Abstract:
A method of manufacturing a surgical instrument includes charging a first component to a first voltage, charging a second component to a second voltage such that a pre-determined voltage differential is established between the first and second components, axially moving at least one of the first and second components relative to the other, monitoring an electrical characteristic to determine whether an axial distance between the first and second components is equal to a target axial distance, and retaining the first and second components in fixed position relative to one another once the axial distance between the first and second components is equal to the target axial distance.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/666,089, filed on Jun. 29, 2012, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to surgical instruments and, more particularly, to microwave antenna probes for treating tissue, e.g., ablating tissue, and methods of manufacturing such microwave antenna probes. 
         [0004]    2. Background of Related Art 
         [0005]    Treatment of certain diseases requires destruction of malignant tissue growths, e.g., tumors. It is known that tumor cells denature at elevated temperatures that are slightly lower than temperatures injurious to surrounding healthy cells. Known treatment methods, such as hyperthermia therapy, are utilized to heat tumor cells above the temperature necessary to destroy the tumor cells, while maintaining adjacent healthy cells at lower temperatures to avoid irreversible damage to the surrounding healthy cells. Such methods typically involve applying electromagnetic radiation to heat tissue, e.g., to ablate and/or coagulate tissue. In particular, microwave energy is used to ablate and/or coagulate tissue to denature or kill cancerous cells. There are several types of microwave antenna probes, e.g., monopole probes and dipole probes, that are currently used to radiate microwave energy generally perpendicularly from the axis of the probe to treat adjacent tissue. 
       SUMMARY 
       [0006]    As used herein, the term “distal” refers to the portion that is being described which is further from a user, while the term “proximal” refers to the portion that is being described which is closer to a user. Further, to the extent they are consistent with one another, any of the aspects described herein may be used in conjunction with any of the other aspects described herein. 
         [0007]    A method of manufacturing a surgical instrument provided in accordance with aspects of the present disclosure generally includes charging a first component to a first voltage, charging a second component to a second voltage such that a pre-determined voltage differential is established between the first and second components, axially moving one or both of the first and second components relative one another, monitoring an electrical characteristic to determine whether an axial distance between the first and second components is equal to a target axial distance, and retaining the first and second components in fixed position relative to one another once the axial distance between the first and second components is equal to the target axial distance. 
         [0008]    In one aspect, the voltage differential between the first and second components is monitored to determine whether electrical discharge has occurred. When electrical discharge occurs, the axial distance between the first and second components is equal to the target axial distance. 
         [0009]    In another aspect, a decrease in the voltage differential between the first and second components is monitored. A decrease in voltage differential indicates the occurrence of electrical discharge between the first and second components. 
         [0010]    In another aspect, the pre-determined voltage differential is selected in accordance with the target axial distance between the first and second components. 
         [0011]    In yet another aspect, conductivity and/or resistivity between the first and second components is monitored to determine the axial distance between the first and second components. In such an aspect, the first and second components may be immersed in a fluid having a pre-determined conductivity and/or pre-determined resistivity. As such, using the voltage differential between the first and second components, the pre-determined conductivity and/or pre-determined resistivity, and the monitored conductivity and/or resistivity between the first and second components, the axial distance between the first and second components can be determined. 
         [0012]    In still another aspect, the target axial distance is determined empirically. Alternatively, the target axial distance may be determined experimentally. 
         [0013]    In yet another aspect, the surgical instrument includes a microwave probe having a radiating portion and a trocar. The radiating portion and the trocar, e.g., the first and second components, are configured to be spaced-apart by the target axial distance. 
         [0014]    In still yet another embodiment, the steps of axially moving the component(s), monitoring the electrical characteristic, and retaining the first and second components, are incorporated into an automated feedback system. 
         [0015]    Another method of manufacturing a surgical instrument provided in accordance with aspects of the present disclosure generally includes providing a first component and a second component, axially moving the first component and/or the second component relative to one another, sensing a characteristic of energy to determine whether an axial distance between the first and second components is equal to a target axial distance, and retaining the first and second components in fixed position relative to one another once the axial distance between the first and second components is equal to the target axial distance. 
         [0016]    In one aspect, the capacitance and/or the inductance between the first and second components is sensed to determine the axial distance between the first and second components. 
         [0017]    In another aspect, one or more magnetic fields are applied to the surgical instrument. In such an aspect, characteristics of the magnetic field are sensed to determine the axial distance between the first and second components. 
         [0018]    In still another aspect, an acoustic response is sensed to determine whether the axial distance between the first and second components is equal to the target axial distance. In such an aspect, the acoustic response is sensed in response to an acoustic excitation signal emitted generally towards the first and second components. 
         [0019]    In yet another aspect, the target axial distance is determined empirically. Alternatively, the target axial distance may be determined experimentally. 
         [0020]    In still yet another aspect, the surgical instrument includes a microwave probe having a radiating portion and a trocar. The radiating portion and the trocar, e.g., the first and second components, are configured to be spaced-apart by the target axial distance. 
         [0021]    In another aspect, the steps of axially moving the component(s), sensing the characteristic of energy, and retaining the first and second components, are incorporated into an automated feedback system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Various aspects of the present disclosure are described herein with reference to the drawings wherein like reference numerals identify similar or identical elements: 
           [0023]      FIG. 1  is a side view of a microwave ablation system provided in accordance with the present disclosure; 
           [0024]      FIG. 2  is a longitudinal, cross-sectional view of a microwave antenna probe of the microwave ablation system of  FIG. 1 ; 
           [0025]      FIG. 3  is an enlarged view of the area of detail indicated as “ 3 ” in  FIG. 2 ; 
           [0026]      FIG. 4  is an enlarged view of the area of detail indicated as “ 4 ” in  FIG. 2 ; 
           [0027]      FIG. 5  is a longitudinal, cross-sectional view of an outer jacket and trocar assembly of the microwave antenna probe of  FIG. 2 ; 
           [0028]      FIG. 6  is a side view of an antenna assembly of the microwave antenna probe of  FIG. 2 ; 
           [0029]      FIG. 7  is an enlarged view of the area of detail indicated as “ 7 ” in  FIG. 6 ; 
           [0030]      FIG. 8  is a longitudinal, cross-sectional view illustrating assembly of the microwave antenna probe of  FIG. 2  in accordance with aspects of the present disclosure; 
           [0031]      FIG. 9  is a longitudinal, cross-sectional view illustrating assembly of the microwave antenna probe of  FIG. 2  in accordance with other aspects of the present disclosure; 
           [0032]      FIG. 10  is a longitudinal, cross-sectional view illustrating assembly of the microwave antenna probe of  FIG. 2  in accordance with other aspects of the present disclosure; and 
           [0033]      FIG. 11  is an enlarged, longitudinal, cross-sectional view of a distal end of the microwave antenna probe of  FIG. 2  illustrating assembly of the microwave antenna probe in accordance with other aspects of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    It has been found that, with respect to surgical instruments configured to apply energy to tissue to treat tissue, proper spacing between the energy radiating portion or portions and other components of the instrument helps facilitate optimal performance of the instrument. With respect to microwave ablation probes in particular, is has been found that proper axial spacing between the distal radiating portion and the trocar helps ensure optimal performance of the microwave ablation probe. More specifically, it has been found that variation in the axial distance may result in a sub-optimal ablation shape, an irregular ablation zone, and/or degraded ablation performance. The various embodiments of probes and methods of manufacturing probes described in detail hereinbelow are configured to help eliminate this variation in axial distance, thereby facilitating optimal performance of the probe. 
         [0035]    Turning now to  FIGS. 1-7 , a microwave ablation system provided in accordance with the present disclosure is shown generally identified by reference numeral  10 . Microwave ablation system  10  includes a microwave antenna probe  12  configured to couple to a microwave generator (not shown) via a flexible coaxial cable  16 . Although the present disclosure is shown and described with reference to a microwave ablation system  10 , the present disclosure is equally applicable for use in determining and/or setting a particular distance between components of any suitable energy-based surgical instrument. For the purposes herein, microwave ablation system  10  is generally described. 
         [0036]    With continuing reference to  FIGS. 1-7 , microwave antenna probe  12  generally includes an antenna assembly  20 , an outer jacket and trocar assembly  70  and a connection hub  80 . Antenna assembly  20  defines a longitudinal axis “X-X” and includes a radiating section that defines a dipole configuration, e.g., the radiating section includes a feed gap  43  and proximal and distal radiating portions  42 ,  44 . A feedline  30  extends proximally from the radiating section into connection hub  80 , ultimately coupling to cable  16  via transition  60  to connect antenna assembly  20  to the generator (not shown) for supplying energy thereto. Feedline  30  defines a coaxial configuration having an inner conductor  32  surrounded by an insulator  34 . Insulator  34 , in turn, is surrounded by an outer conductor  36 , thus defining the coaxial configuration of feedline  30 . Feedline  30  may be formed from a semi-rigid or flexible coaxial cable, although other configurations are also contemplated. 
         [0037]    As mentioned above, and with reference to  FIGS. 2 ,  4 , and  6 - 7 , the radiating section of antenna assembly  20  includes feed gap  43 , proximal radiating portion  42 , and distal radiating portion  44 . Feed gap  43  is defined by the portion of inner conductor  32  and insulator  34  of feedline  30  that extends distally from outer conductor  36 , e.g., outer conductor  36  may be stripped from the distal end of coaxial feedline  30  to define feed gap  43 . Proximal radiating portion  42  is defined by the portion of feedline  30  disposed between the proximal end of feed gap  43  and the distal end of the choke  50 . Distal radiating portion  44  is attached to feed gap  43  via any suitable process and extends distally therefrom. For example, as shown in  FIG. 7 , distal radiating portion  44  may be soldered to inner conductor  32  of feed gap  43  to establish electromechanical contact therebetween. 
         [0038]    Antenna assembly  20 , as shown in  FIGS. 2 ,  4 , and  6 - 7 , further includes a choke or balun  50  disposed about feedline  30 . Choke  50  includes an inner dielectric layer and an outer conductive layer. Choke  50  may be a quarter-wavelength shorted choke that is shorted to outer conductor  36  of feedline  30  at the proximal end of choke  50 , although other configurations are contemplated. The dielectric layer of choke  50  may also be configured to extend distally beyond the conductor layer thereof towards the distal end of antenna assembly  20 . 
         [0039]    With additional reference to  FIG. 3 , as mentioned above, antenna assembly  20  includes a transition  60  from which feedline  30  extends. During assembly, the radiating section and feedline  30  of antenna assembly  20  are inserted through lumen  82  of connection hub  80 , while transition  60  is inserted into proximal port  83  of connection hub  80  sufficiently such that transition  60  is sealingly engaged within proximal port  83  of connection hub  80  via O-ring  62 . Feedline  30  extends into transition  60 , wherein inner conductor  32  is coupled to an inner conductor (not explicitly shown) of coaxial cable  16  and outer conductor  36  is coupled to an outer conductor (not explicitly shown) of coaxial cable  16 , while maintaining the spacing therebetween via an insulator (not explicitly shown). Cable  16  may be secured to feedline  30  within transition  60  via soldering, laser welding, or any other suitable process for establishing electromechanical contact therebetween. 
         [0040]    Outer jacket and trocar assembly  70 , as best shown in  FIGS. 1-3  and  5 , includes an outer jacket  72  configured to surround antenna assembly  20 , e.g., proximal and distal radiating portions  42 ,  44 , feed gap  43 , and feedline  30 , such that a coolant fluid may be circulated thereabout to maintain antenna assembly  20  in a relatively cooled state during use. More specifically, coolant fluid is pumped into lumen  82  of connection hub  80  to circulate through outer jacket  72  via supply tube  17  and inlet  87  and returns to the coolant fluid source (not shown) via outlet  89  and return tube  19 . A ferrule  74  is molded or otherwise engaged about outer jacket  72  towards the proximal end thereof to facilitate sealing engagement of the proximal end of outer jacket  72  within distal port  85  of connection hub  80  via O-ring  76 . 
         [0041]    Connection hub  80 , as mentioned above defines a longitudinal lumen  82  that is configured to receive feedline  30  therethrough, while sealingly engaging outer jacket  72  within distal port  85  and transition  60  within proximal port  83 . Connection hub  80  further includes an outlet fluid port  87  and an inlet fluid port  89  that are disposed in fluid communication with lumen  82 . Outlet and inlet ports  87 ,  89  are configured to receive tubes  17 ,  19  (see  FIG. 1 ), respectively, such that, as mentioned above, coolant fluid from a coolant fluid supply (not shown) may be circulated through connection hub  80  and outer jacket  72 . More specifically, an elastomeric (or otherwise configured) hub divider  81   a  is sealingly engaged within lumen  82  of connection hub  80  to isolate the inlet and outlet portions of lumen  82  of connection hub  80  from one another. Further, an inflow tube  81   b  is coupled to hub divider  81   a  and extends distally through outer jacket  72 . As such, coolant fluid may flow from tube  17 , through inlet port  87 , into the inlet portion of lumen  82 , and distally through inflow tube  81   b , ultimately returning proximally through outer jacket  72  (exteriorly of inflow tube  81   b ), the outlet portion of lumen  82 , outlet port  89 , and into tube  19 . This configuration allows for the circulation of coolant fluid about antenna assembly  20  to maintain antenna assembly  20  in a relatively cooled state during use. The coolant fluid may be a liquid, gas, other flowable material, or combination thereof. 
         [0042]    With reference to  FIGS. 4-5 , outer jacket and trocar assembly  70  further includes a trocar  90  defining a tapered distal end that terminates at a pointed distal tip  92  to facilitate insertion of microwave antenna probe  12  ( FIG. 1 ) into tissue with minimal resistance, although other configurations may also be provided. Trocar  90  may be formed from a variety of heat-resistant materials suitable for penetrating tissue, e.g., metals (stainless steel, for example), various thermoplastic materials (such as polytherimide, polyimide thermoplastic resins, etc.), or any other suitable material. Base  94  of trocar  90  is configured for insertion into the open distal end  78  of outer jacket  72  for sealing engagement therein via any suitable process, e.g., using adhesives or via soldering. As such, trocar  90 , once engaged within distal end  78  of outer jacket  72 , sealingly encloses antenna assembly  20  (see  FIG. 2 ) within outer jacket  72  and connection hub  80 , thus defining an internal chamber for circulation of coolant fluid through microwave antenna probe  12  ( FIG. 1 ) and inhibiting coolant fluid from leaking out of microwave antenna probe  12  during use. Trocar  90  may be secured to distal end  78  of outer jacket  72  prior to engagement of outer jacket and trocar assembly  70  to connection hub  80  and/or engagement of transition to connection hub  80 , or may be secured to distal end  78  of outer jacket  72  after each of these assembly steps are complete. 
         [0043]    Referring again to  FIGS. 1-7 , as mentioned above, it has been found that proper axial spacing between the distal end of distal radiating portion  44  of antenna assembly  20  and the proximal surface of base  94  of trocar  90  helps ensure optimal performance of microwave antenna probe  12 . In particular, it has been found that, if the axial distance between the distal end of distal radiating portion  44  of antenna assembly  20  and the proximal surface of base  94  of trocar  90  is too large, the ablation zone, or ablation shape may be sub-optimal and complete ablation may not be readily achieved. Likewise, where the axial distance between the distal end of distal radiating portion  44  of antenna assembly  20  and the proximal surface of base  94  of trocar  90  is too small, or where distal radiating portion  44  and trocar  90  are in contact with one another, ablation performance may be degraded. 
         [0044]    The optimal axial spacing, e.g., the target axial distance, between distal radiating portion  44  and trocar  90  depends on, among other things, the dimensions and configuration of microwave antenna probe  12 , and may be determined empirically, experimentally, or in any other suitable fashion. Variation in the axial distance may result from: variation in the length of antenna assembly  20 , e.g., due to variation in the attachment point of distal radiating portion  44  to inner conductor  32  and/or variation in the length or size of the individual components of antenna assembly  20 ; variation in the position of transition  60  and/or ferrule  74  relative to connection hub  82  and/or one another; variation in the distance trocar  90  extends from (or extends into) outer jacket  72  once engaged to outer jacket  72 ; variation in the axial position of ferrule  74  relative to outer jacket  72 ; and/or other factors, e.g., the particular manufacturing processes or materials used, the particular components used or relationship between the components, the configuration of the probe in general, etc. 
         [0045]    With reference to  FIG. 8 , in accordance with one embodiment of the present disclosure, as will be described in greater detail below, electrical discharge may be utilized to help achieve the target axial distance between distal radiating portion  44  and trocar  90  during assembly, thereby facilitating optimal performance of microwave ablation probe  12 . 
         [0046]    With continued reference to  FIG. 8 , during assembly, once transition  60  is engaged within proximal port  83  of connection hub  80  via O-ring  62  and once ferrule  74  is engaged within distal port  85  of connection hub  80  via O-ring  76  such that antenna assembly  20 , outer jacket  72 , and connection hub  80  are secured in fixed position relative to one another, base  94  of trocar  90  is inserted into the open distal end  78  of outer jacket  72  for sealing engagement therein via any suitable process, e.g., using adhesives or via soldering. Since, at this point, outer jacket  72  and distal radiating portion  44  have already been fixed in position relative to one another, it is trocar  90  that is moved into a particular axial position corresponding to the target axial distance between the distal end of distal radiating portion  44  and the proximal surface of base  94  of trocar  90 . Once in position, trocar  90  may be adhered, soldered, or otherwise engaged to outer jacket  72  at the particular axial position such that the target axial distance is achieved. 
         [0047]    In order to determine when trocar  90  is properly positioned such that the target axial is achieved between trocar  90  and distal radiating portion  44  during assembly, trocar  90  is charged to a first voltage, while distal radiating portion  44  is charged to a second voltage that is different from the first voltage such that a pre-determined voltage differential is established between trocar  90  and distal radiating portion  44 . As will be described below, the particular voltage differential between trocar  90  and distal radiating portion  44  may be selected in accordance with the target axial distance between distal radiating portion  44  and trocar  90 , among other factors. Further, although  FIG. 8  illustrates trocar  90  being charged to a greater voltage than distal radiating portion  44  such that trocar  90  is the anode, e.g., relatively positive “+,” while distal radiating portion  44  is the cathode, e.g., relatively negative “−,” this configuration may be reversed, e.g., wherein trocar  90  is the cathode and distal radiating portion  44  is the anode. 
         [0048]    With the pre-determined voltage differential established between trocar  90  and distal radiating portion  44 , trocar  90  may be advanced proximally relative to outer jacket  72  (and, thus distal radiating portion  44 ) such that base  94  of trocar  90  is inserted into the open distal end  78  of outer jacket  72 . While monitoring the respective voltages of trocar  90  and distal radiating portion  44  (and/or the voltage differential therebetween), trocar  90  is advanced further proximally relative to distal radiating portion  44 , e.g., further into open distal end  78  of jacket  72 , until electrical discharge occurs between trocar  90  and distal radiating portion  44 , as evidenced by change in voltages of trocar  90  and distal radiating portion  44  or a decrease in the voltage differential therebetween. When discharge occurs, the target axial distance between the distal end of distal radiating portion  44  and the proximal surface of base  94  of trocar  90  has been achieved. More specifically, the pre-determined voltage differential is set in accordance with the target axial distance such that discharge occurs once trocar  90  and distal radiating portion  44  are spaced-apart by the target axial distance. Once this target axial distance is achieved, e.g., once discharge occurs, the supply of voltage to trocar  90  and distal radiating portion  44  may be terminated, and trocar  90  may be engaged to outer jacket  72  at that particular position, thereby establishing the target axial distance between trocar  90  and distal radiating portion  44 . 
         [0049]    As mentioned above, the voltage differential between trocar  90  and distal radiating portion  44  is set such that the distance between trocar  90  and distal radiating portion  44  at which discharge occurs corresponds to the target axial distance between trocar  90  and distal radiating portion  44 . The particular relationship between the voltage differential and the distance at which discharge occurs may be determined experimentally, empirically, or in any other suitable fashion, such that an appropriate voltage differential may be established. Further, the above-described process may be automated, e.g., using robotics or other automated or semi-automated assembly processes, such that trocar  90  is advanced, e.g., incrementally at a pre-determined step size or continuously at a pre-determine rate, until discharge occurs, whereby feedback as to the occurrence of discharge is provided to stop further movement of trocar  90  and maintain trocar  90  in position such that trocar  90  may be engaged to outer jacket  72  at that position, thereby achieving the target axial distance between trocar  90  and distal radiating portion  44 . Any of the other embodiments described herein may similarly be incorporated into an automated or semi-automated feedback system, as described above. 
         [0050]    As opposed to using the occurrence of electrical discharge to determine when proper axial spacing between trocar  90  and distal radiating portion  44  has been achieved, a resistivity or conductivity sensor (see, e.g., sensor assembly  300  (FIG.  11 )), may be used in conjunction with the voltage differential between trocar  90  and distal radiating portion  44  to determine the axial spacing between trocar  90  and distal radiating portion  44 . More specifically, with trocar  90  and distal radiating portion  44  immersed in a conductive fluid, e.g., a conductive gas or liquid, having a known conductivity or resistivity, and with the pre-determined voltage differential established between trocar  90  and distal radiating portion  44 , the known conductivity or resistivity of the fluid, along with the known voltage differential between trocar  90  and distal radiating portion  44 , can be used to determine the axial spacing between trocar  90  and distal radiating portion  44  based upon the sensed conductivity or resistivity between the charged components, e.g., trocar  90  and distal radiation portion  44 . This is because the sensed conductivity or resistivity between the charged components is dependent upon the conductivity or resistivity of the fluid, the distance between the charged components, and the voltage differential between the charged components. Thus, working backwards from the known conductivity or resistance of the fluid and the voltage differential between the charged components, the distance therebetween can be determined. A controller/processor (see, e.g., controller/processor  320  ( FIG. 11 )) may be utilized in conjunction with the resistivity or conductivity sensor to determine and display or provide feedback as to the axial spacing between trocar  90  and distal radiating portion  44 . 
         [0051]    Turning now to  FIG. 9 , in accordance with another embodiment of the present disclosure, a sensing member  200  may be utilized to achieve the target axial distance between trocar  90  and distal radiating portion  44  during assembly. Sensing member  200  is disposed within lumen  82  of connection hub  80  and, more particularly, is disposed with outer jacket  72 . Sensing member  200  is electrically coupled to a controller/processor  210  via one or more wires  220 . Sensing member  200  may be permanently affixed within connection hub  80  and outer jacket  72 , or may be removably disposed therein such that, once trocar  90  is moved into position and engaged to distal end  78  of outer jacket  72 , sensing member  200  may be withdrawn from outer jacket  72  and connection hub  80 . Further, sensing member  200  may be disposed at any suitable position within outer jacket  72 , e.g., in a more distal position towards distal radiating portion  44 , within connection hub  80  (as shown), or at any suitable position therebetween. The particular positioning of sensing member  200 , as can be appreciated, may depend of the particular type of sensing member used. 
         [0052]    Sensing member  200  may be in the form of an acoustic transmitter/receiver configured to emit, via the transmitter, a pre-determined acoustic signal distally into outer jacket  72  and to detect the acoustic response via the receiver. The acoustic response, which is correlated to the axial distance between the distal end of distal radiating portion  44  and the proximal surface of base  94  of trocar  90 , may thus be used to determine the axial distance between trocar  90  and radiating portion  44 . More specifically, the acoustic response detected by the receiver of the acoustic transmitter/receiver is transmitted to controller/processor  210 , which analyzes the response to determine the distance between trocar  90  and distal radiating portion  44 . Alternatively, the response may be compared to a target response value, e.g., the response value corresponding to the target axial distance between trocar  90  and distal radiating portion  44 , that is stored in controller/processor  210 . In such a configuration, the controller/processor  210  determines whether the trocar  90  is in proper position by determining whether or not the responses value match (or are sufficiently similar). If a match is determined, trocar  90  is in the proper position wherein trocar  90  and distal radiating portion  44  are spaced-apart by the target axial distance. Comparison of the sensed response value to the target response value may also be used to determine whether trocar  90  and distal radiating portion  44  are too close or too far from one another, thus indicating the required direction of movement of trocar  90  to achieve the target axial distance between trocar  90  and distal radiating portion  44 . 
         [0053]    The particular relationship between the response values sensed by sensing member  200  and the axial distance between trocar  90  and distal radiating portion  44  may be determined experimentally, empirically, or in any other suitable fashion. Further, similarly as described above with respect to the previous embodiment, sensing member  200  and controller/processor  210  may be incorporated into an automated, feedback-based system. Other suitable sensing members, e.g., piezoelectric sensors, optical sensors, or any other suitable sensor for determining the distance between trocar  90  and distal radiating portion  44 , may also be used. 
         [0054]    With reference to  FIG. 10 , in accordance with another embodiment of the present disclosure, a magnetic field “M,” multiple magnetic fields, changing magnetic field(s), etc., may be selectively applied to microwave antenna probe  12  to determine the positioning of trocar  90  and distal radiating portion  44  relative to one another such that trocar  90  may be moved into position to achieve the target axial distance between trocar  90  and distal radiating portion  44 . More specifically, by analyzing the magnetic field(s) “M,” the various components of microwave antenna probe  12  and the relative positioning therebetween can be determined since the magnetic field(s) “M” exhibits different characteristics adjacent the different components, e.g., adjacent trocar  90  and distal radiation portion  44 . Accordingly, while monitoring the magnetic field(s) “M,” and, thus, while monitoring the axial spacing between trocar  90  and distal radiating portion  44 , trocar  90  may be moved into position to achieve the target axial distance between trocar  90  and distal radiating portion  44 . Once this target axial distance is achieved, trocar  90  may be engaged to outer jacket  72  at the proper position to retain trocar  90  in fixed position relative to distal radiation portion  44 . An appropriate magnetic field(s) “M” may also be applied to retain trocar  90  in position during engagement of trocar  90  to outer jacket  72 , thereby obviating the need to mechanically retain trocar  90  in position. 
         [0055]    Referring to  FIG. 11 , in accordance with another embodiment of the present disclosure, an external sensor assembly  300  may be utilized to achieve the target axial distance between distal radiating portion  44  and trocar  90  during assembly. External sensor assembly  300  is a contactless sensor disposed exteriorly of microwave antenna probe  12  and is configured to determine the axial distance between trocar  90  and distal radiating portion  44  without the need to contact either trocar  90  or distal radiating portion  44  (or any other portion of microwave antenna probe  12 ). Thus, trocar  90  may be moved into position in accordance with the feedback, e.g., the axial distance between trocar  90  and distal radiating portion  44 , obtained from sensor assembly  300  without being inhibited by sensor assembly  300 . Sensor assembly  300  may include cooperating components  310 ,  340 , e.g., an emitter  310  and a detector  340 , although the particular configuration of components  310 ,  340  may depend on the particular type of sensor assembly used, that are coupled to a controller/processor  310  via one or more wires  320 ,  350 , respectively. Controller/processor  310  is configured to analyze the response from sensor components  310 ,  340  to determine the axial spacing between trocar  90  and distal radiating portion  44 . 
         [0056]    Sensor assembly  300  may be in the form of a capacitive proximity sensor, an inductive (eddy current) proximity sensor, a magnetic proximity sensor, or any other suitable external contactless sensor configured to emit a signal and receive a response for determining the axial spacing between trocar  90  and distal radiating portion  44 . More specifically, in use, after emission of a signal, application of an energy field, or other excitation by sensor component  310  and/or sensor component  340 , the response(s) received by sensor component  310  and/or sensor component  340  is sent to controller/processor  310 , which analyzes the response to determine the axial distance between trocar  90  and distal radiating portion  44 . Using this feedback, trocar  90  may be accurately positioned relative to distal radiating portion  44 . 
         [0057]    For example, with respect to a capacitive proximity sensor, capacitance, e.g., capacitance sensed by sensor assembly  300 , can be used to determine the axial distance between trocar  90  and distal radiating portion  44  since capacitance is dependent upon the distance between the components, e.g., trocar  90  and distal radiating portion  44 . With respect to an inductive proximity sensor, since inductance is likewise dependent on distance, an inductive proximity sensor can be used to determine the axial distance between trocar  90  and distal radiating portion  44 , the difference being that capacitive proximity sensors utilize electrical capacitance, while inductive proximity sensors utilized magnetic inductance. 
         [0058]    Referring in general to  FIGS. 1-11 , the above-described embodiments provide for accurate placement of trocar  90  relative to distal radiating portion  44  despite variation among the individual components of microwave antenna probe  12  or the engagements therebetween, e.g., without the need to rely on the accuracy of the dimensions, positioning, or engagement of the other components. That is, placement of trocar  90  relative to distal radiating portion  44  as described above is accomplished irrespective of variation among the components, e.g., variations in length, relative positioning, and/or configuration of one or more of the components. Accordingly, accurate positioning of trocar  90  relative to distal radiating portion  44  can be readily achieved, thereby helping to ensure optimal performance. 
         [0059]    Although the assembly of microwave ablation probe  12  is described above wherein trocar  90  is engaged to outer jacket  72  once transition  60  has been engaged within proximal port  83  of connection hub  80  via O-ring  62  and engagement of ferrule  74  within distal port  85  of connection hub  80  via O-ring  76 , it is also contemplated that above-described assembly methods may similarly be performed wherein the engagement of transition  60  to connection hub  80  or the engagement of outer jacket  72  to connection hub  80  is performed once the other components are fixed relative to one another. For example, with trocar  90  engaged to outer jacket  72  and transition  60  engaged within proximal port  83  of connection hub  80 , any of the above-described embodiments may be utilized to guide the positioning and engagement of ferrule  74  within distal port  85  of connection hub  80  such that the target axial spacing between trocar  90  and distal radiating portion  44  is achieved. Likewise, with trocar  90  engaged to outer jacket  72  and ferrule  74  engaged within distal port  85  of connection hub  80 , any of the above-described embodiments may be utilized to the guide the positioning and engagement of transition  60  within proximal port  83  of connection hub  80  such that the target axial spacing between trocar  90  and distal radiating portion  44  is achieved. 
         [0060]    Although the various embodiments above are described with respect to determining the spacing between trocar  90  and distal radiating portion  44  during assembly of trocar  90  to outer jacket  72 , it is also contemplated that any or all of the above-described embodiments may be used to record, mark, or otherwise note the proper positioning of trocar  90  (and/or the other components of microwave ablation probe  12 ) such that, upon subsequent assembly, trocar  90  (and/or the other components) may be positioned in accordance with the recorded, marked, or otherwise noted position previously obtained. As such, proper positioning of trocar  90  (and/or the other components) can be readily achieved. Alternatively or additionally, the above-described embodiments may be utilized for quality control, e.g., to ensure that the target axial distance between trocar  90  and distal radiating portion  44  has been achieved once assembly has been completed. 
         [0061]    From the foregoing and with reference to the various figure drawings, those skilled in the art will appreciate that certain modifications can also be made to the present disclosure without departing from the scope of the same. While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.