Abstract:
Microwave antenna assemblies incorporating a resilient insulating coupler are described herein. The microwave antenna includes a radiating portion connected by a coaxial feedline to a power generating source, e.g., a generator. Distal and proximal radiating portions of the antenna, which correspond to inner and outer conductors provided by the coaxial feedline, are separated by the resilient insulating coupler. The described coupler includes a proximal threaded portion, and an overmolded insulating portion formed from an elastomeric material. The inner conductor of the coaxial feedline is joined to the threaded portion of the coupler, and is placed under tension to draw together the distal radiating portion, the coupler, and the proximal radiating portion into a single rigid assembly. In use, the resilient coupler provides increased strength and reliability by absorbing mechanical stresses typically encountered during microwave ablation procedures.

Description:
BACKGROUND 
     1. Technical Field 
     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 a microwave antenna having a cooled distal tip and a method of manufacturing the same. 
     2. Background of Related Art 
     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, liver, lung, kidney, and breast. 
     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. 
     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. The inner conductor may be coupled to a portion corresponding to a first dipole radiating portion, and a portion of the outer conductor 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. 
     The typical microwave antenna has a long, thin inner conductor that 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 that 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 combinations thereof. 
     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. 
     At the beginning of an ablation procedure, the water content of targeted or surrounding tissue may desirably enhance the dielectric coupling between a microwave antenna and surrounding tissue. However, as ablation proceeds, the water content of surrounding tissue may decrease due to, for example, thermal desiccation or dehydration, which negatively affects dielectric coupling between a microwave ablation antenna and targeted or surrounding tissue. In certain instances, uneven or undesirable ablation patterns may form as a result thereof, which may lead to uneven or incomplete heating within the targeted tissue, which may, in turn, lead to complications and impaired operative outcomes. Further, 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, e.g., 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. 
     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. 
     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. This effect is exacerbated by the structural properties of conventional dielectric materials, such as porcelain or other ceramic materials, which tend to be brittle. 
     SUMMARY 
     The present disclosure provides a surgical microwave antenna assembly, methods of use therefor, e.g., in microwave antenna assemblies used in tissue ablation applications, and methods of manufacture thereof. In some variations, the microwave antenna assembly has proximal and distal radiating portions. A coupler, or puck, may be a junction member that couples the proximal and distal radiation sections. At least a portion of the coupler may be disposed between the proximal and distal radiating portions. The distal end of the distal radiating portion may include a trocar having 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 includes a coolant chamber disposed within the trocar that is configured to receive a cooling fluid, such as water, via a coolant inflow tube in fluid communication with a source of cooling fluid. The microwave antenna assembly may also be connected to a source of microwave energy. 
     The puck may be formed from elastomeric or ceramic dielectric material. In some embodiments, the puck may be formed from an unbreakable thermoplastic elastomer, such as without limitation, polyether block amide, such as Pebax®, manufactured by The Arkema Group of Colombes, France; polyetherimide (PEI), such as Ultem® and/or Extem®, manufactured by SABIC Innovative Plastics of Saudi Arabia; polyimide-based polymer, such as Vespel®, manufactured by E.I. du Pont de Nemours and Company of Wilmington, Del., United States. In some embodiments, the puck may be formed from ceramic. In some embodiments, tension is applied to the inner conductor, which in turn places the puck in a state of compression, resulting in improved strength and stiffness of the antenna assembly. 
     The proximal and distal radiating portions may include a dielectric coating formed from, for example without limitation, a heat resistant ceramic material such as titanium dioxide and/or zirconium dioxide. During a microwave ablation procedure, desiccation of target and/or surrounding tissue may adversely affect the electrical properties at the surgical site, including without limitation, causing impedance mismatching and/or undesirable ablation volumes. The dielectric coating may reduce the detrimental effects of tissue desiccation on the ablation process, and may improve operative outcomes and decrease patient recovery times. 
     In an embodiment according to the present disclosure, a surgical antenna assembly includes a coaxial feedline having an inner conductor, an outer conductor, and a dielectric disposed therebetween. A trocar screw having a distal threaded section and a cylindrical proximal section is operably electrically coupled to a distal end of the inner conductor. The cylindrical proximal section may include a threaded section. A puck is integrally formed with the trocar screw cylindrical proximal section, by, for example without limitation, overmolding, to form the trocar screw/puck subassembly. The surgical antenna assembly includes an electrically conductive distal radiating section having a distal tapered end and a proximal cylindrical end. In embodiments, the distal radiating section has a generally cylindroconical shape. A cooling chamber is defined within the distal radiating section, having an opening to the proximal end of the distal radiating section and having a threaded section into which is threaded the trocar screw. The disclosed antenna includes a proximal radiating section operably coupled to the outer conductor of the feedline. The proximal radiating section may have a generally cylindrical shape. Additionally or alternatively, the proximal radiating section may have a generally square or hexagonal cross sectional shape. The inner conductor is placed under tension and fastened, which draws together the distal radiating section, the trocar screw/puck subassembly, and the proximal radiating section, to form the antenna assembly. In an embodiment, a tensioning mechanism is generally coupled to the inner conductor Movement of the tensioning mechanism draws the distal radiating section, the puck, and the proximal radiating section under compression to stiffen the antenna assembly. 
     In an embodiment, the puck includes a distal puck section, a central puck section, and a proximal puck section. The outer diameter of the central puck section is greater than that of at least one of the outer diameter of the distal puck section and the outer diameter of the proximal puck section. The outer diameter of the central puck section is about equal to the outer diameter of the proximal cylindrical end of the distal radiating section and/or the outer diameter of the proximal radiating section. 
     In an embodiment, the disclosed surgical antenna includes an outer jacket surrounding at least one of the distal radiating section, the puck, and the proximal radiating section. The outer jacket is formed from polytetrafluoroethylene (PTFE), such as Teflon®, or any suitable lubricious polymer such as polyethylene terephthalate (PET) or polyimide. The outer jacket may enable the antenna assembly to more easily penetrate tissue by reducing friction between the shaft and tissue, and/or by inhibiting the adhesion of biomaterials to the shaft. 
     Also disclosed is a method for manufacturing a surgical antenna. The disclosed method includes the steps of providing a trocar screw adapted to receive a conductor at the proximal end thereof and bonding a conductor to the trocar screw to form a trocar screw subassembly. The conductor may be coupled to the trocar screw using any suitable manner of electrically-conductive bonding, for example without limitation, welding, brazing, soldering, and crimping. The trocar screw subassembly may then be positioned into a mold that is configured to overmold a puck on the trocar screw subassembly. Puck material, for example and without limitation, Pebax®, Ultem®, Extem®, Vespel® and/or ceramic, is injected into the mold and allowed to set, forming a puck assembly. The puck assembly is released from the mold. A trocar adapted at the proximal end thereof to couple to the trocar screw is provided, and coupled to the trocar screw (e.g., by screwing the trocar onto the trocar screw) to form a distal radiating section. A proximal antenna member adapted at the distal end thereof to couple to the puck assembly is provided, and coupled to the puck assembly such that the conductor passes longitudinally through the proximal antenna member and exits at a proximal end thereof. The conductor is tensioned to draw together the distal radiating section, puck assembly, and proximal antenna member under compression to form an antenna assembly, and the conductor is fixed in relation to the proximal antenna member in order to maintain the stiffness of the antenna assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  shows a representative diagram of a variation of a microwave antenna assembly in accordance with an embodiment of the present disclosure; 
         FIG. 2  shows an cross-sectional view of a representative variation of a distal end of microwave antenna assembly in accordance with an embodiment of the present disclosure; 
         FIG. 3  shows a cross-sectional view of a representative variation of a proximal end of microwave antenna assembly in accordance with an embodiment of the present disclosure; 
         FIGS. 4A-4D  show perspective views of a embodiment of a distal portion of a microwave antenna in various stages of assembly in accordance with an embodiment of the present disclosure; 
         FIG. 5  shows a perspective view of an embodiment of a microwave antenna coupler having a tensioned inner conductor in accordance with an embodiment of the present disclosure; and 
         FIGS. 6A-6B  show cross-sectional views of a distal end of a microwave antenna in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
       FIG. 1  shows an embodiment of a microwave antenna assembly  100  in accordance with the present disclosure. The antenna assembly  100  includes a radiating portion  12  that is connected by feedline  110  (or shaft) via cable  15  to connector  16 , which may further connect the assembly  10  to a power generating source  28 , e.g., a microwave or RF electrosurgical generator. Assembly  100 , 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  105  of radiating portion  12  includes a tapered end  120  which terminates at a tip  123  to allow for insertion into tissue with minimal resistance. It is to be understood, however, that tapered end  120  may include other shapes, such as without limitation, a tip  123  that is rounded, flat, square, hexagonal, or cylindroconical. 
     An insulating puck  130  is disposed between distal radiating portion  105  and proximal radiating portion  140 . Puck  130  may be formed from any suitable elastomeric or ceramic dielectric material by any suitable process. In embodiments, the puck  130  is formed by overmolding from polyether block amide (e.g., Pebax®), polyetherimide (e.g., Ultem® and/or Extem®, polyimide-based polymer (e.g., Vespel®), or ceramic. As best illustrated in  FIG. 2 , puck  130  includes coolant inflow port  131  and coolant outflow port  133  to respectively facilitate the flow of coolant into, and out of, coolant chamber  148  of trocar  122  as further described hereinbelow. 
     With reference now to  FIGS. 2 ,  3 , and  4 A- 4 D, distal radiating portion  105  includes a trocar  122  having a generally cylindroconical shape. Proximal radiating portion  140  includes a proximal antenna member  128  having a generally cylindrical shape. Additionally or alternatively, proximal antenna member  128  may have a generally square or hexagonal shape. Trocar  122  and proximal antenna member  128  may be formed from a variety of biocompatible heat resistant conductive material suitable for penetrating tissue, such as without limitation, stainless steel. Antenna assembly  110  includes a coaxial transmission line  138  having, in coaxial disposition, an inner coaxial conductor  150 , an intermediate coaxial dielectric  132 , and an outer coaxial conductor  134 . Nominally, coaxial transmission line  138  has an impedance of about 50 ohms. Inner coaxial conductor  150  and outer coaxial conductor  134  may be formed from any suitable electrically conductive material. In some embodiments, inner coaxial conductor  150  is formed from stainless steel and outer coaxial conductor  132  is formed from copper. Coaxial dielectric  132  may be formed from any suitable dielectric material, including without limitation, polyethylene terephthalate, polyimide, or polytetrafluoroethylene (PTFE) (e.g., Teflon® manufactured by E.I. du Pont de Nemours and Company of Wilmington, Del., United States). Inner coaxial conductor  150  is electrically coupled with trocar  122 . Outer coaxial conductor  134  is electrically coupled to proximal antenna member  128 . 
     A longitudinal opening  146  within trocar  122 , and open to a proximal end thereof, defines a cooling chamber  148  and a threaded section  145  within trocar  122 . Cooling chamber  148  may have a generally cylindrical shape and, additionally or alternatively, may have a stepped, tapered, conical, or other shape that is generally dimensioned in accordance with the shape of the tapered end  120  of the cylindroconical profile of trocar  122  to permit the flow of coolant to more effectively reach the distal regions of trocar  122 . Additionally or alternatively, cooling chamber may have a square, hexagonal, or any suitable shape. Additionally, the dielectric properties of sterile water or saline flowing through cooling chamber  148  may enhance the overall ablation pattern of antenna  100 . A coolant inflow tube  126  is in operable fluid communication at a proximal end thereof with a source of cooling fluid (not explicitly shown), and, at a distal end thereof, coolant inflow tube  126  is in fluid communication with cooling chamber  146  to provide coolant thereto. Coolant inflow tube  126  may be formed from any suitable material, e.g., a polymeric material, such as without limitation, polyimide. In an embodiment, coolant inflow tube  126  passes through coolant inflow port  131 . In some embodiments, a coolant outflow channel  136  may be provided to facilitate removal of coolant from cooling chamber  146 , through antenna assembly  100 , to a collection reservoir (not explicitly shown). The coolant may be any suitable fluid, such as without limitation water, sterile water, deionized water, and/or saline. 
     Threaded section  145  of trocar  122  is configured to receive trocar screw  144 . Trocar screw  144  includes at the proximal end thereof an opening  143  defined therein that is configured to accept the distal end of inner coaxial conductor  150 . In embodiments, distal end of inner coaxial conductor  150  is fixed within opening  143  by any suitable manner of electromechanical attachment, such as without limitation welding, brazing, and/or crimping. As seen in  FIG. 4A , an inflow groove  147  and an outflow groove  149  are disposed longitudinally through the threaded portion of trocar screw  144  to respectively facilitate the flow of coolant into, and out of, cooling chamber  148 . Inflow groove  147  and outflow groove  149  may be configured to accommodate the insertion of coolant inflow tube  126  and/or a corresponding outflow tube (not explicitly shown). A return path  156  in the antenna assembly may additionally or alternatively provide an exit conduit for the cooling fluid. 
     In the illustrated embodiment trocar  122  and proximal antenna member  128  include a dielectric coating  121 ,  127 , respectively, on the respective outer surfaces thereof. The dielectric coating  121 ,  127  may include any suitable dielectric material, such as without limitation, ceramic material. In some embodiments, dielectric coating  121 ,  127  may be formed from titanium dioxide and/or zirconium dioxide. Dielectric coating  121 ,  127  may be applied to trocar  122  and/or proximal antenna member  128  by any suitable process, for example without limitation, plasma spraying or flame spraying. In embodiments, dielectric coating  121 ,  127  has a thickness in the range of about 0.005 inches to about 0.015 inches, During an ablation procedure, the dielectric coating  121 ,  127  may provide improved dielectric matching and/or improved dielectric buffering between the antenna and tissue, which may enable the use of higher power levels, which, in turn, may enable a surgeon to achieve greater ablation rates resulting in increased ablation size, reduced operative times, and/or improved operative outcomes. 
     An outer jacket  124  is disposed about the outer cylindrical surface of antenna assembly  100 , e.g., the distal radiating portion  105 , puck  130 , and proximal radiating section  140 . Outer jacket  124  may be formed from any suitable material, including without limitation polymeric or ceramic materials. In some embodiments, outer jacket  124  is formed from PTFE. Outer jacket  124  may be applied to antenna assembly  100  by any suitable manner, including without limitation, heat shrinking. 
     Continuing with reference to  FIGS. 4A-4D , a method of manufacturing antenna assembly  100  is disclosed wherein inner coaxial conductor  150  is inserted into opening  143  of trocar screw  144 . Inner coaxial conductor  150  is electrically fixed to trocar screw  144  by any suitable manner of bonding, such as without limitation, laser welding, brazing, or crimping. The coaxial transmission line  138  and trocar screw  144  subassembly is placed in a mold (not explicitly shown), such as without limitation an injection micro-mold, that is configured to overmold the puck  130 . Advantageously, inflow groove  147  and outflow groove  149  are aligned with mold features (not explicitly shown) corresponding to coolant inflow port  131  and coolant outflow port  133  such that when molded, a continuous fluid connection is formed between inflow groove  147  and coolant inflow port  131 , and between outflow groove  149  and outflow port  133 . 
     Puck material, e.g., ceramic, Pebax®, Ultem®, Extem®, Vespel®, or any suitable polymer having dielectric properties, is shot into the mold, allowed to cool/and or set, and subsequently released from the mold to form an assembly that includes puck  130 , trocar screw  143  and coaxial transmission line  138  as best illustrated in  FIG. 4B . The formed puck  130  includes a center section  137  having an outer diameter corresponding to the outer diameters of trocar  122  (inclusive of the thickness of dielectric coating  121 ) and/or proximal antenna member  128  (inclusive of the thickness of dielectric coating  127 ). Puck  130  further includes a distal shoulder  141  having an outer diameter corresponding to the inner diameter of trocar  122 , and a proximal shoulder  139  having an outer diameter corresponding to the inner diameter of proximal antenna member  128 . 
     Trocar  122  may then be threaded onto trocar screw  144  to form the distal radiating section  120 , as best shown in  FIG. 4C . Inflow tube  126  may then be inserted into coolant inflow port  131 . Proximal antenna member  128  may then be positioned against puck  130  such that the distal end of proximal antenna member  128  engages the proximal shoulder of puck  130 , thus forming a sealed proximal radiation section  140 . 
     Tension may be applied to inner coaxial conductor  150  and/or dielectric  132  in a proximal direction, thereby drawing together distal radiating section  105 , puck  130 , and proximal radiating section  140 , and placing puck  130  in a state of compression. Inner coaxial conductor  150  and/or dielectric  132  may be fixed in a state of tension at an anchor point  151 , by any suitable manner of fixation, including without limitation spot welding, brazing, adhesive, and/or crimping. In this manner, the antenna sections are “locked” together by the tensile force of inner coaxial conductor  150  and/or dielectric  132 , which may result in improved strength and stiffness of the antenna assembly. 
     Outer jacket  124  may be applied to the outer surface of radiating portion  12  by any suitable method, for example without limitation, heat shrinking, overmolding, coating, spraying, dipping, powder coating, baking and/or film deposition. 
     It is contemplated that the steps of a method in accordance with the present disclosure can be performed in a different ordering than the ordering provided herein. 
     Turning now to  FIGS. 6A and 6B , views of a distal end of a microwave antenna in accordance with an embodiment of the present disclosure are presented wherein  FIG. 6A  illustrates a cross-sectional view taken in a plane which exposes, inter alia, coolant inflow tube  126  and coolant outflow channel  136 .  FIG. 6B  exposes a plane oriented approximately perpendicular to that of  FIG. 6A , which illustrates, inter alia, a relationship between trocar screw  144 , inner conductor  150 , and puck  130 . 
     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.