Abstract:
A marking device includes a handle defining a hollow interior, and a delivery assembly slidably mounted to the handle. The delivery assembly includes a cannula, a stylet assembly, an imaging marker, and an actuator. The cannula has a cannula distal end with a marker recess. The imaging marker is disposed within the marker recess. The actuator is operably coupled to the delivery assembly and is operable to transition the delivery assembly through at least three configurations: a first configuration characterized in that the cannula is positioned in an extended position and the stylet assembly is positioned in a ready position; a second configuration characterized in that the cannula is positioned in the extended position and the stylet assembly is positioned in an implant position; and a third configuration characterized in that the cannula is positioned in the retracted cannula position and the stylet is retracted into the handle.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to a device for implanting an imaging marker in a tissue mass and particularly to a marking device having a cannula that retracts into a handle following implantation of the imaging marker in the tissue mass. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Subcutaneous imaging markers are commonly implanted in humans to identify a particular location in various areas and organs of the body. For example, markers are positioned at biopsy sites so that a practitioner can readily identify the tissue sample location after the biopsy procedure is completed. Markers are also used to denote the locations of lesions for therapeutic procedures, such as chemotherapy. Typically, markers located within the body can be viewed by various imaging techniques, such as radiography, ultrasound, and magnetic resonance imaging (MRI). 
         [0003]    Various devices and methods have been developed for implanting a marker at a predetermined site in a tissue mass. One method of implanting a marker involves inserting a probe into the tissue mass and, with guidance from imaging systems, placing the tip of the probe near a predetermined location. Once the probe is in place and the biopsy is executed, a device comprising a flexible cannula, a stylet slidably mounted in the cannula, and the imaging marker positioned in the cannula distally of the stylet is manually threaded through the probe and positioned with the tip of the cannula at the predetermined location. Thereafter, the stylet is advanced distally to eject the imaging marker from the cannula at the predetermined location, and the cannula and the stylet are removed from the probe. 
         [0004]    Other marking devices are self-contained in that they do not require a pre-inserted probe to guide the device to the predetermined location. Rather, such self-contained devices typically comprise a handle that supports a rigid cannula with a sharpened tip and a stylet mounted in the cannula. The imaging marker is positioned in the cannula distally of the stylet. In operation, the cannula is inserted into the body, and its sharpened, distal tip is placed at the predetermined location using imaging systems for guidance. The imaging marker can be implanted in one of two ways: the stylet advances distally to eject the marker from the cannula, or the cannula retracts relative to the stationary stylet to expose the marker to the predetermined location. Following implantation, the handle is pulled proximally to remove the cannula and the stylet from the body. The practitioner must be careful when pulling the marking device from the body because the sharpened tip of the cannula, which has been in contact with the patient&#39;s blood, is exposed and can potentially stab the practitioner, other persons assisting with the marking procedure, or even the patient if the practitioner accidentally moves the marking device towards the patient after removal of the marking device from the body. Thus, it is desirable for a self-contained marking device to comprise a cannula that retracts entirely into the handle following implantation of the imaging marker at the predetermined location. 
       SUMMARY OF THE INVENTION 
       [0005]    A marking device according to one embodiment of the invention comprises a handle having a handle proximal end and a handle distal end and defining a hollow interior, a cannula having a cannula distal end and slidably mounted to the handle for slidable movement between an extended position where the cannula distal end extends beyond the handle distal end and a retracted position where the cannula distal end is received within the hollow interior, a stylet having a stylet distal end and slidably mounted to the handle for slidable movement between a ready position where the stylet distal end is proximal of the cannula distal end to form a marker recess in the cannula between the cannula distal end and the stylet distal end and an implant position where the stylet distal end extends into at least the marker recess, an imaging marker located within the marker recess, and an actuator operably coupled to the stylet and the cannula to effect movement of the stylet from the ready position to the implant position to eject the marker from the marker recess and movement of the cannula from the extended position to the retracted position. 
         [0006]    The movement of the cannula from the extended position to the retracted position can occur after the movement of the stylet from the ready position to the implant position. 
         [0007]    The stylet distal end can extend to at least the cannula distal end when in the implant position. The stylet distal end can extend beyond the cannula distal end when in the implant position. 
         [0008]    The actuator can be configured to effect movement of the stylet from the implant position to a withdrawn position where the stylet is retracted into the hollow interior of the handle. The actuator can be configured to effect movement of the stylet from the implant position to the withdrawn position when effecting movement of the cannula from the extended position to the retracted position. The stylet distal end can be received within the hollow interior of the handle when in the withdrawn position. 
         [0009]    The actuator can manually move the stylet from the ready position to the implant position. The actuator can automatically move the cannula from the extended position to the retracted position. The actuator can automatically effect movement of the stylet from the implant position to a withdrawn position where the stylet is retracted into the hollow interior of the handle when automatically moving the cannula from the extended position to the retracted position. The stylet distal end can be received within the hollow interior of the handle when in the withdrawn position. 
         [0010]    The actuator can comprise a cannula biasing element operably coupled with the cannula in the handle to bias the cannula to the retracted position. The actuator can further comprise a trigger mounted to the handle and operable between a locked position where the trigger prevents movement of the cannula to the retracted position by the biasing element and a cannula release position where the trigger does not prevent movement of the cannula to the retracted position by the biasing element. The actuator can further comprise a cannula mount that supports a proximal end of the cannula for sliding movement in the hollow interior and operably couples the biasing element with the cannula. The actuator can further comprise a stylet mount that supports a proximal end of the stylet in the hollow interior. The actuator can further comprise a stylet biasing element operably coupled with the stylet mount in the hollow interior to bias the stylet to the ready position. The cannula mount can be operably coupled with the stylet mount so that the cannula mount directs the stylet mount proximally in the hollow interior to move the stylet to a withdrawn position where the stylet is retracted into the hollow interior when the cannula moves to the retracted position. The trigger can comprise a cam surface that rides along the stylet mount as the trigger moves from the locked position to the cannula release position to displace the stylet mount and move the stylet to the implant position. The cam surface can ride off the stylet mount as the trigger reaches the stylet advance position to the cannula release position to effect proximal movement of the stylet mount and the cannula mount. 
         [0011]    The cannula distal end can comprise at least one imageable marking. The cannula can be rigid. The cannula can terminate at a sharpened tip at the cannula distal end. Alternatively, the cannula can be flexible. 
         [0012]    A marking device according to another embodiment of the invention comprises a handle having a handle proximal end and a handle distal end and defining a hollow interior, a cannula having a cannula distal end and slidably mounted to the handle for slidable movement between an extended position where the cannula distal end extends beyond the handle distal end and a retracted position where the cannula distal end is received within the hollow interior, a stylet having a stylet distal end located in the cannula proximal of the cannula distal end to form a marker recess in the cannula between the cannula distal end and the stylet distal end, an imaging marker located within the marker recess, and an actuator operably coupled to the cannula to effect movement of the cannula from the extended position to the retracted position to expose the marker. 
         [0013]    The stylet can be slidably mounted to the handle for slidable movement to a withdrawn position where the stylet is retracted into the hollow interior. The stylet distal end can be received within the hollow interior of the handle when in the withdrawn position. The stylet can be operably coupled to cannula so that the stylet moves to the withdrawn position when the cannula moves to the retracted position. Movement of the stylet to the withdrawn position can be delayed until the cannula distal end is at least at the stylet distal end to eliminate the marker recess. 
         [0014]    The actuator can comprise a cannula biasing element operably coupled with the cannula in the handle to bias the cannula to the retracted position. The stylet can be operably coupled with the cannula so that movement of the cannula to the retracted position by the biasing element moves the stylet with the cannula to a withdrawn position where the stylet is retracted into the hollow interior. 
         [0015]    The cannula distal end can comprise at least one imageable marking. 
         [0016]    A method according to one embodiment of the invention of implanting an imaging marker into a tissue mass with a marking device comprising a handle defining a hollow interior, a cannula having a cannula distal end and slidably mounted to the handle, a stylet having a stylet distal end located in the cannula proximal of the cannula distal end to form a marker recess in the cannula between the cannula distal end and the stylet distal end, and an imaging marker located within the marker recess comprises implanting the imaging marker from the marker recess into the tissue mass, and retracting the cannula entirely into the handle. 
         [0017]    The retracting of the cannula entirely into the handle can comprise retracting the cannula distal end into the hollow interior. The retracting of the cannula entirely into the handle can comprise automatically retracting the cannula entirely into the handle. The method can further comprise retracting the stylet with the cannula. The method can further comprise positioning the cannula distal end in the tissue mass with an imaging system. 
         [0018]    The method can further comprise retracting the stylet into the handle. The retracting of the stylet into the handle can occur during the retracting of the cannula entirely into the handle. The retraction of the stylet can be delayed until the cannula distal end is retracted to at least at the stylet distal end to eliminate the marker recess. The implanting of the imaging marker can occur during the retracting of the cannula to expose the imaging marker to the tissue mass. Alternatively, the implanting of the imaging marker can comprise extending the stylet at least into the marker recess to expel the imaging marker from the marker recess. The extending of the stylet at least into the marker recess can comprise manually extending the stylet at least into the marker recess. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the drawings: 
           [0020]      FIG. 1  is a perspective view of a marking device according to one embodiment of the invention. 
           [0021]      FIG. 2  is an enlarged sectional view of the area indicated in  FIG. 1 . 
           [0022]      FIG. 3  is an exploded view of the marking device of  FIG. 1 . 
           [0023]      FIG. 4  is a perspective sectional view of a handle from the marking device of  FIG. 1 . 
           [0024]      FIG. 5A  is a front perspective view of a cannula mount for supporting a cannula of the marking device of  FIG. 1 . 
           [0025]      FIG. 5B  is a rear perspective view of the cannula mount from  FIG. 5A . 
           [0026]      FIG. 5C  is a sectional view of the cannula mount taken along line  5 C- 5 C of  FIG. 5A . 
           [0027]      FIG. 6A  is a front perspective view of a stylet mount for supporting a stylet of the marking device of  FIG. 1 . 
           [0028]      FIG. 6B  is a rear perspective view of the stylet mount from  FIG. 6A . 
           [0029]      FIG. 6C  is a sectional view of the stylet mount taken along line  6 C- 6 C of  FIG. 6A . 
           [0030]      FIG. 7A  is a sectional view taken along line  7 - 7  of  FIG. 1  with the cannula in an extended position and the stylet in a ready position. 
           [0031]      FIG. 7B  is an enlarged view of the area indicated in  FIG. 7A . 
           [0032]      FIG. 7C  is an enlarged view of the area indicated in  FIG. 7B . 
           [0033]      FIG. 8A  is a sectional view taken along line  8 A- 8 A of  FIG. 7A , with the stylet moved to an implant position. 
           [0034]      FIG. 8B  is an enlarged view of the area indicated in  FIG. 8A . 
           [0035]      FIG. 8C  is a sectional view taken along line  8 C- 8 C of  FIG. 7A , with the stylet moved to the implant position. 
           [0036]      FIG. 8D  is an enlarged view of the area indicated in  FIG. 8C . 
           [0037]      FIG. 9  is an enlarged sectional view of the area indicated in  FIG. 8 . 
           [0038]      FIG. 10A  is a sectional view similar to  FIG. 8A  with the cannula in a retracted position and the stylet in a withdrawn position. 
           [0039]      FIG. 10B  is an enlarged view of the area indicated in  FIG. 10A . 
           [0040]      FIG. 10C  is a sectional view similar to  FIG. 8C  with the cannula in the retracted position and the stylet in the withdrawn position. 
           [0041]      FIG. 10D  is an enlarged view of the area indicated in  FIG. 10C . 
           [0042]      FIG. 11  is a side view of the marking device of  FIG. 1  inserted into a tissue mass. 
           [0043]      FIG. 12  is an enlarged view of the area indicated in  FIG. 11  showing a distal end of the marking device positioned at a predetermined location in the tissue mass. 
           [0044]      FIG. 13  is an enlarged view similar to  FIG. 12  with an imaging marker expelled from the marking device at the predetermined location. 
           [0045]      FIG. 14  is a sectional view of a marking device according to another embodiment of the invention, with a handle that supports a cannula in an extended position and a stylet in a ready position. 
           [0046]      FIG. 15  is a sectional view similar to  FIG. 14 , with the cannula in a first retracted position to expose an imaging marker. 
           [0047]      FIG. 16  is a sectional view similar to  FIG. 15  with the cannula further retracted into the handle. 
           [0048]      FIG. 17  is a sectional view similar to  FIG. 16  with the cannula in a second retracted position and the stylet in a withdrawn position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0049]    Referring now to the figures,  FIG. 1  illustrates a marking device  10  according to one embodiment of the invention for implanting an imaging marker  12 , seen in  FIG. 2 , at a predetermined location in a tissue mass. Referring additionally to  FIG. 3 , the marking device  10  comprises a handle  14  that supports a cannula  16  slidably mounted thereto and a stylet  18  received within the cannula  16  and slidably mounted to the handle  14 . An actuator  20  also mounted to the handle  14  effects movement of the stylet  18  and the cannula  16  to eject the imaging marker  12  from the marking device  10  and to retract the cannula  16  into the handle  14  following ejection of the imaging marker  12 . The imaging marker  12  can be any suitable imaging marker made of any suitable non-bioabsorbable material, bioabsorbable material, or combinations thereof. Exemplary materials include, but are not limited to, metals, such as titanium and stainless steel, and polymers, such as polyvinyl alcohol (PVA), including combinations of such materials Examples of suitable imaging markers are disclosed in U.S. Pat. Nos. 6,356,782; 6,371,904; and 6,575,991, which are incorporated herein by reference in their entirety. 
         [0050]    As best seen in  FIGS. 3 and 4 , the handle  14  comprises a distal section  30  that terminates in an open distal end  32  and an integral proximal section  34  that terminates at a closed proximal end  36 . The distal section  30  includes a grip area  38  having a reduced outer diameter to accommodate a generally resilient grip  40  that surrounds the grip area  38  and has an aperture  42  to accommodate a trigger mount  44  located in the grip area  38  of the handle  14 . The trigger mount  44  comprises a pair of spaced side walls  46 , each having a pivot aperture  48 , joined by a distal wall  50  and a proximal wall  52 . The walls  46 ,  50 ,  52  surround a trigger opening  54  in the grip area  38  sized to receive and accommodate movement of the actuator  20 , as will be described in more detail below. The proximal section  34  gradually tapers proximally from the grip area  38  and distally from the proximal end  36  to a hand rest area  56  contoured to support a palm portion of the user&#39;s hand. 
         [0051]    Together, the distal section  30  and the proximal section  34  have an inner surface  60  that defines a generally cylindrical hollow interior  62 . As best seen in  FIG. 4 , the inner surface  60  includes a stop  64  that extends radially into the hollow interior  62  from the grip area  38  near the trigger mount  44 . Additionally, a pair of diametrically opposed guide grooves  66 , one of which is visible in  FIG. 4 , is formed along the inner surface  60  from a proximal side of the trigger mount  44  to the proximal end  36 . The handle  14  further includes a proximal stop  68  projecting into the hollow interior  62  from the proximal end  36 . 
         [0052]    Referring again to  FIG. 3 , the distal end  32  of the handle  14  is closed by a handle cap  70 . The handle cap  70  comprises a generally hollow frustoconical body  72  with a distal endwall  74  from which extends a nose  76  sized to slidably receive the cannula  16 . A plurality of resilient prongs  78  project proximally from the body  72  and mate with the distal end  32  of the handle  14  to mount the handle cap  70  to the handle  14 . For convenience of this description, the handle cap  70  is described as being separate from the handle  14 . However, the handle cap  70  can be considered as part of the handle  14  and can even be integrated with the handle  14 . 
         [0053]    The actuator  20  comprises a cannula mount  90  and a stylet mount  92  that slidably support the cannula  16  and the stylet  18 , respectively, in the handle  14 . As shown in  FIGS. 5A-5C , the cannula mount  90  includes an elongated cannula support shaft  94  integral with a generally orthogonal annular body  96  having an annular distal face  97 . A pair of opposed legs  98  having an arcuate outer surface  100  and a generally straight inner surface  102  extend proximally from the annular body  96 , and each of the legs  98  has a channel  104  formed therein that terminates at a corresponding opening  106  formed through the annular body  96 . The channels  104  are formed in the inner surface  102  so that the channels  104  face one another. The cannula mount  90  further comprises a pair of diametrically opposed resilient prongs  110  positioned between the legs  98 . The resiliency of each prong  110  is enhanced by a U-shaped notch  112  at the juncture between the prong  110  and the annular body  96 . Each prong  110  comprises a raised stop  114  disposed distally of a distal flat surface  116  joined to a proximal flat surface  118  by an inclined surface  120 , and each prong  110  terminates at an outwardly projecting tang  122  adjacent the proximal flat surface  118 . 
         [0054]    The stylet mount  92 , as shown in  FIGS. 6A-6C , comprises an elongated stylet support shaft  130  integral with a generally orthogonal cylindrical body  132 . The body  132  has a pair of diametrically opposed prong apertures  134  formed therein from a distal face  142  to a proximal face  144  of the body  132  and sized to receive the prongs  110  of the cannula mount  90 . As best viewed in  FIG. 6C , the prong apertures taper from the distal face  142  to the proximal face  144 . The body  132  further includes a pair of guide projections  136  extending radially from the body  132  in radial alignment with the prong apertures  134 . A pair of diametrically opposed prongs  138  extends distally from the body  132 , and each prong  138  terminates in an outwardly projecting tang  140 . The prongs  138  are oriented along a diameter generally orthogonal to a diameter that contains the prong apertures  134  with the stylet support shaft  130  between the prongs  138 . 
         [0055]    Referring back to  FIG. 3 , the actuator  20  further comprises a trigger  150  rotatably mounted to the trigger mount  44  of the handle  14 . Although the trigger  150  can move relative to the handle  14 , it will be described with respect to the orientation shown in  FIG. 3 . The trigger  150  includes a distally facing arcuate finger rest  152  and an irregularly shaped body  154  having a pivot member  156  on each side thereof. The body  154  is bounded by a sloped upper surface  158  extending proximally of the finger rest  152  and joined to a generally straight proximal surface  160  by a fillet  162 . The rest of the body  154  is defined by a curved cam surface having a distal cam surface  166  and a lower cam surface  164 . The distal cam surface  166  extends from the finger rest  152  to the lower cam surface  164 , which terminates at the straight proximal surface  160 . 
         [0056]    In addition to the cannula mount  90 , the stylet mount  92 , and the trigger  150 , the actuator  20  comprises a pair of biasing members: a cannula mount biasing member  170  and a stylet mount biasing member  172 . According to the illustrated embodiment of the invention, the biasing members  170 ,  172  are compression springs. Preferably, the cannula mount biasing member  170  tapers from a distal end  174  to a proximal end  176 . The cannula  16  is generally hollow and comprises a distal end  180  defining a tip  182  and a proximal end  184  mounted to the cannula support shaft  94  of the cannula mount  92 . The cannula  16  is preferably sufficiently rigid to permit the direct insertion of the cannula  16  into a tissue mass. Alternatively, the cannula  16  can be flexible for use with a probe or the like. The tip  182  is preferably pointed for insertion through skin and into the tissue mass; however, the tip  182  can optionally be blunt, for example, if the marking apparatus  10  is utilized with a probe or the like. Further, the distal end  180  of the cannula  16  can be beveled, as best seen in  FIG. 2 , from a bevel proximal edge  179  to a bevel distal edge  181  to define a bevel opening  183 . Preferably, the cannula  16  is a 17-gage (0.058 inch outer diameter) cannula, with an inner diameter ranging from 0.049 to 0.051 inches. Furthermore, the distal end  180  of the cannula  16  can be designed for enhanced visibility using common imaging techniques, such as radiography, ultrasonography, and magnetic resonance imaging (MRI). For example, the distal end  180  can include imageable markings  186 , as seen in  FIG. 3 . With continued reference to  FIG. 3  and additional reference to  FIG. 2 , the cannula  16  slidingly receives the stylet  18 , which comprises a distal end  190  located in the cannula  16  and a proximal end  192  mounted to the stylet support shaft  130  of the stylet mount  92 . Prior to use of the marking device  10 , the distal end  190  of the stylet  16  is spaced inwardly from the tip  182  to form a marker recess  194 , as best viewed in  FIG. 2 , for housing the imaging marker  12 . 
         [0057]    When the marking device  10  is in an assembled condition, as shown in  FIG. 7A , the stylet mount  92  is mounted in the hollow interior  62  with the guide projections  136  positioned in general alignment with the guide grooves  66 . The stylet  18  extends from the stylet support shaft  130 , through the cannula support shaft  94  of the cannula mount  90 , which is located distally of the stylet mount  92  in the hollow interior  62 , and out the distal end  32  of the handle  14  through the nose  76  of the handle cap  70 . The cannula mount  90  is positioned so that the cannula  16  also leaves the distal end  32  of the handle  14  through the nose  76  of the handle cap  70 . The relative positioning of the cannula mount  90  and the stylet mount  92  in the hollow interior  62  is such that the distal end  190  of the stylet  18  is spaced from the tip  182  to form the marker recess  194  ( FIG. 2 ). In this condition, the cannula  16  is in an extended position where it extends from the distal end  32  of the handle  14 , and the stylet  18  is in a ready position in the extended cannula  16 . 
         [0058]    As best seen in  FIGS. 7B and 7C , the cannula mount  90  and the stylet mount  92  are axially aligned in the hollow interior  62  with the stylet mount prongs  138  partially inserted into the channels  104  of the cannula mount  90  and the stylet support shaft  130  partially received in the cannula support shaft  94  of the cannula mount  90 . Additionally, the cannula mount prongs  110  extend through the prong apertures  134  of the stylet mount  92  with the tangs  122  abutting the proximal face  144  of the body  132  and the proximal flat surfaces  118  positioned in the prong apertures  134 . The cannula mount prongs  110  naturally spread apart from one another to facilitate securing the cannula mount  90  to the stylet mount  92  in the position best seen in  FIGS. 7B and 7C . Additionally, as a result of the natural resiliency of the cannula mount prongs  110 , the stops  114  extend radially outward and abut the stop  64  of the handle  14  to help prevent proximal movement of the cannula mount  90  even though the cannula mount  90  is biased away from the handle cap  70  by the cannula mount biasing member  170 , which abuts the handle cap  70  at the distal end  174  and the annular body  96  at the proximal end  176 . Similarly, the stylet mount  92  is biased away from the cannula mount  90  by the stylet mount biasing member  172 , which extends between the annular body  96  and the body  132  of the stylet mount  92 . The interaction between the cannula mount prongs  110  and the stylet mount body  132  prevents retraction of the stylet mount  92  beyond the position shown in  FIGS. 7B and 7C . Additionally, proximal movement of the stylet mount  92  and the cannula mount  90  is prevented in part by the trigger  150 . The pivot mounts  156  are rotatably received by the pivot apertures  48  to mount the trigger  150  in the trigger mount  44  of the handle  14 . The trigger  150  extends through the trigger opening  54  in a locked condition, shown in  FIGS. 7B and 7C , where the proximal surface  160  abuts the proximal wall  52  of the trigger mount  44  to prevent counterclockwise rotation, relative to the orientation of  FIGS. 7B and 7C , of the trigger  150 , and the distal cam surface  166  faces the stylet mount  92 . 
         [0059]    The trigger  150  is movable from the locked position shown in  FIGS. 7A-7C  to a stylet advance position shown in  FIGS. 8A and 8C  to displace the stylet  18  proximally and eject the imaging marker  12  from the marker recess  194 , as shown in  FIG. 9 . Rotation of the trigger  150  clockwise, relative to the orientation of  FIG. 8A , such as by rotation of the finger rest  152  by the user, causes the cam surface formed by the distal cam surface  166  and the lower cam surface  164  to abut the body  132  of the stylet mount  92  and ride along the proximal face  144  of the body  132  between the cannula mount prongs  110  while pushing the stylet mount  92  distally toward the cannula mount  90  against the bias of the stylet mount biasing member  172 , as best seen in  FIG. 8B . As a result, the tangs  140  of the stylet mount prongs  138  slide along the channels  104  of the cannula mount  90  until the tangs  140  slide through the openings  106  in the annular body  96  and flex outward to abut the distal face  97  of the annular body  96  and thereby secure the stylet mount  92  to the cannula mount  90  together in the position shown in  FIG. 8B . At the same time, the body  132  rides distally along the cannula mount prongs  110 , particularly along the inclined surfaces  120 , as best seen in  FIG. 8D . As the body  132  moves along the prongs  110 , the taper of the prong apertures  134  forces the prongs  110  to flex toward each other at their respective notches  112  so that the stops  114  are no longer in abutting contact with the stop  64  on the interior surface  60  of the handle  14 . Distal movement of the stylet mount  92  ceases when the body  132  reaches the distal flat surfaces  116 . In this position, the trigger  150  prevents proximal movement of the cannula mount  90  and the stylet mount  92  by the cannula mount biasing member  170 . Because the stylet mount  92  moves distally while the cannula mount  90  remains stationary, the stylet  16  advances distally into the marker recess  194  to an implant position to eject the imaging marker  12  therefrom, as shown in  FIG. 9 . Preferably, the stylet  18  is sized so that when the stylet  18  is in the implant position, the distal end  190  of the stylet  18  extends to at least the bevel proximal edge  179  at the bevel opening  183  to ensure that the imaging marker  12  reaches the bevel opening  183  for ejection from the marker recess  194 . The stylet distal end  190  can also extend to a position between the bevel proximal edge  179  and the bevel distal edge  181  (i.e., a center point of the bevel and the bevel opening  183 ). Further, the stylet distal end  190  can extend to near the tip  182  of the cannula  16  (i.e., the bevel distal edge  181 ) or beyond the tip  182  to ensure complete ejection of the imaging marker  12  from the marker recess  194 . 
         [0060]    Continuing rotation of the trigger  150  beyond the stylet advance position to a cannula release position shown in  FIGS. 10A and 10C  retracts the cannula  16  and the stylet  18  into the hollow interior  62 . While the trigger  150  rotates to the cannula release position, the cam surface formed by the distal cam surface  166  and the lower cam surface  164  rides off of the proximal face  144  of the stylet mount body  132  so that the trigger  150  no longer prevents proximal movement of the stylet mount  92  and the cannula mount  90  in the handle  14 . With the trigger  150  no longer an obstacle and the stops  114  on the cannula mount prongs  110  no longer abutting the stop  64 , the cannula mount biasing member  170  forces the cannula mount  90  and thereby the stylet mount  92 , which is fixed to the cannula mount  90  by the stylet mount prongs  138  and the cannula mount prongs  110 , proximally within the hollow interior  62  toward the proximal end  36  of the handle  14 . Movement of the cannula mount  90  and the stylet mount  92  ceases when the stylet mount  92  abuts the proximal stop  68  with the prongs  110  on the cannula mount  90  straddling the stop  68 , as best viewed in  FIGS. 10B and 10D . During this movement, the guide projections  136  enter the guide grooves  66  formed in the interior surface  60  of the handle  14  to prevent rotation of the stylet mount  92  and thereby the cannula mount  90 . Proximal movement of the cannula mount  90  and the stylet mount  92  retracts the cannula  16  and the stylet  18  into the hollow interior  62  to a retracted position and a withdrawn position, respectively. Preferably, when the cannula  16  is in the retracted position, the entire cannula  16 , including the tip  182 , is received within the handle  14  as seen in  FIGS. 10A and 10C . Similarly, the entire stylet  18  is preferably received within the handle  14  when in the withdrawn position, but it within the scope of the invention for the distal end  190  to project from the nose  76  when the stylet  18  is in the withdrawn position. 
         [0061]    In operation, a practitioner grasps the marking device  10  at the hand rest area  56  and inserts the cannula tip  182  through the skin of patient&#39;s body into a tissue mass  196 . An exemplary tissue mass  196  is a breast, as shown in  FIG. 11 . The practitioner places the tip  182  typically under the guidance of aforementioned imaging systems at or near a predetermined site  198 , such as a biopsy site, as shown in  FIG. 12 . Once the cannula tip  182  is at the predetermined site  198 , the practitioner places an index finger on the finger rest  152  of the trigger  150  and rotates the trigger  150  to move the trigger  150  from the locked position of  FIGS. 7A-7C  to the stylet advance position of  FIGS. 8A-8D  to move the stylet  18  from the ready position of  FIGS. 7A-7C  to the implant position of  FIGS. 8A-8D  and eject the imaging marker  12  from the marker recess  194  at the predetermined site  198 , as illustrated in  FIG. 13 . The practitioner continues to the rotate the trigger  150  to the cannula release position of  FIGS. 10A and 10B  to simultaneously move the cannula  16  from the extended position of  FIGS. 7A-7C  and  8 A- 8 D to the retracted position of  FIGS. 10A-10D  and the stylet  18  from the implant position of  FIGS. 8A-8D  to the withdrawn position of  FIGS. 10A-10D  to remove the cannula  16  and the stylet  18  from the tissue mass  196  as they retract into the handle  14 . Preferably, rotation of the trigger  150  between the locked, stylet advance, and cannula release positions is substantially continuous such that the practitioner can implant the imaging marker  12  and retract the cannula  16  into the handle  14  in effectively a single operational step. With the cannula  16  retracted into the handle  14 , the practitioner cannot accidentally stab himself or herself, others assisting with the procedure, or the patient with the marking device  10  following implantation of the imaging marker  12 . 
         [0062]    A marking device  210  according to another embodiment of the invention for implanting an imaging marker  212  at a predetermined location in a tissue mass is illustrated in  FIGS. 14-17 . Referring particularly to  FIG. 14 , the marking device  210  comprises a handle  214  that supports a cannula  216  slidably mounted thereto and a stylet  218  received within the cannula  216  and slidably mounted to the handle  214 . An actuator  220  also mounted to the handle  214  effects proximal movement of the cannula  216  to expose the imaging marker  212  and to retract the cannula  216  and the stylet  218  into the handle  214  after exposing the imaging marker  212 . 
         [0063]    The handle  214  of the marking device  210  is similar to the handle  14  of the first embodiment marking device  10  and comprises a distal section  230  that terminates in an open distal end  232  and an integral proximal section  234  that terminates at a closed proximal end  236 . A trigger mount  238  in the distal section  230  comprises a pivot mount  240  for mounting a portion of the actuator  220 , as will be described in more detail below. Together, the distal section  230  and the proximal section  234  have an inner surface  242  that defines a generally cylindrical hollow interior  244 . The handle  214  comprises a pair of stops  245  extending radially inward from the inner surface  242  in the hollow interior  244 . The handle  214  further includes a proximal stop  268  projecting into the hollow interior  244  from the proximal end  236 . The hollow interior  244  is closed at the distal end  232  of the handle  214  by a handle cap  246 . The handle cap  246  comprises a generally hollow frustoconical body  248  with a distal endwall  250  from which extends a nose  252  sized to slidably receive the cannula  216 . For convenience of this description, the handle cap  246  is described as being separate from the handle  214 . However, the handle cap  246  can be considered as part of the handle  214  and can even be integrated with the handle  214 . 
         [0064]    The actuator  220  comprises a cannula mount  260  and a stylet mount  262  that slidably support the cannula  216  and the stylet  218 , respectively, in the handle  214 . The cannula mount  260  includes an elongated cannula support shaft  264  integral with a generally orthogonal annular body  266  with a peripheral wall  274  having a trigger detent  272  formed therein. A pair of legs  269  having a sloped terminal cam surface  270  extends proximally from the annular body  266 . The stylet mount  262  comprises an elongated stylet support shaft  276  integral with a generally orthogonal body  278  having a pair of diametrically opposed resilient arms  280  extending distally from the body  278  on opposite sides of the stylet support shaft  276 . Each arm  280  comprises a proximal sloped stop surface  282  near the body  278  and terminates at an inclined cam follower surface  284 . 
         [0065]    With continued reference to  FIG. 14 , the actuator  220  further comprises a trigger  288  pivotally mounted to the trigger mount  238  of the handle  214 . The trigger  288  includes a proximal finger rest  290  and a downwardly extending projection  292  integral with the finger rest  290 . In addition to the cannula mount  260 , the stylet mount  262 , and the trigger  288 , the actuator  220  comprises a biasing member  293 . According to the illustrated embodiment of the invention, the biasing member  293  is a compression spring. 
         [0066]    The cannula  216  is generally hollow and comprises a distal end  294  defining a tip  296  and a proximal end  298  mounted to the cannula support shaft  264  of the cannula mount  260 . The tip  296  is preferably pointed for insertion through skin and into the tissue mass; however, the tip  296  can optionally be blunt, for example, if the marking apparatus  210  is utilized with a probe or the like. Preferably, the cannula  216  is a 17-gage (0.058 inch outer diameter) cannula, with an inner diameter ranging from 0.049 to 0.051 inches. Furthermore, the distal end  294  of the cannula  216  can be designed for enhanced visibility using common imaging techniques, such as radiography, ultrasonography, and magnetic resonance imaging (MRI), similar to the first embodiment cannula  16 . The cannula  216  slidingly receives the stylet  218 , which comprises a distal end  295  located in the cannula  216  and a proximal end  297  mounted to the stylet support shaft  276  of the stylet mount  262 . Prior to use of the marking device  210 , the distal end  295  of the stylet  216  is spaced inwardly from the tip  296  to form a marker recess  299  for housing the imaging marker  212 . 
         [0067]    When the marking device  210  is in an assembled condition, as shown in  FIG. 14 , the stylet mount  262  is mounted in the hollow interior  244  adjacent the stops  245  with the stop surfaces  282  on the arms  280  abutting the stops  245  on the handle  214  to prevent proximal movement of the stylet mount  262  in the hollow interior  244 . The stylet  218  extends from the stylet support shaft  270 , through the cannula support shaft  264  of the cannula mount  260 , which is located distally of the stylet mount  262  in the hollow interior  244 , and out the distal end  232  of the handle  214  through the nose  252  of the handle cap  246 . The cannula mount  260  is positioned so that the cannula  216  also leaves the distal end  232  of the handle  214  through the nose  252  of the handle cap  246 . The trigger projection  292  resides in the trigger detent  272  of the cannula mount  260  to prevent proximal movement of the cannula mount  260  by the biasing member  293 , which is positioned between the distal end wall  250  of the handle cap  246  and the body  266  of the cannula mount  260 . The relative positioning of the cannula mount  260  and the stylet mount  262  is such that the former is spaced from the latter in the hollow interior  244 , and the distal end  295  of the stylet  218  is spaced from the tip  296  to form the marker recess  299 . In this condition, the cannula  216  is in an extended position where it extends from the distal end  232  of the handle  214 , and the stylet  218  is in a ready position in the extended cannula  216 . 
         [0068]    Referring now to  FIG. 15 , the cannula  216  is slidably movable in the hollow interior  244  relative to the stylet  218  in a proximal direction to expose the imaging marker  212 . Retraction of the cannula  216  occurs when the projection  292  of the trigger  288  is removed from the trigger detent  272  on the cannula mount  260  by pivotal movement of the trigger finger rest  290 . When the trigger  288  releases the cannula mount  260 , the biasing member  293  forces the cannula mount  260  and thereby the cannula  216  proximally to a first retracted position, shown in  FIG. 15 , to expose the imaging marker  214 . 
         [0069]    After exposing the imaging marker  212 , the cannula  216  continues to retract into the handle  214 , and the cannula mount  260  contacts the stylet mount  262 , as shown in  FIG. 16 . In particular, the proximally extending legs  269  of the cannula mount  260  contact the distally extending arms  280  of the stylet mount  262 . The cam surfaces  270  of the legs  269  contact the corresponding cam follower surfaces  284  of the arms  280  to deflect the arms  280  radially inward. As a result, the stop surfaces  282  deflect inward such that the stops  245  no longer prevent proximal movement of the stylet mount  262 , and the stylet mount  262  and thereby the stylet  218  can retract with the cannula mount  260  and the cannula  218 , as shown in  FIG. 17 . Preferably, the cannula mount  260  and the stylet mount  262  are spaced to ensure that the distal end  294  of the cannula  216  is adjacent to or extends proximally of the tip  296  for eliminating the marker recess  299  (i.e., the stylet distal end  295  is located at or extends beyond the tip  296 ). Thus, retraction of the stylet  218  is delayed until the cannula  218  has been sufficiently retracted relative to the stylet  218 . If the marker recess  299  is present during simultaneous retraction of the cannula  216  and the stylet  218 , tissue or the imaging marker  212  can potentially be undesirably drawn in to the marker recess  299 . 
         [0070]    Proximal movement of the cannula mount  260  and the stylet mount  262  retracts the cannula  216  and the stylet  218  into the hollow interior  244  to a second retracted position and a withdrawn position, respectively. Proximal movement of the cannula mount  260  and the stylet mount  262  ceases when the stylet mount  262  abuts the proximal stop  268 . Preferably, when the cannula  216  is in the retracted position, the entire cannula  216 , including the tip  296 , is received within the handle  214 . Similarly, the entire stylet  218  is preferably received within the handle  214  when in the withdrawn position, but it within the scope of the invention for the distal end  295  to project from the nose  252  when the stylet  218  is in the withdrawn position. 
         [0071]    In operation, a practitioner grasps the marking device  210  and inserts the cannula tip  296  through the skin of patient&#39;s body into a tissue mass. The practitioner places the tip  296  typically under the guidance of aforementioned imaging systems at or near a predetermined site, such as a biopsy site. Once the cannula tip  296  is at the predetermined site, the practitioner places an index finger or other suitable finger on the finger rest  290  of the trigger  288  and pivots the trigger  288  to move the trigger  288  from a locked position of  FIG. 14  to a cannula retract position of  FIG. 15  to move the cannula  218  from the extended position of  FIG. 14  to the first retracted position of  FIG. 15 , whereby the imaging marker  212  becomes exposed to the predetermined site, and the second retracted position of  FIG. 17 , whereby the cannula  218  retracts entirely into the handle  214 . As described above, retraction of the cannula  218  from the first retracted position to the second retracted position also retracts the stylet from the ready position of  FIGS. 14-16  to the withdrawn position of  FIG. 17  to remove the stylet  218  along with the cannula  216  from the tissue mass as they retract into the handle  214 . As in the first embodiment marking device  10 , with the cannula  216  retracted into the handle  214 , the practitioner cannot accidentally stab himself or herself, others assisting with the procedure, or the patient with the marking device  210  following implantation of the imaging marker  212 . 
         [0072]    While the embodiments of the marking device  10 ,  210  according to invention have been shown and described as comprising an actuator that automatically retracts the cannula and the stylet, such as by force of a biasing element, the actuator can alternatively move the cannula and the stylet manually. For example, the actuator can comprise a slide operably coupled to the cannula mount, and proximal movement of the slide by the user can retract the cannula and the stylet or the cannula alone into the handle. The actuator can comprise a single actuator to effect movement of the cannula and the stylet or, alternatively, individual actuators for the cannula and the stylet. Further, while the first embodiment of the marking device  10  according to invention has been shown and described as comprising an actuator that manually advances the stylet to eject the imaging marker from the marker recess, the actuator can alternatively automatically advance the stylet, such as under the force of a biasing member. 
         [0073]    The marking device according to the invention accurately implants the imaging marker at the predetermined site and, due to the retraction of the cannula into the handle, is safe to use. With the tip of the cannula retracted into the handle, the potential for the practitioner to injure himself/herself or others is eliminated. As a result, the practitioner can focus on the implanting procedure and does not have to be concerned with safety while withdrawing the marking device from the patient. Additionally, the actuator is easy to use and facilitates accurate implantation of the imaging marker. 
         [0074]    While the embodiments of the marking device according to the invention have been shown and described with respect to implanting a single imaging marker, it is within the scope of the invention for the marking device to implant multiple imaging markers, either at the same location or different locations in the tissue mass. Additionally, the biasing element of the actuator is not limited to a spring, as shown and described in the above embodiments. It is within the scope of the invention to employ other types of baising elements. For example, the biasing element can comprise a source of compressed gas so that the stylet is advanced with air pressure, and the cannula and the stylet are retracted with a decrease in air pressure. Another example of a biasing element is a electric coil powered by a battery, and the coil in an energized size deploys the stylet and in de-energized state retracts the cannula and the stylet. 
         [0075]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.