Abstract:
The present application is directed to an image-guided, vacuum assisted, percutaneous, coring, cable driven breast biopsy instrument which may be conveniently mounted to an x-ray machine wherein the biopsy instrument incorporates a rotation knob at the proximal end of the instrument to manually rotate the distal end of the probe, thus allowing the clinician to conveniently position the tissue port next to the tissue to be sampled.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/240,492, filed Oct. 13, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates, in general, to an improved surgical biopsy instrument and, more particularly, to a remote thumbwheel mechanism for use in a surgical biopsy instrument. 
     BACKGROUND OF THE INVENTION 
     The diagnosis and treatment of patients with cancerous tumors, pre-malignant conditions, and other disorders has long been an area of intense interest in the medical community. Non-invasive methods for examining tissue and, more particularly, breast tissue include palpation, X-ray imaging, MRI imaging, CT imaging, and ultrasound imaging. When a physician suspects that tissue may contain cancerous cells, a biopsy may be done using either an open procedure or in a percutaneous procedure. In an open procedure, a scalpel is used by the surgeon to create an incision to provide direct viewing and access to the tissue mass of interest. The biopsy may then be done by removal of the entire mass (excisional biopsy) or a part of the mass (incisional biopsy). In a percutaneous biopsy, a needle-like instrument is inserted through a very small incision to access the tissue mass of interest and to obtain a tissue sample for examination and analysis. The advantages of the percutaneous method as compared to the open method are significant: less recovery time for the patient, less pain, less surgical time, lower cost, less disruption of associated tissue and nerves and less disfigurement. Percutaneous methods are generally used in combination with imaging devices such as X-ray and ultrasound to allow the surgeon to locate the tissue mass and accurately position the biopsy instrument. 
     Generally there are two ways to percutaneously obtain a tissue sample from within the body, aspiration or core sampling. Aspiration of the tissue through a fine needle requires the tissue to be fragmented into small enough pieces to be withdrawn in a fluid medium. Application is less intrusive than other known sampling techniques, but one can only examine cells in the liquid (cytology) and not the cells and the structure (pathology). In core biopsy, a core or fragment of tissue is obtained for histologic examination which may be done via a frozen or paraffin section. The type of biopsy used depends mainly on various factors and no single procedure is ideal for all cases. 
     A number of core biopsy instruments which may be used in combination with imaging devices are known. Spring powered core biopsy devices are described and illustrated in U.S. Pat. Nos. 4,699,154, 4,944,308, and Re. 34,056. Aspiration devices are described and illustrated in U.S. Pat. Nos. 5,492,130; 5,526,821; 5,429,138 and 5,027,827. 
     U.S. Pat. No. 5,526,822 describes and illustrates an image-guided, vacuum-assisted, percutaneous, coring, breast biopsy instrument which takes multiple tissue samples without having to re-puncture the tissue for each sample. The physician uses this biopsy instrument to “actively” capture (using the vacuum) the tissue prior to severing it from the body. This allows the physician to sample tissues of varying hardness. The instrument described in U.S. Pat. No. 5,526,822 may also be used to collect multiple samples in numerous positions about its longitudinal axis without removing the instrument from the body. A further image-guided, vacuum-assisted, percutaneous, coring, breast biopsy instrument is described in commonly assigned U.S. Ser. No. 08/825,899, filed on Apr. 2, 1997 and in U.S. Pat. Nos. 6,007,497; 5,649,547; 5,769,086; 5,775,333; and 5,928,164. A handheld image-guided, vacuum-assisted, percutaneous, coring, breast biopsy instrument is described in U.S. Pat. No. 6,086,544 and in U.S. Pat. No. 6,120,462. The instrument described therein moves drive motors and other electronic components into a control unit separate from and remotely located from the biopsy probe. Biopsy probe cutter rotational and translational motion is transferred from the motors in the control unit to the biopsy probe via flexible coaxial cables. This arrangement improves the cleanability of the reusable hardware that remains in close proximity to the biopsy site as well as improves the life and durability of the electric motors and electronic components now remotely located from the biopsy probe. The biopsy instrument described and illustrated in U.S. Pat. No. 6,086,544 and in U.S. Pat. No. 6,120,462 was designed primarily to be a “hand held” instrument to be used by the clinician in conjunction with real time ultrasound imaging. Several imageguided, vacuum-assisted, percutaneous, coring, breast biopsy instruments are currently sold by Ethicon Endo-Surgery, Inc. under the Trademark MAMMOTOME™. 
     The majority of breast biopsies done today, however, utilize an x-ray machine as the imaging modality. Using x-ray requires that the biopsy instrument be affixed to the x-ray machine by some type of bracket arrangement. Since the biopsy instrument is fixed to a portion of the x-ray machine there is now a need for a means to conveniently rotate the biopsy probe once it is advanced into the breast in order to accurately position the vacuum port at the distal end of the probe. 
     In U.S. Pat. No. 5,769,086 a biopsy probe is disclosed which includes an electric motor, connected to the proximal end of the biopsy probe via a gear train. Activating the motor causes rotation of the piercing element of the biopsy probe so that multiple tissue specimens may be obtained by the clinician at any location around the center axis of the probe. U.S. Pat. No. 5,649,547 illustrates and describes a biopsy instrument which includes a “thumb wheel” at the proximal end of the biopsy probe piercing element. The thumb wheel provides a convenient place for the clinician to grasp the piercing element to manually rotate the biopsy probe about its center axis so that multiple tissue samples could be taken at any position, as determined by the clinician, about the axis of the probe. There are a couple of problems, however, that become evident when this arrangement is put into clinical use. First, when the biopsy probe is used in combination with and mounted to an x-ray machine, it can be difficult for the clinician to get access to the thumb wheel portion of the biopsy probe because of brackets, hoses, and other obstructions in the area around the probe. 
     It would, therefore, be advantageous to design an image-guided, vacuum assisted, percutaneous, coring, cable driven breast biopsy instrument which may be conveniently mounted to an x-ray machine, and incorporate in it a remotely located means to manually rotate the probe, located in an area away from the surgical site and easily accessible by the clinician. It would further be advantageous to design an image-guided, vacuum assisted, percutaneous, coring, cable driven breast biopsy instrument which may be conveniently mounted to an x-ray machine which would incorporate a port rotation knob located at the proximal end of the biopsy instrument. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a biopsy instrument including a base assembly including a firing mechanism movably attached to a distal end of the base assembly, a probe assembly detachably mounted to the base assembly and a drive assembly detachably mounted to the cutter assembly and including a flexible drive shaft operatively connected to the cutter. The probe assembly including a piercer assembly and a cutter assembly detachably affixed to the base assembly. The piercer assembly including a piercer and a probe mount supporting the piercer. The piercer including a distal port, a vacuum lumen, a cutter lumen and a first gear mechanism affixed to a proximal end of the piercer. The cutter assembly includes a cutter adapted to move through the cutter lumen, an adjustment wheel extending from a proximal end of the cutter assembly and a drive rod connected to the adjustment wheel, the drive rod being operatively connected to the first gear mechanism. 
     The present invention is further directed to a biopsy instrument including a base assembly including a firing mechanism moveably attached to a distal end of the base assembly, a probe assembly moveably attached to the base assembly and a drive assembly detachably mounted to the cutter assembly, the drive assembly including a flexible drive shaft operatively connected to the cutter. The probe assembly including a piercer assembly which includes a piercer moveable from a proximal position to a distal position, a probe mount supporting the piercer and a cutter assembly detachably affixed to the base assembly. The piercer including a distal port, a vacuum port, a cutter lumen and a first gear affixed to a proximal end of the piercer. The probe mount including a second gear affixed to a drive shaft and the second gear meshing with the first gear and a fork coupling detachably mountable to the firing mechanism. The cutter assembly including a cutter adapted to move through the cutter lumen, an adjustment wheel extending from a proximal end of the cutter assembly and a drive rod connected to the adjustment wheel, the drive rod being slideably affixed to a proximal end of the drive shaft such that rotation of the adjustment wheel rotates the piercer as the piercer moves from the proximal position to the distal position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to organization and methods of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is an isometric view of a surgical biopsy system of the present invention comprising a biopsy device, control unit, and remote. 
     FIG. 2 is an isometric view of the biopsy probe assembly and base assembly, shown separated, with the upper base housing shown removed. 
     FIG. 3 is an isometric view of the biopsy probe assembly with the top shell and bottom shell shown separated to expose internal components. 
     FIG. 4 is an exploded isometric view of the biopsy probe assembly of the present invention without the top shell and bottom shell. 
     FIG. 5 is a longitudinal section view of the distal end of the biopsy probe assembly. 
     FIG. 6 is an exploded isometric view of the lower transmission assembly of the present invention. 
     FIG. 7 is an isometric view of the transmission showing the upper transmission assembly exploded. 
     FIG. 8 is an isometric view of the biopsy probe assembly and base assembly, separated, with the upper base housing not shown, as viewed from the proximal end. 
     FIG. 9 is an exploded isometric view of the firing mechanism of the present invention. 
     FIG. 10 is an exploded isometric view of an embodiment of the firing fork assembly. 
     FIG. 11 is an exploded isometric view of the triggering mechanism of the present invention. 
     FIG. 12 is an isometric view of the safety latch. 
     FIG. 13 is an isometric view of the safety button. 
     FIG. 14 is a top view of the firing mechanism of the present invention showing the mechanism in the post-fired position. 
     FIG. 15 is a partial, plan sectional view of the firing mechanism in the post-fired position showing the firing latch and firing rod. 
     FIG. 16 is a top view of the firing mechanism of the present invention showing the mechanism in the pre-fired position. 
     FIG. 17 is a partial, plan sectional view of the firing mechanism in the pre-fired position showing the firing latch and firing rod. 
     FIG. 18 is a top view of the firing mechanism of the present invention showing the arming mechanism in the relaxed position. 
     FIG. 19 is a partial, plan sectional view of the firing mechanism in the relaxed position showing the firing latch and firing rod. 
     FIG. 20 is an isometric view of the safety latch and safety button shown in the locked position. 
     FIG. 21 is an isometric view of the safety latch and safety button shown in the firing position. 
     FIG. 22 is an exploded isometric view of an alternate embodiment of the firing fork assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is an isometric view showing a surgical biopsy system  10  comprising biopsy device  40 , a control unit  100 , and remote  20 . Biopsy device  40  comprises probe assembly  42  operatively and removably attached to base  44 . Base  44  is removably attached to a moveable table  12  such as a stereotactic guidance system as may be found on mammographic x-ray machines, an example of which is Model MAMMOTEST PLUS/S available from Fischer Imaging, Inc., Denver, Colo. 
     Probe assembly  42  includes an elongated piercer  70  having a piercer tip  72  for penetrating soft tissue of a surgical patent. Piercer  70  comprises a piercer tube  74  and vacuum chamber tube  76 . Vacuum chamber tube  76  of piercer  70  may be fluidly connected to control unit  100 . Similarly, axial vacuum to probe assembly  42  may be obtained by fluid connection to control unit  100 . MAMMOTOME™ system tubing set Model No. MVAC1 available from Ethicon Endo-Surgery Inc., Cincinnati, Ohio is suitable for use to permit detachable fluid connection of lateral vacuum line  32  and axial vacuum line  34  to control unit  100 . Lateral vacuum line  32  and axial vacuum line  34  are made from a flexible, transparent or translucent material, such as silicone tubing, allowing for visualization of the material flowing through them. Lateral connector  33  and axial connector  35  are female and male luer connectors, respectively, commonly known and used in the medical industry. Base  44  is operatively connected to control unit  100  by control cord  26 , translation shaft  22 , and rotation shaft  24 . Translation shaft  22  and rotation shaft  24  are preferably flexible so as to permit for ease of mounting of biopsy device  40  to moveable table  12 . 
     Control unit  100  is used to control the sequence of actions performed by biopsy device  40  in order to obtain a biopsy sample from a surgical patient. Control unit  100  includes motors and a vacuum pump, and controls the activation of vacuum to probe assembly  42  and the translation and rotation of the cutter (not visible) in probe assembly  42 . A suitable Control unit  100  is a MAMMOTOME™ system control module Model No. SCM12 with software Model No. SCMS1 available from Ethicon Endo-Surgery Inc., Cincinnati, Ohio. 
     Remote  20  is operatively and removably connected to control unit  100 . Remote  20  may be used by the surgical biopsy system operator to control the sequence of actions performed by biopsy device  40 . Remote  20  may be a hand operated or foot operated device. A suitable remote  20  is MAMMOTOME™ Remote Key-pad Model No. MKEY1 available from Ethicon Endo-Surgery Inc., Cincinnati, Ohio. 
     FIG. 2 is an isometric view showing probe assembly  42  and base  44  separated. Upper base housing  50  is normally fixedly attached to base  44 , but has been shown removed from base  44  to provide a view of transmission  301 . Top shell tab  46  is located on the distal end of cantilever beam  41  and projects above the top surface of gear shell  18 . Top shell tab  46  inserts into tab window  48  in upper base housing  50  upon assembly of probe assembly  42  to base  44 . Once probe assembly  42  and base  44  are properly assembled, top shell tab  46  must be pushed down through tab window  48  by the user before probe assembly  42  and base  44  can be separated. A plurality of raised ribs  58  is provided on gear shell  18  to improve the user&#39;s grip on the instrument. Post  14  extends above the top surface of base shell  38  and inserts into keyhole  16  (not visible) located on the underside of gear shell  18 . Tube slot  68  in upper base housing  50  provides clearance for axial vacuum line  34 . First tang  54  and second tang  56  protrude from opposite sides of probe housing  52  and insert into first recess  64  and second recess  66 , respectively, in firing fork  62 . The proximal end of probe housing  52  fits slidably within gear shell  18  and firing fork  62  fits slidably within base shell  38 . Thus, once probe assembly  42  and base  44  are operatively assembled, probe housing  52  and firing fork  62  are able to move a fixed linear distance in a distal and proximal direction in front of gear shell  18  and base shell  38 . FIGS. 1 and 2 show probe housing  52  and firing fork  62  in their most distal position. 
     FIGS. 3 and 4 are views of probe assembly  42 . FIG. 3 is an isometric view of probe assembly  42  with the top shell  17  and bottom shell  19  shown separated, the top shell  17  rotated ninety degrees, to expose internal components. FIG. 4 is an exploded isometric view of the same probe assembly  42  without top shell  17  or bottom shell  19 . Gear shell  18  is formed from top shell  17  and bottom shell  19 , each injection molded from a rigid, biocompatible thermoplastic material such as polycarbonate. Upon final assembly of probe assembly  42 , top shell  17  and bottom shell  19  are joined together by ultrasonic welding along joining edge  15 , or joined by other methods well known in the art. Probe assembly  42  comprises piercer  70  having an elongated, metallic piercer tube  74  and a piercer lumen  80  (see FIGS.  4  and  5 ). On the side of the distal end of piercer tube  74  is port  78  for receiving tissue to be extracted from the surgical patient. Joined along side piercer tube  74  is an elongated, tubular, metallic vacuum chamber tube  76  having a vacuum lumen  82  (see FIGS.  4  and  5 ). Piercer lumen  80  is in fluid connection with vacuum lumen  82  via a plurality of vacuum holes  77  (See FIG. 5) located in the bottom of the “bowl” defined by port  78 . Vacuum holes  77  are small enough to remove the fluids but not large enough to allow excised tissue portions to be removed through lateral vacuum line  32 , which is fluidly connected to vacuum lumen  82 . A metallic, sharpened piercer tip  72  is fixedly attached to the distal end of piercer  70 . It is designed to penetrate soft tissue, such as the breast tissue of a female surgical patient. In the present embodiment piercer tip  72  is a three sided, pyramidal shaped point, although the tip configuration may also have other shapes. 
     Refer now, momentarily, to FIG.  5 . FIG. 5 is a section view of the distal end of probe assembly  42 , illustrating primarily probe housing  52 , piercer  70 , and union sleeve  90 . The proximal end of piercer  70  is fixedly attached to union sleeve  90  having a longitudinal bore  84  through it. Union sleeve  90  contains a first o-ring groove  27  and second o-ring groove  28 , spaced apart so as to allow for a traverse opening  37  between them in fluid communication with longitudinal bore  84 . First o-ring  29  and second o-ring  30  mount in first o-ring groove  27  and second o-ring groove  28 , respectively. Sleeve gear  36  is integral to union sleeve  90  and is located at its most proximal end. Lead-in cone  25  is a conical shaped metallic structure that attaches to the proximal end of union sleeve  90 . Union sleeve  90  is inserted into housing bore  57  located in the distal end of probe housing  52 , and rotatably supports the proximal end of piercer  70 . Positioning wheel  31  slides over piercer  70  and the distal end of union sleeve  90  and rotatably attaches to probe housing  52 , hence trapping lead-in cone  25  and union sleeve  90  within housing bore  57  in the distal end of probe housing  52 . Locating projection  11  on the distal end of union sleeve  90  functionally engages alignment notch  13  in positioning wheel  31 . Thus, rotating positioning wheel  31  likewise causes the rotation of piercer  70 . This allows port  78  to be readily positioned anywhere within the 360° axis of rotation of piercer  70 . 
     Referring again to FIGS. 3 and 4, housing extension  47  is located at the proximal end of probe housing  52 . Housing flange  53  is located at the most proximal end of housing extension  47  on probe housing  52  and is assembled just inside of top shell front slot  55  in top shell  17 . Shell insert  39  is assembled into top shell front slot  55 . First insert tab  59  and second insert tab  60 , both located on shell insert  39 , engage first shell recess  61  and second shell recess  63 , located within top shell front slot  55 , respectively. Thus, upon complete assembly of probe assembly  42 , the most proximal end of probe housing  52  containing housing flange  53  is trapped within gear shell  18 , yet slideable along housing extension  47  distal and proximal within top shell front slot  55 . Tissue sampling surface  65  is a recessed surface within probe housing  52  which provides a surface where each tissue sample will be deposited during the operation of the present invention, prior to retrieval by the clinician. 
     An elongated, metallic, tubular cutter  96  (see FIG. 5) is axially aligned within cutter bore  51  of probe housing  52 , longitudinal bore  84  of union sleeve  90 , and piercer lumen  80  of piercer  70  so that cutter  96  may slide easily in both the distal and proximal directions. Cutter  96  has a cutter lumen  95  through the entire length of cutter  96 . The distal end of cutter  96  is sharpened to form a cutter blade  97  for cutting tissue held against cutter blade  97  as cutter  96  is rotated. The proximal end of cutter  96  is fixedly attached to the inside of cutter gear bore  102  of cutter gear  98 . Cutter gear  98  may be metal or thermoplastic, and has a plurality of cutter gear teeth  99 , each tooth having a typical spur gear tooth configuration as is well known in the art. Cutter seal  79  is a lip type seal and is fixedly attached to the proximal end of cutter gear  98 , and is made of a flexible material such as silicone. Tissue remover  132  fits rotatably and slidably through cutter seal  79 . Probe seal  81  is also a lip type seal made of a flexible material such as silicone rubber and is fixedly inserted into the proximal end of cutter bore  51  at the proximal end of probe housing  52 . Cutter  96  fits rotatably and slidably through cutter seal  79 . Cutter seal  79  and probe seal  81  operate to prevent fluids from entering the space within gear shell  18  during a surgical biopsy procedure. 
     Still in FIGS. 3 and 4, cutter gear  98  is driven by elongated drive gear  104  having a plurality of drive gear teeth  106  designed to mesh with cutter gear teeth  99 . The function of elongated drive gear  104  is to rotate cutter gear  98  and cutter  96  as they translate in both longitudinal directions. Elongated drive gear  104  is preferably made of a thermoplastic material, such as liquid crystal polymer. Distal drive axle  108  projects from the distal end of elongated drive gear  104  and mounts rotatably into an axle support rib (not visible) molded on the inside of top shell  17  and held in place by first gear support rib located on bottom shell  19 . Gear shaft  110  projects from the proximal end of drive gear  104  and is rotatably supported by a gear shaft slot  69  located in the proximal end of top shell  17  and by second gear support rib  137  located on bottom shell  19 . Drive gear slot  101  is located on the most proximal end of gear shaft  110  as a means for rotationally engaging drive gear  104 . 
     Still referring to FIGS. 3 and 4, cutter carriage  124  is provided to hold cutter gear  98  and to carry cutter gear  98  as it is rotated and translated in the distal and proximal directions. Cutter carriage  124  is preferably molded from a thermoplastic material and is generally cylindrically shaped with a threaded bore  126  through it and with carriage foot  130  extending from its side. Carriage foot  130  has a foot recess  128  formed into it and foot slot  127  for rotatably holding cutter gear  98  in the proper orientation for cutter gear teeth  99  to mesh properly with drive gear teeth  106 . Lower carriage guide  103  projects down from cutter carriage  124  and slidably engages lower guide slot  107  molded on the inside surface of bottom shell  19 . Upper carriage guide  105  projects up from carriage foot  130  and slidably engages a upper guide slot  109  molded on the inside of top shell  17 . Cutter carriage  124  is attached via threaded bore  126  to elongated screw  114 , which is parallel to drive gear  104 . Screw  114  has a plurality of conventional lead screw threads  116  and is preferably made of a thermoplastic material. The rotation of elongated screw  114  in one direction causes cutter carriage  124  to move distally, while the reverse rotation of elongated screw  114  causes cutter carriage  124  to move proximally. As a result, cutter gear  98  moves distally and proximally according to the direction of the screw rotation, which in turn advances cutter  96  distally or retracts it proximally. In the present embodiment, elongated screw  114  is shown with a right hand thread so that clockwise rotation (looking from the proximal to distal direction) causes cutter carriage  124  to translate in the proximal direction. Distal screw axle  118  projects from the distal end of elongated screw  114  and mounts rotatably into an axle support rib (not visible) molded on the inside of top shell  17  and held in place by first screw support rib  111  located on bottom shell  19 . Screw shaft  120  projects from the proximal end of elongated screw  114  and is rotatably supported by a screw shaft slot  71  located in the proximal end of top shell  17  and by second screw support rib  112  located on bottom shell  19 . Lead screw slot  122  is located on the most proximal end of screw shaft  120  as a means for rotationally engaging elongated screw  114 . 
     At this point in the detailed description it should be pointed out that during the operation of the biopsy instrument cutter  96  translates in either direction between a fully retracted position, just proximal to tissue sampling surface  65  as referenced by cutter blade  97 , and a fully deployed position wherein cutter blade  97  is located just distal to port  78 . As cutter  96  translates between these end points there are a number of intermediate positions wherein adjustments may be made to the cutter rotational and translational speed as commanded by control unit  100 . These intermediate positions and the adjustments made to the cutter depend on the programming of control unit  100 . 
     Referring now to FIG. 5, the distal end of lateral vacuum line  32  is attached to lateral fitting  92  located on the distal end of probe housing  52 . Lateral fitting  92  has lateral hole  117  through it along its axis in fluid communication with housing bore  57 . Lateral hole  117  in lateral fitting  92  is positioned within housing bore  57  such that when union sleeve  90  is inserted into housing bore  57  lateral hole  117  is located in the space created between first and second o-rings,  29  and  30  respectively. Locating lateral hole  117  in the space between first and second o-rings  29  and  30 , respectively, allows for the communication of fluids between vacuum lumen  82  and control unit  100 . 
     Referring again to FIGS. 3 and 4, axial vacuum line  34  is fluidly attached to tissue remover support  129  which is in turn fluidly attached to the proximal end of an elongated, metallic, tubular tissue remover  132 . Axial vacuum line  34  allows for the communication of fluids between piercer lumen  80 , cutter lumen  95 , and control unit  100 . Tissue remover support  129  fits into axial support slot  73  located in the proximal end of top shell  17 . Strainer  134  is located on the distal end of tissue remover  132  and functions to prevent passage of fragmented tissue portions through it and into control unit  100 . Tissue remover  132  inserts slidably into cutter lumen  95  of cutter  96 . During the operation of the biopsy instrument, tissue remover  132  is always stationary, being fixedly attached at its proximal end to tissue remover support  129  which is fixed within axial support slot  73  located in the proximal end of top shell  17 . When cutter  96  is fully retracted to its most proximal position, the distal end of tissue remover  132  is approximately even with the distal end of cutter  96  (see FIG.  5 ). The distal end of cutter  96 , when at its most proximal position, and probe housing  52  at its most distal position, is slightly distal to housing wall  67  which is proximal and perpendicular to tissue sampling surface  65 . 
     Probe rotation rod  85  is an elongated, solid metal rod. Rotation rod gear  86  is a spur gear fixedly attached to the distal end of probe rotation rod  85 . Rotation rod flat  87  is located at the proximal end of probe rotation rod  85 . Rotation rod flat  87  is approximately one-third to one-half the rod diameter in depth and extending from its proximal end approximately one inch in length. Rotation rod flat  87  thus creates a “D” shaped geometry at the proximal end of probe rotation rod  85 . Rod bushing  88  is made of molded thermoplastic and is cylindrical in shape. At its distal end is bushing bore  89  which is a “D” shaped hole approximately one inch in depth, designed to slidably receive the proximal end of probe rotation rod  85 . Rod bushing  88  fits rotatably into axial support slot  73  below tissue remover support  129  at the proximal end of top shell  17 . The longitudinal position of rod bushing  88  is fixed by the raised sections on both sides of bushing groove  93 , upon assembly into the proximal end of top shell  17 . Rod bushing drive slot  91  is located on the most proximal end of rod bushing  88  as a means for rotationally engaging rod bushing  88 . Rotation gear  86  is rotatably fixed into gear cavity  115  on the underside of probe housing  52 , the opening being in communication with housing bore  57  (see FIG.  5 ). Rotation rod gear  86  operably engages sleeve gear  36  located at the proximal end of union sleeve  90 . The distal end of probe rotation rod  85  with rotation rod gear  86  attached is rotatably fixed to the underside of probe housing  52  by rotation gear cover  94 . Rotation gear cover  94  is molded from a thermoplastic material and is fixedly attached to probe housing  52  by four raised cylindrical pins which press fit into four holes (not visible) in probe housing  52 . Probe rotation rod  85  inserts rotatably and slidably through rod hole  43  in shell insert  39 . The proximal end of probe rotation rod  85  slidably engages bushing bore  89  in rod bushing  88 . Thus, rotation of rod bushing  88  causes rotation of probe rotation rod  85  which is fixedly attached to rotation rod gear  86  causing rotation of union sleeve  90  which is fixedly attached to piercer  70 , which contains port  78 . 
     It is important for the user of the surgical biopsy system of the present invention to be able to “fire” the piercer  70  into the tissue of a surgical patient. It is also important that the user be able to rotate piercer  70  about its axis so as to properly position port  78 , regardless of linear position of piercer  70  pre-fired vs. post-fired (positions discussed later). The slidable interface between probe rotation rod  85  and rod bushing  88  plays an important role in providing this capability. Probe rotation rod  85  follows the linear movement of piercer  70 , while the linear movement of rod bushing  88  is restricted by the fact that it is rotatably attached to top shell  17 . Thus the “D” shaped geometry on the proximal end of rotation rod  85  and the “D” shaped hole in the distal end of rod bushing  88 , designed to slidably receive the proximal end of rotation rod  85 , permit the user to turn port rotation knob  45 , which is operably connected to rod bushing  88  through a chain of elements described later, and effect the rotation of piercer  70 , irrelevant of the linear position of piercer  70 . 
     Bottom shell  19  fixedly attaches to top shell  17  as described earlier. Its function is to hold in place and contain the elements previously described, which have been assembled into top shell  17 . Keyhole  16  is centered at the distal end of bottom shell  19 . It slidably and removably engages post  14  (See FIG.  2 ), permitting probe assembly  42  to be operatively and removably connected to base  44 . First screw support rib  111  and second screw support rib  112  are each integrally molded to bottom shell  19  and support the distal and proximal ends, respectively, of elongated screw  114 . First gear support rib  136  and second gear support rib  137  likewise are each integrally molded to bottom shell  19  and support the distal and proximal ends, respectively, of elongated drive gear  104 . Rod bushing support rib  139  integrally molded to bottom shell  19  supports the distal end of rod bushing  88 . 
     FIG. 6 is an exploded isometric view of lower transmission assembly  302 . Translation shaft  22  and rotation shaft  24  is each a flexible coaxial cable comprising a flexible rotatable center core surrounded by a flexible tubular casing, as is well known in the art. At their most proximal ends is provided a coupling means for removably and operatively connecting translation shaft  22  and rotation shaft  24  to control unit  100 . The distal ends of translation shaft  22  and rotation shaft  24  each insert through first boot bore  309  and second boot bore  311 , respectively. Flex boot  303  is molded from a thermoplastic elastomer such as, for example, polyurethane, and functions as a “flex relief” for translation shaft  22 , rotation shaft  24 , and control cord  26 . Rotation shaft ferrule  305  is a metallic tubular structure comprising a through bore with a counter bore at its proximal end for fixedly attaching, via crimping or swaging as is well known in the art, to the outer tubular casing of rotation shaft  24 . At the distal end of rotation shaft ferrule  305  is a flared, counter bored section for receiving first bearing assembly  315 . A suitable example of first bearing assembly  315  is Model No. S9912Y-E1531PSO, available from Stock Drive Products, New Hyde Park, N.Y. Rotation shaft adapter  319  is made of stainless steel and has a proximal end with a counter bore. Its proximal end inserts through the bore of first bearing assembly  315  and the counter bore slips over the distal end of the rotatable center core of rotation shaft  24  and is fixedly attached by crimping or swaging. The distal end of rotation shaft adapter  319  is inserted through the bore in first bevel gear  321  and is fixedly attached by a slotted spring pin. Similarly, translation shaft ferrule  307  is a metallic tubular structure comprising a through bore with a counter bore at its proximal end for fixedly attaching, via crimping or swaging, to the outer tubular casing of translation shaft  22 . At the distal end of translation shaft ferrule  307  is a flared, counter bored section for receiving thrust washer  317 . Translation shaft adapter  323  is made of stainless steel and has a proximal end with a counter bore. Its proximal end inserts through the bore of thrust washer  317  and the counter bore slips over the distal end of the rotatable center core of translation shaft  22  and is fixedly attached by crimping or swaging. The distal end of translation shaft adapter  323  is slotted as a means to engage the proximal end of encoder shaft  312 , which extends through encoder  310 . Encoder  310  communicates information to control unit  100  about the translation position and translation speed of cutter  96 . Encoder  310  includes an electrical cord containing a plurality of electrical conductors, which has an electrical connector affixed at its most distal end for removable electrical connection to printed circuit board  262  (See FIG.  9 ). A suitable miniature encoder  310  is commercially available as Model sed10-300-eth2 from CUI Stack, Inc. Encoder shaft  312  has two opposing flats on its proximal end, which engage translation shaft adapter  323 , and a cylindrical distal end which is inserted into a counter bore in the proximal end of gear adapter  316  and is fixedly attached by a slotted spring pin. The distal end of gear adapter  316  is inserted through the bore of second bearing assembly  318 , through the bore of shaft spacer  322 , and finally through the bore in second bevel gear  325  which is fixedly attached to gear adapter  316  by a slotted spring pin. 
     Encoder housing assembly  329  comprises left encoder housing half  326  and right encoder housing half  328 , which are molded thermoplastic shells. When assembled, left encoder housing half  326  and right encoder housing half  328  encase encoder  310  and capture the distal end of translation shaft  22  and rotation shaft  24 . Left encoder housing half is attached to transmission plate  330  (see FIG. 7) using a cap screw. Encoder  310  is placed in first shell cavity  332 , preventing rotational or lateral movement of the outer housing of encoder  310 . The distal end of rotation shaft ferrule  305  rests in second shell cavity  334 , which prevents lateral movement of rotation shaft  24 . The distal end of translation shaft ferrule  307  rests in third shell cavity  336 , which again prevents lateral movement of translation shaft  22 . Second bearing assembly  318  rests in fourth shell cavity  338 . Right encoder housing half  328 , containing essentially a mirror image of the cavities found inside left encoder housing half  326 , assembles to left encoder housing half  326  and transmission plate  330  via two cap screws. 
     Still referring to FIG. 6, control cord  26  is flexible and contains a plurality of electrical conductors for communication information between biopsy device  40  and control unit  100  (see FIG.  1 ). At the proximal end of control cord  26  is provided a means of removable electrical connection to control unit  100 . The distal end of control cord  26  inserts through third boot bore  313  located in flex boot  303 . Control cord strain relief  369  is a flexible thermoplastic material and is over molded to the distal end of control cord  26  and is fixedly attached to transmission plate  330  in a recessed area at strain relief bore  371  (see FIG.  7 ), to restrict linear and rotational movement of the distal end of the cord. The most distal end of control cord  26  contains a connector for removably and electrically affixing control cord  26  to printed circuit board  262  (see FIG.  9 ). 
     FIG. 7 is an isometric view of transmission  301 . Upper transmission assembly  304  is shown exploded. Translation coupling assembly  337  consists of translation drive coupling  340 , third bearing assembly  344 , first coupling spacer  348 , and third bevel gear  350 . Third bearing assembly  344  is press fit into first counter bore  345  in transmission plate  330 . Translation drive coupling  340  has a flat bladed distal end which will operatively couple with lead screw slot  122  (see FIG. 8) located at the proximal end of elongated screw  114 . The cylindrical proximal end of translation drive coupling  340  inserts through first counter bore  345 , through the bore of third bearing assembly  344 , through the bore of first coupling spacer  348 , and finally through the bore in third bevel gear  350  which is fixedly attached to translation drive coupling  340  by a slotted spring pin. The gear teeth of third bevel gear  350  mesh with the gear teeth of second bevel gear  325 . Thus, rotation of the center core of translation shaft  22  results in the rotation of translation drive coupling  340 . When translation drive coupling  340  is operatively coupled to elongated screw  114  via lead screw slot  122 , rotation of translation shaft  22  causes rotation of elongated screw  114  which results, as discussed earlier, in the distal or proximal translation of cutter  96 , depending on the direction of translation shaft  22  rotation. 
     In a similar manner, rotation coupling assembly  339  consists of rotation drive coupling  342 , fourth bearing assembly  346 , second coupling spacer  349 , and fourth bevel gear  351 . Fourth bearing assembly  346  is press fit into second counter bore  347  in transmission plate  330 . A suitable example of fourth bearing assembly  346 , as well as second and third bearing assemblies  318  and  344 , respectively, is available as Model No. S9912Y-E1837PSO, available from Stock Drive Products, New Hyde Park, N.Y. Rotation drive coupling  342  has a flat bladed distal end which will operatively couple with drive gear slot  101  (see FIG. 8) located at the proximal end of elongated drive gear  104 . The cylindrical proximal end of rotation drive coupling  342  inserts through second counter bore  347 , through the bore of fourth bearing assembly  346 , through the bore of second coupling spacer  349 , and finally through the bore in fourth bevel gear  351 , which is fixedly attached to rotation drive coupling  342  by a slotted spring pin. The gear teeth of fourth bevel gear  351  mesh with the gear teeth of first bevel gear  321 . Thus, rotation of the center core of rotation shaft  24  results in the rotation of rotation drive coupling  342 . When rotation drive coupling  342  is operatively coupled to elongated drive gear  104  via drive gear slot  101 , rotation of rotation shaft  24  causes rotation of elongated drive gear  104 , which results in the rotation of cutter  96 . A suitable example of first, second, third, and fourth bevel gears  321 ,  325 ,  350 , and  351 , respectively, is Model No. A1M-4-Y32016-M available from Stock Drive Products, New Hyde Park, N.Y. 
     Continuing in FIG. 7, port drive coupling  353  has a flat bladed distal end which will operatively couple with rod bushing drive slot  91  (see FIG. 8) located at the proximal end of rod bushing  88 . The cylindrical proximal end of port drive coupling  353  inserts through the bore in first port gear  355 , which is fixedly attached by a slotted spring pin, then inserted through first port coupling bore  359 . First coupling washer  362  slips over the proximal end of drive port coupling  353  and first coupling e-ring  364  snaps into a groove at the most proximal end of drive port coupling  353 , which now rotatably secures the assembly to transmission plate  330 . Knob post  367  is made of stainless steel, is generally cylindrical, and has a flange on its most distal end and a flat approximately one-third to one-half its diameter in depth and extending from its proximal end one half inch in length. Knob post  367  inserts through the bore of second port gear  357 , which is fixedly attached by a slotted spring pin to the distal end of knob post  367 . Suitable examples of first and second port gears  355  and  357 , respectively, are available as Model No. A1N1-N32012, available from Stock Drive Products, New Hyde Park, N.Y. The proximal end of knob post  367  is inserted through second port coupling bore  360  until second port gear  357  aligns and meshes with first port gear  355 . Second coupling washer  363  slips over the proximal end of knob post  367  and second coupling e-ring  365  snaps into a groove located adjacent to the distal end of knob post  367 , thus rotatably securing the assembly to transmission plate  330 . Port rotation knob  45  fixedly attaches to the proximal end of knob post  367 . A suitable port rotation knob  45  is Model No. PT-3-P-S available from Rogan Corp., Northbrook, Ill. Thus, when port drive coupling  353  is operatively coupled to rod bushing  88  via rod bushing drive slot  91 , user rotation of port rotation knob  45  causes rotation of rod bushing  88  which results in the rotation of piercer  70 . This allows port  78  to be readily positioned anywhere within the 360° axis of rotation of piercer  70 . 
     Transmission plate  330  attaches to the proximal end of upper base shell  161  via two screws. 
     There is an important benefit derived from the design of transmission  301  just described. The fact that the translation shaft  22 , rotation shaft  24 , and control cord  26  enter the biopsy device  40  at a right angle to the device&#39;s center axis permits for a short overall length for the biopsy device. This allows the device to fit into a smaller area than would accommodate a device with the shafts protruding directly out the back (proximal end) parallel to the center axis. 
     FIG. 8 is an isometric view of probe assembly  42  and base  44 , as viewed from their proximal ends. Upper base housing  50  is not shown so as to permit a clear view of transmission  301  fully assembled. Also clearly visible are lead screw slot  122 , drive gear slot  101 , and rod bushing drive slot  91 , which operably connect to transmission  301  as previously described. 
     FIG. 9 is an exploded isometric view of firing mechanism  160 . Upper base shell  161  is shown exploded and lower base shell  204  is shown exploded and rotated 90 degrees clockwise. Also exploded and rotated 90 degrees clockwise for clarity is printed circuit board  262  and frame screw  163 . 
     Firing mechanism  160 , shown in FIG. 9, operates to fire the distal end of probe assembly  42  into tissue. Base shell  38  (see FIG. 2) supports and houses firing mechanism  160 , and is assembled from upper base shell  161  and lower base shell  204 . Base hooks  165  on lower base shell  204  insert into base slots  162  in upper base shell  161  to enable assembly of the components to create base shell  38 . Frame screw  163  inserts through a clearance hole in frame bottom  204  and fastens into firing latch block  242  to tie upper base shell  161  and lower base shell  204  together. 
     Firing fork  62  extends from firing mechanism  160  through to the exterior of base shell  38  to accept probe housing  52  of probe assembly  42  (see FIG.  2 ). FIG. 9 shows firing fork  62  in its most distal allowable position and shows other components of firing mechanism  160  in appropriate positions for firing fork  62  to be at its most distal allowable position. 
     Upon mating of the probe assembly  42  with the base  44 , first tang  54  and second tang  56  insert into first recess  64  and second recess  66 , respectively, in firing fork  62  at the distal end of firing fork assembly  164 . Features on firing fork  62  also include probe slot  167 , which is approximately “U” shaped to accept probe assembly  42 , and clearance slot  169 , allowing clearance for probe rotation rod  85 . 
     Firing fork assembly  164 , shown exploded in FIG. 10, is a unique assembly detachable from the rest of firing mechanism  160  without the use of tools. Firing fork  62  slides over the outer diameter of firing spade  178  while firing fork keys  181  insert into firing spade slots  180 . Firing spade slots  180  prevent rotation of firing fork  62  relative to firing spade  178 . Firing spade  178  possesses a threaded internal diameter at its distal end and a proximal spade end  196  at its proximal end. Proximal spade end  196  can comprise a flattened section, resembling, for example, the working end of a flathead screwdriver. The threaded diameter at the distal end of firing spade  178  receives screw  182  to hold firing fork  62  to firing spade  178 . The head  184  of screw  182  abuts the distal end of firing spade  178  upon tightening. Abutting the head  184  of screw  182  against the distal end of firing spade  178  prevents tightening of the screw against the firing fork  62 . The head  184  of screw  182  and the proximal end  186  of firing spade slot  180  provide proximal and distal stops for firing fork  62  while allowing slight axial play. 
     Firing spacer  188  attaches at the proximal end of firing spade  178  with the aid of dowel pins  190 . Firing spacer  188  slips onto and is rotatable relative to firing spade  178 . It should be noted that minimizing the clearance between the inside diameter of firing spacer  188  and the outside diameter of firing spade  178  improves the stability of firing fork assembly  164 , an important attribute. 
     Near the proximal end of firing spacer  188 , easily visible depth marker line  189  is inscribed. Dowel pins  190  press into receiving holes  192  on firing spacer  188  and ride within firing spade groove  194  to allow rotation of firing spacer  188  relative to firing spade  178  while preventing axial movement of firing spacer  188  relative to firing spade  178 . A threaded internal diameter at the proximal end of firing spacer  188  facilitates assembly and removal of the firing fork assembly  164  for cleaning. 
     FIG. 9 shows that firing fork assembly  164  threads onto end fitting  166 , pinned at the distal end of firing fork shaft  168 . End fitting  166  can be made of a soft stainless steel for easy machining of slot and threads while firing fork shaft  168  can be made of a hardenable stainless to accommodate induced stress. Proximal spade end  196  fits into spade slot  198  of end fitting  166  to prevent rotation of firing fork assembly  164  relative to firing fork shaft  168 . The threaded internal diameter of the proximal end of firing spacer  188  screws onto the threaded outer diameter of end fitting  166  to removably attach firing fork assembly  164 . Small firing bushings  170 , fashioned from a plastic such as acetal, support firing fork shaft  168  and allow it to move proximally and distally. Proximal saddle support  172  and distal saddle support  173 , machined into upper base shell  161 , support small firing bushings  170  while long clamp plate  174  and short clamp plate  175  capture and retain small firing bushings  170  into proximal and distal saddle supports  172  and  173 , respectively. Long clamp plate  174  and short clamp plate  175  can attach to proximal saddle support  172  and distal saddle support  173  using fasteners, such as, for example, clamp plate mounting screws  176 . Flanges at each end of the small firing bushings  170  bear against the proximal and distal sides of saddle supports  172  and clamp plates  174  to restrain small firing bushings  170  from moving proximally and distally with the movement of firing fork shaft  168 . Additional support is gained by the large firing bushing  200  surrounding firing spacer  188 . Large firing bushing  200 , split for easy assembly, resides in firing bushing housing  202  machined into upper base shell  161  and lower base shell  204 . 
     Firing fork shaft  168  carries other parts that facilitate the operation of firing mechanism  160 . Spring collar roll pin  212  fixedly attaches spring collar  214  to firing fork shaft  168 . Shock pad  216  adheres to the distal side of spring collar  214  and contacts distal interior wall  218  of base shell  38  when firing fork shaft  168  is in its distal position. Shock pad  216  can be made from many shock-absorbing materials, such as, for example, rubber. Main spring  217  surrounds firing fork shaft  168  and bears against the distal side of distal saddle support  173  and the proximal side of spring collar  214  to force firing fork shaft  168  distally. Magnet holder roll pin  208  fixedly attaches magnet holder  206  to firing fork shaft  168 . Magnet  210  is crimped into magnet holder  206 . Nearer the proximal end of firing fork shaft  168 , firing main link pin  224  passes through firing fork shaft slot  225  to hold firing fork shaft  168  to carriage  220 . Firing main link pin  224  also captures curved firing levers  222  retaining them to the carriage  220 . Firing main link pin  224  is flanged on one end. The other end of firing main link pin  224  extends through carriage  220  to retain carriage  220 , firing fork shaft  168 , and curved firing levers  222 , where it is retained by welding to the lower curved firing lever. 
     Curved firing levers  222  and firing linkages  226  drive the arming of firing mechanism  160 . Curved firing levers  222  pin to firing linkages  226  using firing link pins  228  which are welded to firing levers  222 . Firing linkages  226  in turn pin to upper base shell  161  using frame link dowel pins  230  pressed into upper base shell  161 . Long clamp plate  174  retains firing linkages  226  using clamp plate mounting screws  176 . Each pinned joint of curved firing levers  222 , firing linkages  226 , and carriage  220  is rotatably movable about the axis of the pin. 
     Each curved firing lever  222  has a portion that extends laterally outwards through a slot located on either side of base shell  38  (See FIG.  2 ). A curved firing lever end  232  is attached to each curved firing lever  222  on the extension of curved firing lever  222  external to base shell  38 . Curved firing lever end  232  provides a convenient user interface for arming the firing mechanism. Arming the mechanism will be described later. The coil of torsion spring  234  surrounds each pinned joint of curved firing levers  222  and firing linkages  226 . The legs of link torsion springs  234  extend outwardly to hook into curved firing levers  222  and firing linkages  226 , applying a torque rotating them relative to each other. 
     Locating firing linkages  226  and curved firing levers  222  at different distances from upper base shell  161  allows them clearance to pass by each other upon operation. Curved firing levers  222  have bends to offset them in a direction perpendicular to upper base shell  161 . The offset bends let them move within planes at different distances from upper base shell  161  while having the curved firing lever ends emerge from the slot created for that purpose in upper base shell  161 . Spacer  223  separates the links on the pin  230 . Having a curved firing lever  222  and firing linkage  226  on each side of the longitudinal centerline allows access by the user to operate firing mechanism  160  from either side of base shell  38 . 
     Fasteners secure a printed circuit board  262  to lower base shell  204  and latch block  242 . Printed circuit board  262  contains Hall-effect switch  264  for sensing the proximity of magnet  210 . A suitable Hall-effect switch  264  is Model No. A3142ELT available from Allegro Microsystems, Inc., Worcester, Mass. When firing fork  168  and associated magnet  210  are in the most proximal position (pre-fired position, as described later), magnet  210  is held in a position near Hall-effect switch  264 . 
     FIG. 11 is an exploded isometric view of triggering mechanism  235 , seen in FIG.  9 . Triggering mechanism  235  safely latches and fires firing fork shaft  168 . Triggering mechanism  235  comprises firing latch  236 , firing latch block  242 , firing button shaft  244  and roller  241 , firing latch spring  246 , firing button shaft spring  247 , safety block  248 , safety latch  250 , safety latch torsion spring  251 , safety latch cover  252 , and firing button  254 . 
     Firing latch block  242  encloses the proximal portion of firing latch  236  and serves as a mounting platform for components of triggering mechanism  235 . Firing latch pin  237  and firing block pin  239  rigidly retain firing latch block  242  to upper base shell  161 . Firing latch pin  237  rotatably pins firing latch  236  to upper base shell  161  while passing through firing latch block  242 . Firing latch  236  pivots within a slot in upper base shell  161 . Firing latch spring  246  is compressed between firing latch block  242  and firing latch  236 , thereby forcing the distal end of firing latch  236  towards firing fork shaft  168 . Firing latch  236  possesses a firing latch hook  238  at its distal end, which removably latches into a firing fork shaft retainer  240  located at the proximal end of firing fork shaft  168 . Firing button shaft  244  slidably moves proximally and distally within a bore in firing latch block  242  and has roller  241  rotatably pinned to its distal portion to engage firing latch  236  to cause rotation of firing latch  236 . Firing button shaft spring  247  forces firing button shaft  244  proximally. Firing button shaft  244  is retained by safety block  248 , which is mounted to the proximal side of firing latch block  242 . Safety latch  250  resides within a counter bore on the proximal side of safety block  248  and is retained by safety latch cover  252 . Fasteners such as screws hold safety latch cover  252  in place. 
     Safety latch  250  is designed to facilitate locking and unlocking of the firing mechanism. Safety latch  250  can be rotated within the counter bore on safety block  248  through a rotation angle, while safety latch torsion spring  251  has extending legs hooked into safety block  248  and safety latch  250  to apply torque to safety latch  250 . Safety block  248  defines a locked position safety latch stop  245  and an unlocked position safety latch stop  243  separated by the rotation angle. Safety latch handle  249  extends radially from safety latch  250  to facilitate grasping and rotating of safety latch  250  by the user. Safety latch handle  249  also forms surfaces to abut safety latch stops  245  and  243  to limit the rotation angle. In the locked position, safety latch torsion spring  251  forces safety latch handle  249  against the locked position safety latch stop  245 , while in the unlocked position, the user forces safety latch handle  249  against unlocked position safety latch stop  243 . In the illustrated embodiment of the invention, the rotation angle through which safety latch  250  can be rotated is about thirty-five degrees. FIG. 12 shows that safety latch  250  contains two firing button stops  256  with one firing button stop  256  on each side of the longitudinal axis of firing button  254  at assembly. The firing button stops  256  interact with firing button  254  to effect locking (preventing lateral movement) and unlocking (allowing lateral movement) of firing button  254 . 
     FIG. 13 shows an isometric view of firing button  254 . Firing button  254  fixedly attaches to firing button shaft  244  (see FIG.  11 ), extends proximally through the center of safety latch  250  (see FIG.  12 ), and presents a proximal, flattened, cylindrical thumb pad  257  located at its most proximal end to the user. Firing button  254  comprises a smaller firing button outer diameter  258  having narrow flats  259  and wide flats  261  angularly offset from each other by the rotation angle traveled by safety latch  250 . Larger firing button outer diameter  260  is free of flats. A distal contact surface  255  exists proximally of narrow flats  259  and is substantially perpendicular to the longitudinal axis of firing button  254 . Firing button stops  256 , located on safety latch  250 , are separated by a distance slightly larger than the distance between wide flats  261  and less than the smaller firing button outer diameter  258 . Firing button stops  256  can flex in the radial direction, but resist flexing in the axial direction. The difference in stiffness in different directions can be accomplished by, for example, different thicknesses of the firing button stops  256  in the axial direction and in the radial direction. 
     When safety latch  250  is in the locked position, pushing firing button  254  will force distal contact surface  255  against firing button stops  256 . Firing button stops  256  prevent further proximal axial movement of firing button  254  because of rigidity in the axial direction. 
     Following is a functional description of the operation of the firing mechanism of the present invention: 
     A user arms and fires the firing mechanism during use of the probe assembly  42  in a surgical procedure. The user begins in the fired position depicted in FIGS. 14 and 15, grasps one of the curved firing lever ends  232 , and moves outboard end of curved firing lever  222  proximally. This begins action wherein each grasped curved firing lever  222 , each firing linkage  226 , carriage  220 , and upper base shell  161  act as four-bar linkage systems with upper base shell  161  being the stationary link and carriage  220  being a translational link. Motion can be described of all three movable links relative to the upper base shell  161 . Either curved firing lever end  232  can be moved by the user. Duplicity exists in the illustrated embodiment of the invention to facilitate user access from either side of base  44 . 
     Rotating either curved firing lever  222  in a direction that moves the curved firing lever end  232  proximally effects motion of the two members pinned to curved firing member  222 . Curved firing member  222  transfers motion through one pinned joint to carriage  220  to move it proximally along firing fork shaft  168 . Curved firing member  222  also transfers motion through a second pinned joint to firing linkage  226 , rotating the pinned joint towards firing fork shaft  168 . Firing linkage  226  is pinned to stationary upper base shell  161  and rotates about the pinned joint located on upper base shell  161 . 
     Carriage  220 , driven by curved firing member  222 , translates proximally along firing fork shaft  168  carrying main link pin  224  within firing fork shaft slot  225  until firing main link pin  224  reaches the proximal end of firing fork shaft slot  225 . Further proximal motion of carriage  220  and firing main link pin  224  begins to drive proximal motion of firing fork shaft  168 . Firing fork shaft  168  translates proximally through small firing bushings  170 . 
     As firing fork shaft  168  translates proximally, it carries with it attached firing fork assembly  164 . Firing fork shaft  168  also carries proximally attached spring collar  214 , decreasing the distance between spring collar  214  and distal saddle support  173 . Main spring  217 , located between spring collar  214  and distal saddle support  173 , becomes more compressed exerting more force against spring collar  214 . Firing fork shaft  168  continues to move proximally and continues to compress main spring  217  until the proximal end of firing fork shaft  168  reaches firing latch  236  (see FIG.  15 ). The proximal end of firing fork shaft  168  contacts firing latch  236  and exerts a force rotating it out of the path of proximally advancing firing fork shaft  168 . The proximal end of firing fork shaft  168  and the distal end of firing latch  236  have contoured surfaces to act as cams to assist in lifting firing latch  236 . Rotating firing latch  236  compresses firing latch spring  246 , exerting a force to hold firing latch  236  onto the proximal end of firing fork shaft  168 . Once the firing fork shaft retainer  240  has proceeded proximally to a position under firing latch hook  238 , firing latch spring  246  urges firing latch hook  238  into firing fork shaft retainer  240  by rotating firing latch  236  towards firing fork  168 . Firing assembly  160  is now in the pre-fire position shown in FIGS. 16 and 17. 
     The user can now release curved firing lever end  232 . Once the user releases curved firing lever end  232 , main spring  217  applies force urging firing fork  168  distally along its axis. The distal force moves firing fork shaft retainer  240  towards firing latch hook  238  extending down into firing fork shaft retainer  240  (see FIG.  19 ). The proximal wall of firing fork shaft retainer  240  is angled so that the reactive force of the proximal wall of firing fork shaft retainer  240  against firing latch hook  238  rotates firing latch hook  238  further into the firing fork shaft retainer  240 , preventing inadvertent release. The proximal wall of firing latch hook  238  is angled to mate with the angle of the proximal wall of firing fork shaft retainer  240 . After the user has released curved firing lever end  232 , link torsion springs  234  apply torque to curved firing levers  222  and firing linkages  226  rotating them towards each other. Rotating curved firing levers  222  and firing linkages  226  towards each other initiates motion that returns carriage  220  to its distal position. With firing fork  168  held by firing latch  236  while firing levers  222  and firing linkages  226  are in the most distal position, firing mechanism  160  is in the relaxed position shown in FIGS. 18 and 19. When carriage  220  returns to its distal position, curved firing levers  222  contact stops on the sides of raised bosses on upper base shell  161 . 
     Firing fork shaft  168  has now carried magnet  210  (see FIG. 9) which is located within magnet holder  206  proximally into a position near Hall-effect switch  264  on printed circuit board  262 . Hall-effect switch  264  senses the presence of magnet  210  and communicates with control unit  100  that firing fork  168  is in a proximal position and ready to fire. 
     Safety latch  250  “guards” firing button  254 . In the locked position shown in FIG. 20, firing button stops  256  on the safety latch  250  are located distally of distal contact surface  255  on firing button  254 . Firing button stops  256  on safety latch  250  are also located on either side of narrow flats  259  (see FIG.  13 ). Smaller firing button outer diameter  258  is larger than the distance between firing button stops  256 . Attempting to push firing button  254  distally will cause distal contact surface  255  to contact firing button stops  256 . The rigidity of the firing button stops  256  in the axial direction prevents further distal movement of the firing button and prevents inadvertent firing of the mechanism. 
     After the user has determined the proper location in which to insert the piercer  70  of biopsy device  40  into a surgical patient, the user can now unlock and fire firing mechanism  160 . Unlocking and firing the mechanism requires two separate actions, rotating the safety latch  250  and pressing the firing button  254 . The operator first grasps safety latch handle  249  to rotate safety latch  250  against the torque applied to it by safety latch torsion spring  251  (not visible). FIG. 21 shows rotating safety latch  250  so that safety latch handle  249  travels from locked position safety latch stop  245  to unlocked position safety latch stop  243  which aligns firing button stops  256  with wide flats  261  on smaller firing button outer diameter  258 . Since the distance between firing button stops  256  is larger than the distance between wide flats  261 , clearance now exists for wide flats  261  to pass between firing button stops  256 . Safety latch  250  is now in the “firing” position. 
     In the next step, the operator presses firing button  254  by placing force on cylindrical thumb pad  257  to urge firing button  254  distally. When firing button  254  is pressed, wide flats  261  move between firing button stops  256  allowing firing button  254  to proceed distally. Firing button  254 , attached to firing button shaft  244 , pushes firing button shaft  244  distally. The roller  241  on firing button shaft  244  contacts the cam surface on firing latch  236  to rotate firing latch  236  so that firing latch hook  238  lifts out of firing fork shaft retainer  240  (see FIG.  19 ). Once firing latch hook  238  is clear of firing fork shaft retainer  240 , main spring  217  drives firing fork shaft  168  distally carrying firing fork assembly  164  and piercer  70  of probe assembly  42  towards the target. Distal motion of firing fork shaft  168  continues until shock pad  216  contacts distal interior wall  218  of base shell  38  (see FIG.  14 ). Hall-effect switch  264  senses the departure of magnet  210  distally and communicates the departure to control unit  100 . 
     After firing the firing mechanism  160  the user releases firing button  254 , then releases safety latch handle  249 . When the user releases firing button  254 , firing button shaft spring  247  forces firing button shaft  244  proximally. Firing button  254  moves proximally as well, returning distal contact surface  255  and firing button smaller diameter  258  proximal of firing button stops  256 . The proximal movement of firing button  254  also places narrow flats  259  between firing button stops  256 . Releasing safety latch handle  249  allows safety latch torsion spring  251  to rotate safety latch  250  back towards the locked position with safety latch handle  249  forced against locked position safety latch stop  245 . With only narrow flats  259  and wide flats  261  between firing button stops  256 , safety latch  250  can freely rotate without interference from firing button stops  256 . 
     When firing button shaft  244  travels proximally, the roller  241  of firing button shaft  244  and cammed surface of firing latch  236  separate (see FIG.  15 ). Firing latch spring  246  then rotates firing latch  236  into a position where firing latch hook  238  is moved towards firing fork shaft  168 . An arming and firing cycle is now complete. Firing assembly  160  has returned to the post-fired position depicted in FIGS. 14 and 15. 
     It should be noted that if, after firing, the user of the firing mechanism  160  does not release firing button  254  before releasing safety latch handle  249 , the mechanism still operates properly because of incorporated unique design features. When firing button  254  is in the distal, pressed position, smaller firing button outer diameter  258  is between firing button stops  256 . Clearance for firing button stops  256  is made by alignment of firing button stops  256  with wide flats  261 . Releasing safety latch handle  249  before releasing firing button  254  causes safety latch torsion spring  251  to rotate safety latch  250  back towards the locked position and causes firing button stops  256  to rotate out of alignment with wide flats  261 . When the firing button stops  256  rotate out of alignment with wide flats  261  smaller firing button outer diameter  258  comes between firing button stops  256 . Smaller firing button outer diameter  258  is larger than the distance between firing button stops  256 . However, firing button stops  256 , designed to flex in the radial direction, separate by bending away from each other in the center when forced apart by smaller firing button outer diameter  258 . Because of the radial flexibility of firing stops  256 , firing button stops  256  apply little force to smaller firing button outer diameter  258 . With little force applied, firing button  254  slides easily through firing button stops  256  while returning to the proximal position. Firing button  254  returning to its proximal position brings smaller firing button outer diameter  258  between firing button stops  256  to allow safety latch  250  to continue to rotate back to the locked position. The difference in flexibility of the firing button stops radially and axially allows latching and release of triggering mechanism  235  regardless of order of operation of the components. Rigidity in the axial direction stops inadvertent operation of firing button  254  and flexibility in the radial direction allows interference with smaller firing button outer diameter  258  while still maintaining smooth release operation. 
     If desired, firing fork assembly  164  can be disassembled without tools from the rest of firing mechanism  160  and cleaned. Before a subsequent firing, an operator can attach a clean firing fork assembly  164  by mating proximal spade end  196  with spade slot  198  and threading firing spacer  188  onto end fitting  166 . When assembling firing fork assembly  164  with the firing mechanism in the post-fired position, an assembler can use depth marker line  189  to ensure proper assembly. The assembler can check alignment of depth marker line  189  with the outside surface of base shell  38 . A depth marker line  189  aligned with base shell  38  denotes a proper assembly. A depth marker line  189  that is misaligned with base shell  38  could indicate an improper assembly such as cross threading of firing spacer  188  or incomplete tightening of firing spacer  188 . 
     FIG. 22 shows an alternate embodiment of firing fork assembly  164 . Thumbscrew  191  threads into a threaded hole  187  on firing fork  62 . Threaded hole  187  on firing fork  62  passes through to a larger counter bore hole with flats on either side, commonly called a double-D hole  213 . Firing fork assembly  164  comprises thumbscrew  191  threaded onto firing fork  62 . Undercut  195  has an outer diameter less than the minor diameter of threaded hole  187  on firing fork  62  and thus maintains clearance between threaded hole  187  and undercut  195 . Thumbscrew  191 , after assembly to firing fork  62 , can thus turn freely on firing fork  62  utilizing the clearance between threaded hole  187  and undercut  195 . An alternate embodiment of firing fork shaft end fitting  166 , shown in FIG. 22, has end fitting flats  211  machined on either side of the second embodiment of end fitting  166 . End fitting  166  is welded to the distal end of firing fork shaft  168 . The configuration of end fitting  166  with end fitting flats  211  will accept double-D hole  213  of the alternate embodiment of firing fork  62 . Use of end fitting flats  211  with double-d hole  213  prevents rotation of firing fork  62  relative to end fitting  166  and firing fork shaft  168 . The alternate embodiment of firing fork assembly  164  threads into alternate embodiment of end fitting  166  which is welded onto firing fork shaft  168 . The alternate embodiment end fitting  166  has a threaded internal diameter  193  to accept the threaded proximal end of thumbscrew  191 . Thumbscrew  191  has a knurled, easily grasped surface so that the alternate embodiment of firing fork assembly  164  can be assembled and disassembled without the use of tools. 
     Dual four-bar mechanisms have been utilized in the present embodiment of the invention to facilitate ease of use by providing access by the user from either side of base  44 . A variation that would become evident to one skilled in the art after reading the description would be a single four-bar mechanism to create the firing mechanism. 
     While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.