Abstract:
A method of relieving vacuum in a biopsy apparatus includes applying vacuum through at least one motor to an inner cannula lumen; providing a continuously open leak path that permits fluid communication between the outer cannula lumen and atmosphere, wherein fluid is drawn from the leak path through the outer cannula; retracting the inner cannula proximally to permit tissue to prolapse into a tissue receiving opening of the outer cannula due to the vacuum; translating the inner cannula distally to sever the prolapsed tissue; aspirating the severed tissue through the inner cannula lumen; and selectively relieving vacuum distally of the severed tissue by retracting the inner cannula proximally to permit the inner cannula lumen to communicate with the respective outer cannula lumen and the leak path while a portion of the biopsy apparatus, including the tissue receiving opening, is positioned within tissue.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of application Ser. No. 10/970,269 filed on Oct. 21, 2004, which is a Continuation of application Ser. No. 10/848,278 filed on May 18, 2004 which is a Divisional of application Ser. No. 09/707,022 filed Nov. 6, 2000, now U.S. Pat. No. 6,758,824; and this application is related to application Ser. No. 10/639,569 filed Aug. 12, 2003 which is a Divisional of application Ser. No. 09/864,031 filed on May 23, 2001, now U.S. Pat. No. 6,638,235, which is a Continuation-in-Part of application Ser. No. 09/707,022 filed Nov. 6, 2000, now U.S. Pat. No. 6,758,824, which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to biopsy instruments and methods for taking a biopsy. More specifically, this invention relates to a method for removing several tissue samples using a single insertion. 
     BACKGROUND 
     In the diagnosis and treatment of breast cancer, it is often necessary to remove multiple tissue samples from a suspicious mass. The suspicious mass is typically discovered during a preliminary examination involving visual examination, palpitation, X-ray, MRI, ultrasound imaging or other detection means. When this preliminary examination reveals a suspicious mass, the mass must be evaluated by taking a biopsy in order to determine whether the mass is malignant or benign. Early diagnosis of breast cancer, as well as other forms of cancer, can prevent the spread of cancerous cells to other parts of the body and ultimately prevent fatal results. 
     A biopsy can be performed by either an open procedure or a percutaneous method. The open surgical biopsy procedure first requires localization of the lesion by insertion of a wire loop, while using visualization technique, such as X-ray or ultrasound. Next, the patient is taken to a surgical room where a large incision is made in the breast, and the tissue surrounding the wire loop is removed. This procedure causes significant trauma to the breast tissue, often leaving disfiguring results and requiring considerable recovery time for the patient. This is often a deterrent to patients receiving the medical care they require. The open technique, as compared to the percutaneous method, presents increased risk of infection and bleeding at the sample site. Due to these disadvantages, percutaneous methods are often preferred. 
     Percutaneous biopsies have been performed using either Fine Needle Aspiration or core biopsy in conjunction with real-time visualization techniques, such as ultrasound or mammography (X-ray). Fine Needle Aspiration involves the removal of a small number of cells using an aspiration needle. A smear of the cells is then analyzed using cytology techniques. Although Fine Needle Aspiration is less intrusive, only a small amount of cells are available for analysis. In addition, this method does not provide for a pathological assessment of the tissue, which can provide a more complete assessment of the stage of the cancer, if found. In contrast, in core biopsy a larger fragment of tissue can be removed without destroying the structure of the tissue. Consequently, core biopsy samples can be analyzed using a more comprehensive histology technique, which indicates the stage of the cancer. In the case of small lesions, the entire mass may be removed using the core biopsy method. For these reasons core biopsy is preferred, and there has been a trend towards the core biopsy method, so that a more detailed picture can be constructed by pathology of the disease&#39;s progress and type. 
     The first core biopsy devices were of the spring advanced, “Tru-Cut” style consisting of a hollow tube with a sharpened edge that was inserted into the breast to obtain a plug of tissue. This device presented several disadvantages. First, the device would sometimes fail to remove a sample, therefore, requiring additional insertions. This was generally due to tissue failing to prolapse into the sampling notch. Secondly, the device had to be inserted and withdrawn to obtain each sample, therefore, requiring several insertions in order to acquire sufficient tissue for pathology. 
     The biopsy apparatus disclosed in U.S. Pat. No. 5,526,822 to Burbank, et al was designed in an attempt to solve many of these disadvantages. The Burbank apparatus is a biopsy device that requires only a single insertion into the biopsy site to remove multiple tissue samples. The device incorporates a tube within a tube design that includes an outer piercing needle having a sharpened distal end for piercing the tissue. The outer needle has a lateral opening forming a tissue receiving port. The device has an inner cannula slidingly disposed within the outer cannula, and which serves to cut tissue that has prolapsed into the tissue receiving port. Additionally, a vacuum is used to draw the tissue into the tissue receiving port. 
     Although the Burbank device presented an advancement in the field of biopsy devices, several disadvantages remain and further improvements are needed. For example, the inner cutter must be advanced manually, meaning the surgeon manually moves the cutter back and forth by lateral movement of a knob mounted on the outside of the instrument or by one of the three pedals at the footswitch. Also, the vacuum source that draws the tissue into the receiving port is typically supplied via a vacuum chamber attached to the outer cannula. The vacuum chamber defines at least one, usually multiple, communicating holes between the chamber and the outer cannula. These small holes often become clogged with blood and bodily fluids. The fluids occlude the holes and prevent the aspiration from drawing the tissue into the receiving port. This ultimately prevents a core from being obtained, a condition called a “dry tap.” In light of the foregoing disadvantages, a need remains for a method of tissue removal that reliably applies a vacuum. 
     BRIEF SUMMARY 
     A method of relieving vacuum in a biopsy apparatus that comprises an outer cannula defining a first inner lumen therethrough and a tissue-receiving opening in communication with the first inner lumen; an inner cannula slidably disposed in the first inner lumen of the outer cannula, wherein the inner cannula defines a second inner lumen therethrough, at least one motor for moving the inner cannula relative to the outer cannula, and a vacuum source in fluid communication with the second inner lumen of the inner cannula, is disclosed. The method comprises applying vacuum from the vacuum source to the second inner lumen of the inner cannula; providing a leak path that permits fluid communication between the first inner lumen of the outer cannula and the atmosphere at a proximal end of the outer cannula; retracting the inner cannula away from a distal end of the outer cannula so as to permit tissue to prolapse into the tissue receiving opening due to the vacuum created through the second inner lumen of the inner cannula; translating the inner cannula toward the distal end of the outer cannula to sever the tissue that has prolapsed into the tissue receiving opening; aspirating the severed tissue through the second inner lumen of the inner cannula; and selectively relieving vacuum distally of the severed and aspirating tissue. The vacuum relief is achieved by retracting the inner cannula away from the distal end of said outer cannula thereby permitting the second inner lumen to communicate with the first inner lumen and the leak path while a portion of the biopsy apparatus, including the tissue receiving opening, is positioned within tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of a tissue biopsy apparatus in accordance with one embodiment of the present invention 
         FIG. 2  is a top elevational view of the tissue biopsy apparatus shown in  FIG. 1 . 
         FIG. 3A  and  FIG. 3B  are side cross-sectional views of the tissue biopsy apparatus depicted in  FIGS. 1 and 2 , with the tissue cutting inner cannula shown in its retracted and extended positions. 
         FIG. 3C  is an enlarged view of encircled area  3 C taken from  FIG. 3B . 
         FIG. 4  is a perspective view of a cover for the tissue biopsy apparatus as shown  FIG. 1 . 
         FIG. 5  is an enlarged side cross-sectional view of the operating end of the tissue biopsy apparatus depicted in  FIGS. 1 and 2 . 
         FIG. 6  is a side partial cross-sectional view of working end of a tissue biopsy apparatus in accordance with an alternative embodiment. 
         FIG. 7  is an end cross-sectional view of the apparatus depicted in  FIG. 6 , taken along lines  7 - 7  as viewed in the direction of the arrows. 
         FIG. 8  is an end cross-sectional view similar to  FIG. 7  showing a modified configuration for a stiffening member. 
         FIG. 8(   a ) is an end cross-sectional view similar to  FIG. 7  showing a modified configuration for another stiffening member. 
         FIG. 9  is an enlarged side cross-sectional view of a fluid introduction port at the hub connecting the outer cannula to the handpiece for a tissue biopsy apparatus as depicted in  FIG. 1 . 
         FIG. 10  is a schematic drawing of the hydraulic control system for the operation of the tissue biopsy apparatus shown in  FIG. 1 ; 
         FIG. 11  is a schematic drawing of an electric motor control system according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. The invention includes any alterations and further modifications in the illustrated devices and described methods and further applications of the principles of the invention which would normally occur to one skilled in the art to which the invention relates. 
     A tissue biopsy apparatus  10  in accordance with one embodiment of the present invention is shown in  FIGS. 1-5 . The apparatus  10  includes a cutting element  11  mounted to a handpiece  12 . The cutting element  11  is sized for introduction into a human body. Most particularly, the present invention concerns an apparatus for excising breast tissue samples. Thus, the cutting element  11  and the overall biopsy apparatus  10  are configured for ease of use in this surgical environment. In the illustrated embodiment, the biopsy apparatus  10  is configured as a hand-held device. However, the same inventive principles can be employed in a tissue biopsy apparatus that is used stereotatically in which the apparatus is mounted on a support fixture that is used to position the cutting element  11  relative to the tissue to be sampled. Nevertheless, for the purposes of understanding the present invention, the tissue biopsy apparatus will be described as a hand-held device. 
     The cutting element  11  is configured as “tube-within-a-tube” cutting device. More specifically, the cutting element  11  includes an outer cannula  15  terminating in a tip  16 . Preferably, the tip is a trocar tip that can be used to penetrate the patient&#39;s skin. Alternatively, the tip  16  can simply operate as a closure for the open end of the cannula  15 . In this instance, a separate introducer would be required. 
     The cutting element  11  further includes an inner cannula  17  that fits concentrically within the outer lumen  27  ( FIG. 5 ) of the outer cannula  15 . In the most preferred embodiment, both a rotary motor  20  ( FIG. 1 ) and a reciprocating motor  22  drive the inner cannula  17 . Both motors are supported within the handpiece  12 . Again, in accordance with the preferred embodiment the rotary motor  20  and reciprocating motor  22  are configured for simultaneous operation to translate the inner cannula  17  axially within the outer cannula  15 , while rotating the inner cannula  17  about its longitudinal axis. 
     One specific configuration of the working end of the cutting element  11  is depicted in  FIG. 5 . The outer cannula  15  defines a tissue-receiving opening  25 , which communicates with the outer lumen  27 . A pair of opposite longitudinal edges  26  ( FIGS. 1 and 2 ) define the tissue-receiving opening  25 . The outer cannula  15  is open at its distal end  28  with the trocar tip  16  engaged therein. Preferably, the trocar tip  16  forms an engagement hub  30  that fits tightly within the distal end  28  of the outer cannula  15 . The hub  30  can be secured by welding, press-fit, adhesive or other means suitable for a surgical biopsy instrument. 
     The working end of the cutting element  11  further includes a cuffing board  31  that is at least snugly disposed within the outer lumen  27  at the distal end  28  of the outer cannula  15 . Most preferably, the cutting board  31  is in direct contact with the engagement hub  30  of the trocar tip  16 . The cutting board  31  can be permanently affixed within the outer cannula  15  and/or against the engagement hub  30  of the trocar tip. 
     The inner cannula  17  defines an inner lumen  34  that is hollow along the entire length of the cannula to provide for aspiration of the biopsy sample. The inner cannula  17  terminates in a cutting edge  35 . Preferably the cutting edge  35  is formed by an inwardly beveled surface  36  to provide a razor-sharp edge. The inwardly beveled surface helps eliminate the risk of catching the edge  35  on the tissue-receiving opening  25  of the outer cannula. In addition, the beveled surface  36  helps avoid pinching the biopsy material between the inner and outer cannulas during a cutting stroke. 
     In a specific embodiment, both the outer cannula  15  and the inner cannula  17  are formed of a surgical grade metal. Most preferably, the two cannulae are formed of stainless steel. In the case of an MRI compatible device, the cannulae can be formed of Inconel, Titanium or other materials with similar magnetic characteristics. Likewise, the trocar tip  16  is most preferably formed of stainless steel honed to a sharp tip. The trocar tip  16  can be suitably bounded to the outer cannula  15 , such as by welding or the use of an appropriate adhesive. 
     The cutting board  31  is formed of a material that is configured to reduce the friction between the cutting edge  35  of the inner cannula  17  and the cutting board  31 . The cutting edge  35  necessarily bears against the cutting board  31  when the inner cannula  17  is at the end of its stroke while severing a tissue sample. Since the inner cannula is also rotating, the cutting edge necessarily bears directly against the cutting board  31 , particularly after the tissue sample has been cleanly severed. In prior devices, the impact-cutting surface has been formed of the same material as the cutting element. This leads to significant wear or erosion of the cutting edge. When numerous cutting cycles are to be performed, the constant wear on the cutting edge eventually renders it incapable of cleanly severing a tissue sample. 
     Thus, the present invention contemplates forming the cutting board  31  of a material that reduces this frictional wear. In one embodiment, the cutting board  31  is formed of a material that is mechanically softer than the material of the cutting edge  35 . However, the cutting board  31  cannot be so soft that the cutting edge  35  forms a pronounced circular groove in the cutting board, which significantly reduces the cutting efficiency of the inner cannula. In a most preferred embodiment of the invention, the cutting board  31  is formed of a plastic material, such as polycarbonate, ABS or DELRIN.RTM. 
     Returning again to  FIGS. 1 ,  2  and  3 A- 3 B, the rotary motor  20  includes a motor housing  39  that is sized to reciprocate within the handpiece  12 . The housing  39  defines a pilot port  40  that is connected to the hydraulic control system  150  (see  FIG. 10 ) by appropriate tubing. The present invention contemplates that the motor  20  can be a number of hydraulically powered rotating components. Most preferably, the motor  20  is an air motor driven by pressured air. Thus, the motor  20  includes a vaned rotor  42  that is mounted on a hollow tubular axle  43  extending through the motor housing  39 . The axle  43  is supported on bearings  44  at opposite ends of the housing so that the rotor  42  freely rotates within the motor housing  39  under pneumatic pressure. 
     In the illustrated embodiment, tubular axle  43  is connected to the proximal end  37  of the inner cannula  17  by way of a coupler  46 . The ends of the two tubes are mounted within the coupler  46  and held in place by corresponding set screws  47 . Preferably the coupler  46  is formed of a plastic material that provides a generally airtight seal around the joint between the inner cannula  17  and the tubular axle  43 . It is important that the coupler  46  provide a solid connection of the inner cannula  17  to the rotating components of the motor  20  so that the inner cannula  17  does not experience any torrential slip during the cutting operation. 
     Since the inner cannula  17  provides an avenue for aspiration of the biopsy sample, the invention further contemplates an aspiration tube  50  that mates with the tubular axle  43 . Thus, the tissue aspiration path from the working end of the cutting element  11  is along the inner lumen  34  of the inner cannula  17 , through the tubular axle  43  of the rotary motor  20 , and through the aspiration tube  50  to a tissue collection location in the form of a collection trap  55 . In order to maintain the vacuum or aspiration pressure within this aspiration path, the aspiration tube  50  must be fluidly sealed against the tubular axle  43 . Thus, the motor housing  39  defines a mounting hub  51  into which the aspiration tube  50  is engaged. The position of the aspiration tube  50  is fixed by way of a setscrew  52  passing through the mounting hub  51 . In contrast to the joint between the inner cannula  17  and the tubular axle  43 , the joint between the aspiration tube  50  and the tubular axle  43  allows relative rotational between the two components. The tubular axle  43 , of course, rotates with the rotor  42 . However, the aspiration tube  50  need not rotate for use with the biopsy apparatus of the present invention. The mounting hub  51  can include an arrangement of seal rings (not shown) at the joint between the aspiration tube  50  and the tubular axle  43  to further seal the aspiration system. 
     The aspiration tube  50  communicates with a collection trap  55  that is removably mounted to the handpiece  12 . The collection trap  55  includes a pilot port  107  that is connected by appropriate tubing to the hydraulic control system  150 , as described in more detail herein. For the present purposes, it is understood that a vacuum or aspiration pressure is drawn through the pilot port  107  and the collection trap  55 . This vacuum then draws a tissue sample excised at the working end of the cutting element  11 , all the way through the inner cannula  17 , tubular axle  43  and aspiration tube  50  until it is deposited within the trap. Details of the collection trap  55  will be discussed herein. 
     As explained above, the present invention contemplates an inner cannula  17  that performs its cutting operation by both rotary and reciprocating motion. Thus, the handpiece  12  supports a reciprocating motor  22 . In one aspect of the invention, both motors  20  and  22  are hydraulically powered, most preferably pneumatically. This feature allows the motors to be formed of plastic, since no electrical components are required. In fact, with the exception of the outer cannula  15 , trocar tip  16  and inner cannula  17 , every component of the biopsy apparatus  10  in accordance with the present invention can be formed of a non-metallic material, most preferably a medical grade plastic. Thus, the biopsy apparatus  10  is eminently compatible with surgical imaging systems that may be used during the biopsy procedure. The compatibility of the apparatus  10  with Magnetic Resonance Imaging (MRI) is important because MRI is currently the only non-invasive visualization modality capable of defining the margins of the tumor. In addition, since the biopsy apparatus is formed of a relatively inexpensive plastic (as opposed to a more expensive metal), the entire apparatus can be disposable. Moreover, the elimination of substantially all metal components reduces the overall weight of the handpiece  12 , making it very easily manipulated by the surgeon. 
     Referring most specifically to  FIGS. 3A and 3B , the reciprocating motor  22  includes a pneumatic cylinder  60 . The cylinder  60  includes a pilot port  61  that connects the cylinder to the hydraulic control system  150  through appropriate tubing. The motor  22  includes a piston  63  that reciprocates within the cylinder  60  in response to hydraulic fluid pressure provided at the pilot port  61 . The piston  63  includes a central bore  64  for mounting the piston  63  to the aspiration tube  50 . In one embodiment, the aspiration tube  50  is press-fit within the bore  64 . The engagement between the aspiration tube  50  and the piston  63  can be enhanced by use of a set screw (not shown) or an adhesive or epoxy. At any rate, it is essential that the aspiration tube  50  and piston  63  move together, since the motor  22  must eventually drive the inner cannula  17  axially within the outer cannula. 
     It should be understood that in addition to powering the inner cannula, the piston  63  also reciprocates the rotary motor  20 , which is essentially mounted to the reciprocating aspiration conduit. This movement is depicted by comparing the position of the rotary motor  20  between  FIG. 3A  and  FIG. 3B . More specifically, the motor  20  as well as the aspiration conduit, including the inner cannula  17 , moves within the handpiece  12 . Preferably, the handpiece housing  70  is provided with openings  73  ( FIG. 3B ) at its opposite ends for slidably supporting the aspiration tube  50  and inner cannula  17 . Since the distal housing  70  is preferably formed of a plastic material, no thrust bearings or rotary bearings are necessary to accommodate low friction axial movement of the cannula through the housing openings  73 . 
     The biopsy apparatus  10  includes a handpiece  12  that carries all of the operating components and supports the outer and inner cannulas. The handpiece  12  includes a distal housing  70  within which is disposed the rotary motor  20 . The distal end  71  of the housing  70  is configured into a fitting  72 . This fitting  72  engages a mating flange  77  on an outer cannula hub  75 . The hub  75  supports the outer cannula  15  within an engagement bore  76  (see  FIG. 3B ). 
     In accordance with one aspect of the invention, the engagement between the outer cannula hub  75  and the distal end  71  of the housing need not be airtight. In other words, the mating components of the fitting between the two parts need not be capable of generating a fluid-tight seal. In accordance with one embodiment of the invention, the engagement between the hub  75  and the housing  70  for supporting the outer cannula  15  provides a leak path  79  through the outer lumen  27  to the atmosphere. As be seen best in  FIG. 3C , the leak path  79  extends between the housing  70  and the mating flange  77  of the outer cannula hub  75 . In the use of the tissue biopsy apparatus  10 , providing aspiration through the inner lumen  34  of the inner cutting cannula  17  will draw tissue through the inner lumen. As the tissue advances farther along the lumen, in some instances a vacuum can be created behind the advancing tissue. At some point in these instances, the tissue will stop advancing along the length of the inner lumen because the vacuum behind the tissue sample equals the vacuum in front of the tissue sample that is attempting to draw the sample to the collection trap  55 . Thus, the leak path  79  through the outer lumen  27  allows atmospheric air to fall in behind the tissue sample when the inner cutter is retracted from the cutting board. The atmospheric air helps to relieve the vacuum behind the advancing tissue and aids in drawing the tissue down the length of the aspiration channel to the collection trap  55 . However, in some applications, particularly where smaller “bites” of the target tissue are taken, the atomospheric air leak path  79  is not essential. 
     Preferably the fitting  72  and the mating flange  77  can be engaged by simple twisting motion, most preferably via Luer-type fittings. In use, the cannula hub  75  is mounted on the handpiece  12 , thereby supporting the outer cannula  15 . The handpiece can then be used to project the outer cannula into the body adjacent the sample site. In certain uses of the biopsy apparatus  10 , it is desirable to remove the handpiece  12  from the cannula hub  75  leaving the outer cannula  15  within the patient. For example, the outer cannula  15  can be used to introduce an anesthetic. In other applications, once the target tissue has been completely excised, the outer cannula can be used to guide a radio-opaque marker to mark the location the removed material. 
     Returning again to the description of the housing  70 , the housing defines an inner cavity  79  (best seen in  FIG. 1 ) that is open through an access opening  81 . The access opening  81  is preferably provided to facilitate assembly of the tissue biopsy apparatus  10 . The distal end  71  of the housing  70  can be provided with a pair of braces  80  that add stiffness to the distal end  71  while the apparatus is in use. The braces  80  allow the distal end of housing  70  to be formed as a thin-walled plastic housing. Similar braces can be provided at the opposite end of the housing  70  as necessary to add stiffness to the housing. 
     The distal housing is configured to support the reciprocating motor  22  and in particular the cylinder  60 . Thus, in one embodiment of the invention, the proximal end  83  of the distal housing  70  defines a pressure fitting  84 . It is understood that this pressure fitting  84  provides a tight leak-proof engagement between the distal end  88  of the cylinder  60  and the proximal end  83  of the housing. In one specific embodiment, the pressure fitting  84  forms a spring cavity  85  within which a portion of the return spring  66  rests. In addition, in a specific embodiment, the pressure fitting  84  defines distal piston stop  86 . The piston  63  contacts these stops at the end of its stroke. The location of the piston stop  86  is calibrated to allow the cutting edge  35  to contact the cutting board  31  at the working end of the cutting element  11  to allow the cutting edge to cleanly sever the biopsy tissue. 
     In the illustrated embodiment, the cylinder  60  is initially provided in the form of an open-ended cup. The open end, corresponding to distal end  88 , fastens to the pressure fitting  84 . In specific embodiments, the pressure fitting can include a threaded engagement, a press-fit or an adhesive arrangement. 
     The cylinder cup thus includes a closed proximal end  89 . This proximal end defines the pilot port  61 , as well as a central opening  62  ( FIG. 3B ) through which the aspiration tube  50  extends. Preferably, the proximal end  89  of the cylinder  60  is configured to provide a substantially airtight seal against the aspiration tube  50  even as it reciprocates within the cylinder due to movement of the piston  63 . The proximal end  89  of the cylinder  60  defines a proximal piston stop  90 , which can either be adjacent the outer cylinder walls or at the center portion of the proximal end. This proximal piston stop  90  limits the reverse travel of the piston  63  under action of the return spring  66  when pressure within the cylinder has been reduced. 
     In a further aspect of the invention, the collection trap  55  is mounted to the handpiece  12  by way of a support housing  93 . It should be understood that in certain embodiments, the handpiece  12  can be limited to the previously described components. In this instance, the collection trap  55  can be situated separate and apart from the handpiece, preferably close to the source of vacuum or aspiration pressure. In this case, the proximal end of the aspiration tube  50  would be connected to the collection trap by a length of tubing. In the absence of the collection trap  55 , the aspiration tube  50  would reciprocate away from and toward the proximal end of the cylinder  60 , so that it is preferable that the handpiece includes a cover configured to conceals the reciprocating end of the aspiration tube. 
     However, in accordance with the most preferred embodiment, the collection trap  55  is removably mounted to the handpiece  12 . A pair of longitudinally extending arms  94 , that define an access opening  95  therebetween, forms the support housing  93 . The support housing  93  includes a distal end fitting  96  that engages the proximal end  89  of cylinder  60 . A variety of engagements are contemplated, preferably in which the connection between the two components is generally airtight. The proximal end  97  of the support housing  93  forms a cylindrical mounting hub  98 . As best shown in  FIG. 1 , the mounting hub  98  surrounds a proximal end of the collection trap  55 . The hub forms a bayonet-type mounting groove  99  that receives pins  103  attached to the housing  102  of the trap  55 . A pair of diametrically opposite wings  104  can be provided on the housing  102  to facilitate the twisting motion needed to engage the bayonet mount between the collection trap  55  and the support housing  93 . While the preferred embodiment contemplates a bayonet mount, other arrangements for removably connecting the collection trap  55  to the support housing  93  are contemplated. To be consistent with one of the features of the invention, it is preferable that this engagement mechanism be capable of being formed in plastic. 
     In order to accommodate the reciprocating aspiration tube, the support housing  93  is provided with an aspiration passageway  100  that spans between the proximal and distal ends of the housing. Since the aspiration tube  50  reciprocates, it preferably does not extend into the collection trap  55 . As excised tissue is drawn into the trap  55 , a reciprocating aspiration tube  50  can contact the biopsy material retained within the trap. This movement of the tube can force tissue into the end of the tube, clogging the tube. Moreover, the reciprocation of the aspiration tube can compress tissue into the end of the trap, thereby halting the aspiration function. 
     The collection trap  55  includes a housing  102 , as previously explained. The housing forms a pilot port  107 , which is connectable to a vacuum generator. Preferably in accordance with the present invention, appropriate tubing to the hydraulic control system  150  connects the pilot port  107 . The trap  55  includes a filter element  110  mounted within the trap. In the preferred embodiment, the filter element is a mesh filter than allows ready passage of air, blood and other fluids, while retaining excised biopsy tissue samples, and even morcellized tissue. In addition, the filter element  110  is preferably constructed so that vacuum or aspiration pressure can be drawn not only at the bottom end of the filter element, but also circumferencially around at least a proximal portion of the element  110 . In this way, even as material is drawn toward the proximal end of the filter, a vacuum can still be drawn through other portions of the filter, thereby maintaining the aspiration circuit. 
     The handpiece  12  can include individual covers for closing the access opening  81  in the distal housing  70  and the access openings  95  in the support housing  93 . Those covers can support tubing for engagement with the pilot ports  40  and  61 . Alternatively and most preferably, a single cover  13  as depicted in  FIG. 4 , is provided for completely enclosing the entire handpiece. The distal end  71  of the housing  70  can define a number of engagement notches  115  equally spaced around the perimeter of the distal end. The handpiece cover  13  can then include a like number of equally distributed tangs  117  projecting inwardly from the inner surface from the  118 . These tangs are adapted to snap into the engagement notches  115  to hold the cover  113  in position over the handpiece  12 . The cover can be attached by sliding axially over the handpiece  12 . The cover  13  can include fittings for fluid engagement with the two pilot ports  40  and  61 . Alternatively, the cover can be formed with openings for insertion of engagement tubing to mate with the respective pilot ports to provide hydraulic fluid to the rotary motor  20  and the reciprocating motor  22 . In a specific embodiment, the cover  13  extends from the distal end  71  of the distal housing  70  to the proximal end  97  of the support housing  93 . The cover can thus terminate short of the bayonet mounting feature between the support housing and the collection trap  55 . Although not shown in the figures, the proximal end  97  of the support housing  93  can be configured to include a similar array of engagement notches with a corresponding array of mating tangs formed at the proximal end of the cover  13 . 
     Referring now to  FIGS. 6-8 , alternative embodiments of the outer cannula are depicted. As shown in  FIG. 6  an outer cannula  125  includes a tissue-receiving opening  126 . The opening is formed by opposite longitudinal edges  127 . In one specific embodiment, a number of teeth  129  are formed at each longitudinal edge  127 . As depicted in the figure, the teeth are proximally facing—i.e., away from the cutting board  31  (not shown) at the distal end of the outer cannula. With this orientation, the teeth  129  help prevent forward motion of tissue drawn into the opening  126  as the inner cannula  17  moves forward toward the cutting board. In prior devices, as the reciprocating cutting element advances through the outer cannula, the cutting edge not only starts to sever the tissue, it also pushes tissue in front of the inner cannula. Thus, with these prior devices, the ultimate length of the biopsy sample retrieved with the cut is smaller than the amount of tissue drawn into the tissue-receiving opening of the outer cannula. With the teeth  129  of the outer cannula  125  of this embodiment of the invention, the tissue sample removed through the inner cannula  17  is substantially the same length as the tissue-receiving opening  126 . As the inner cannula  17  advances into the tissue, each of the teeth  129  tends to hold the tissue in place as the cutting edge  35  severs the tissue adjacent the outer cannula wall. With this feature, each “bite” is substantially as large as possible so that a large tissue mass can be removed with much fewer “bites” and in a shorter period of time. In addition to supporting the subject tissue as the inner cannula advances, the teeth can also cut into the tissue to prevent it from retracting out of the opening as the inner cutting cannula  17  advances. 
     The outer cannula  125  depicted in  FIG. 6  can also incorporate a stiffening element  131  opposite the tissue-receiving opening  126 . The stiffening element  131  adds bending stiffness to the outer cannula  125  at the distal end in order to maintain the longitudinal integrity of the outer cannula  125  as it is advanced into a tissue mass. In some prior devices that lack such a stiffening element, the working end of the cutting device is compromised as it bends slightly upward or downward as the outer cannula passes into the body. This bending can either close or expand the tissue-receiving opening, which leads to difficulties in excising and retrieving a tissue sample. The cutting mechanism of the present invention relies upon full, flush contact between the cutting edge of the inner cannula  17  and the cutting board  31 . If the end of the outer cannula  125  is slightly askew, this contact cannot be maintained, resulting in an incomplete slice of the tissue sample. 
     As depicted in the cross-sectional view of the  FIG. 7 , the stiffening element  131  in one embodiment is a crimp extending longitudinally in the outer wall of the cannula substantially coincident with the tissue-receiving opening  126 . The outer cannula  125 ′ depicted in  FIG. 8  shows two additional versions of a stiffening element. In both cases, a bead of stiffening material is affixed to the outer cannula. Thus in one specific embodiment, a bead  131 ′ is adhered to the inner wall of the outer cannula. In a second specific embodiment, a bead  131 ″ is affixed to the outside of the outer cannula. In either case, the beads can be formed of a like material with the outer cannula, and in both cases, the beads provide the requisite additional bending stiffness. Another version of a stiffening element is shown if  FIG. 8(   a ). In this case, a layer  131 ″′ of additional stainless steel is bonded to the outer wall of the outer cannula  125 ″. 
     Returning to  FIG. 6 , a further feature that can be integrated into the outer cannula  125  is the dimple  135 . One problem frequently experienced by tube-within-a-tube cutters is that the inner reciprocating cutter blade contacts or catches on the outer cannula at the distal edge of the tissue-receiving opening. With the present invention, the dimple  135  urges the inner cannula  17  away from the tissue-receiving opening  126 . In this way, the dimple prevents the cutting edge of the inner cannula  17  from catching on the outer cannula as it traverses the tissue-receiving opening. In the illustrated embodiment of  FIG. 6 , the dimple  135  is in the form of a slight crimp in the outer cannula  125 . Alternatively, as with the different embodiments of the stiffening element, the dimple  135  can be formed by a protrusion affixed or adhered to the inner surface of the outer cannula. Preferably, the dimple  135  is situated immediately proximal to the tissue-receiving opening to help maintain the distance between the cutting edge and the tissue-receiving opening. 
     As previously described, the outer cannula  15  is supported by a hub  75  mounted to the distal end of the handpiece. In an alternative embodiment depicted in  FIG. 9 , the outer cannula hub  140  provides a mean for introducing fluids into the outer lumen  27  of the outer cannula. Thus, the hub  140  includes an engagement bore  141  within which the outer cannula  15  is engaged. The hub also defines a flange  142  configured for mating with the fitting  72  at the distal end  71  of the housing  70 . Thus, the outer cannula hub  140  is similar to the hub  75  described above. With this embodiment, however, an irrigation fitting  145  is provided. The fitting defines an irrigation lumen  146  that communicates with the engagement bore  141 . 
     Ultimately, this irrigation lumen is in fluid communication with the outer lumen  27  of the outer cannula  15 . The irrigation fitting  145  can be configured for engagement with a fluid-providing device, such as a syringe. The hub  140  thus provides a mechanism for introducing specific fluids to the biopsy site. In certain procedures, it may be necessary to introduce additional anesthetic to the sampling site, which can be readily accommodated by the irrigation fitting  145 . 
     As discussed above, the preferred embodiment of the tissue biopsy apparatus  10  according to the present invention relies upon hydraulics or pneumatics for the cutting action. Specifically, the apparatus includes a hydraulic rotary motor  20  and a hydraulic reciprocating motor  22 . While the apparatus  10  can be adapted for taking a single biopsy slice, the preferred use is to completely remove a tissue mass through successive cutting slices. In one typical procedure, the cutting element  11  is positioned directly beneath a tissue mass, while an imaging device is disposed above the mass. The imaging device, such as an ultra-sound imager, provides a real-time view of the tissue mass as the tissue biopsy apparatus  10  operates to successively remove slices of the mass. Tissue is continuously being drawn into the cutting element  11  by the aspiration pressure or vacuum drawn through the inner cannula  17 . Successive reciprocation of the inner cannula  17  removes large slices of the mass until it is completely eliminated. 
     In order to achieve this continuous cutting feature, the present invention contemplates a hydraulic control system  150 , as illustrated in the diagram of  FIG. 10 . Preferably the bulk of the control system is housed within a central console. The console is connected to a pressurized fluid source  152 . Preferably the fluid source provides a regulated supply of filtered air to the control system  150 . 
     As depicted in this diagram of  FIG. 10 , pressurized fluid from the source as provided at the several locations  152  throughout the control system. More specifically, pressurized fluid is provided to five valves that form the basis of the control system. 
     At the left center of the diagram of  FIG. 10 , pressurized fluid  152  passes through a pressure regulator  154  and gauge  155 . The gauge  155  is preferably mounted on the console for viewing by the surgeon or medical technician. The pressure regulator  154  is manually adjustable to control the pressurized fluid provided from the source  152  to the two-position hydraulic valve  158 . The valve  158  can be shifted between a flow path  158   a  and a flow path  158   b . A return spring  159  biases the hydraulic valve to its normal position  158   a.    
     In the normally biased position of flow path  158   a , the valve  158  connects cylinder pressure line  161  to the fluid source  152 . This pressure line  161  passes through an adjustable flow control valve  162  that can be used to adjust the fluid flow rate through the pressure line  161 . Like the pressure gauge  155  and pressure regulator  154 , the adjustable flow control valve  162  can be mounted on a console for manipulation during the surgical procedure. 
     The pressure line  161  is connected to the pilot port  61  of the reciprocating motor  22 . Thus, in the normal or initial position of the hydraulic control system  150 , fluid pressure is provided to the cylinder  60  to drive the piston  63  against the biasing force of the return spring  66 . More specifically with reference to  FIG. 3B , the initial position of the hydraulic valve  158  is such that the reciprocating motor and inner cannula are driven toward the distal end of the cutting element. In this configuration, the inner cannula  17  covers the tissue-receiving opening  25  of the outer cannula  15 . With the inner cannula so positioned, the outer cannula can be introduced into the patient without risk of tissue filling the tissue-receiving opening  25  prematurely. 
     Pressurized fluid along cylinder pressure  161  is also fed to a pressure switch  165 . The pressure switch has two positions providing flow paths  165   a  and  165   b . In addition, an adjustable return spring  166  biases this switch to its normal position at which fluid from the pressure source  152  terminates within the valve. However, when pressurized fluid is provided through cylinder pressure line  161 , the pressure switch  165  moves to its flow path  165   b  in which the fluid source  152  is hydraulically connected to the pressure input line  168 . This pressure input line  168  feeds an oscillating hydraulic valve  170 . It is this valve that principally operates to oscillate the reciprocating motor  22  by alternately pressurizing and releasing the two-position hydraulic valve  158 . The pressure switch  165  is calibrated to sense an increase in pressure within the cylinder pressure line  161  or in the reciprocating motor cylinder  60  that occurs when the piston  66  has reached the end of its stroke. More specifically, the piston reaches the end of its stroke when the inner cannula  17  contacts the cutting board  31 . At this point, the hydraulic pressure behind the piston increases, which increase is sensed by the pressure valve  165  to stroke the valve to the flow path  165   b.    
     The oscillating hydraulic valve  170  has two positions providing flow paths  170   a  and  170   b . In position  170   a , input line  179  is fed to oscillating pressure output line  172 . With flow path  170   b , the input line  179  is fed to a blocked line  171 . Thus, with fluid pressure provided from pressure switch  165  (through flow path  165   b ), the oscillating valve  170  opens flow path  170   a  which completes a fluid circuit along output line  172  to the input of the hydraulic valve  158 . 
     Fluid pressure to output line  172  occurs only when there is fluid pressure within input line  179 . This input line is fed by valve  176 , which is operated by foot pedal  175 . The valve  176  is biased by a return spring  177  to the initial position of flow path  176   a . However, when the foot pedal  175  is depressed, the valve  176  is moved against the force of the spring to flow path  176   b . In this position, pressurized fluid from the source  152  is connected to the foot pedal input line  179 . When the oscillating hydraulic valve  170  is in its initial position flow path  170   a , pressurized fluid then flows through input line  179  to output line  172  and ultimately to the hydraulic valve  158 . 
     The fluid pressure in the output line  172  shifts the valve  158  to the flow path  158   b . In this position, the fluid pressure behind the piston  63  is relieved so that the return spring  66  forces the piston toward the proximal end. More specifically, the return spring retracts the inner cannula  17  from the tissue cutting opening  25 . The relief of the fluid pressure in line  161  also causes the pressure switch  165  to return to its initial neutral position of flow path  165   a , due to the action of the return spring  166 . In turn, with the flow path  165   a , the pressure input line  168  is no longer connected to the fluid source  152 , so no pressurized fluid is provided to the oscillating hydraulic valve  170 . Since this valve is not spring biased to any particular state, its position does not necessarily change, except under conditions described herein. 
     Returning to the foot pedal  175  and valve  176 , once the foot pedal is released, the biasing spring  177  forces the valve  176  from its flow path  176   b  to its normal initial flow path  176   a . In this position the foot pedal input line  179  is no longer connected to the fluid source  152 . When the oscillating valve  170  is at flow path  170   a , the fluid pressure through output line  172  is eliminated. In response to this reduction in fluid pressure, hydraulic valve  158  is shifted to its original flow path  158   a  by operation of the return spring  159 . In this position, the cylinder pressure line  161  is again connected to the fluid source  152 , which causes the reciprocating motor  22  to extend the inner cannula  17  to its position blocking the tissue-receiving opening  25 . Thus, in accordance with the present invention, the hydraulic control system  150  starts and finishes the tissue biopsy apparatus  10  with the tissue-receiving opening closed. It is important to have the opening closed once the procedure is complete so that no additional tissue may be trapped or pinched within the cutting element  11  as the apparatus is removed from the patient. 
     Thus far the portion of the hydraulic control system  150  that controls the operation of the reciprocating motor  22  has been described. The system  150  also controls the operation of the rotary motor  20 . Again, in the most preferred embodiment, the motor  20  is an air motor. This air motor is controlled by another hydraulic valve  182 . As shown in  FIG. 10 , the initial position of the valve provides a flow path  182   a  in which the fluid source  152  is connected to blocked line  183 . However, when the hydraulic valve  182  is pressurized, it moves to flow path  182   b  in which the fluid source  152  is connected to the pilot port  140  of the air motor. In this position, pressurized fluid continuously drives the air motor  20 , thereby rotating the inner cannula  17 . It can be noted parathentically that a muffler M can be provided on the air motor to reduce noise. 
     The rotary motor hydraulic valve  182  is controlled by fluid pressure on pressure activation line  180 . This activation line  180  branches from the foot pedal input line  179  and is connected to the foot pedal switch  176 . When the foot pedal  175  is depressed, the switch moves to its flow path  176   b . In this position the pressure activation line  180  is connected to the fluid source  152  so fluid pressure is provided directly to the rotary motor hydraulic valve  182 . As with the other hydraulic valves, the valve  182  includes a biasing spring  184  that must be overcome by the fluid pressure at the input to the valve. 
     It should be understood that since the fluid control for the rotary motor  20  is not fed through the oscillating hydraulic valve  170 , the motor operates continuously as long as the foot pedal  175  is depressed. In addition, it should also be apparent that the speed of the rotary motor  20  is not adjustable in the illustrated embodiment. Since the motor  20  is connected directly to the fluid source  152 , which is preferably regulated at a fixed pressure, the air motor actually operates at one speed. On the other hand, as discussed above, the reciprocating motor  22  is supplied through a pressure regulator  154  and a flow control valve  162 . Thus, the speed of reciprocation of the cutting blade  35  is subject to control by the surgeon or medical technician. The reciprocation of the cutting element  11  can be a function of the tissue being sampled, the size of the tissue biopsy sample to be taken, and other factors specific to the particular patient. These same factors generally do not affect the slicing characteristic of the cutting edge  35  achieved by rotating the inner cannula. 
     The hydraulic control system  150  also regulates the aspiration pressure or vacuum applied through the aspiration conduit, which includes the inner cannula  17 . In the illustrated embodiment, the pressure activation line  180  branches to feed an aspiration valve  185 . The valve is movable from its initial flow path  185   a  to a second flow path  185   b . In the initial flow path, the fluid source  152  is connected to a blocked line  186 . However, when fluid pressure is applied on line  180 , the valve  185  shifts against the biasing spring  187  to the flow path  185   b . In this path, the venturi element  190  is connected to the fluid source. This venturi element thus generates a vacuum in a vacuum control line  193  and in aspiration line  191 . Again, as with the air motor, the venturi element  190  can include a muffler M to reduce noise within the handpiece. 
     As long as the foot pedal  175  is depressed and the valve  176  is in its flow path  176   b , fluid pressure is continuously applied to the aspiration hydraulic valve  195  and the venturi element  190  generates a continuous vacuum or negative aspiration pressure. As with the operation of the rotary motor, this vacuum is not regulated in the most preferred embodiment. However, the vacuum pressure can be calibrated by a selection of an appropriate venturi component  190 . 
     When the venturi component  190  is operating, the vacuum drawn on control line  193  operates on vacuum switch  194 . A variable biasing spring  195  initially maintains the vacuum switch  194  at its flow path  194   a . In this flow path, the vacuum input line  196  is not connected to any other line. However, at a predetermined vacuum in control line  193 , the valve moves to flow path  194   b . In this position, the vacuum input line  196  is connected to pressure line  192 . In the preferred embodiment, the vacuum switch  194  operates in the form of a “go-nogo” switch—in other words, when the aspiration vacuum reaches a predetermined operating threshold, the vacuum switch is activated. When the vacuum switch  184  is initially activated, it remains activated as long as the foot pedal is depressed. Thus vacuum input line  196  is continuously connected to pressure line  192  as long as the foot pedal  175  is depressed. 
     Looking back to the hydraulic valve  158 , the fluid pressure in line  192 , and ultimately in vacuum input line  196 , is determined by the state of valve  158 . When the valve  158  is in its flow path  158   a  in which regulated fluid pressure is provided to the reciprocating motor  22 , the pressure line  192  is dead. However, when the valve  158  moves to flow path  158   b , pressure line  192  is connected to the regulated fluid source. Pressurized fluid then flows from pressure line  192 , through vacuum switch flow path  194   b , through vacuum input line  196  to the left side of oscillating valve  170 , causing the valve to stroke to flow path  170   b . When the oscillating valve  170  is in this flow path, output line  172  is dead, which allows valve  158  to move to its flow path  158   a  under the effect of the return spring  159 . In this state, valve  158  allows pressurized fluid to again flow to the reciprocating motor  22  causing it to move through the next cutting stroke. 
     Thus, when both the valve  158  and the vacuum switch  194  are moved to their alternate states, pressurized fluid passes from line  192 , through vacuum input line  196 , and through an adjustable flow control valve  197  to a second input for the oscillating hydraulic valve  170 . Pressure on the vacuum input line  196  shifts the oscillating valve  170  to its second position for flow path  170   b . In this position, pressurized fluid passing through the foot pedal valve  176  terminates within valve  170 . As a consequence, the pressure in output line  172  drops which allows the hydraulic valve  158  shift back to its original position  158   a  under operation of the return spring  159 . In this position, fluid pressure is again supplied to the reciprocating motor  22  to cause the piston  66  to move through its cutting stroke. 
     It should be appreciated that the oscillating valve  170  is influenced by fluid pressure on lines  168  and  196 , and that these lines will not be fully pressurized at the same time. When the system is initially energized, pressure from source  152  is automatically supplied to reciprocating motor  22  and pressure valve  165 , causing the valve to move to flow path  165   b . In this state, line  168  is pressurized which shifts oscillating valve  170  to the left to state  170   a . The oscillating valve will remain in that state until line  196  is pressurized, regardless of the position of pressure switch  165 . It can also be appreciated that in the preferred embodiment, the fluid pressure on line  196  does not increase to operating levels until the foot pedal  175  has been depressed and the aspiration circuit has reached its operating vacuum. 
     In an alternative embodiment, the vacuum switch  194  can be calibrated to sense fine changes in vacuum. In this alternative embodiment, the completion of this return stroke can be determined by the state of the vacuum switch  194 . The vacuum switch  194  can operate as an indicator that a tissue sample has been drawn completely through the aspiration conduit into the collection trap  55 . More specifically, when the vacuum sensed by vacuum switch  194  has one value when the inner cannula is open to atmospheric pressure. This vacuum pressure changes when a tissue sample is drawn into the inner cannula  17 . The vacuum pressure changes again when the tissue is dislodged so that the inner cannula is again open to atmospheric pressure. At this point, the inner cannula  17  is clear and free to resume a cutting stroke to excise another tissue sample. Thus, the vacuum switch  194  can stroke to its flow path  194   b  to provide fluid pressure to the left side of the oscillating valve  170 , causing the valve to stroke to flow path  170   b.    
     It can be appreciated from this detail explanation that the hydraulic control system  150  provides a complete system for continuously reciprocating the axial motor  22 . In addition, the system provides constant continuous pressure to both the rotary motor  20  and the aspiration line  191 , so long as the foot pedal  175  is depressed. Once the foot pedal is released, fluid pressure in activation line  180  drops which causes the air motor control valve  182  and the aspiration control valve  185  to shift to their original or normal positions in which fluid pressure is terminated to those respective components. However, in the preferred embodiment, pressure is maintained to the reciprocating motor  22  because the motor is fed through valve  158 , which is connected directly to the fluid source  152 . 
     The hydraulic control system  150  in the illustrated embodiment incorporates five controllable elements. First, the fluid pressure provided to activate the reciprocating motor  22  is controlled through the regulator  154 . In addition, the fluid flow rate to the piston  66  is controlled via the adjustable control valve  162 . The pressure at which the pressure switch  165  is activated is determined by an adjustable return spring  166 . Likewise, the aspiration pressure vacuum at which the vacuum switch  194  is activated is controlled by an adjustable return spring  195 . Finally the adjustable flow control valve  197  controls the fluid flow from the vacuum switch  194  to the oscillating hydraulic valve  170 . Each of these adjustable elements controls the rate and duration of oscillation of the reciprocating motor  22 . 
     In the preferred embodiment, the pressure switch  165  essentially operates as an “end of stroke” indicators. In other words, when the inner cannula  17  reaches the end of its forward or cutting stroke, it contacts the cutting board  31 . When it contacts the cutting board, the pressure in the cylinder pressure line  161  changes dramatically. It is this change that causes the pressure switch  165  to change states. This state change causes the oscillating valve  170  to shift valve  158  to terminate fluid pressure to the motor  22 , causing it to stop its cutting stroke and commence its return stroke. 
     During this return stroke, the excised tissue sample is gradually drawn along the aspiration conduit. Also during the return stroke, fluid pressure bleeds from pressure line  161  and pressure switch  165  and ultimately from line  168  feeding oscillating valve  170 . When this valve strokes, fluid pressure bleeds from valve  158  allowing the valve to return to state  158   a  to pressurize the motor  22  for a new cutting stroke. The operation of each of these hydraulic valves introduces an inherent time delay so that by the time the pressure to the reciprocating motor  22  has been restored the aspiration vacuum has pulled the tissue sample through the entire aspiration conduit and into the collection trap  55 . 
     The use of a hydraulically controlled inner cutting cannula provides significant advantages over prior tissue cutting devices. The use of hydraulics allows most of the operating components to be formed of inexpensive and light-weight non-metallic materials, such as medical-grade plastics. The hydraulic system of the present invention eliminates the need for electrical components, which means that electrical insulation is unnecessary to protect the patient. 
     Perhaps most significantly, the hydraulically controlled reciprocation of the inner cutting cannula provides a cleaner and better-controlled cut of biopsy tissue. Since the reciprocating motor  22  is fed from a substantially constant source of pressurized fluid, the pressure behind the motor piston  63  remains substantially constant throughout the cutting stroke. This substantially constant pressure allows the inner cutting cannula to advance through the biopsy tissue at a rate determined by the tissue itself. 
     In other words, when the cutting edge  35  encounters harder tissue during a cutting stroke, the rate of advancement of the motor piston  63  and therefor the inner cannula  17  decreases proportionately. This feature allows the cutting edge to slice cleanly through the tissue without the risk of simply pushing the tissue. The rotation of the cutting edge can facilitate this slicing action. When the inner cannula encounters less dense tissue, the constant pressure behind the piston  63  allows the cutting edge to advance more quickly through the tissue. 
     In alternative embodiment, the rotary motor  20  can consist of an electric motor, rather than a pneumatic motor. As depicted in  FIG. 11 , the pressure activation line  180  can be fed to an on-off pressure switch  198  that is governed by an adjustable bias spring  199 . When the activation line  180  is pressurized the switch  198  establishes a connection between an electric reciprocating motor  20  and a battery pack  200 . Preferably, the battery pack  200  is mounted within the handpiece  12 , but can instead be wired to an external battery contained within the console. 
     In the preferred embodiment, the tissue biopsy apparatus  10  depicted in  FIG. 1  has an overall length of under sixteen inches (16″) and an outer diameter less than one and one quarter inches (1.25″). The outer cannula and therefore the cutting element  11  have a length measured from the handpiece  12  of approximately five inches (5″). The outer cannula preferably has a nominal outer diameter of 0.148″ and a nominal inner diameter of 0.136″. The inner cannula most preferably has a nominal outer diameter of 0.126″ so that it can reciprocate freely within the outer cannula without catching on the tissue cutting opening. The inner cannula has a nominal wall thickness of 0.010″, which yields a nominal inner lumen diameter of about 0.106.″ 
     The length of the tissue-receiving opening determines the length of biopsy sample extracted per each oscillation of the reciprocating motor  22 . In one specific embodiment, the opening has a length of about 0.7″, which means that a 0.7″ long tissue sample can be extracted with each cutting cycle. In order to accommodate a large number of these biopsy tissue slugs, the collection trap can have a length of about 2.5″ and a diameter of about 0.05″. Of course, the interior volume of the collection trap can vary depending upon the size of each biopsy slug and the amount of material to be collected. In a specific embodiment, the filter disposed within the collection trap  55  manufactured by Performance Systematix, Inc. of Callondoni, Mich. 
     In accordance with a specific embodiment, the cutting stroke for the inner cannula is about 0.905″. The return spring  66  within the reciprocating motor  22  is preferably a conical spring to reduce the compressed height of the spring, thereby allow a reduction in the overall length of the hydraulic cylinder  60 . In addition, the return spring  66  can be calibrated so that the return stroke occurs in less than about 0.3 seconds. Preferably, the inwardly beveled surface  36  of cutting edge  35  is oriented at an approximately 30.degree. angle. 
     The aspiration pressure vacuum is nominally set at 27 in.Hg. during the cutting stroke. When the cannula is retracted and the outer lumen  27  is open, the vacuum pressure is reduced to 25 in.Hg. This aspiration pressure normally allows aspiration of a tissue sample in less than about 1 second and in most cases in about 0.3 second. In accordance with a most preferred embodiment, the hydraulic control system  150  preferably is calibrated so that the inner cannula dwells at its retracted position for about 0.3 seconds to allow complete aspiration of the tissue sample. Adjusting the return spring  195  of the vacuum switch  194  can control this dwell rate. 
     In a preferred embodiment, the inner cannula  17  can advance through the cutting stroke in about two seconds. This stroke speed can be accomplished with a regulated pressure at source  152  of about 20 p.s.i. When the inner cannula reaches the end of its cutting stroke, the pressure can increase at about five p.s.i. per second. Preferably, the return spring  166  of the pressure switch  165  is set so that the end of cutting stroke is sensed within about 0.5 seconds. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It should be understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. 
     EXAMPLES 
     Example 1 
     Eighteen trial biopsies were performed upon patients after obtaining informed consent and preparing the patients according to standard biopsy procedures. In each case, biopsies were performed according to the following procedure. The patient was positioned on her back on the surgical table, and the lesion was located using ultrasound. A small incision was made in the breast. While viewing the lesion using ultrasound, an early embodiment of the present invention was inserted into the breast with the tissue receiving opening adjacent the lesion. The cutter was engaged to sample and/or remove the lesion. The lesions varied in size from 6-22 mm. The surgeon&#39;s comments are provided in Table 1. TABLE-US-00001 TABLE 1 Surgeon&#39;s Comments Regarding the Use of Early Embodiments of the Present Biopsy Device Trial Number Surgeon&#39;s Comments 1 Went very well, lesion took approximately 50 seconds to go away 2 Large fatty breast, very difficult to get needle to mass; eventually successfully removed 3 Successfully removed without problems 4 Went very well; lesion gone in 4-5 cores 5 Two lesions attempted (1) lesion easily removed, (2) inner cutter was riding up and catching the opening 6 Only took 4-5 cores to disappear 7 Started getting good cores, then stopped cutting due to secondary electrical break 8 Lesion appeared to be totally gone, cores were up to 25 mm in length 9 Only got 4-5 good cores, then stopped cutting due to inner cutter riding up 10 No problems 11 No problems at all 12 Lesion was easily palpable but very mobile which made access difficult. Used tactile sensation to manipulate tumor into aperture which worked very well; very good cores; Took 4.5 minutes but many of the cores were fatty as a lot of the time I was missing the lesion before realizing that palpitation was better 13 Took 3-4 cores then quit cutting, blade was dulled, probably due to deflection of tip downward 14 Went very well, no problems 15 Went well, no problems 16 Went well, no problems 17 Went very well 18 Went very well, the suction tubing collapsed, need stronger tubing; filter did fill up requiring stopping to empty, might need larger filter. 
     Table 1 illustrates the success of the present invention in its early stage of development. A majority of the trials, trials 1-6, 8, 1-12, and 14-18, resulted in a successful removal of the lesion with little to no problems. Lesions were removed quickly and, in some cases, only a few cores were required (see trials 1, 4, and 6). In trial number 8 it was noted that the cores were up to 25 mm in length. 
     In some trials, the surgeon experienced difficulties removing the lesion because the inner cutting blade would ride up and catch on the tissue receiving opening (see trials 5, and 9). However, this problem has been resolved in the present invention by integrating a crimp in the outer cannula. The crimp forms a dimple that protrudes from the inner surface of the cannula and into the outer lumen. As the inner cannula passes the dimple, the dimple forces the inner cannula away from the tissue-receiving opening and prevents the inner cannula from riding up into the opening. In a further embodiment, the cutting edge of the inner cannula is inwardly beveled. This inwardly beveled surface also helps eliminate risk of catching by guiding the inner cannula back into the hollow outer cannula. In addition, to prevent the deflection of the tip downward, as noted in trial 13, a stiffening element is provided on the outer cannula opposite the tissue-receiving opening. 
     Example 2 
     Surgeons performing biopsies using the device of this invention and a device having the features of U.S. Pat. No. 5,526,822 to Burbank provided feedback as to the efficiency of each device. The surgeons&#39; input was used to calculate the amount of time and the number of strokes necessary to remove a lesion. Table 2 compares the amount of time and the number of strokes necessary to remove comparable lesions using each device. TABLE-US-00002 TABLE 2 Comparison of Removal Times and Number of Strokes of the Present Biopsy Device with the Prior Art Device Present Biopsy Device Prior Art Removal Times (sec) Lesion Diameter 10 80 500 13 135 845 16 205 1280 No. of Strokes Lesion Diameter 10 16 25 13 27 42 16 41 64. 
     This data demonstrates that the present tissue biopsy apparatus consistently removes a lesion with fewer strokes and in less time than the prior cutter. The present tissue biopsy device performs 80% faster than the prior cutter, which ultimately results in reduced trauma to the tissue. 
     CONCLUSION 
     The biopsy devices of this invention reliably, quickly and efficiently sample and remove lesions in tissue.