Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 60/828,955, filed 10 Oct. 2006, which is hereby incorporated by reference as though fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    A. Field of the Invention 
         [0003]    The present invention relates to irrigated catheter assemblies. The present invention further relates to ablation electrodes and assemblies, including electrode assemblies having distal irrigation fluid flow. The present invention further relates to ablation electrode assemblies having at least one temperature sensing device and a mechanism for irrigating the ablation assembly and targeted areas. The present invention further relates to methods for improved assembly and accurate measurement and control of the electrode temperatures while effectively irrigating the device and target areas. 
         [0004]    B. Background Art 
         [0005]    Electrophysiology catheters are used for an ever-growing number of procedures. Catheters are used for diagnostic, therapeutic, and ablative procedures, to name just a few examples. Typically, a catheter is manipulated through the patient&#39;s vasculature and to the intended site, for example, a site within the patient&#39;s heart. The catheter typically carries one or more electrodes, which may be used for ablation, diagnosis, or other treatments. 
         [0006]    There are a number of methods used for ablation of desired areas, including for example, radiofrequency (RF) ablation. Ablation may be facilitated by transmission of energy from an electrode assembly to ablate tissue at the target site. Because ablation may generate significant heat, which if not controlled can result in excessive tissue damage, such as steam pop, tissue charring, and the like, it is desirable to include a mechanism to irrigate the target area and the device with biocompatible fluids, such as water or saline solution. The use of irrigated ablation catheters can also prevent the formation of soft thrombus and/or blood coagulation. 
         [0007]    Typically, there are two classes of irrigated electrode catheters, open and closed irrigation catheters. Closed ablation catheters usually circulate a cooling fluid within the inner cavity or lumen provided by the ablation electrode. Open ablation catheters typically deliver the cooling fluid through open outlets or openings to a surface of the electrode. Open ablation catheters use an inner cavity or lumen of the electrode, as a manifold to distribute saline solution, or other irrigation fluids known to those skilled in the art, to one or more passageways that lead to an opening/outlet provided on the surface of the electrode. The cooling fluid thus flows through the outlets of the passageways onto the electrode member. This flow through the electrode tip lowers the temperature of the tip during operation, often making accurate monitoring and control of the ablative process more difficult. 
         [0008]    In general, open irrigated ablation catheters may improve the function and safety associated with catheter ablation by preventing protein aggregation and blood coagulation. A particular area of the electrode/catheter where the formation of coagulum or thrombus may occur during ablation procedures is at the distal end or tip of the electrode. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention is directed to improved ablation electrode assemblies and methods useful in conjunction with irrigated catheter devices and other ablation catheters. Embodiments of the present invention provide an irrigated catheter having irrigation fluid directed at target areas where coagulation is more likely to occur so as to minimize blood coagulation and associated problems. The present invention includes various embodiments of irrigation electrode assemblies having a passageway for minimizing the blood coagulation and related problems occurring at or about the distal end of the electrode. 
         [0010]    Accordingly, the present invention includes an irrigated ablation electrode assembly. The electrode assembly includes a proximal member having an outer surface and an inner lumen. The electrode assembly further includes a distal member having an outer surface and a distal end. The proximal member and distal member are configured for connection with one another. The assembly further includes at least one proximal passageway extending from the inner lumen to the outer surface of the proximal member. The assembly further includes a distal passageway extending from the inner lumen through the distal member to the distal end of the electrode assembly. In an embodiment, the proximal passageway is separated from and does not come in contact with the distal member. 
         [0011]    The present invention further includes an alternate embodiment of an irrigated ablation electrode assembly. In an alternate embodiment, the electrode assembly includes a proximal member having an outer surface and an inner lumen. The electrode assembly further includes a distal member having an outer surface and a distal end. The proximal member and distal member are configured for connection with one another. The assembly further includes at least one proximal passageway extending from the inner lumen to the outer surface of the proximal member. The assembly further includes a distal passageway extending from the inner lumen through the distal member to the distal end of the electrode assembly. According to the alternate embodiment, the proximal member has a lower thermal conductivity than the distal member. 
         [0012]    The present invention further includes an alternate embodiment of an irrigated ablation electrode assembly. In an alternate embodiment, the electrode assembly includes a proximal member having an outer surface and an inner lumen. The electrode assembly further includes a distal member having an outer surface and a distal end. The proximal member and distal member are configured for connection with one another. The assembly further includes at least one proximal passageway extending from the inner lumen to the outer surface of the proximal member. The assembly further includes a distal passageway extending from the inner lumen through the distal member to the distal end of the electrode assembly. The assembly further includes an insulating member at least partially separating the distal passageway from the distal member, wherein the insulating member has a lower thermal conductivity than the distal member. 
         [0013]    The present invention further includes an alternate embodiment of an irrigated ablation electrode assembly. In an alternate embodiment, the electrode assembly includes a proximal member having an outer surface and an inner lumen. The electrode assembly further includes a distal member having an outer surface and a distal end. The proximal member and distal member are configured for connection with one another. The assembly further includes at least one proximal passageway extending from the inner lumen to the outer surface of the proximal member. The assembly further includes a distal passageway extending from the inner lumen through the distal member to the distal end of the electrode assembly. In accordance with an alternate embodiment, the inner lumen includes a hydrophilic coating. 
         [0014]    The foregoing and other aspects, features, details, utilities, and advantages of the present invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]      FIG. 1  is an isometric view of an ablation electrode according to an embodiment of the present invention; 
           [0016]      FIG. 2  is an enlarged isometric view of the distal end of the ablation electrode as shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a side cross-sectional view of a distal member of an ablation electrode according to an alternate embodiment of the present invention; 
           [0018]      FIG. 4  is a side cross-sectional view of a distal member of an ablation electrode according to an alternate embodiment of the present invention; 
           [0019]      FIGS. 5-7  are side cross-sectional views of ablation electrodes according to alternate embodiments of the present invention; 
           [0020]      FIG. 8  is an illustrative view of visualized irrigation flow from an ablation electrode according to an alternate embodiment of the present invention; and 
           [0021]      FIG. 9  graphically depicts general bench test results for ablation electrode assemblies in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    In general, the instant invention relates to irrigated ablation electrode assemblies, to catheter assemblies, as well as ablation systems employing the irrigated ablation electrode assemblies ,  10  and  10 ′, in connection with catheter assemblies. For purposes of this description, similar aspects among the various embodiments described herein will be referred to by the same reference number. As will be appreciated, however, the structure of the various aspects may differ with respect to alternate embodiments. 
         [0023]    As generally shown in the embodiment illustrated in  FIG. 1 , the ablation electrode assembly  10  may comprise part of an irrigated ablation catheter assembly  12 . The embodiments describe RF ablation electrodes and assemblies, but it is contemplated that the present invention is equally applicable to any number of other ablation electrodes and assemblies where the temperature of the device and the targeted tissue area may be factors during the procedure.  FIGS. 3-8  as discussed in more detail below, illustrate ablation electrode assemblies  10 ,  10 ′ according to alternate embodiments of the present invention. 
         [0024]    In accordance with an embodiment,  FIG. 1  generally illustrates an ablation electrode assembly  10  connected to catheter shaft  14  as part of irrigated ablation catheter assembly  12 . The assembly  12  includes at least one fluid delivery tube  16 . Ablation electrode assembly  10  includes a proximal member  18 , also referred to as an irrigation member or manifold, and a distal member  20 , also referred to as an ablation electrode member. Proximal member  18  and distal member  20  are configured to be connected together. The orientation of members  18 ,  20  are generally such that distal member  20 , which provides an ablation electrode or an ablative surface, is situated at the distal end of assembly  10 . Proximal member  18 , or irrigation member, is located at the proximal end of assembly  10 , although for some embodiments the orientation could be reversed. Proximal member  18  includes an outer surface  22 . Proximal member  18  further includes at least one fluid or irrigation passageway  24 , also referred to as proximal passageway  24 , that extends from an inner lumen  26 , for example as generally shown in  FIGS. 5-7 , to outer surface  22  of proximal member  18 . Inner lumen  26  is in fluid communication with fluid delivery tube  16 . As can be further seen in  FIGS. 2-4 , distal member  20  includes a distal passageway  28  that extends to distal end  30  of electrode assembly  10 . Fluid passageways  24  of proximal member  18  and distal passageway  28  allow for increased irrigation of electrode assembly  10  during the ablation of tissue. Proximal passageway  24  is separated from and does not come in contact with distal member  20 . 
         [0025]    Distal member  20 , as shown in  FIGS. 3 and 4 , is generally comprised of an electrically, and potentially thermally, conductive material known to those of ordinary skill in the art for delivery of ablative energy to target tissue areas. Examples of electrically conductive material include gold, platinum, iridium, palladium, stainless steel, and various mixtures and combinations thereof. In an embodiment, the distal member may be hemispherical or semispherical in shape, although other configurations may be used. 
         [0026]    Distal member  20  may further include an inner cavity  32  for receiving a portion of proximal member  18 , as further discussed below. Distal member  20  further includes an aperture  34  therein forming distal passageway  28 . Aperture  34  extends through distal member  20  to distal end  30  therein providing an opening or outlet for distal passageway  28  on the surface of distal member  20 . Distal member  20  may further be configured with one or more component cavities  36  for receiving and/or housing additional components within distal member  20 . 
         [0027]    As can be seen in  FIG. 4 , at least one temperature sensor  38 , also referred to as a temperature or thermal sensing device, may be provided within a portion (e.g., cavity  36 ) of distal member  20 . In an alternate embodiment, two temperature sensors may be provided within cavities  36  of distal member  20 . Various configurations of distal member  20  may include temperature sensor  38  in different locations and proximities within distal member  20 . In an alternate embodiment, the temperature sensor  38  may be either partially or completely surrounded by or encapsulated by an insulation liner  40  that is made of thermally conductive and electrically non-conductive materials. Insulation liner  40  may be provided in various configurations, such as provided by a tube-like configuration, as shown in  FIG. 4 . Liner  40  may be comprised of various materials, such as for example polyimide tubing. 
         [0028]    As generally illustrated in  FIG. 4 , distal member  20 , may further include an insulating member  42 , i.e. thermal liner, disposed within aperture  34 , forming distal passageway  28  of distal member  20 . Insulating member  42  may be comprised of a non and/or poor thermally conductive material. Such material may include, but is not limited to, high-density polyethylene, polyimides, polyaryletherketones, polyetheretherketones, polyurethane, polypropylene, oriented polypropylene, polyethylene, crystallized polyethylene terephthalate, polyethylene terephthalate, polyester, polyetherimide, acetyl, ceramics, and various combinations thereof. Insulating member  42  may be generally provided in a configuration that reflects the size and shape of aperture  34 , although the insulating member  42  generally extends to meet and connect to inner lumen  26  of proximal member  18 . Distal passageway  28  is therein created for the flow of fluid from proximal member  18 , for example, as generally shown in  FIGS. 5-7 , through distal passageway  28  to distal end  30  of assembly  10 . 
         [0029]    An alternate embodiment of distal member  20  includes a cavity  44  for receiving a power wire  46  (see, e.g.,  FIGS. 5-7 ) for connecting distal member  20  to an energy source, such as an RF energy source. In an alternate embodiment, cavity  44  may further include a non and/or poor thermally conductive material. Furthermore, in an alternate embodiment, power wire  46  may be soldered directly to distal member  20 , or attached and/or connected to distal member  20  through the use of an adhesive or any other connection method known to one of ordinary skill in the art. 
         [0030]      FIGS. 5-7  generally illustrate alternate embodiments of electrode assembly  10 ,  10 ′ of the present invention. As previously described, proximal member  18 ,  18 ′ and distal member  20  are configured to be connected and/or coupled together with one another. Proximal member  18 ,  18 ′ is comprised of a thermally nonconductive or reduced (i.e. poor) thermally conductive material that serves to insulate the fluid from the remaining portions of electrode assembly  10 , in particular distal member  20 . Moreover, proximal member  18 ,  18 ′ may comprise an electrically nonconductive material. Comparatively, overall, proximal member  18 ,  18 ′ may have lower thermal conductivity than distal member  20 . In an embodiment, proximal member  18 ,  18 ′ is made from a reduced thermally conductive polymer. A reduced thermally conductive material is one with physical attributes that decrease heat transfer by about 10% or more, provided that the remaining structural components are selected with the appropriate characteristics and sensitivities to maintain adequate monitoring and control of the process. One reduced thermally conductive material may include polyether ether ketone (“PEEK”). Further examples of reduced thermally conductive materials useful in conjunction with the present invention include, but are not limited to, high-density polytheylene, polyimides, polyaryletherketones, polyetheretherketones, polyurethane, polypropylene, oriented polypropylene, polyethylene, crystallized polyethylene terephthalate, polyethylene terephthalate, polyester, polyetherimide, acetyl, ceramics, and various combinations thereof. Moreover, proximal member  18  is substantially less thermally conductive than distal member  20 . As a result, the irrigation fluid flowing through proximal member  18  has very little thermal effect on distal member  20  due to the poor thermal conductivity of proximal member  18  (e.g. less than 5% effect), and preferably nearly 0% effect. In general, characteristics and descriptions (e.g. composition and materials) regarding proximal member  18  and  18 ′ may be used interchangeably, among various embodiments except for the specific descriptions provided regarding the design of proximal member  18 ′ in accordance with the embodiment provided in  FIG. 7 . 
         [0031]    The proximal member  18  may further be configured to include a coupling portion  48  that extends into inner cavity  32  of distal member  20 . Proximal member  18  may be generally cylindrical in shape. Moreover, for some embodiments, distal member  20  of ablation electrode assembly  10  may have a generally cylindrical shape terminating in a hemispherical distal end  30 . The cylindrical shape of proximal member  18  and distal member  20  may be substantially similar to one another and generally have the same overall diameter, which can provide or create a smooth outer body or profile for electrode assembly  10 . Distal member  20  may be configured to accept portion  48  of proximal member  18  for attachment thereto. The distal member  20  may be connected by any known mechanism including adhesives, press-fit configurations, snap-fit configurations, threaded configurations, or any other mechanism known to one of ordinary skill in the art. 
         [0032]    Proximal member  18  may further include an inner lumen  26  that is connected to fluid delivery tube  16 . The inner lumen  26  may act as a manifold or distributor for transporting and/or distributing fluid throughout electrode assembly  10 . In particular, proximal member  18  may be configured to receive a fluid delivery tube  16  carried within at least a portion of catheter assembly  12 . Proximal member  18  includes a plurality of passageways  24 . Proximal member  18  may serve as a manifold or distributor of fluid to electrode assembly  10  through the use of passageways  24 . Proximal passageways  24  may extend from inner lumen  26  axially toward outer surface  22  of proximal member  18 . In an embodiment, a plurality of passageways  24  are substantially equally distributed around proximal member  18  to provide substantially equal distribution of fluid to the targeted tissue area and/or the outside of electrode assembly  10 . Electrode assembly  10  may be configured to provide a single, annular passageway  24 , or a number of individual passageways  24  equally distributed around the proximal member  18 . Moreover, the passageways  24  may be generally tubular and may have a constant diameter along the length of the passageway. Alternate configurations having various diameters along all or portions of the length of the passageways may be used. 
         [0033]    As shown in  FIGS. 5-7 , proximal passageways  24  may be directed towards or extend towards distal member  20  of electrode assembly  10  at an angle (Θ) less than 90 degrees from the central longitudinal axis of proximal member  18 . In an embodiment, passageways  24  extends at an angle (Θ) between about 20 to about 70 degrees, and for some embodiments, between about 30 to about 60 degrees. Alternate positions and angles of the passageway(s)  24  may be provided in alternate embodiments of electrode assembly  10 . 
         [0034]    Distal passageway  28  is provided for and extends along the central longitudinal axis of proximal member  18  through distal member  20  to distal end  30  of electrode assembly  10 . As shown in  FIGS. 5 and 6 , distal passageway  28  may further be fully or partially surrounded by a thermally non-conductive material, such as that provided by insulating member  42 . Insulating member  42  prevents saline or any other biocompatible fluid from coming in contact with distal member  20 . Insulating member  42  may be comprised of a thermally non-conductive material such as, but not limited to, high-density polyethylene, polyimides, polyaryletherketones, polyetheretherketones, polyurethane, polypropylene, oriented polypropylene, polyethylene, crystallized polyethylene terephthalate, polyethylene terephthalate, polyester, polyetherimide, acetyl, ceramics, and various combinations thereof. 
         [0035]    Distal passageway  28  extends from inner lumen  26  provided by proximal member  18 . In general, the diameter of distal passageway  28  is less than the diameter of inner lumen  26  of proximal member  18 . Accordingly, in one embodiment, inner lumen  26  and distal passageway  28  may be connected by a tapered transition portion  50  therein providing constant fluid communication. The angle of the tapered transition portion may vary depending on the diameters of the inner lumen  26  and distal passageway  28 , as well as the length of proximal member  18 . The presence of the tapered transition portion  50  between inner lumen  26  and distal passageway  28  prevents air bubbles from being trapped inside the proximal member during fluid flow through the lumen and passageways. In an embodiment, distal passageway  28  is slightly larger in diameter than passageways  24  provided by the proximal member. The diameter of passageways  24  and distal passageways  28  may vary depending on the configuration and design of electrode assembly  10 . In an embodiment, distal passageway  28  includes a diameter within the range of about 0.012 to about 0.015 inches, more particularly about 0.013 to about 0.014 inches. In another embodiment, proximal passageways  24  include a diameter within in the range of about 0.011 to about 0.014 inches, more particularly about 0.011 to about 0.013 inches. 
         [0036]    In another embodiment, the inner surface of inner lumen  26  may be either coated with a hydrophilic coating or surface treated to create a hydrophilic surface. The treatment of inner lumen  26  with a hypdrophilic surface or coating results in another method of preventing air bubbles from becoming trapped inside proximal member  18 . The hydrophilic coating materials may include, but are not limited to, block copolymers based of ethylene oxide and propylene oxide, polymers in the polyethylene glycol family and silicone. For example, those materials selected from the group including PLURONIC® from BASF, CARBOWAX® from Dow Chemical Company and SILASTIC MDX® from Dow Corning. 
         [0037]    Alternate embodiments of the present invention provide the incorporation of at least one temperature sensor  38  in combination with distal passageway  28 . In particular, an embodiment, as shown in  FIG. 5 , includes two temperature sensors  38  provided within cavities  36  of distal member  20 . In an alternate embodiment, as shown in  FIG. 6 , one temperature sensor is provided within a single cavity  36 . Temperature sensors may include various temperature sensing mechanisms, such as a thermal sensor, disposed therein for measurement and control of electrode assembly  10 . The temperature sensor  38  can be any mechanism known to one of skill in the art, including for example, thermocouples or thermistors. The temperature sensor  38  may further be surrounded, or encapsulated, by a thermally conductive and electrically non-conductive material, as previously discussed. This thermally conductive and electrically non-conductive material can serve to hold temperature sensor  38  in place within distal member  20  and provide improved heat exchange between temperature sensor  38  and distal member  20 . This material may be comprised of a number of materials known to one of ordinary skill in the art, including for example, thermally conductive resins, epoxies, or potting compounds. 
         [0038]    In another embodiment of electrode assembly  10 , as seen in  FIG. 7 , proximal member  18 ′ includes proximal end  52  and an extended distal end  54  that is received within aperture  34  of distal member  20  when proximal member  18 ′ and distal member  20  are configured for connection. Distal member  20  provides a proximal surface  56  and well the surface  60  provided by inner cavity  32  that may be connected to proximal member  18 ′ through the use of bonding or adhesive  58 , therein coupling and/or connecting proximal member  18 ′ with distal member  20 . Inner lumen  26 ′ extends from proximal end  52  to distal end  54  of proximal member  18 ′. Accordingly proximal member  18  is configured to provide the insulating portion of distal passageway  28  through distal member  20 . As a result, the non-thermally conductive material of the proximal member, as previously described above, insulates distal passageway  28  through distal member  20 . Proximal member  18 ′ further includes proximal passageways  24 , as described above that allow fluid flow from inner lumen  26 ′ to outer surface  22 ′ of proximal member  18 ′. Passageways  24  are directed towards distal member  20  to increase the fluid flow around the intersection of the proximal member to the distal member. 
         [0039]    The flow of fluid through inner lumen  26 ′ provided by fluid tube  16  and ultimately through proximal passageways  24  and distal passageway  28  is reflected in  FIG. 7 . In particular,  FIG. 8  provides an irrigation flow visualization wherein the fluid from proximal passageways  24  is directed at a 30 degree angle from the central longitudinal axis of proximal member  18 , as shown in  FIG. 7 . The flow visualization further shows the flow of fluid out of distal passageway  28 , as shown in  FIGS. 5-7 , from distal end  30  of electrode assembly  10 ′. 
         [0040]      FIG. 9  graphically depicts bench test results for ablation electrode assemblies in accordance with an embodiment of the present invention. The purpose of the testing was to confirm that adequate temperature control was being accomplished through the use of the irrigated electrode including a distal passageway as the ablation system was subjected to an overall increase in power (W) (e.g. wattage). Overall, the testing was performed using an embodiment of the present invention wherein ablation was being performed using an electrode assembly that maintained irrigation flow of fluid was 13 mL/M at a perpendicular orientation to the muscle tissue being ablated. The testing showed, as reflected in  FIG. 9 , that an adequate temperature response was exhibited by the ablation electrode assembly, upon the continued increase of power (W) provided to the ablation system. Overall, the ablation electrode, as provided by the present invention, having a distal irrigation passageway was able to maintain adequate temperature control, for performing ablation, while at the same time sufficiently cooling the electrode tip. Accordingly, it is desirable to provide an irrigated ablation electrode assembly in accordance with the present invention that can achieve adequate temperature response within a desired range for performing ablation procedures. 
         [0041]    As previously discussed, the ablation electrode assembly  10 ,  10 ′ of the present invention may comprise part of an irrigated ablation catheter assembly  12 , operably connected to a pump assembly and an RF generator assembly which serves to facilitate the operation of ablation procedures through monitoring any number of chosen variables (e.g. temperature of the ablation electrode, ablation energy, and position of the assembly), assist in manipulation of the assembly during use, and provide the requisite energy source delivered to the electrode assembly  10 ,  10 ′. Although the present embodiments describe RF ablation electrode assemblies and methods, it is contemplated that the present invention is equally applicable to any number of other ablation electrode assemblies where the temperature of the device and the targeted tissue areas is a factor during the procedure. 
         [0042]    In addition to the preferred embodiments discussed above, the present invention contemplates methods for improved measure and control of a temperature of an irrigated ablation electrode assembly  10 ,  10 ′ or a target site and minimization of coagulation and excess tissue damage at and around the target site. According to one method, an ablation electrode assembly  10 ,  10 ′ is provided, having at least one temperature sensor  38  within distal member  20  and proximal member  18  is separate from distal member  20 . An irrigation pathway  24  is provided within the proximal member  18  for delivery of fluid to the outer surface  22  of the proximal member  18 . A distal passageway  28  is further provided for delivery of fluid to the distal end of distal member  20 , thereby allowing for the benefits of irrigation of the target site and external portions of electrode assembly  10 , such as minimizing tissue damage, such as steam pop, preventing rising impedance of the ablation assembly, and minimizing blood coagulation. 
         [0043]    Other embodiments and uses of the devices and methods of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The specification and examples should be considered exemplary only with the true scope and spirit of the invention indicated by the following claims. Although a number of embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. 
         [0044]    All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.

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