      FIG. 1  shows an exemplary embodiment of a microwave antenna assembly  10  in accordance with the present disclosure. The antenna assembly  10  includes a radiating portion  12  that is connected by feedline  14  (or shaft) via cable  15  to connector  16 , which may further connect the assembly  10  to a power generating source  28 , e.g., a generator. Assembly  10 , as shown, is a dipole microwave antenna assembly, but other antenna assemblies, e.g., monopole or leaky wave antenna assemblies, may also utilize the principles set forth herein. Distal radiating portion  20  of radiating portion  12  may have a tapered end  24  which terminates at a tip  26  to allow for insertion into tissue with minimal resistance. Alternatively, tip  26  may be rounded or flat. Proximal radiating portion  22  is joined to distal radiating portion  20  by insulating coupler  18 . 
         [0049]      FIGS. 2A and 2B  illustrate generally aspects of a prior art insulating coupler  210  configured to couple a proximal radiating portion  260  and a distal radiating portion  250  of a microwave antenna assembly  200 . As seen in the exploded view of  FIG. 2A  and the assembled view of  FIG. 2B , insulating coupler  210  includes a central portion  215  having an outer diameter similar to that of proximal radiating portion  260  and distal radiating portion  250 . Prior art insulating coupler  210  further includes threaded coupling sections  220  and  225  that are configured to mate with corresponding internal threads  230  and  235  provided by the distal and proximal radiating portions, respectively. Prior art insulating coupler  210  may also include a channel  240  defined therein through which inner conductor  265  may pass from the proximal portion  260  to the distal portion  250  of antenna assembly  200 . As can be seen in  FIG. 3 , prior art insulating coupler  210  may have drawbacks in that mechanical forces bearing upon threaded section  220  and/or threaded section  230  may cause mechanical failure of the coupler. For instance, cracks may form in prior art insulating coupler  210  as shown, by example only, at C 1 , C 2  and C 3 . The cracks are particularly troublesome when the prior art coupler is formed from brittle material, where cracks may lead to fragmentation of the coupler, and/or sudden catastrophic failure of the antenna assembly. 
         [0050]    Turning now to  FIGS. 4-8 , there is presented an improved high-strength microwave antenna coupler  400  in accordance with the present disclosure. Coupler  400  includes an insulating member  405  and at least one coupling member  460 ,  460 ′. Insulating member  405  may be formed from any suitable dielectric material, such as glass, porcelain, ceramic, or polymeric material. Insulating member  405  may include a central portion  410  having a radius similar to the radius of the outer conductor, i.e., a radiating portion  500 ,  510 . Coupler  400  may further include at least one sleeve portion  420 ,  420 ′ having a radius configured to engage the inner diameter  485  of coupling member  460 , and, an end portion  425 ,  425 ′ having a radius configured to retain the coupling member  460  to insulating member  405 . A channel  430  may be disposed axially in the insulating member  405  for permitting the passage therethough of, for example without limitation, conductors, tubes, actuators, and the like. 
         [0051]    Sleeve portion  420  may additionally include at least one longitudinal rib  450 ,  450 ′ that is configured to engage with a corresponding longitudinal slot  470  defined in coupling member  460 . Additionally or alternatively, coupling member  460  has defined upon the inner surface  485  thereof a longitudinal channel (not shown) configured to engage rib  450 ,  450 ′. Rib  450 ,  450 ′ may extend from end face  426 ,  426 ′ of end portion  425 ,  425 ′ to central face  427 ,  427 ′ of central portion  410 . In embodiments, rib  450 ,  450 ′ may extend from end face  426 ,  426 ′ to an intermediate point between end face  426 ,  426 ′ and central face  427 ,  427 ′ (not shown). Additionally or alternatively, rib  450 ,  450 ′ may extend from central face  427 ,  427 ′ to an intermediate point between end face  426 ,  426 ′ and central face  427 ,  427 ′ (not shown). In embodiments, coupling member  460  may include exterior threads  462  for engaging coupler  400  to corresponding interior threads  481 ,  491  provided by radiating portion  480 ,  490 . 
         [0052]    The end portion may further include a bevel  440 ,  440 ′ to facilitate joining of coupling member  460  to insulating member  405  during manufacture. For example, a method of manufacture is envisioned wherein a coupling member  460  to be joined with an insulating member  405  is axially aligned with insulating member  405  in a first step, and in a second step, slot  470  is indexed (i.e., rotationally aligned) with rib  450 . In a third step, coupling member  460  is pressed onto insulating member  405 . In greater detail, as coupling member  460  makes contact with end portion  425 , the inner diameter  485  of coupling member  460  rides over bevel  440 , thus widening slot  470  causing coupling member  460  to radially expand in a c-clamp like fashion, which permits coupling member  460  to ride over end portion  425 . Additionally or alternatively, slot  470  may be temporarily widened by, for example, a tool, prior to being pressed onto sleeve  420 , in order to ease the placement of coupling member  460  onto sleeve  420 . Once coupling member  460  is fully pressed onto sleeve  420 , i.e., positioned between end face  426  and central face  427 , coupling member  460  clears end portion  425  whereupon the resiliency of coupling member  460  causes coupling member  460  to assume its original, unexpanded shape, thereby “locking” coupling member  460  into place on sleeve  420  between end face  426  and central face  427  and by the engagement of slot  470  with rib  450 . It is contemplated that the steps of the method in accordance with the present disclosure can be performed in a different ordering than the ordering provided herein. 
         [0053]    Turning now to  FIGS. 10-11 , embodiments according to the present disclosure are envisioned wherein opposing ribs  550  and  551  are provided by sleeve  520 . In these embodiments, a split coupling member is provided wherein opposing semi-circular coupling members  560  and  561  are positioned on corresponding halves of sleeve  520 . Semi-circular coupling members  560  and  561  may be retained on sleeve  520  by any suitable method, such as adhesive bonding, or additionally or alternatively, held in place by a fixture during manufacturing and held in place by the compressive force between coupling members  560 ,  561  and an outer conductor, i.e., a radiating portion of a microwave antenna assembly. 
         [0054]    The transitions between differing radii may be stepped (discontinuous), as illustrated in  FIGS. 4-5 , or, may be tapered (continuous) as can be seen in the embodiments illustrated by  FIG. 12  et seq. As best illustrated in  FIGS. 12A and 12B , certain embodiments of a high-strength microwave antenna coupler  600  include an insulating member  605 , which may include a tapered section  621 ,  621 ′ between sleeve  620 ,  620 ′ and a shoulder  622 ,  622 ′. A tapered section as described herein may strengthen insulating member  605  by, for example, dissipating stress concentrations which may otherwise be formed within insulating member  605 , and/or reinforcing insulating member  605  with the additional material contained within tapered region  621 ,  621 ′. In embodiments, the transition between differing radii may be effectuated by a fillet. 
         [0055]    Insulating member  605  may include a central portion  610  having a diameter similar to the outside diameter of an outer conductor, e.g., the outside diameter of radiating portion  680 ,  690 . Insulating member  605  may include a shoulder  622 ,  622 ′. In embodiments, shoulder  622 ,  622 ′ may have a diameter dimensioned to provide a suitable fit, such as a interference fit, between shoulder  622 ,  622 ′ and with the inside diameter of an outer conductor, as shown in  FIG. 17 . 
         [0056]    High-strength microwave antenna coupler  600  may additionally include at least one coupling member  660 ,  660 ′. Sleeve portion  420 ,  420 ′ may have a radius configured to engage the inner diameter (not explicitly shown) of coupling member  660 , and, an end portion  625 ,  625 ′ having a radius configured to retain the coupling member  660  to insulating member  605 . As shown in  FIGS. 15 and 16 , a channel  630  may be disposed axially in the insulating member  605  for permitting the passage therethough of, for example without limitation, conductors, tubes, actuators, and the like. Coupling member  660  may be joined with an insulating member  605  in the manner previously described herein. 
         [0057]    In another aspect best illustrated in  FIG. 12A , a rib  650  is provided on one sleeve of the insulating member  605 , for example, the distal sleeve, that is positioned 180° (measured as an angle around the longitudinal axis of insulating member  605 ) from a corresponding rib  651  provided on the opposite sleeve of insulating member  605 . In these embodiments, coupling member  660  is rotationally oriented such that slot  670  is aligned with the corresponding rib  650 . 
         [0058]    With reference now to  FIGS. 18-21 , a microwave antenna coupler  700  in accordance with the present disclosure includes a coupling member  760  having a substantially cylindrical reinforcing collar  765 , and an insulating member  705  having a generally cylindrical slot  766  disposed therein dimensioned to operably engage collar  765 . The extension of collar  765  into insulating member  705  may increase the strength of thinner regions of insulating member  705 , and additionally or alternatively, may transfer stresses to thicker regions of insulating member  705 , i.e., central region  710 . 
         [0059]    In embodiments, collar  765  may be formed integrally with coupling member  760  from any suitable material, such as stainless steel. Microwave antenna coupler  700  may be manufactured by any suitable process, for example without limitation, by an insert molding process or by a two-shot molding process. In an insert molding process, at least one coupling member  760  is introduced as an insert into a mold dimensioned to form insulating member  710 . Coupling member  760  may be placed manually, or by automated means such as a robotic placing device. Thereafter, insulating material is injected or otherwise introduced into the mold to form insulating member  710  in situ with coupling member  760 . Insulating member  705  may be formed from polymeric materials using injection molding. Alternatively, insulating member  710  may be formed from ceramic materials, such as aluminum oxide ceramics. 
         [0060]    For example, dry powder insert molding technique may be used to form insulating member  710  wherein a mechanical or hydraulic press compacts component ceramic powder. In other embodiments, insulating member  710  may be formed by an insert casting process wherein liquid ceramic material is injected into an elastomeric mold which may additionally retain and position coupling members  760 ,  760 ′ for insert casting. Thereafter, insulating member  710  may optionally be fired to set or harden the ceramic material. Composite materials, which may include ceramic and polymeric components, may also be advantageously used to form insulating member  705 . 
         [0061]    The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Further variations of the above-disclosed embodiments and other features and functions, or alternatives thereof, may be made or desirably combined into many other different systems or applications without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.