Abstract:
A microwave surgical ablation probe having an arrangement of coolant channels in fluid communication with a cooling chamber disposed within the distal end of the probe is disclosed. A hypotube having one or more longitudinal ribs extending radially inward from an inner surface thereof is coaxially disposed around a coaxial feedline. The longitudinal ribs of the hypotube engage an outer sheath of the feedline to define a fluid inflow channel to deliver coolant to the cooling chamber, and a fluid outflow channel to receive fluid from the cooling chamber. The cooling chamber may be formed from porous ceramic or porous metallic material that provides structural support to the probe while permitting coolant to circulate therethrough. The probe includes dielectric and choke members that are adapted to control the microwave radiation pattern (e.g., ablation shape), and which may provide improved coupling of the probe to tissue.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to systems and methods for providing energy to biological tissue and, more particularly, to a microwave ablation surgical probe having a porous core through which coolant is circulated and methods of use and manufacture therefor. 
         [0003]    2. Background of Related Art 
         [0004]    Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal, laser, etc.) are applied to tissue to achieve a desired result. Microwave energy can be delivered to tissue using an antenna probe. 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 positioned proximally of the dielectric junction, and the other portion is positioned distally of the dielectric junction. In monopole and dipole antenna probes, microwave energy generally radiates perpendicularly from the axis of the conductor. 
         [0005]    A 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. 
         [0006]    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 inserted percutaneously. 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. 
         [0007]    One approach to controlling probe and/or tissue temperature is to circulate coolant within the probe to extract excess heat from the probe. However, providing coolant passages within a probe may reduce probe strength, because such passages necessitate the introduction of voids into the probe structure. 
         [0008]    In some surgical procedures, a microwave antenna probe may be inserted percutaneously into, for example, a chest wall of a patient. During such a procedure, negotiating the probe through, for example, fibrous thoracic tissue and ribs may place undue stresses on the probe. Additionally, a cooled probe may lack sufficient strength to withstand the stresses imposed by such percutaneous insertions, which may result in probe failure. 
       SUMMARY 
       [0009]    The present disclosure provides a high-strength electromagnetic surgical ablation probe that includes a cooled and dielectrically buffered antenna assembly. A cable provides electromagnetic energy to the probe via a coaxial conductor and/or provides coolant via a fluid conduit to improve power delivery performance and power handling, and to reduce component temperatures. Suitable coolants include deionized water, sterile water, or saline. 
         [0010]    The disclosed ablation probe includes a coaxial feedline having in coaxial arrangement an outer sheath, an outer conductor, an inner conductor, and a dielectric disposed between the outer conductor and the inner conductor. The inner conductor extends distally beyond the outer sheath, the outer conductor, and the dielectric, e.g., the outer layers of the feedline may be stripped leaving the inner conductor extending distally. A hypotube is coaxially disposed around the feedline. The hypotube includes one or more longitudinal ribs extending radially inward from an inner surface of the hypotube. The ribs extend from the inner surface of the hypotube to an outer surface of the feedline to define one or more fluid channels between the feedline and the hypotube. During manufacture, the ribs may be formed in the hypotube by being drawn into the tubing, extrusion, and/or formed by welding two or more semicircular “clamshell” halves of the hypotube together. 
         [0011]    A feed point seal joins a distal end of the hypotube to a porous core enclosed within the probe distal radiating section. The feed point seal includes one or more an openings defined therethrough to provide a fluid path between the fluid channels and the porous core. The feed point seal includes an opening, which may be axially positioned, to enable the inner conductor to pass therethough, e.g., to extend distally into the porous core. The feed point seal additionally or alternative seals one or more conductors of the feedline, which may help prevent coaxial feedline short circuiting (e.g., shorts between conductors and/or other elements of the probe). 
         [0012]    A microwave ablation antenna in accordance with the present disclosure may be configured to operate in a range of about 915 MHz to about 2.45 GHz, or within any other suitable frequency range. In one embodiment, the hypotube ribs press into the coaxial cable thereby forming a separate fluid inflow channel and fluid outflow channel. A coolant, such as saline or dionized water, is introduced into a proximal end of the inflow channel, from where it flows distally, though openings in the feed point seal into a radiating section that includes a radiating section having a porous core. The porous core is perfused with coolant, which may help to reduce probe temperatures, and may provide improved dielectric coupling between the probe and tissue. The dual-chamber design of the disclosed probe may provide better coolant dispersion within the probe, thereby providing increased coolant efficiency, and allowing the size of the probe to be greatly reduced. 
         [0013]    The porous perfused core may include a separator to define a two chamber perfusion arrangement wherein coolant would first travel distally past the distal radiating section through an inflow chamber region, then return proximally through an outflow chamber region. The porous core may be formed from porous ceramic, porous metal, or any suitable material that permits coolant fluid to circulate. Additionally, the porous core may add strength to the dielectric surface of the probe. 
         [0014]    A dielectric coating may enclose the entire probe and act as the dielectric match between the probe and tissue The coating may act as a sealing layer for the entire probe, and may be formed form lubricious material to facilitate the insertion of the probe percutaneously into tissue. 
         [0015]    Also disclosed is a microwave ablation system that includes a source of ablation energy, e.g., a microwave generator, that is operably coupled to a perfused core dielectrically loaded dipole microwave antenna probe as described herein. The disclosed system may include a source of coolant operably coupled to the probe, e.g., to the hypotube. 
         [0016]    Also disclosed is a method of manufacturing a perfused core dielectrically loaded dipole microwave antenna probe that includes the steps of providing a hypotube having one or more longitudinal ribs extending radially inward from an inner surface thereof. A coaxial feedline is provided. The coaxial feedline has, in coaxial arrangement, an outer sheath, an outer conductor, an inner conductor, and a dielectric disposed between the outer conductor and the inner conductor. The inner conductor extends distally beyond the outer sheath, the outer conductor, and the dielectric. The inner conductor may be extended by, for example and without limitation, stripping the outer layers of the coaxial feedline to expose the inner conductor. The hypotube is mounted over the feedline to form a fluid channel between the inner surface of the hypotube, the one or more ribs, and an outer surface of the feedline. A feed point seal is overmolded at a distal end of at least one of the hypotube, the sheath, the outer conductor, or the dielectric, and the porous core is mounted to a distal end of the feed point seal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    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: 
           [0018]      FIG. 1  shows a diagram of a microwave ablation system having a cooled electromagnetic surgical ablation probe in accordance with an embodiment of the present disclosure; 
           [0019]      FIG. 2  shows a cross sectional view of an embodiment of a cooled surgical ablation probe in accordance with the present disclosure; 
           [0020]      FIG. 3A  shows a section view of the cooled surgical ablation probe of  FIG. 2 ; 
           [0021]      FIG. 3B  shows another section view of the cooled surgical ablation probe of  FIG. 2 ; 
           [0022]      FIG. 3C  shows yet another section view of the cooled surgical ablation probe of  FIG. 2 ; and 
           [0023]      FIG. 4  shows a perspective view depicting coolant flow of an embodiment of cooled surgical ablation probe in accordance with the present disclosure; 
           [0024]      FIG. 5A  shows a detail, perspective view of a hypotube in accordance with the present disclosure; and 
           [0025]      FIG. 5B  shows a detail, perspective view of another hypotube in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Particular embodiments of the present disclosure will be described hereinbelow with reference to the accompanying drawings; however, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms. Well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. 
         [0027]    In the drawings and in the descriptions that follow, the term “proximal,” as is traditional, shall refer to the end of the instrument that is closer to the user, while the term “distal” shall refer to the end that is farther from the user. 
         [0028]      FIG. 1  shows an embodiment of a microwave ablation system  100  in accordance with the present disclosure. The microwave ablation system  100  includes an ablation probe  10  connected by a cable  15  to connector  16 , which may further operably connect the probe  10  to a generator assembly  28 . Probe  10  includes a proximal radiating section  140  and a distal radiating section  105 . 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. Alternatively, tip  123  may be rounded or flat, and may include a forceps or a blade. Generator assembly  28  may be a source of ablation energy, e.g., microwave energy in the range of about 915 MHz to about 2.45 GHz. Cable  15  may additionally or alternatively provide a conduit (not explicitly shown) configured to provide coolant from a coolant source  18  to the ablation probe  10 . 
         [0029]    With additional reference to  FIG. 2 , an embodiment of an ablation probe  100  includes a coaxial feedline  110  that extends from a proximal end of the probe  10 , which may include a handle (not explicitly shown), wherein the coaxial feedline  110  is adapted to provide radiofrequency and/or microwave ablation energy to the probe  10  generally, and more specifically, to proximal radiating portion  140  and distal radiating portion  105 . Coaxial feedline  110  may exhibit an impedance of 50Ω. Coaxial feedline  110  includes, in coaxial arrangement, an outer coaxial conductor  152 , a dielectric layer  154  coaxially disposed within outer coaxial conductor  152 , and an inner conductor  156  coaxially disposed within dielectric layer  154 . Inner conductor  156  of coaxial feedline  110  extends distally through a feed point seal  135  into porous core  114 , as will be described further hereinbelow. An insulating outer sheath  150  may be coaxially disposed around outer coaxial conductor  152 . 
         [0030]    A tubular hypotube  134  is positioned coaxially around feedline  100  to form one or more fluid channels  141 ,  142 . Hypotube  134  extends from a proximal end of the probe  10  to the feed point seal  135 . Hypotube  134  includes one or more dividing ribs  136  ( FIG. 3A ) positioned longitudinally along an inner surface  137  of hypotube  134 . Dividing ribs  136  are dimensioned to extend from an inner surface  137  of hypotube  134  to an outer surface  151  of outer sheath  150  of feedline  100 , as seen in  FIGS. 3A and 5A . Inner edge  139  of rib  136  is adapted to engage the outer sheath  150  of feedline  100 . In an embodiment, ribs  136  are dimensioned to press into outer sheath  150  to form a fluid-tight seal. Additionally or alternatively, hypotube  134  may have a double-walled construction as best seen in  FIG. 5B , wherein ribs  136  extend inwardly to an inner hypotube tube  138  concentrically positioned therein. Inner hypotube  138  has an inner diameter dimensioned to receive feedline  110 , e.g., the inner diameter of inner hypotube  138  is about equal to the outer diameter of outer sheath  150 . 
         [0031]    Hypotube  134  and ribs  136  (as arranged around outer sheath  150  and/or inner hypotube  138 ) define a fluid inflow channel  141  and a fluid outflow channel  142 , each having a proximal end and a distal end. A proximal end of fluid inflow channel  141  may be in operable fluid communication with a source of coolant  18 , such as without limitation, saline and/or deionized water. A proximal end of fluid outflow channel  142  may be configured to expel spent coolant. Additionally or alternatively, outflow channel  142  may be configured to direct spent fluid to a reservoir (not explicitly shown), and/or to direct coolant to a circulator for re-use. 
         [0032]    Continuing with reference to  FIG. 3B , feed point seal  135  is positioned at a distal end  143  of hypotube  134 . Feed point seal  135  includes one or more inflow holes  171  and/or outflow holes  172  defined therein that are adapted to permit the passage of coolant through feed point seal  135 . Inflow holes  171  are positioned at a distal end of inflow channel  141  and are adapted to direct coolant to flow from inflow channel  141  into an inflow region  115  of porous core  114 . Outflow holes  172  are positioned at a distal end of outflow channel  142  and are adapted to direct coolant flow from an outflow region  116  of porous core  114  to outflow channel  142 . 
         [0033]    As shown in  FIG. 4 , during use, coolant flows distally through inflow channel  141 , through inflow holes  171 , and into an inflow region  115  of porous core  114 . Coolant flows proximally from an outflow region  116  of porous core  114 , though outflow holes  172 , and continues proximally though outflow channel  142 . Coolant circulating through porous core  114  in the described manner cools distal radiating section  105  and/or tip  120 , and may dielectrically load ablation energy radiating from inner conductor  156  to tissue. Feed point seal  135  includes a center opening  157  defined therein that is configured to accommodate the passage of inner conductor  156  therethough and to provide a fluid-tight seal to prevent leakage or backflow of coolant into coaxial feedline  110 . 
         [0034]    Feed point seal  135  is sealably coupled to hypotube  134  using any suitable manner of fluid sealing. Feed point seal  135  may additionally or alternatively form a fluid-tight seal around inner conductor  156 . Feed point seal  135  may additionally or alternatively encapsulate a distal end of one or more of outer sheath  150 , outer conductor  152 , and/or dielectric layer  154 , which may prevent electrical short circuiting therebetween. Feed point seal  135  may be formed by overmolding over a distal end  143  of hypotube  134 , e.g., formed by molding feed point seal  135  in place thereby forming a fluid-tight seal between a distal end  143  of hypotube  134  and feed point seal  134 . Feed point seal  135  may be formed from any suitable material that can withstand probe operating temperatures and that is electrically non-conductive, for example without limitation, polyether block amide, such as Pebax®, manufactured by The Arkema Group of Colombes, France; polyetherimide (PEI), such as Ultem® and/or Extern®, manufactured by SABIC Innovative Plastics of Saudi Arabia; and/or polyimide-based polymer, such as Vespel®, manufactured by E.I. du Pont de Nemours and Company of Wilmington, Del., United States. 
         [0035]    Distal radiating section  105  includes an outer dielectric surface  106  and a porous core  114  therein. Porous core  114  may include an inflow region  115  and an outflow region  116  having a separator  175  disposed therebetween. One or more openings (not explicitly shown) may be defined within separator  175  to enable coolant to flow from inflow region  115  to outflow region  116 . Porous core  114  may be formed from any suitable material that provides radial support to outer dielectric surface  106  and that enables coolant perfusion within porous core  114 . For example, and without limitation, porous core  114  may be formed from a porous ceramic material having an open cell, closed cell, tangle fiber network, and/or membrane structure. In an embodiment, porous core  114  may be formed from a metallic material, such as without limitation, stainless steel, titanium, nickel, nickel alloys, and bronze formed by any suitable manner of manufacture, e.g., powder compaction sintering, gravity sintering, powder rolling and sintering, isostatie compaction and sintering, metal spraying, metal coating and sintering, metal injection molding and sintering, and/or any other suitable manner of porous metal forming. 
         [0036]    As best illustrated in  FIG. 2 , probe  10  includes a substantially cylindrical dielectric choke  130  concentrically disposed about a proximal portion of hypotube  134  wherein an inner diameter of dielectric choke  130  is about equal to an outer diameter of hypotube  134 . Dielectric choke includes a distal portion  131  that has an outer diameter about equal to the outer diameter of distal radiating section  105 , and includes a proximal portion  132  that has an outer diameter about equal to an inner diameter of a tubular choke outer jacket  116 . Choke outer jacket  116  may be formed from any suitable heat-resistant metallic material, e.g., stainless steel. Dielectric choke  130  may be formed from material having low electrical conductivity at probe operating frequencies, e.g., elastomeric polymers, epoxy-fiber composites, and the like. A distal end  131  of dielectric choke  130  is joined to a proximal end  117  of outer dielectric surface  106 . Hypotube  134  extends distally beyond a distal end  131  of dielectric choke  130  and/or extends distally beyond a proximal end  117  of outer dielectric surface  106  such that feed point seal  135  is positioned within outer dielectric surface  106  at a point distally of proximal end  117  of outer dielectric surface  106 . 
         [0037]    An outer surface of the probe  10 , e.g., an outer surface of choke outer jacket  116 , dielectric choke  130 , dielectric surface  106 , and/or tip  120 , may include a dielectric coating (not explicitly shown). The dielectric coating may be formed from any suitable material having the ability to withstand the operating temperature of the probe and having a low electrical conductivity at probe operating frequencies, such as without limitation, polytetrafluoroethylene (a.k.a. PTFE or Teflon®, manufactured by the E.I. du Pont de Nemours and Co. of Wilmington, Del., USA), polyethylene tephthalate (PET), or the like. Additionally or alternatively, an outer surface of the probe  10  as previously described may include a heat shrink covering, such as polyolefin tubing, or any suitable heat-shrink material. The dielectric coating and/or heat shrink covering may provide a lubricious interface between the probe  10  and tissue to reduce or prevent undesirable adhesion of tissue to the probe  10 , and to aid insertion of the probe  10  into tissue. 
         [0038]    A method of manufacturing an ablation probe  10  in accordance with the present disclosure includes the steps of providing a hypotube  134  having one or more longitudinal ribs  136  extending radially inward from an inner surface  137  thereof. Hypotube  134  and/or ribs  136  may be formed by any suitable manner of manufacture, including without limitation by extrusion and/or welding. Hypotube  134  may be constructed by joining two or more semicircular sections (not explicily shown) along a common longitudinal edge thereof to form the generally tubular shape of hypotube  134 . A coaxial feedline  110  may be provided, wherein the feedline includes (in coaxial arrangement) an outer sheath  150 , an outer conductor  152 , an inner conductor  156 , and a dielectric  154  disposed between the outer conductor  152  and the inner conductor  156 , wherein the inner conductor  156  extends distally beyond the outer sheath  150 , the outer conductor  152 , and the dielectric  154 . The inner conductor  156  may be extended by stripping outer sheath  150 , outer conductor  152 , and dielectric  154  as will be familiar to the skilled artisan. 
         [0039]    Hypotube  134  is mounted over the feedline  134  to form one or more fluid channels defined between an inner surface  137  of hypotube  134 , the one or more ribs  136 , and an outer surface of the sheath (not explicitly shown). A distal end  143  of hypotube  134  is substantially aligned with a distal end of outer sheath  150 , outer conductor  152 , and/or dielectric  154 . A feed point seal  135  may be mounted at a distal end of at least one of the sheath  150 , the outer conductor  152 , or the dielectric  154 . The feed point seal  135  may be formed in place by overmolding whereby the sheath  150 , the outer conductor  152 , and/or the dielectric  154  are encapsulated within the feed point seal  135 . During the overmolding step, the inner conductor  156  extends distally through the feed  134 . In this manner, a fluid-tight seal may be formed between inner conductor  156  and feed point seal  134 . 
         [0040]    A proximal end of porous core  114  is mounted to a distal end of the feed point seal  135 . Porous core  114  may be mounted within distal radiating section  105  and/or tip  120 . Porous core  114  may additionally or alternatively be formed within distal radiating section  105  and/or tip  120 , and mounted to a distal end of the feed point seal. Feed point seal  135  may additionally or alternatively be overmolded over the combination of feedline  110  (including without limitation sheath  150 , outer conductor  152 , dielectric  154 , and/or inner conductor  156 ) and porous core  114 . 
         [0041]    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.