Abstract:
An ultrasonic probe transmits vibration along longitudinal axis from the proximal toward the distal end, including: first area including proximal and distal end portions, a center axis parallel to the longitudinal axis, the first area having a vibration antinode position at the distal end, wherein maximum distance from the center axis to an outer peripheral surface in radial direction orthogonal to the center axis is a first distance; a treatment section located on a distal end side&#39;s barycenter position displaced from the center axis; a second area located between the first area and treatment section continuous with the distal end of the first area and gravity center axis parallel to the center axis to pass through the barycenter, wherein maximum distance from the center axis to the outer surface in the radial direction orthogonal to the center axis is a second distance equal to or shorter than the first distance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation Application of PCT Application No. PCT/JP2013/65263, filed May 31, 2013 and based upon and claiming the benefit of priority from U.S. Provisional Application No. 61/680,534, filed Aug. 7, 2012, the entire contents of all of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an ultrasonic probe which is configured to transmit longitudinal vibration parallel to a longitudinal axis as a result of transmittance of ultrasonic vibration, and a manufacturing method of the ultrasonic probe. 
         [0004]    2. Description of the Related Art 
         [0005]    For example, WO2010/047395A1 discloses a treatment device with a treatment section located at a distal end portion of an ultrasonic probe and shaped like a hook. The treatment device generates ultrasonic vibration with the treatment section hooked to a biological tissue. Pulling the treatment section toward an operator allows the biological tissue to be treated. 
         [0006]    The treatment device keeps the whole probe in balance based on the shape of the treatment section. Specifically, according to WO2010/047395A1, a distal end hook section is formed on an upper surface side of the treatment section disposed at the distal end of a probe main body section, and a recess portion is formed on a lower surface side of the treatment section. The treatment section is appropriately formed as described above so that the center of gravity of the treatment section coincides with the center of gravity of the probe main body section, thus stabilizing vibration. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    One aspect of an ultrasonic probe configured to transmit ultrasonic vibration along a longitudinal axis defined by a proximal end and a distal end thereof from the proximal end toward the distal end, according to the present invention includes: a first area including a proximal end portion, a distal end portion and a center axis which is defined by the proximal end portion and the distal end portion and which is parallel to the longitudinal axis, the first area having an antinode position of the ultrasonic vibration at the distal end portion, wherein a maximum distance from the center axis to an outer peripheral surface of the ultrasonic probe in a radial direction orthogonal to the center axis is a first distance; a treatment section located on a distal end side with respect to the distal end portion of the first area and having a center of gravity at a position displaced from the center axis of the first area; and a second area located between the first area and the treatment section so as to be continuous with the distal end portion of the first area and configured to have a gravity center axis positioned parallel to the center axis of the first area so as to pass through the center of gravity of the treatment section or be closer to the center of gravity than the center axis, wherein a maximum distance from the center axis to the outer peripheral surface of the ultrasonic probe in the radial direction orthogonal to the center axis is a second distance equal to or shorter than the first distance. 
         [0008]    Another aspect of a manufacturing method of an ultrasonic probe with a proximal end and a distal end, according to the present invention includes: producing a first area adjacent to the proximal end of the ultrasonic probe to define a center axis of the first area, while leaving a site of a preparation body corresponding to a treatment section of the ultrasonic probe unprocessed, out of the preparation body that is long along a longitudinal axis defined by the proximal end and the distal end; machining the site corresponding to the treatment section and located at a distal end of the ultrasonic probe to define a center of gravity of the treatment section located at the distal end of the ultrasonic probe, at a position displaced from the center axis of the first area; and machining a second area between the first area and the treatment section in such a manner that a center of gravity of the second area is positioned parallel to the center axis of the first area so as to pass through the center of gravity of the treatment section. 
         [0009]    Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
           [0011]      FIG. 1  is a schematic diagram showing an ultrasonic treatment system according to an embodiment of the present invention; 
           [0012]      FIG. 2  is a schematic vertical cross-sectional view showing a part of an ultrasonic vibration generating unit and an ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0013]      FIG. 3A  is a schematic diagram showing an ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0014]      FIG. 3B  is a schematic horizontal cross-sectional view of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, the cross-sectional view being taken along line  3 B- 3 B in  FIG. 3A ; 
           [0015]      FIG. 3C  is a schematic diagram showing a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0016]      FIG. 4A  is a schematic diagram showing a preparation body used to produce the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0017]      FIG. 4B  is a schematic diagram showing that, in production of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, a site of the preparation body shown in  FIG. 4A  which corresponds to a first area and a second area of the probe main body section is machined to form the first area, and a site of the preparation body corresponding to a treatment area is left unprocessed; 
           [0018]      FIG. 4C  is a schematic diagram showing that, in production of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, a site of the preparation body shown in  FIG. 4B  and corresponding to the second area of the probe main body section is machined, and a site of the preparation body shown in  FIG. 4B  and corresponding to the treatment area is left unprocessed; 
           [0019]      FIG. 4D  is a schematic diagram showing that a site of the preparation body shown in  FIG. 4C  and corresponding to the treatment area is machined to form a hook-shaped treatment area; 
           [0020]      FIG. 4E  is a schematic diagram showing that a site of the preparation body shown in  FIG. 4D  and corresponding to the second area is machined and partly removed to form the second area; 
           [0021]      FIG. 5A  is a schematic diagram showing a preparation body used to produce the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0022]      FIG. 5B  is a schematic diagram showing that, in production of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, a site of the preparation body shown in  FIG. 5A  which corresponds to the first area and the second area of the probe main body section is machined to form the first area, and a site of the preparation body corresponding to the treatment area is left unprocessed; 
           [0023]      FIG. 5C  is a schematic diagram showing that, in production of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, a site of the preparation body shown in  FIG. 5B  and corresponding to the second area of the probe main body section is machined, and a site of the preparation body shown in  FIG. 5B  and corresponding to the treatment area is left unprocessed; 
           [0024]      FIG. 5D  is a schematic diagram showing that a site of the preparation body shown in  FIG. 5C  and corresponding to the second area is machined to form the second area; 
           [0025]      FIG. 5E  is a schematic diagram showing that a site of the preparation body shown in  FIG. 5D  and corresponding to the treatment area is machined to form a hook-shaped treatment area; 
           [0026]      FIG. 6A  is a schematic top view showing a spatula-shaped treatment area in a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, as seen in a direction shown by arrow  6 A in  FIG. 6B ; 
           [0027]      FIG. 6B  is a schematic side view showing the spatula-shaped treatment area in the variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, as seen in a direction shown by arrow  6 B in  FIG. 6A  and by arrow  6 B in  FIG. 6C ; 
           [0028]      FIG. 6C  is a schematic top view showing the spatula-shaped treatment area in the variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention, as seen in a direction shown by arrow  6 C in  FIG. 6B ; 
           [0029]      FIG. 7  is a schematic side view showing a scissors-shaped treatment area in a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0030]      FIG. 8A  is a schematic horizontal cross-sectional view showing a second area of a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0031]      FIG. 8B  is a schematic horizontal cross-sectional view showing a second area of a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0032]      FIG. 8C  is a schematic horizontal cross-sectional view showing a second area of a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0033]      FIG. 8D  is a schematic horizontal cross-sectional view showing a second area of a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0034]      FIG. 8E  is a schematic horizontal cross-sectional view showing a second area of a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0035]      FIG. 8F  is a schematic horizontal cross-sectional view showing a second area of a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention; 
           [0036]      FIG. 9A  is a schematic horizontal cross-sectional view showing a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention in which the first area of the probe main body section is shaped like a regular hexagon, and in which the second area is formed by machining and partly removing the regular hexagon so that the center of gravity of the second area is displaced from the center of gravity of the first area; and 
           [0037]      FIG. 9B  is a schematic horizontal cross-sectional view showing a variation of the ultrasonic probe of the ultrasonic probe unit of the ultrasonic treatment system according to the embodiment of the present invention in which the first area of the probe main body section is shaped like a regular pentagon, and in which the second area is formed by machining and partly removing the regular pentagon so that the center of gravity of the second area is displaced from the center of gravity of the first area. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    An embodiment of the present invention including variations thereof will be described with reference to  FIGS. 1 to 9B . 
         [0039]    As shown in  FIG. 1 , an ultrasonic treatment system  10  includes a power supply unit  12  and an ultrasonic treatment unit  14  serving as an ultrasonic treatment device. The ultrasonic treatment unit  14  includes an ultrasonic vibration generating unit  16  and an ultrasonic probe unit  18 . 
         [0040]    The power supply unit  12  includes an electrical current supply section  22  that supplies electrical current to the ultrasonic vibration generating unit  16  and an input section  24 . The input section  24  is connected to, for example, a foot switch (not shown in the drawings) to enable switching between a state where the electrical current supply section  22  supplies electrical current and a state where the supply of electrical current is stopped. Furthermore, an ultrasonic transducer  34  described below can be vibrated at an appropriate amplitude based on an operational state of the foot switch. 
         [0041]    As shown in  FIG. 2 , the ultrasonic vibration generating unit  16  includes a transducer case  32  serving as an outer shell, an ultrasonic transducer  34  located inside the transducer case  32  and serving as a vibration generating unit, and a cable  36  extending from a proximal end of the transducer case  32  and detachably connected to the power supply unit  12 . The transducer case  32  is formed of, for example, an insulating resin material. 
         [0042]    The ultrasonic transducer  34  is, for example, of a BLT type. Electric wires  38   a  and  38   b  are connected to the ultrasonic transducer  34  at one end of each electric wire. The electric wires  38   a  and  38   b  pass through the cable  36  and are connected to the electrical current supply section  22  of the power supply unit  12  at the other end of each electric wire. The electrical current supply section  22  supplies electrical current to the ultrasonic transducer  34  via the electric wires  38   a  and  38   b  in the cable  36 . Thus, the ultrasonic transducer  34  generates ultrasonic vibration. A horn  40  is coupled to a distal end direction side of the ultrasonic transducer  34  to increase the amplitude of ultrasonic vibration. The horn  40  is attached to, for example, the transducer case  32 . Furthermore, an internal thread portion  42  is formed at a distal end portion of the horn  40 . 
         [0043]    As shown in  FIG. 2 , the ultrasonic probe unit  18  includes an ultrasonic probe  52  and a sheath  54 . The sheath  54  is formed of an electrically insulating resin material or the like. The sheath  54  is formed to cover the entire outer peripheral surface of a first area  72  and a second area  74  of the ultrasonic probe  52 , both of which will be described below, and to expose a treatment area  64  from a distal end  54   a  of the sheath  54 . A proximal end  54   b  of the sheath  54  is detachably fixed to the transducer case  32 . Furthermore, a ring  56  formed of, for example, a rubber material having insulating properties, is disposed between the ultrasonic probe  52  and the sheath  54  at a vibration node position. This enables an outer peripheral surface of the ultrasonic probe  52  to be separated from an inner peripheral surface of the sheath  52 . If the ultrasonic probe  52  has a plurality of vibration node positions, the ring  56  is preferably disposed at each of the vibration node positions. For example, an annular recess portion is also preferably formed at the position where the ring  56  is disposed (vibration node position). 
         [0044]    The sheath  54  and the ring  56  according to the embodiment may be unwanted depending on a usage state of the ultrasonic treatment unit  14 . 
         [0045]    The ultrasonic probe  52  shown in  FIG. 3A  is formed of, for example, a titanium alloy. The ultrasonic probe  52  includes a probe main body section  62  and a treatment area (treatment section)  64  provided closer to a distal end of the ultrasonic probe  52  than the probe main body section  62  to treat a biological tissue. 
         [0046]    The probe main body section  62  includes an external thread portion  66  on an outer peripheral portion of a proximal end of the probe main body section  62 . The external thread portion  66  engages, in a threaded manner, with the internal thread portion  42  formed on the horn  40  as shown in  FIG. 2 . Thus, the ultrasonic probe  52  is attached to the ultrasonic vibration generating unit  16 . The ultrasonic probe  52  attached to the ultrasonic vibration generating unit  16  allows ultrasonic vibration generated by the ultrasonic transducer  34  to be transmitted to the ultrasonic probe  52 . The ultrasonic vibration transmitted to the ultrasonic probe  52  enables the ultrasonic probe  52  to generate longitudinal vibration that is parallel to a center axis C in the direction of vibration and in the direction of transmission. 
         [0047]    As shown in  FIG. 3A , the probe main body section  62  extends in a longitudinal direction along the center axis C. The probe main body section  62  includes the first area  72  located on a proximal end side of the probe main body section  62  in a longitudinal direction thereof and including the external thread portion  66  formed at a most proximal end and the second area  74  provided on a distal end direction side of the first region  72 . Preferably, the first area  72  is formed to be straight, and all transverse sections are the same in size and shape. Furthermore, the second area  74  is preferably formed to be straight, and all transverse sections are the same in size and shape. The second area  74  includes a treatment area  64  on a distal end direction side of the second region  74 . For example, both the first area  72  and the second area  74  may be tapered so that transverse sections on the proximal end side are formed to be larger than cross sections on the distal end side. 
         [0048]    According to the embodiment, the first area  72  shown in  FIG. 3A  and  FIG. 35  is formed to be, for example, cylindrical. Thus, in the first area  72 , the center axis C coincides with the center of gravity (gravity center axis) at the position of each transverse section orthogonal to the center axis C. That is, at any position between the distal end and the proximal end of the first area  72 , the center axis C coincides with the center of gravity on a transverse section orthogonal to the center axis C. In other words, the center of gravity on each circular transverse section orthogonal to the longitudinal direction of the first area  72  corresponds to the center of the transverse section. Thus, the center axis C is defined by a set of centers of gravity on the respective cross sections between a distal end portion  73   a  and a proximal end portion  73   b  of the first area  72 . 
         [0049]    A boundary between the first area  72  and the second area  74 , that is, the distal end portion  73   a  of the first area  72  and a proximal end portion  75   b  of the second area  74 , is adjusted to correspond to an antinode position of vibration. For example, when a drive frequency is 47 kHz and the ultrasonic probe  52  is formed of 6-4Ti and has an outer diameter of approximately 6 mm, a half-wavelength is approximately 51 mm to approximately 52 mm. Thus, when the ultrasonic vibration generating unit  16  and the ultrasonic probe  52  are joined together at the antinode of the vibration, the length from a distal end of the ultrasonic transducer  34  (a proximal end of the horn  40 ) to the distal end portion  73   a  of the first area  72  of the probe main body section  62  is 51 mm to 52 mm×n (n: an integer of one or larger). In other words, the length from the distal end of the ultrasonic transducer  34  (the proximal end of the horn  40 ) to the distal end portion  73   a  of the first area  72  of the probe main body section  62  is an integral multiple of the half-wavelength (n times as large as the half-wavelength). The total length of the second area  74  and the treatment area  64  is preferably an integral multiple of the half-wavelength (n times as large as the half-wavelength). 
         [0050]    When the ultrasonic transducer  34  has a resonant frequency of 23.5 kHz, the half-wavelength is approximately 102 mm to approximately 104 mm. In this case, the length from the distal end of the ultrasonic transducer  34  (the proximal end of the horn  40 ) to the distal end portion  73   a  of the first area  72  of the probe main body section  62  is an integral multiple of, for example, 102 mm to 104 mm. Furthermore, the total length of the second area  74  and the treatment area  64  is an integral multiple of, for example, 102 mm to 104 mm. 
         [0051]    The treatment region  64  shown in  FIG. 3A  is bent relative to the distal end portion  75   a  of the second area  74  of the probe main body section  62 . In the embodiment, the treatment area  64  is shaped like a hook. In the treatment area  64 , the center of gravity is displaced to a position shown by reference symbol G0 in  FIG. 3A  relative to the center axis C of the first area  72 . In particular, the center of gravity G0 of the treatment area  64  in  FIG. 3A  is displaced toward an upper side of  FIG. 3A  and  FIG. 3B  relative to the center axis C. 
         [0052]    A set of centers of gravity on transverse sections in the second area  74  which are orthogonal to the center axis C of the first area  72  is linear as shown by reference symbol G in  FIG. 3A  and  FIG. 3B . The straight line shown by reference symbol G is parallel to the center axis C of the first area  72 , but is not the same as and is positioned differently from the center axis C. For example, when the treatment area  64  is formed as shown in  FIG. 3A  and the center of gravity G0 of the treatment area  64  is displaced upward from the center axis C in  FIG. 3A  and  FIG. 3B , the second area  74  is formed by machining such that the straight line G, a set of centers of gravity on transverse sections orthogonal to the center axis C of the first area  72 , passes through the barycenter G0 of the treatment area  64 , or closer to the center of gravity G0 than the center axis C. That is, the straight line G (center axis) passing through the center of gravity of the second area  74  is parallel to the center axis C, passing through the center of gravity of the first area, and is not the same as and is positioned differently from the center axis C. In other words, the center axis of the second area (straight line G) is parallel to the center axis C of the first area and passes through the center of gravity G0, or closer to the center of gravity G0 than the center axis C. 
         [0053]    The center of gravity G is isolated at the boundary between the first area  72  and the second area  74 , and the boundary position corresponds to the antinode position of the vibration. The antinode position of the vibration is displaced more significantly than the other positions. However, the state of a medium near the antinode position of the vibration remains unchanged, resulting in no stress, as is the case where no wave is generated. Thus, even when the center of gravity is displaced at the antinode position of the vibration, no or substantially no adverse effect is exerted on the vibration. Furthermore, both in the first area  72  and in the second area  74 , the center of gravity lies on a straight line parallel to the center axis C and is constant over every half-wavelength. This allows longitudinal vibration to be stabilized. 
         [0054]    A procedure for manufacturing (method for manufacturing) the ultrasonic probe  52  will be described with reference to  FIG. 4A  to  FIG. 4E . In this case, an example will be described in which the treatment area  64  is shaped like a hook as shown in  FIG. 3A . 
         [0055]    First, as shown in  FIG. 4A , a rod-like member (preparation body) is prepared which is formed of, for example, a titanium alloy material (preparation body)  52   a  and which is long and straight along a longitudinal direction (longitudinal axis) L. An outer peripheral surface of a transverse section orthogonal to the longitudinal direction of the rod-like member  52   a  may be, for example, circular or polygonal. The length of the rod-like member  52   a  is determined by the resonant frequency of the ultrasonic transducer  34  used, the length of the connected horn  40 , a target biological tissue to be treated, and the like. 
         [0056]    When the outer peripheral surface of a transverse section of the rod-like member  52   a  is not circular, the outer peripheral surface of the rod-like member  52   a  is preferably machined to be circular using a lathe or the like. The maximum outer diameter of the rod-like member  52   a  is appropriately determined based on, for example, the inner diameter (for example, 5 mm, 10 mm, 12 mm, or the like) of a trocar inserted into a body cavity, though the maximum outer diameter depends on whether or not the sheath  54  is arranged on the outer periphery of the ultrasonic probe  52  and the thickness of the sheath  54 . 
         [0057]    The rod-like member  52   a  shown in  FIG. 4A  is placed on a lathe, and the outer peripheral surface of a site  72   a  of the first area  72  is machined so as to be shaped like the first area  72  as shown in  FIG. 4B . At this time, the outer peripheral surface of a site  74   a  corresponding to the second area  74  is also preferably machined so as to have an outer diameter similar to the outer diameter of the first area  72 . Furthermore, a cylindrical portion  64   a  forming the treatment area  64  is left on a distal end direction side of the site  74   a  corresponding to the second area  74 . At this stage, the first area  72  is formed. 
         [0058]    A site  66   a  corresponding to the external thread portion  66  may be formed at this stage or after the treatment area  64  and the second area  74  are formed. Alternatively, the site  66   a  corresponding to the external thread portion  66  may be formed before the first area  72  is formed. Threads may subsequently be formed in the site  66   a  corresponding to the external thread portion  66  at any stage. 
         [0059]    Then, as shown in  FIG. 4C , the outer peripheral surface of the site  74   a  corresponding to the second area  74  is further machined so as to have a smaller outer diameter than the first area  72 . At this time, the center of gravity on the first area  72  and the center of gravity on the site  74   a  corresponding to the second area  74  both still lie on the same center axis C of the first area  72 . 
         [0060]    Then, as shown in  FIG. 4D , the site  64   a  corresponding to the treatment area  64  is appropriately machined using, for example, a five-axis NC lathe or forging, to produce a treatment area  64 . When, for example, an ultrasonic probe  52  used in a trocar with an inner diameter of 5 mm is produced, the treatment area  64  is formed such that the range of the treatment area  64  relative to the center axis C does not exceed 2.5 mm. In other words, the treatment area  64  is formed such that an upper side of the treatment area  64  relative to the center axis C in  FIG. 4D  is smaller than 2.5 mm, and a lower side of the treatment area  64  relative to the center axis C in  FIG. 4D  is smaller than 2.5 mm so as to permit insertion into a trocar with an inner diameter of 5 mm. The thus-determined shape of the treatment area  64  determines the center of gravity G0 of the treatment area  64 . In this case, the center of gravity G0 of the treatment area  64  lies above the center axis C in  FIG. 4D . The center of gravity of the site  74   a  corresponding to the second area  74  lies on the same center axis C of the first area  72 . Thus, the center of gravity G0 of the treatment area  64  is displaced from the center of gravity of the site  74   a  corresponding to the second area  74 . 
         [0061]    As shown in  FIG. 4E , the site  74   a  corresponding to the second area  74  is partly removed using, for example, a milling machine so that an imaginary straight line G passing and through the center of gravity G0 and parallel to the center axis C of the treatment area  64  provide a set of centers of gravity in the second area  74 . In the embodiment, the lower portion in  FIG. 4D  is partly removed flat to form a flat surface  76  shown in  FIG. 3A ,  FIG. 3E , and  FIG. 4E . That is, the barycenter G of the second area  74  is displaced upward, in  FIG. 4E , relative to the center of gravity of the site  74   a  corresponding to the second area  74 . 
         [0062]    For example, when the treatment area  64  shown in FIG.  4 D and shaped like a hook or the like is formed, the barycenter G0 of the treatment area  64  is consequently defined displaced from the center axis C of the first area  72 . Thus, as shown in  FIG. 4E , the second area  74  is machined from the distal end to the proximal end thereof so that the center of gravity of the second area  74  is positioned parallel to the center axis C so as to pass through the center of gravity G0 of the treatment area  64  or closer to the center of gravity G0 than the center axis C. 
         [0063]    As described above, the ultrasonic probe  52  can be produced such that the center of gravity (gravity center axis) G between the distal end and proximal end of the second area  74  is displaced parallel to the center axis C so as to coincide with the center of gravity G0 of the treatment area  64  or to be closer to the center of gravity G0 than the center axis C. 
         [0064]    In this case, the example has been described in which the formation of the treatment area  64  is followed by the machining of the second area  74 . However, the machining of the second area  74  may of course be followed by the formation of the treatment area  64 . This will be described in brief using  FIGS. 5A to 5E .  FIG. 5A  corresponds to  FIG. 4A ,  FIG. 5B  corresponds to  FIG. 4B , and  FIG. 5C  corresponds to  FIG. 4C . Thus, description of  FIGS. 5A to 5C  is omitted. 
         [0065]    As shown in  FIG. 5D , unlike in  FIG. 4D , the second area  74  is formed before the formation of the treatment area  64  based on machining, and the gravity center axis G of the second area  74  is defined at a position displaced from the center axis C of the first area  72 . This is because the center of gravity G0 can be easily determined after the treatment area  64  is machined based on, for example, experience in forming a large number of ultrasonic probes  52  with the same shape and design. 
         [0066]    Then, as shown in  FIG. 5E , unlike in  FIG. 4E , the second area  74  is formed, and the treatment area  64  is formed by machining to have a predetermined shape (a shape specified by design). At this time, the treatment area  64  can be formed so that the center of gravity G of the second area  74  passes through the center of gravity G0 of the treatment area  64 , or be closer to the center of gravity G0 than the center axis C. 
         [0067]    Effects will be described in brief which are exerted using the ultrasonic treatment system  10  shown in  FIG. 1  and, for example, including the ultrasonic probe  52  produced in steps described with reference to  FIGS. 4A to 4E  or  FIGS. 5A to 5E . 
         [0068]    The external thread portion  66  at the proximal end of the ultrasonic probe  52  is engaged with the internal thread portion  42  of the horn  40  in a threaded manner. 
         [0069]    A trocar (not shown in the drawings) is pierced into, for example, the abdominal cavity and fixed. In this state, the treatment area  64  of the ultrasonic probe unit  18  is guided, via the trocar, through the body cavity toward the biological tissue to be treated. For example, with the treatment area  64  shaped like a hook hooked to the biological tissue, the foot switch (not shown in the drawings) is operated to transmit a signal to the electrical current supply section  22  via the input section  24  to switch to the state where the electrical current supply section  22  supplies electrical current. Thus, the ultrasonic transducer  34  vibrates to transmit vibration to the ultrasonic probe  52  via the horn  40 . That is, the ultrasonic probe  52  transmits longitudinal vibration resulting from ultrasonic vibration from the proximal end toward the distal end of the ultrasonic probe  52  along the longitudinal axis L defined by the proximal end and distal end. 
         [0070]    At this time, the center axis (center of gravity) C is straight from the proximal end of the horn  40  to the distal end portion  73   a  of the first area  72  of the ultrasonic probe  52  and is not displaced. Thus, the longitudinal vibration from the ultrasonic transducer  34  is stably transmitted through the horn  40  to the distal end portion  73   a  of the first area  72  without vibration loss. 
         [0071]    The center of gravity in the first area  72  and the center of gravity in the second area  74  are shifted from each other at the boundary between the distal end portion  73   a  of the first area  72  and the proximal end portion  75   b  of the second area  74 . However, the boundary corresponds to the antinode position of the vibration and thus does not affect the vibration. The gravity center axis G is straight from the proximal end portion  75   b  to the distal end portion  75   a  of the second area  74  and is not displaced. Thus, the longitudinal vibration from the ultrasonic transducer  34  is stably transmitted through the horn  40  and the first area  72  to the distal end portion  75   a  of the second area  74  without vibration loss. The center of gravity G0 of the treatment area  64  lies on an axis corresponding to an extension of the barycenter axis G of the second area  74 . Consequently, the longitudinal vibration from the ultrasonic transducer  34  is stably transmitted through the horn  40 , the first area  72 , and the second area  74  to the distal end of the treatment area  64  without vibration loss. 
         [0072]    Therefore, the ultrasonic vibration can be transmitted to the hooked biological tissue through the treatment area  64  with vibration loss minimized. Thus, pulling the treatment area  64  toward the operator allows the biological tissue to be appropriately treated, for example, incised. 
         [0073]    When the treatment region  64  is appropriately shaped, the center of gravity of the second area  74  may be correspondingly adjusted. This ensures an appropriate degree of freedom for the shape of the treatment area  64 . For example, the treatment area  64  is not limited to the hook shape shown in  FIG. 3A , but the treatment area  64  shaped like a paddle as shown in  FIGS. 6A to 6C , or like scissors as shown in  FIG. 7 , may be suitably used. The center of gravity of the second area  74  is adjusted such that the center of gravity G defined by a set of centers of gravity on transverse sections in the second area  74  orthogonal to the center axis C of the first area  72  coincides with the center of gravity G0 of the treatment area  64 , or is closer to the center of gravity G0 than the center axis C. Thus, stable longitudinal vibration can be transmitted to the first area  72 , to the second area  74 , and further to the treatment area  64 . 
         [0074]    In the ultrasonic probe  52  according to the embodiment, the longitudinal vibration can be prevented from being disturbed, or be made difficult to disturb, by setting the center of gravity of the ultrasonic probe  52  to be straight over a half-wavelength portion or an integral multiple thereof on the distal end side of the ultrasonic probe  52 . In the ultrasonic probe  52  according to the embodiment, since the boundary between the first area  72  and the second area  74  corresponds to the antinode position of the vibration, the center of gravity of the first area  72  and the center of gravity of the second area  74  are displaced from each other at the boundary between the first area  72  and the second area  74 , the center of gravity of the first area  72  lies on the center axis C, and the center of gravity in the second area  74  and the treatment area  64  lies on the straight line G which is parallel to the center axis C, the longitudinal vibration from the ultrasonic transducer  34  can be stably transmitted to the treatment area  64  via the ultrasonic probe  52 . That is, since the longitudinal vibration can be made difficult to disturb simply by adjusting the center of gravity over a half-wavelength portion or an integral multiple thereof on the distal end side of the ultrasonic probe  52 , undesirable vibration such as a transversal wave can be prevented from being generated, particularly in the probe main body section  62  of the ultrasonic probe  52 , without an increase in machining costs. 
         [0075]    Furthermore, in the above-described procedure of manufacturing the ultrasonic probe  52 , the step has been described in which the site  74   a  corresponding to the second area  74  is formed to have an outer diameter smaller than the outer diameter of the first area  72  as shown in  FIG. 4C  and  FIG. 5C . However, this step may be omitted. That is, if the gravity center axis G can be displaced relative to the center axis C by machining the site  74   a  corresponding to the second area  74  to form, for example, the flat surface  76  as shown in  FIG. 3C , then the diameter of the site  74   a  need not necessarily be reduced. Instead, the second area  74  may be formed to have a larger diameter. 
         [0076]    For example, the second area  74  may be formed like a cylinder with a center axis displaced from the center axis C of the cylindrical first area  72  (that is, the second area  74  is made eccentric to the first area  72 ). That is, the second area  74  can also be formed to be cylindrical. However, the formation of the cylindrical second area  74  with a center of gravity displaced from the center of gravity of the first area  72  incurs higher machining costs than the formation in the example shown in  FIGS. 4A to 4E  or  FIGS. 5A to 5E  described above. Thus, it is advantageous in terms of costs to set both the cylindrical first and second areas  72  and  74  to have the same center axis and then to adjust the center of gravity of the second area  74  by machining one surface (for example, a flat surface  76 ) of the second area  74 . 
         [0077]    In this case, in addition to cutting a part of the cylinder so that the second area  74  has the flat surface  76  shown in  FIG. 3B , shaping the second area  74  as shown in  FIGS. 8A to 8F  is also suitable. Any of various well-known machine tools may be used to machine the second area  74  as shown in  FIGS. 8A to 8F . Machined portions (removed surfaces)  76   a ,  76   b ,  76   c ,  76   d ,  76   e , and  76   f  removed as shown in  FIGS. 8A to 8F  allow the center of gravity G to be displaced upward relative to the center C of an imaginary circle in each of the figures. That is, in the second area  74 , the barycenter G can be displaced by forming an odd-shaped portion which is not circular and which fails to exhibit point symmetry with respect to the center axis C of the first area  72 , for example, as shown by reference numerals  76 ,  76   a ,  76   b ,  76   c ,  76   d ,  76   e , and  76   f . Even in such cases as shown by reference numerals  76 ,  76   a ,  76   b ,  76   c ,  76   d , and  76   e , the ultrasonic probe  52  can be formed more inexpensively than in the case where the shape of the second area  74  is kept cylindrical. 
         [0078]    The first area  72  of the above-described ultrasonic probe  52  is formed to exhibit point symmetry with respect to the center axis C of the first area  72 . The second area  74  is formed to exhibit asymmetry with respect to the gravity center axis G so that the gravity center axis G passes through the center of gravity G0 of the treatment area  64 . 
         [0079]    In the embodiment, the case has been described in which the outer peripheral surface of the first area  72  is circular, whereas the outer peripheral surface of the second area  74  is partly shaped like a part of a circle. Also, the first area is preferably shaped like a polygon with 2n sides (n: a natural number) such as a hexagon as shown by reference numeral  172  in  FIG. 9A  or like a polygon with 2n+1 sides (n: a natural number) such as a pentagon as shown by reference numeral  272  in  FIG. 9B . Furthermore, a machined portion (in this case, the flat surface  76 ) is preferably formed in the second area as shown by reference numeral  174  in  FIG. 9A  by machining and removing a part of a hexagon. Similarly, a machined portion (in this case, the flat surface  76 ) is preferably formed in the second area as shown by reference numeral  274  in  FIG. 9B  by machining and removing a part of a pentagon. 
         [0080]    When the first area is shaped like a regular pentagon as shown by  272  in  FIG. 9B , the center of gravity of the first area  272 , that is, the center axis C, lies at a position where a perpendicular line of a midpoint of one side (first side) extended to a vertex (first vertex) opposite to the first side intersects a perpendicular line of a midpoint of another side (second side) extended to a vertex (second vertex) opposite to the second side. 
         [0081]    Furthermore, the first area and the second area are suitably formed by appropriately combining the hexagon shown in  FIG. 9A  with the pentagon shown in  FIG. 9B . That is, the probe main body section  62  is suitably formed by, for example, shaping the first area  72  like a pentagon and shaping the second area  74  like a hexagon and removing and partly removed. Alternatively, the probe main body section  62  may be suitably formed by, for example, shaping the first area  72  like a hexagon and shaping the second area  74  like a pentagon and removing part of the shape by machining. 
         [0082]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.