Patent Document

FIELD OF THE INVENTION  
       [0001]     The present invention relates in general to biopsy devices, and more particularly to biopsy devices having a cutter for severing tissue.  
       BACKGROUND OF THE INVENTION  
       [0002]     The diagnosis and treatment of patients with cancerous tumors, pre-malignant conditions, and other disorders has long been an area of intense investigation. Non-invasive methods for examining tissue include: palpation, X-ray imaging, magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging. When a physician suspects that tissue may contain cancerous cells, a biopsy may be done using either an open procedure or a percutaneous procedure. For an open procedure, a scalpel is used to create a large incision to provide direct visualization of and access to the tissue mass of interest. The entire mass (excisional biopsy) or a part of the mass (incisional biopsy) may then be removed. In percutaneous biopsy procedures, a needle-shaped instrument is inserted through a small incision to access the tissue mass of interest and obtain a tissue sample for later examination and analysis.  
         [0003]     Aspiration and core sampling are two percutaneous methods for obtaining tissue from within the body. In an aspiration procedure, tissue is fragmented into pieces and drawn through a fine needle in a fluid medium. The aspiration method is less intrusive than most other sampling techniques, however, it has limited application since the structure of tissue excised by aspiration is destroyed, leaving only individual cells for analysis. In core biopsy, a core or fragment of tissue is obtained in a manner that preserves both the individual cell and the tissue structure for histological examination. The type of biopsy used depends on various factors, no single procedure is ideal for all cases.  
         [0004]     A biopsy instrument now marketed under the tradename MAMMOTOME™ is commercially available from Ethicon Endo-Surgery, Inc. for use in obtaining breast biopsy samples, such as described in U.S. patent application No. 2003/0199753, published Oct. 23, 2003 to Hibner et al., which is hereby incorporated by reference in its entirety. The MAMMOTOME™ biopsy instrument is adapted to obtain multiple tissue samples from a patient with only one percutaneous insertion of a piercing element or piercer into the patient&#39;s breast. An operator uses the MAMMOTOME™ biopsy instrument to “actively” capture (using vacuum) tissue prior to severing it from surrounding tissue. Tissue is drawn into a lateral port at the distal end of the piercer by a remotely actuated vacuum system. Once the tissue is in the lateral port, a cutter is rotated and advanced through a lumen of the piercer past the lateral port. As the cutter advances past the lateral port opening, it severs the tissue in the port from the surrounding tissue. When the cutter retracts, it pulls the tissue with it and deposits the tissue sample outside of the patient&#39;s body.  
         [0005]     This version of the MAMMOTOME™ core sampling biopsy instrument is advantageously compatible with use in a Magnetic Resonance Imaging (MRI) system. In particular, ferrous materials are avoided in the instrument so that the strong magnetic field of the MRI system does not attract the instrument. In addition, materials and circuitry are chosen to avoid artifacts in the MRI image by not interfering with the weak RF fields emanated by the tissue being examined. In particular, a control console that is remotely placed from the instrument provides the vacuum, cutter motor control, and graphical user interface. Thus, a flexible driveshaft couples the rotational motions for cutter translation and rotation.  
         [0006]     While such an instrument provides a number of advantages for clinical diagnostic and therapeutic procedures in an MRI system, there are clinical applications wherein it is desirable to provide an MRI-compatible core sampling instrument that is not tethered, via a flexible driveshaft, to a control console. The driveshaft, although flexible, still is imposes constraints due to its limited radius of bending. In addition, the drive shaft has an amount of inherent twist per length that creates a mechanical delay that may adversely impact closed-loop control, especially if a longer drive shaft is desired.  
         [0007]     Another generally known approach to performing a core biopsy sampling is described in U.S. Pat. No. 6,758,824 wherein pneumatic pressure is used to turn a hydraulic rotary motor for cutter rotation and a hydraulic reciprocating actuator for cutter translation. While use of a remote pneumatic source connected through flexible pneumatic conduits is believed by some to be convenient and economical, such generally-known pneumatically-powered core biopsy systems do have some shortcomings.  
         [0008]     An inherent issue with pneumatic drive motors is slow response time and inability to maintain a desired output shaft speed under loaded conditions. This phenomenon is associated with the compressibility of the gas that drives the system. In the case of a biopsy device containing a hollow cutter that rotates and translates, if dense tissue is encountered, the rotational speed of the pneumatically driven cutter may slow resulting in inconsistent tissue samples. And if the cutter is translated via a pneumatically driven piston-cylinder mechanism, the translation speed of the cutter may or may not change due to the density of the tissue. Therefore, the uncoordinated relationship between the cutter rotation speed and translation speed, coupled with the inherent poor response of the pneumatically driven cutter, often results in variations in the tissue sample weight when sampling heterogeneous tissue. It is believed that tissue sample weights are larger and more consistent when the number of rotations of the cutter through the aperture exceeds a minimum number of rotations.  
         [0009]     Consequently, a significant need exists for a core biopsy device that is capable of use in proximity to an MRI machine as well as other imaging modalities yet avoids the inconveniences of being tethered by relatively long mechanical driveshafts as well as the inconsistent sample sizes produced by generally-known pneumatically-powered core sampling biopsy systems.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention addresses these and other problems of the prior art by providing a core sampling biopsy system that is compatible with use proximate to a Magnetic Resonance Imaging (MRI) system yet does require a rotating mechanical drive shaft. Instead, a flexible power conduit powers a rotary nonferrous motor coupled to a biopsy handpiece.  
         [0011]     In one aspect consistent with aspects of the invention, a biopsy device includes a rotary hydraulic drive motor that is coupled to a pressurized pneumatic source. The drive motor in turn drives a cutter drive assembly that rotates a cylindrical cutter down a cutter lumen at a fixed ratio to its longitudinal translation. It is understood that cutter rotations through the aperture are proportional to cutter rotation speed and inversely related to translation speed. Therefore the uncoordinated relationship between the cutter rotation speed and translation speed coupled with the inherent poor response of the pneumatically driven cutter can result in variations in the tissue sample weight when sampling heterogeneous tissue due to variations in cutter rotations through the aperture. However, the cutter drive assembly described below advantageously maintains a fixed relationship between the cutter rotation speed and translation speed at any speed based on the fixed gear ratios between the rotation drive shaft and translation drive shaft. For example, as the cutter rotation speed decreases, the cutter translation speed also decreases resulting in the same number of cutter rotations through the aperture. Likewise, as the cutter rotation speed increases, the cutter translation speed also increases resulting in the same number of cutter rotations through the aperture. Therefore, the inconsistent number of cutter rotations through the aperture associated with a pneumatically driven cutter is eliminated because the cutter drive assembly described below inherently maintains the number of cutter rotations through the aperture regardless of the density of the tissue encountered.  
         [0012]     In another aspect of the invention, the fixed ratio cutter drive assembly is powered by a piezoelectric drive motor that is advantageously compatible with use near an MRI system.  
         [0013]     These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed the same will be better understood by reference to the following description, taken in conjunction with the accompanying drawings in which:  
         [0015]      FIG. 1  is a partial isometric and partial schematic view of a core sampling biopsy system that includes a handpiece with a short stroke cutter that is advantageously pneumatically driven;  
         [0016]      FIG. 2  is a partial isometric and partial schematic view of a core sampling biopsy system that includes a handpiece with a short stroke cutter that is advantageously piezoelectrically driven;  
         [0017]      FIG. 3  is an isometric view of a probe assembly of the handpiece of  FIG. 1  with a holster removed;  
         [0018]      FIG. 4  is a cross sectional isometric view of the probe assembly of  FIG. 3  taken along line  4 - 4  with a cutter and carriage assembly positioned at a proximal position;  
         [0019]      FIG. 5  is a cross-sectional isometric view of the probe assembly of  FIG. 3  taken along line  4 - 4  with the cutter and carriage assembly positioned between proximal and distal end positions;  
         [0020]      FIG. 6  is a cross-sectional isometric view of the probe assembly of  FIG. 3  taken along line  4 - 4  with the cutter and carriage assembly positioned at the distal end position;  
         [0021]      FIG. 7  is an exploded isometric view of the probe assembly of  FIG. 3 ; and  
         [0022]      FIG. 8  is ian exploded isometric view of a single input—dual output driven drive assembly for the holster of  FIGS. 1-2 , viewed in the proximal direction.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Pneumatic Biopsy Device.  
         [0024]     In  FIG. 1 , a pneumatic core sampling biopsy system  10  includes a handpiece  30  that may be held comfortably in a single hand, and may be manipulated with a single hand. Handpiece  30  may include a probe assembly  32  and a detachably connected holster  34 . Probe assembly  32  may be operatively connected to a vacuum source  36 , such as by a first, lateral tube  38  and a second, axial tube  40 . First and second tubes  38 ,  40  may be made from a flexible, transparent or translucent material, such as silicon tubing, PVC tubing or polyethylene tubing. Using a transparent material enables visualization of the matter flowing through tubes  38 ,  40 .  
         [0025]     First tube  38  may include a Y connector  42  for connecting to multiple fluid sources. A first proximal end of Y connector  42  may extend to a first solenoid controlled rotary valve  44  in a control module  46 , while the second proximal end of the Y connector  42  may extend to a second solenoid controlled rotary valve  48  in control module  46 . The first solenoid controlled rotary valve  44  in control module  46  may be operable to connect either the vacuum source  36  or a compressed air source  50  to lateral tube  38 . It is understood within this specification that compressed air means air pressure at or above atmospheric pressure. In one configuration, when valve  44  is activated, vacuum is supplied to tube  38  from vacuum source  36 , and when valve  44  is not activated, pressurized air from compressed air source  50  is supplied through tube  38 . The solenoid associated with valve  44  may be controlled by a microprocessor  52  in control module  46 , as indicated by dashed line  54 . The microprocessor  52  may be employed to adjust the position of valve  44  automatically based upon the position of a cutter  55  (as shown in  FIG. 7 ) movably supported within probe assembly  32 . The second solenoid controlled rotary valve  48  in control module  46  may be employed to either connect a saline supply  56  (such as a saline supply bag, or alternatively, a pressurized reservoir of saline) to a tube  58  or to seal off the proximal end of tube  58 . For instance, rotary valve  48  may be activated by microprocessor  52  to supply saline when one of switches  60  on handpiece  30  is actuated. When rotary valve  48  is activated, first rotary valve  44  may be automatically deactivated (such as by microprocessor  52 ) to prevent the interaction of vacuum and saline within lateral tube  38 . A stopcock  61  may be included in lateral vacuum tube  38  to allow for a syringe injection of saline directly into the tube  38 , if desired. For instance, a syringe injection may be employed to increase the saline pressure in the tube to dislodge any clogs that may occur, such as tissue clogging fluid passageways.  
         [0026]     In one version, axial vacuum tube  40  may be employed to communicate vacuum from source  36  to probe assembly  32  through a tissue storage assembly  62 . Axial tube  40  may provide vacuum through the cutter  55  within probe assembly  32  to assist in prolapsing tissue into a side aperture  64  prior to cutting. After cutting occurs, the vacuum in axial tube  40  may be employed to help draw a severed tissue sample from probe assembly  32  and into tissue storage assembly  62 . Holster  34  may include a control cord  66  for operationally connecting handpiece  30  to control module  46 .  
         [0027]     A pneumatic drive motor  70  advantageously replaces a rotatable drive cable used in generally-known MRI-compatible core sampling biopsy systems. The pneumatic drive motor  70  would be located proximal of the handpiece  30 . The pneumatic drive motor  70  has two pneumatic input lines  68  and  69 . When compressed gas is applied to one of the two lines  68 ,  69 , the output shaft (not shown) of pneumatic drive motor  70  rotates in a given direction. When compressed gas is applied to the other line  69 ,  68 , the output shaft of the pneumatic drive motor  70  rotates in the opposite direction. In each case, the pneumatic input line  68 ,  69  that does not carry the compressed gas is the exhaust or vent line for the compressed gas. This switching between OFF/Input  1  ON and Input  2  Vent/Input  1  Vent and Input  2  ON may be accomplished by microprocessor  52  commanding a pneumatic switching valve  72  that receives compressed air from a source  73  and selectively switches the compressed air to pneumatic input lines  68 ,  69 . The compressed gas rotates the output shaft of the pneumatic drive motor  70  via a rotor blade assembly (not shown). The output shaft of the pneumatic drive motor  70  then drives the input shaft of a cutter drive assembly (not shown in  FIG. 1 ).  
         [0028]     An example of a pneumatic drive motor  70  is available from Pro-Dex Micro Motors Inc. model MMR-0700.  
         [0029]     Switches  10  are mounted on holster upper shell  74  to enable an operator to use handpiece  30  with a single hand. One-handed operation allows the operator&#39;s other hand to be free, for example, to hold an ultrasonic imaging device. Switches  60  may include a two-position rocker switch  76  for manually actuating the motion of the cutter  55  (e.g. forward movement of the rocker switch  76  moves the cutter  55  in the forward (distal) direction for tissue sampling and rearward movement of the rocker switch  76  actuates the cutter  55  in the reverse (proximal) direction). Alternatively, the cutter  55  could be automatically actuated by control module  46 . An additional switch  78  may be provided on holster  34  for permitting the operator to activate saline flow on demand into lateral tube  38  (for instance, switch  78  may be configured to operate valve  48  for providing saline flow to tube  38  when switch  78  is depressed by the user).  
         [0030]     As an alternate configuration, it should be noted that the pneumatic drive motor drive assembly described herein could rotate and translate a cutter within biopsy devices where the cutter translates the entire length of the needle to extract the tissue from the patient.  
         [0031]     Piezoelectric Motor-Drive Core Sampling Biopsy System.  
         [0032]     In  FIG. 2 , a piezoelectrically-driven biopsy system  10   a  is similar to that described above for  FIG. 1  but includes some changes. In particular, a piezoelectric motor  70   a  is advantageously completely or partially replacing a generally known mechanical rotatable drive cable. The piezoelectric drive motor  70   a  may be located immediately proximal of the cutter drive assembly (not shown in  FIG. 2 ). The piezoelectric drive motor  70   a  is driven by motor driver circuitry  77 , which is powered by power source  72 , via electrical cable  79 . It should be appreciated that the motion of a piezoelectric crystal material rotates a rotor attached to the output shaft (not shown) of the piezoelectric drive motor  70   a.  The output shaft of the piezoelectric drive motor  70   a  then drives the input shaft of the cutter drive assembly. An example of a piezoelectric drive motor  70   a  is available from Shinsei Corporation drive motor model USR 10-E3N and electronic driver model D6060.  
         [0033]     A design aspect of current piezoelectric motors is the low power density of the motors. This results in piezoelectric motors with a relatively large volume when compared to conventional DC motors at a given power rating. In the event the piezoelectric drive motor  70   a  is too large to be attached directly to the input shaft of the cutter drive assembly  107  ( FIG. 3 ), the output of the piezoelectric drive motor  70   a  may drive a rotatable drive cable  81 . This would allow the piezoelectric drive motor  70   a  to be located some distance from the holster to reduce the holster mass. As an additional alternate configuration, one piezoelectric motor could rotate the cutter assembly and a second piezoelectric motor could translate the cutter assembly. Piezoelectric motors are particularly suited for MRI applications based on their material properties. It should be noted that the piezoelectric motor drive assembly described herein could rotate and translate a cutter within biopsy devices where the cutter translates the entire length of the needle to extract the tissue from the patient.  
         [0034]     Short Stroke Cutter Drive Assembly.  
         [0035]     With the pneumatic drive motor  70  of  FIG. 1  or the alternative piezoelectric drive motor  70   a  of  FIG. 2  omitted, the components of the handpiece  30  will now be described.  FIG. 3  shows probe assembly  32  disconnected from holster  34 . Probe assembly  32  includes an upper shell  80  and a lower shell  82 , each of which may be injection molded from a rigid, biocompatible plastic, such as a polycarbonate. Upon final assembly of probe assembly  32 , upper and lower shells  80 ,  82  may be joined together along a joining edge  84  by any of a number of methods well known for joining plastic parts, including, without limitation, ultrasonic welding, snap fasteners, interference fit, and adhesive joining.  
         [0036]      FIGS. 4-7  illustrate probe assembly  32  in greater detail.  FIG. 4  depicts a cutter assembly and carriage  86  retracted proximally.  FIG. 5  depicts the cutter assembly and carriage  86  partially advanced.  FIG. 6  depicts the cutter assembly and carriage  86  advanced distally. With particular reference to  FIG. 7 , the probe assembly  32  may include a biopsy needle (probe)  88  located at a distal end of a handle  89  of the probe assembly  32  for insertion into a patient&#39;s skin to obtain a tissue sample. Needle  88  comprises an elongated, metallic cannula  90 , which may include an upper cutter lumen  92  for receiving the cutter  55  and a lower vacuum lumen  94  for providing a fluid and pneumatic passageway. Cutter  55  may be disposed within cannula  90 , and may be coaxially disposed within cutter lumen  92 .  
         [0037]     Cannula  90  may have any suitable cross-sectional shape, including a circular or oval shaped cross-section. Adjacent and proximal of the distal end of cannula  90  is the side (lateral) tissue receiving port (side aperture)  64  for receiving the tissue to be severed from the patient. The sharpened tip of needle  88  may be formed by a separate endpiece  96  attached to the distal end of cannula  90 . The sharpened tip of endpiece  96  may be used to pierce the patient&#39;s skin so that the side tissue receiving port may be positioned in the tissue mass to be sampled. Endpiece  96  may have a two-sided, flat-shaped point as shown, or any number of other shapes suitable for penetrating the soft tissue of the patient.  
         [0038]     The proximal end of needle  88  may be attached to a union sleeve  98  having a longitudinal bore  100  therethrough, and a transverse opening  102  into a widened center portion of the bore  100 . The distal end of lateral tube  38  may be inserted to fit tightly into transverse opening  102  of union sleeve  98 . This attachment allows the communication of fluids (gas or liquid) between the lower vacuum lumen  94  and the lateral tube  38 .  
         [0039]     The cutter  55 , which may be an elongated, tubular cutter, may be disposed at least partially within upper cutter lumen  92 , and may be supported for translation and rotation within cutter lumen  92 . Cutter  55  may be supported within vacuum lumen  94  so as to be translatable in both the distal and proximal directions. Cutter  55  may have a sharpened distal end  106  for cutting tissue received in upper cutter lumen  92  through side tissue receiving port  64 . The cutter  55  may be formed of any suitable material, including without limitation a metal, a polymer, a ceramic, or a combination of materials. Cutter  55  may be translated within cutter lumen  92  by a suitable cutter drive assembly  107  such that distal end  106  travels from a position proximal of the side tissue port  64  (illustrated in  FIG. 4 ) to a position distal of side tissue port  64  (illustrated in  FIG. 6 ), in order to cut tissue received in cutter lumen  92  through the side tissue port  64 . In an alternative embodiment, an exterior cutter (not shown) may be employed, with the exterior cutter sliding coaxially with an inner cannular needle, and the inner needle may include a side tissue receiving port.  
         [0040]     Union sleeve  98  is supported between probe upper and lower shells  80 ,  82  to ensure proper alignment between cutter  55  and the union sleeve  98 . The cutter  55  may be a hollow tube, with a sample lumen  108  extending axially through the length of cutter  55 . The proximal end of cutter  55  may extend through an axial bore of a cutter gear  110 . Cutter gear  110  may be metallic or polymeric, and includes a plurality of cutter gear teeth  112 . Cutter gear  110  may be driven by a rotary drive shaft  114  having a plurality of drive gear teeth  116  designed to mesh with cutter gear teeth  112 . Drive gear teeth  116  may extend along the length of drive shaft  114  so as to engage cutter gear teeth  112  as the cutter  55  translates from a proximal most position to a distal most position, as illustrated in  FIGS. 4-6 . Drive gear teeth  116  may be in continual engagement with cutter gear teeth  112  to rotate cutter  55  whenever drive shaft  114  is rotatably driven. Drive shaft  114  rotates cutter  55  as the cutter advances distally through tissue receiving port  64  for the cutting of tissue. Drive shaft  114  may be injection molded from a rigid engineered plastic such as liquid crystal polymer material or, alternatively, could be manufactured from a metallic or non-metallic material. Drive shaft  114  includes a first axial end  120  extending distally from the shaft  114 . Axial end  120  is supported for rotation within probe lower shell  82 , such as by a bearing surface feature  122  molded on the inside of the probe shells  80 ,  82 . Similarly, a second axial end  124  extends proximally from rotary drive shaft  114  and is supported in a second bearing surface feature  126 , which may also be molded on the inside of probe lower shell  82 . An O-ring and bushing (not shown) may be provided on each axial end  120 ,  124  to provide rotational support and audible noise dampening of the shaft  114  when rotary drive shaft  114  is mounted in probe lower shell  82 .  
         [0041]     As shown in  FIGS. 4-6 , a drive carriage  134  is provided in probe assembly  32  to hold cutter gear  110 , and carry the cutter gear and attached cutter  55  during translation in both the distal and proximal directions. Drive carriage  134  may be molded from a rigid polymer and has a cylindrically-shaped bore  136  extending axially therethrough. A pair of J-shaped hook extensions  140  extend from one side of drive carriage  134 . Hook extensions  140  rotatably support cutter  55  on either side of cutter gear  110  to provide proximal and distal translation of the cutter gear  110  and cutter  55  during proximal and distal translation of drive carriage  134 . Hook extensions  140  align cutter  55  and cutter gear  110  in the proper orientation for cutter gear teeth  112  to mesh with drive gear teeth  116 .  
         [0042]     Drive carriage  134  is supported on a translation shaft  142 . Shaft  142  is supported generally parallel to cutter  55  and rotary drive shaft  114 . Rotation of the translation shaft  142  provides translation of the drive carriage  134  (and thus also cutter gear  110  and cutter  55 ) by employing a lead screw type drive. Shaft  142  includes an external lead screw thread feature, such as lead screw thread  144 , on its outer surface. The screw thread  144  extends into the bore  136  in drive carriage  134 . The screw thread  144  engages an internal helical threaded surface feature (not shown) provided on the inner surface of bore  136 . Accordingly, as shaft  142  is rotated, the drive carriage  134  translates along the threaded feature  144  of the shaft  142 . The cutter gear  110  and the cutter  55  translate with the drive carriage  134 . Reversing the direction of rotation of shaft  142  reverses the direction of translation of the drive carriage  134  and the cutter  55 . Translation shaft  142  may be injection molded from a rigid engineered plastic such as liquid crystal polymer material or, alternatively, could be manufactured from a metallic or non-metallic material. Translation shaft  142  with lead screw thread feature  144  may be molded, machined, or otherwise formed. Likewise, drive carriage  134  may be molded or machined to include an internal helical thread in bore  136 . Rotation of shaft  142  drives the carriage and cutter gear  110  and cutter  55  in the distal and proximal directions, depending upon the direction of rotation of shaft  142 , so that cutter  55  translates within probe assembly  32 . Cutter gear  110  is rigidly attached to cutter  55  so that the cutter translates in the same direction and at the same speed as drive carriage  134 .  
         [0043]     In one version, at the distal and proximal ends of lead screw thread  144 , the helical thread is cut short so that the effective pitch width of the thread is zero. At these distal most and proximal most positions of thread  144 , translation of drive carriage  134  is no longer positively driven by shaft  142  regardless of the continued rotation of shaft  142 , as the carriage effectively runs off the thread  144 . Biasing members, such as compression coil springs  150   a  and  150   b  ( FIG. 7 ), are positioned on shaft  142  adjacent the distal and proximal ends of the screw thread  144 . Springs  150   a - b  bias drive carriage  134  back into engagement with lead screw thread  144  when the carriage runs off the thread  144 . While shaft  142  continues rotating in the same direction, the zero pitch width thread in combination with springs  150   a - b  cause drive carriage  134  and, therefore, cutter  55  to “freewheel” at the end of the shaft. At the proximal end of the threaded portion of shaft  142 , the drive carriage  134  engages spring  150   a.  At the distal end of the threaded portion of shaft  142 , the drive carriage  134  engages spring  150   b.  When the drive carriage  134  runs off the screw thread  144 , the spring  150   a  or  150   b  engages the drive carriage  134  and biases the drive carriage  134  back into engagement with the screw thread  144  of shaft  142 , at which point continued rotation of the shaft  142  again causes the drive carriage  134  to run off the screw thread  144 . Accordingly, as long as rotation of shaft  142  is maintained in the same direction, the drive carriage  134  (and cutter  55 ) will continue to “freewheel”, with the distal end of the cutter  55  translating a short distance proximally and distally as the carriage is alternately biased onto the thread  144  by spring  150   a  or  150   b  and then run off the screw thread  144  by rotation of shaft  142 . When the cutter is in the distal most position shown in  FIG. 6 , with the distal end  106  of the cutter  55  positioned distal of side tissue port  64 , spring  150   b  will engage drive carriage  134 , and repeatedly urge drive carriage  134  back into engagement with screw thread  144  when drive carriage  134  runs off the screw thread  144 . Accordingly, after the cutter  55  is advanced such that the distal end  106  of the cutter  55  translates distally past the side tissue port  64  to cut tissue, to the position shown in  FIG. 6 , continued rotation of the shaft  142  will result in the distal end  106  oscillating back and forth, translating a short distance proximally and distally, until the direction of rotation of shaft  142  is reversed (such as to retract the cutter  55  distally to the position shown in  FIG. 4 ). With the cutter  55  in its distal most position shown in  FIG. 6 , the slight movement of drive carriage  134  into engagement with the screw thread  144  and out of engagement with the screw thread  144  against the biasing force of spring  150   b,  causes the distal end  106  of cutter  55  to repetitively reciprocate a short distance within cannula  90 , which distance may be about equal to the pitch of threads  144 , and which distance is shorter than the distance the cutter travels in crossing the side tissue port  64 . This reciprocal movement of the cutter  55  may provide alternate covering and uncovering of at least one fluid passageway disposed distally of the side tissue port  64 , as described below.  
         [0044]     The zero pitch width ends of lead screw thread  144  provide a defined stop for the axial translation of cutter  55 , thereby eliminating the need to slow drive carriage  134  (i.e. cutter  55 ) as it approaches the distal and proximal ends of the thread. This defined stop reduces the required positioning accuracy for drive carriage  134  relative to shaft  142 , resulting in reduced calibration time at the initialization of a procedure. The freewheeling of drive carriage  134  at the distal and proximal most positions of translation shaft  142  eliminates the need to rotate the shaft  142  a precise number of turns during a procedure. Rather, translation shaft  142  only needs to translate at least a minimum number of turns to insure drive carriage  134  has translated the entire length of lead screw thread  144  and into the zero width thread. Additionally, the freewheeling of drive carriage  134  eliminates the need to home the device, allowing probe assembly  32  to be inserted into the patient&#39;s tissue without first being attached to holster  34 . After probe assembly  32  is inserted, holster  34  is attached and sampling may be commenced.  
         [0045]     As shown in  FIG. 7 , a non-rotating rear tube  152  may be provided in which tube  152  may extend from the proximal end of cutter  55  just proximal of cutter gear  110 . Rear tube  152  may be hollow and may have substantially the same inner diameter as cutter  55 , and may be comprised of the same material as the cutter  55 . A seal  154  may be positioned between cutter  55  and rear tube  152  to enable the cutter  55  to rotate relative to the rear tube  152  while providing a pneumatic seal between the rear tube  152  and the cutter  55 . A rear lumen  156  may extend through the length of tube  152  and may be aligned with sample lumen  108  in cutter  55 . Rear lumen  156  transports excised tissue samples from sample lumen  108  through probe assembly  32  to the tissue storage assembly  62 . Sample lumen  108  and rear lumen  156  are axially aligned to provide a continuous, generally straight line, unobstructed passageway between tissue receiving port  64  and tissue storage assembly  62  for the transport of tissue samples. The inner surfaces of cutter  55  and tube  152  may be coated with a hydrolubricous material to aid in the proximal transport of the excised tissue samples.  
         [0046]     A lateral extension  158  may be supported by and extend distally from rear tube  152  for securing the tube  152  to drive carriage  134 . The extension  158  connects tube  152  to drive carriage  134  so that tube  152  translates with cutter  55 , and maintains lumens  108 ,  156  in continuous fluid-tight communication throughout the cutting cycle.  
         [0047]     Single Input-Dual Output Holster Gearbox Assembly.  
         [0048]     In  FIG. 8 , the rotary drive shaft  114  and translation shaft  142  are driven by a single drive input  180  via a single rotatable input  55  (also shown in  FIG. 1 ) via a holster gearbox assembly  182 . The single drive input  180  is driven in turn by either the pneumatic drive motor  70  ( FIG. 1 ) or the piezoelectric motor  70   a  ( FIG. 2 ). Rotatable drive input  180  attaches to a drive cable input coupling  352  for providing rotational drive to holster  34 . A drive shaft  354  from input coupling  352  extends to a proximal housing  356 . Within proximal housing  356 , an input gear  360  is mounted on input drive shaft  354  between spacer  362  and bearing  389  so as to engage corresponding gears on a translation drive shaft  364  and a rotation drive shaft  366 . The interaction of the input gear  360  with translation shaft gear  370  and rotation shaft gear  372  transmits the rotational drive to translation and rotation drive shafts  364 ,  366 . Translation and rotation drive shafts  364 ,  366  extend from proximal housing  356  through a pair of bores in a center housing  374 . Translation and rotation gears  370 ,  372  are spaced between the proximal and center housings by bearings  376 .  
         [0049]     Distal of center housing  374 , holster  34  includes a rotary encoder  380  for providing a feedback signal to control module  46  regarding rotation of the drive shafts. Encoder  380  may be mounted on either the translation or the rotation drive shafts. Holster  34  also includes an optional planetary gearbox  382  on translation drive shaft  364 . Gearbox  382  provides a gear reduction between the rotary drive shaft  114  and translation shaft  142  to produce differing speeds for the translation of drive carriage  134  and the rotation of cutter  55 . Distal of gearbox  382  and encoder  380 , drive assembly  350  includes a housing  384 . Housing  384  includes connections for coupling the translation shaft  142  with translation drive input shaft  386 , and the rotational drive shaft  114  with rotary drive input shaft  388 . Each of the drive input shafts  386 ,  388  has a distal end shaped to operatively engage slots on corresponding drive shafts  114 ,  142  in probe assembly  32 . In particular, translation drive input shaft  386  is shaped to engage a slot of translation shaft  142  (shown in  FIG. 7 ), and rotary drive input shaft  388  is shaped to engage a slot of rotary drive shaft  114 . Alternatively, drive input shafts may have molded interfaces rather than the mating slots and tips as shown in  FIGS. 7 and 8  to reduce the coupling length between the shafts. Translation and rotary drive shafts  386 ,  388  extend distally from housing  384  for engagement with drive and translation shafts  114 ,  142  when probe assembly  32  and holster  34  are connected.  
         [0050]     While illustrative versions 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 spirit and scope of the appended claims. Additionally, each element described in relation to the invention may be alternatively described as a means for performing that element&#39;s function.  
         [0051]     For example, while a microprocessor control console  46  is advantageously described, it should be appreciated that an alternate control approach may be employed. For instance, switchology on a handpiece may activate pneumatic valves to cause rotation and translation. For instance, a single pneumatic input line to the handpiece may be manually switched at the handpiece to a rotary motor to achieve one of three conditions: Off, Clockwise, and Counterclockwise.  
         [0052]     For another example, a core sampling biopsy system as described in U.S. Pat. No. 6,273,862 that performs a long cutting stroke to take samples and to retract them from the probe may also advantageously benefit from an MRI-compatible power source (e.g., pneumatic, piezoelectric) as described herein.  
         [0053]     For a further example, while vacuum assist is advantageously described herein to assist in functions such as prolapsing tissue and retracting samples through the probe, it should be appreciated that applications consistent with the present invention would benefit from pneumatic or piezoelectric driven biopsy devices.  
         [0054]     For yet a further example, while a version described herein illustrates compressed air to drive a cutter drive assembly, it should be appreciated that a incompressible fluid may be used in applications consistent with aspects of the present invention.  
         [0055]     For yet a further example, while a version described herein illustrates compressed air to drive a cutter drive assembly, it should be appreciated that vacuum may be used to drive the pneumatic motor to then drive the cutter drive assembly, in applications consistent with aspects of the present invention.

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