Abstract:
A microwave applicator having a probe which comprises an elongate shaft ( 14 ), the shaft having an external tubular wall ( 18 ), a radiating portion ( 15 ) disposed at the distal end of the shaft ( 14 ), a transmission line ( 17 ) extending to the radiating portion internally of the tubular external wall ( 18 ), and an elongate flow dividing member ( 19 ) which co-extends with the transmission line ( 17 ) longitudinally of the shaft ( 14 ), the side wall of the transmission line ( 17 ) and the side wall of the flow dividing member ( 19 ) contacting each other and contacting the internal surface of the external tubular wall ( 18 ) at two-spatially separated discrete positions, thereby defining a pair of flow channels ( 20, 21 ) inside the shaft ( 14 ). In use, cooling fluid can pass down one channel ( 20 ) and return via the other channel ( 21 ). The structure of the probe is uncomplicated and the probe is straightforward to assemble.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119(e) to U.S. Non-provisional patent application Ser. No. 12/866,288, issued as U.S. Pat. No. 9,084,619 filed Feb. 9, 2009, and PCT Application No. PCT/GB09/50113, filed Feb. 5, 2009, which are incorporated herein by reference. 
     BACKGROUND 
     It&#39;s well known to ablate body tissue using a microwave applicator which heats and destroys the surrounding tissue. One use of such an applicator is in the non-invasive treatment of cancer in an internal body organ such as the liver. GB2415630 discloses an applicator of the above-mentioned type comprising a probe having a thin elongate shaft, which can be inserted into the patient. The proximal end of the probe comprises a handle which is connected to an external microwave generator by an elongate flexible cable. A thin elongate microwave transmission line extends inside the probe from the handle to a radiating tip disposed at or adjacent the distal end of the probe. In use, the microwave field radiated from the tip heats and ablates the surrounding tissue in a localised area. 
     A disadvantage of the above-mentioned applicator is that the probe can heat up for a variety of reasons. Firstly, power losses can occur in the transmission line extending along the probe to the tip, which power losses heat the transmission line and the surrounding parts of the probe. Secondly, the radiated microwave energy can heat the probe. Thirdly, the heat from the ablation can be conducted back along the probe. Such heating of the probe is undesirable, since it can burn the patient&#39;s skin at the point of entry of the probe or it can burn other parts of the patient&#39;s body adjacent the shaft of the probe. Indeed, UK government regulations specify that no external part of any medical apparatus should exceed 48° in temperature. 
     In order to overcome the above-mentioned problems, it is well known to pass a liquid, such as a saline solution, along the probe so as to cool the probe. In use, the liquid passes out of the apertures in the distal end of the probe into the surrounding body cavity. A disadvantage of this arrangement is that the liquid fills the wound and undesirably either flows out of or into the body. Furthermore, the radiated microwave energy can heat the liquid in the body cavity. 
     In order to overcome the above-mentioned problems, WO2005/011049, DE2407559 and U.S. Pat. No. 4,375,220 each disclose microwave applicators in which cooling fluid is passed along the probe to its distal end along one flow passage and then returned along another flow passage. 
     In order to achieve this, each of the above-mentioned applicators comprise a complicated arrangement of cooling pipes or formers inside the probe, which define the flow and return passages. It will be appreciated that microwave applicator probes are advantageously thin, in order to enable them to be used as non-invasively as possible. However, a disadvantage of the pipes and formers used in the above-mentioned applicators is that the flow and return passages need to be relatively large in order to achieve the desired flow rates and it will be appreciated that this correspondingly increases the overall diameter of the probe. Furthermore, the probe also needs to be of a relatively large diameter in order to facilitate the insertion of the pipes or former. 
     We have now devised a microwave applicator which alleviates the above-mentioned problems. 
     FIELD OF THE INVENTION 
     This invention relates to a microwave applicator for medical use. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with the present invention, there is provided a microwave applicator having a probe which comprises an elongate shaft, the shaft having an external tubular wall, a microwave radiating portion disposed at the distal end of the shaft and a transmission line extending to said radiating portion internally of said tubular external wall, wherein an elongate flow dividing means extends internally along said tubular external wall and sealingly contacts the internal surface of said tubular wall along its length at two-spatially separated discrete positions around its periphery, the periphery of said flow dividing means being out of contact with said tubular wall between said two positions to define first and second discrete flow passages which extend longitudinally of said shaft for carrying cooling fluid. 
     In use, cooling fluid can be passed along the first passage to cool the probe, the cooling fluid then returning along the second passage. Since the flow dividing means and external tubular wall together define the flow passages, the need for complicated pipes and formers is avoided and hence the diameter of the probe can be minimised. The flow dividing means is also relatively straightforward to insert into the probe, as will be explained hereinafter. 
     In one embodiment, the flow dividing means comprises a single flow dividing member having an external cross-sectional shape which is different from the internal cross-sectional shape of the external tubular wall. For instance, the external cross-sectional shape of the flow dividing means may be circular and the internal cross-sectional shape of the tubular wall may be oval or vice-versa. 
     Said flow dividing member may comprise a hollow tube carrying said transmission line or the transmission line may itself form said flow dividing member. 
     In an alternative embodiment, said flow dividing means comprises said transmission line and an elongate flow dividing member which co-extends with said transmission line longitudinally of said shaft, the side wall of the transmission line and the side wall of the flow dividing member contacting each other and contacting said internal surface of the external tubular wall at said two-spatially separated discrete positions. 
     Said flow dividing member can be relatively thin and preferably has a diameter substantially equal to or greater than the difference between the internal diameter of said tubular external wall of the shaft and the external diameter of said transmission line. 
     It is often desirable to be able to sense a parameter such as temperature at the radiating tip. In order to achieve this, said now dividing member may comprise a tube or a cable carrying one or more wires to the distal end of the shaft. In use the wire(s) may carry a measuring signal from a sensor at the distal end of the shaft. 
     The transmission line preferably comprises a conductor which is also connected to the sensor and forms a signal pair with the wire of the flow dividing member. 
     Preferably, said flow dividing member comprises a tube or a cable carrying at least one wire of a thermocouple, said one wire preferably being formed of a first metal such as constantan. The distal end of the wire of said first metal is preferably connected at its distal end to said conductor of the transmission line, the conductor being formed of a second metal such as copper. Preferably, a body of said second metal is deposited on the distal end of the wire of said first metal in order to form a reliable junction between said metals. The body of second metal is preferably held in electrical contact with said conductor of the transmission line within the probe. 
     Said flow passages preferably have substantially equal cross-sectional areas, the combined cross-sectional areas of the flow passages preferably being equal to the internal cross-sectional area of the tubular external wall minus the cross-sectional area of the transmission line minus the cross-sectional area of the flow dividing member. 
     Preferably the distal end of the flow dividing means terminates prior to said radiating portion of the probe, in order to form a cross-over between said flow passages. 
     Preferably at least one of said flow passages is closed at the proximal end of the probe by a seal or other member. 
     Preferably the proximal end of the shaft extends into a manifold, which preferably forms a handle of the probe. 
     Preferably the manifold comprises first and second compartments which are sealingly separated from each other, said first and second flow passages respectively communicating with said first and second compartments. Preferably the first and second compartments of the manifold are arranged at respective positions longitudinally of the axis of the shaft. 
     Preferably an aperture is formed in the tubular external wall of the shaft at the proximal end thereof, wherein said aperture connects a said flow passage with a said compartment of the manifold. 
     Preferably one of the chambers of the manifold comprises a port for connecting to an external flow duct carrying cooling fluid. This flow duct preferably carries cooling fluid into the probe from a pump or other pressurised source of cooling fluid. 
     Preferably the other chamber of the manifold comprises a port which connects to the distal end of an elongate flexible cable of the applicator, which cable extends from a source of microwave radiation, said cable comprising a flow duct for carrying said cooling fluid. The flow duct of the cable preferably carries cooling fluid out of the probe to a drain or a collection vessel. The flow of fluid along the cable thus further serves to cool the cable, which can become hot due to power losses. 
     Preferably the proximal end of the cable comprises a port which acts as an inlet or outlet of the flow duet of the cable. 
     Also in accordance with the present invention, there is provided a method of forming a microwave applicator probe comprising providing an elongate tube, deforming the tube perpendicular to its longitudinal axis, inserting elongate flow dividing means into the deformed tube and releasing the tube to allow the tube to recover its shape. 
     The deformation of the tube allows the elongate fluid dividing means to be easily inserted into the tube. Once released, the tube recovers its shape and compresses the elongate flow dividing means into a position where it contacts the internal surface of the wall at two spatially separated positions around the periphery thereof. In this manner, two sealingly-separated flow passages are formed along the tube. 
     Preferably the method comprises inserting an elongate transmission line into the tube. The elongate transmission line may form said flow dividing means either alone or in conjunction with an elongate flow-dividing member. In the latter case, the transmission line and the flow dividing member may be inserted into the tube simultaneously or one after the other. In the latter case, one of the members may be inserted into the tube prior to the deformation thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a first embodiment of microwave applicator in accordance with the present invention; 
         FIG. 2  is a perspective outline view of the distal end of a probe of the applicator of  FIG. 1 ; 
         FIG. 3  is a perspective outline view of the proximal end of a shaft of the probe of the applicator of  FIG. 1 ; 
         FIG. 4  is a perspective outline view of the proximal end of the probe and a microwave feed cable of the applicator of  FIG. 1 ; 
         FIG. 5  is a perspective outline view of a portion of a manifold of the probe of the apparatus of  FIG. 1 ; 
         FIG. 6  is a perspective outline view of an outlet chamber of the feed cable of the applicator of  FIG. 1 ; 
         FIG. 7  is a perspective schematic view illustrating the method of manufacture of the shaft of the probe of the applicator of  FIG. 1 ; 
         FIG. 8  is a longitudinal sectional view through the shaft of a probe of a second embodiment of microwave applicator probe in accordance with the present invention; 
         FIG. 9  is a sectional view along the line IX-IX of  FIG. 8 ; and 
         FIG. 10  is a transverse sectional view through the shaft of a probe of a third embodiment of microwave applicator probe in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  of the drawings, there is shown a microwave applicator probe comprising a microwave generator  10  connected to an applicator probe  11  via an elongate flexible feed cable  12 . The probe  11  comprises a handle portion  13  and an elongate shaft portion  14  extending from the handle  13 . In use, the generator  10  generates a microwave signal which is transmitted along the feed cable  12  to the probe  11 . The microwave signal is then transmitted along the shaft  14  of the probe to a radiating tip  15  at the distal end thereof. 
     Referring to  FIG. 2  of the drawings, the shaft  14  comprises an external elongate tubular wall  14  formed of stainless steel. A co-axial transmission line  17  extends internally of the tubular wall  14 , the transmission line  17  being coupled at its proximal end to the microwave feed cable  12  and at its distal end to a radiating antenna  16  disposed inside the tip  15  of the probe  11 . An elongate flow dividing member  19 , in the form of a solid cable or wire, co-extends with the co-axial transmission line  17  along a substantial part of the length thereof, the member  19  terminating a short distance away from the radiating antenna  16 . 
     The combined diameter of the transmission line  17  and the flow dividing member  19  is slightly greater than the internal diameter of the tubular external wall  18 , such that the transmission line  17  and flow dividing member both positively contact the internal surface of the external tubular wall  18  and each other along a substantial part of the length of the shaft  14 . The transmission line  17  and flow dividing member  19  thus together define two flow channels  20 ,  21 , which extend longitudinally of the shall  14  from the proximal end to the point at which the flow dividing member  19  terminates. The two flow channels  20 ,  21  are interconnected beyond the point at which the flow dividing member  19  terminates. 
     Referring to  FIGS. 3 and 4  of the drawings, one of the channels  20  is sealed by a member  22  at the proximal end of the shaft  14 . A plurality of apertures  27  are formed in the external tubular wall  18  of the shaft  14  at the proximal end thereof, the apertures  27  communicating with the sealed channel  20 . The proximal end of the shaft  14  extends into a manifold  23  disposed inside the handle  13  of the probe  11 . The manifold  23  is generally cylindrical and is divided into two axially-disposed chambers  24 ,  25  by a boundary well  26  which extends normal to the longitudinal axis of the shaft  14 . The proximal end of the shaft  14  extends into the manifold  23  and through the boundary wall  26 , such that the apertures  27  open into the distal chamber  24  of the manifold  23 , the second (un-sealed) flow channel  21  of the shaft  14  opening into the proximal chamber  25  of the manifold  23 . An inlet port  28  extends radially outwardly from the side wall of the manifold  23 , the inlet port  28  communicating with the distal chamber  24  of the manifold  23 . 
     The proximal end wall  13  of the manifold  23  is connected to the feed cable  12 , the feed cable  12  comprising an outer tube  28  and a co-axial cable  29  extending loosely inside the tube  28 . The co-axial cable  29  extends through the proximal end wall  30  of the manifold  23  and is connected inside the chamber  25  to the co-axial transmission line  17  by a co-axial coupling  31 . The distal end of the tube  28  is sealingly coupled to an aperture in the proximal end wall  30  of the manifold  23 , such that the interior of the tube  28  opens into the proximal chamber  25  of the manifold  23 . 
     Referring to  FIG. 6  of the drawings, the proximal end of the feed cable  12  is connected to an elongate cylindrical outlet chamber  32 . The proximal end of the tube  28  of the feed cable  12  is coupled to the outlet chamber  32 , such that the interior of the tube  28  opens into the outlet chamber  32 . The co-axial cable  29  extends through the outlet chamber  32  to a co-axial connector  34  on the external face of the proximal end wall of the chamber  32 . An outlet port  32  extends radially outwardly from the side wall of the outlet chamber  32 . 
     In use, the co-axial connector  34  is connected to the microwave generator  10 . The inlet port  28  of the manifold  23  is connected to a pump via an elongate tube (not shown). The outlet port  33  is connected to a collection vessel via an elongate tube (not shown). When energised, the pump pumps cooling fluid into the distal chamber  24  of the manifold  23  through the inlet port  28 . The cooling fluid then flows through the apertures  27  in the external tubular wall  18  of the shaft  14  and into the flow channel  20 . The cooling fluid then flows longitudinally of the shaft  14 , thereby cooling the external wall  18  of the shaft and the transmission line  17 . The cooling fluid then crosses from the flow channel  20  to the other flow channel  21  at the distal end of the shaft  14 , beyond the point at which the flow dividing member  19  terminates. The cooling fluid then returns along the shaft  14  via the cooling channel  21 , whereupon it flows into the proximal chamber  25  of the manifold  23 . The fluid then flows out of the manifold  23  and into the feed cable  12 , whereupon it flows along the cable  12  in an annular flow channel defined between the outer tube  28  and the co-axial cable  29 . The fluid then flows out of the outlet chamber  32  through the outlet port  33  to a collection vessel. In this manner, the cooling fluid also cools the co-axial cable  29 . 
     Referring to  FIG. 7  of the drawings, the co-axial transmission line  17  and the flow dividing member  19  are inserted into the external tubular wall  18  of the shaft  14  by compressing the external tubular wall  18  transverse its longitudinal axis into an oval shape. The transmission line  17  and the flow dividing member  19  can then be easily inserted into the deformed external tubular wall  18 . Once inserted, the applied force can be removed, thereby allowing the external tubular wall  18  to recover its shape, such that the co-axial transmission line  17  and the flow dividing member  19  become compressed against each other and against the external tubular wall  18 . 
     Referring to  FIGS. 8 and 9  of the drawings, there is shown an alternative embodiment of microwave applicator probe which is similar to the probe of  FIGS. 1-7  and like parts are have given like reference numerals. In this embodiment, the elongate flow dividing member  19  is replaced by a thin tube, e.g. formed of stainless steel. An elongate insulated wire  36  of constantan extends from a measuring instrument  43  through the tube  35 . The insulation is removed from the distal end of the constantan wire and a body  37  of copper material is deposited onto the exposed conductor of the constantan wire  36 . The transmission line  17  comprises an outer copper sleeve  40 . An elongate central conductor  38  extends inside the copper sleeve  40  and is insulated therefrom by a dielectric sleeve  39 . The body  37  of copper on the constantan wire  36  makes contact with the copper sleeve  40  of the transmission line  17 . The body  37  of copper has a diameter which is substantially equal to the diameter of the tube  35 , such that it is held tightly in contact with the copper sleeve  40  of the transmission line  17 . The external surface of the copper body  37  may be electro-plated to ensure a reliable contact with the copper sleeve  40  of the transmission line  17 . The proximal end of the copper conductor  40  is connected via a wire  42  to the measuring instrument  43 . The tube  35  is preferably sealed by the constantan wire  36  or another member against fluid flow. In this way, the risk of fluid using the tube  35  as a return path is avoided. 
     It will be appreciated that a complete circuit from the thermocouple instrument  43  is thus created by the constantan wire  36 , the copper body  37  and the copper sleeve  40  of the transmission line  17 . The copper-constantan junction inside the body  37  forms a thermocouple junction which can be used to provide an indication of the temperature at the tip of the probe  11 . 
     The two thermocouple wires  36 , 42  extending from the measuring instrument  43  preferably extend into the outlet manifold  32  and along the cable  12  in the annular flow channel defined between the outer tube  28  and the co-axial cable  29 . The wires  36 , 42  then extend through the manifold  13  to the shaft  14  of the probe  11 . This arrangement helps to hide the wires  36 , 42  and improves the overall appearance of the applicator. 
     Referring to  FIG. 10  of the drawings, there is shown an alternative embodiment of microwave applicator probe, which is similar to the embodiment of  FIGS. 8 and 9  and like parts are given like reference numerals. In this embodiment, the separate flow-dividing member  19  is omitted and instead, the transmission line  17  acts on its own to define two flow-channels  120 ,  121 . This is achieved by providing the shaft  14  with an external tubular wall  118  which is normally oval in section. The transmission line  17  is inserted into the external wall  118  by deforming the wall transverse its longitudinal axis until it comes generally circular in shape: this allows the transmission line  17  to be inserted, whereupon the deforming force can be removed such that the transmission line  17  contacts the external wall  118  at diametrically opposed positions. 
     A microwave applicator probe in accordance with the present invention is relatively simple and inexpensive in construction, yet enables the probe to be reliably cooled.