Patent Publication Number: US-10327805-B2

Title: Biopsy cannula adjustable depth stop

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 12/368,317, “BIOPSY CANNULA ADJUSTABLE DEPTH STOP” to Hibner et al., filed on Feb. 10, 2009, issued as U.S. Pat. No. 9,433,401 on Aug. 17, 2016, which is a Divisional of U.S. patent application Ser. No. 11/414,988, “BIOPSY CANNULA ADJUSTABLE DEPTH STOP” to Hibner et al., filed on May 1, 2006, issued as U.S. Pat. No. 7,507,210 on Mar. 24, 2009. 
     The present application is related to the co-pending and commonly-owned U.S. patent application Ser. No. 11/415,467, “GRID AND ROTATABLE CUBE GUIDE LOCALIZATION FIXTURE FOR BIOPSY DEVICE” to Hibner et al., filed on May 1, 2006, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to biopsy devices, and more particularly to biopsy devices having a cutter for severing tissue, and even more particularly to a localization and guidance fixture that guides insertion of a probe, or a sleeve that subsequently receives the probe of a biopsy device. 
     BACKGROUND OF THE INVENTION 
     When a suspicious tissue mass is discovered in a patient&#39;s breast through examination, ultrasound, MRI, X-ray imaging or the like, it is often necessary to perform a biopsy procedure to remove one or more samples of that tissue in order to determine whether the mass contains cancerous cells. A biopsy may be performed using an open or percutaneous method. 
     An open biopsy is performed by making a large incision in the breast and removing either the entire mass, called an excisional biopsy, or a substantial portion of it, known as an incisional biopsy. An open biopsy is a surgical procedure that is usually done as an outpatient procedure in a hospital or a surgical center, involving both high cost and a high level of trauma to the patient. Open biopsy carries a relatively higher risk of infection and bleeding than does percutaneous biopsy, and the disfigurement that sometimes results from an open biopsy may make it difficult to read future mammograms. Further, the aesthetic considerations of the patient make open biopsy even less appealing due to the risk of disfigurement. Given that a high percentage of biopsies show that the suspicious tissue mass is not cancerous, the downsides of the open biopsy procedure render this method inappropriate in many cases. 
     Percutaneous biopsy, to the contrary, is much less invasive than open biopsy. Percutaneous biopsy may be performed using fine needle aspiration (FNA) or core needle biopsy. In FNA, a very thin needle is used to withdraw fluid and cells from the suspicious tissue mass. This method has an advantage in that it is very low-pain, so low-pain that local anesthetic is not always used because the application of it may be more painful than the FNA itself. However, a shortcoming of FNA is that only a small number of cells are obtained through the procedure, rendering it relatively less useful in analyzing the suspicious tissue and making an assessment of the progression of the cancer less simple if the sample is found to be malignant. 
     During a core needle biopsy, a small tissue sample is removed allowing for a pathological assessment of the tissue, including an assessment of the progression of any cancerous cells that are found. The following patent documents disclose various core biopsy devices and are incorporated herein by reference in their entirety: U.S. Pat. No. 6,273,862 issued Aug. 14, 2001; U.S. Pat. No. 6,231,522 issued May 15, 2001; U.S. Pat. No. 6,228,055 issued May 8, 2001; U.S. Pat. No. 6,120,462 issued Sep. 19, 2000; U.S. Pat. No. 6,086,544 issued Jul. 11, 2000; U.S. Pat. No. 6,077,230 issued Jun. 20, 2000; U.S. Pat. No. 6,017,316 issued Jan. 25, 2000; U.S. Pat. No. 6,007,497 issued Dec. 28, 1999; U.S. Pat. No. 5,980,469 issued Nov. 9, 1999; U.S. Pat. No. 5,964,716 issued Oct. 12, 1999; U.S. Pat. No. 5,928,164 issued Jul. 27, 1999; U.S. Pat. No. 5,775,333 issued Jul. 7, 1998; U.S. Pat. No. 5,769,086 issued Jun. 23, 1998; U.S. Pat. No. 5,649,547 issued Jul. 22, 1997; U.S. Pat. No. 5,526,822 issued Jun. 18, 1996; and US Patent Application 2003/0199753 published Oct. 23, 2003 to Hibner et al. 
     In U.S. Pat. Appln. Publ. No. 2005/0283069A1, “MRI biopsy device localization fixture” to Hughes et al., the disclosure of which is hereby incorporated by reference in its entirety, a localization mechanism, or fixture, is described that is used in conjunction with a breast coil for breast compression and for guiding a core biopsy instrument during prone biopsy procedures in both open and closed Magnetic Resonance Imaging (MRI) machines. The localization fixture includes a three-dimensional Cartesian positionable guide for supporting and orienting an MRI-compatible biopsy instrument, and, in particular, a sleeve to a biopsy site of suspicious tissues or lesions. 
     A z-stop enhances accurate insertion, and prevents over-insertion or inadvertent retraction of the sleeve. In particular, the Z-stop is engaged to the localization fixture at a distance from the patient set to abut a handle of the biopsy device as an attached biopsy probe reaches the desired depth. Similarly, another biopsy cannula may be a sleeve with a hub corresponding to a handle that contacts the z-stop. 
     While such a localization fixture with a depth stop feature provides clinical advantages, some surgeons may prefer other types of methods of positioning a biopsy probe or similar biopsy cannula. For instance, some clinicians may prefer a manually guided biopsy probe, such as when being directed by on-going diagnostic imaging (e.g., ultrasonic). It would thus be desirable to incorporate preventing over-insertion of a biopsy probe when not employing a three-axis insertion guidance apparatus. 
     SUMMARY OF THE INVENTION 
     The present invention addresses these and other problems of the prior art by providing an apparatus and method for use of a depth stop device longitudinally positioned on a biopsy cannula prior to insertion into tissue. The depth stop device advantageously has an unlocked condition that allows positioning followed by a locking condition such that inadvertent over-insertion is affirmatively blocked. Thereby, even manual insertion of a biopsy device or trocar/sleeve has the benefits of guided procedures to prevent overshooting with a piercing tip of the biopsy cannula. 
     In one aspect of the invention, a device serves as the depth stop by presenting a guiding portion that substantially circumferentially encompasses a shaft of a biopsy cannula. A locking portion moves into binding engagement with the biopsy cannula when at a desired longitudinal position thereon. A transverse portion of the device precludes over insertion by coming into abutment with the skin of the patient or some proximate structure that localizes the body portion being biopsied. 
     In another aspect of the invention, a biopsy cannula has measurement indicia that aids in longitudinal positioning of a depth stop device, the measurement indicia being representative of depth of penetration achieved thereby. 
     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 
       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: 
         FIG. 1  is an isometric view of a biopsy system including a control module remotely coupled to a biopsy device, and including a localization fixture with a lateral grid plate used in conjunction with a rotatable cube to position a trocar/obturator or a probe of the biopsy device to a desired insertion depth as set by a ring stop. 
         FIG. 2  is an isometric view of the breast coil receiving the localization fixture of  FIG. 1 . 
         FIG. 3  is an isometric view of the biopsy device inserted through the rotatable cube within the cube plate of the localization fixture attached to a breast coil of  FIG. 1 . 
         FIG. 4  is an isometric view of a two-axis rotatable guide cube of the biopsy system of  FIG. 1 . 
         FIG. 5  is a diagram of nine guide positions achievable by the two-axis rotatable guide cube of  FIG. 5 . 
         FIG. 6  is an isometric view of a two-axis rotatable guide cube inserted into a lateral grid with the backing of the localization fixture of  FIG. 1 . 
         FIG. 7  is an isometric view of the trocar and sleeve of the biopsy system of  FIG. 1 . 
         FIG. 8  is an isometric exploded view of the trocar and sleeve of  FIG. 7 . 
         FIG. 9  is an isometric view of a trocar and sleeve of  FIG. 7  with a depth stop device of  FIG. 1  inserted through the guide cube and grid plate of  FIG. 6 . 
         FIG. 10  is an alternative guide cube for the biopsy system of  FIG. 1  with two-axes of rotation and self-grounding features. 
         FIG. 11  is an isometric view of the trocar and sleeve of  FIG. 7  inserted into one of two guide cubes of  FIG. 10  inserted into the grid plate of  FIG. 1 . 
         FIG. 12  is an aft isometric view of a further alternative guide cube with four angled, parallel guide holes for the biopsy system of  FIG. 1 . 
         FIG. 13  is a front isometric view of the guide cube of  FIG. 12 . 
         FIG. 14  is a right side view of the guide cube of  FIG. 12  with the angled, parallel guide holes depicted in phantom. 
         FIG. 15  is an aft view in elevation of yet another alternative guide cube for the biopsy system of  FIG. 1  with a pair of converging guide holes and a pair of diverging guide holes. 
         FIG. 16  is a left side view of the guide cube of  FIG. 15  taken in cross section along lines  16 - 16  through the pair of converging guide holes. 
         FIG. 17  is a left side view of the guide cube of  FIG. 15  taken in cross section along lines  17 - 17  through the pair of diverging guide holes. 
         FIG. 18  is an isometric view of a two hole guide cube for the biopsy system of  FIG. 1 . 
         FIG. 19  is an isometric view of a one-hole guide cube for the biopsy system of  FIG. 1 . 
         FIG. 20  is a rotating guide for guiding the trocar and sleeve of  FIG. 7  into either of the two-hole guide cube of  FIG. 18  or the one-hole guide cube of  FIG. 19 . 
         FIG. 21  is an aft isometric view of the trocar and sleeve of  FIG. 7  inserted through the rotating guide of  FIG. 20  into the two-hole guide cube of  FIG. 18 . 
         FIG. 22  is an isometric locking O-ring for the biopsy system of  FIG. 1 . 
         FIG. 23  is an aft view of the locking O-ring of  FIG. 22  with a cross section of a biopsy instrument cannula shown in both an unlocked orientation and rotated a quarter turn into a locked orientation depicted in phanton. 
         FIG. 24  is an isometric view of a cylindrical rotating guide formed of elastomeric material with an oval through hole for the biopsy system of  FIG. 1 . 
         FIG. 25  is an aft view of the cylindrical rotating guide of  FIG. 24  with a cross sectional view of an unlocked oval-shaped biopsy instrument cannula inserted in the oval through hole. 
         FIG. 26  is an aft view of the cylindrical rotating guide and biopsy instrument cannula of  FIG. 25  with the cylindrical rotating guide rotated a quarter turn relative to the cannula to elastomerically lock thereon. 
         FIG. 27  is an isometric view of a flattened oval rotating guide for the biopsy system of  FIG. 1 . 
         FIG. 28  is an isometric view of a triangular clip depth stop for the biopsy system of  FIG. 1 . 
         FIG. 29  is an isometric view of a scissor-like depth stop clip for the biopsy system of  FIG. 1 . 
         FIG. 30  is an aft isometric view of a shutter depth stop with an inserted biopsy instrument cannula for the biopsy system of  FIG. 1 . 
         FIG. 31  is an aft view of the shutter depth stop of  FIG. 30  prior to use. 
         FIG. 32  is a front isometric view of the shutter depth stop and inserted biopsy instrument cannula of  FIG. 30 . 
         FIG. 33  is an aft view of the shutter depth stop and biopsy instrument cannula of  FIG. 30  with the shutter depth stop vertically compressed into an unlocked state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to the Drawings, wherein like numerals denote like components throughout the several views, in  FIGS. 1-3 , a Magnetic Resonance Imaging (MRI) compatible biopsy system  10  has a control module  12  that typically is placed outside of a shielded room containing an MRI machine (not shown) or at least spaced away to mitigate detrimental interaction with its strong magnetic field and/or sensitive radio frequency (RF) signal detection antennas. As described in U.S. Pat. No. 6,752,768, which is hereby incorporated by reference in its entirety, a range of preprogrammed functionality is incorporated into the control module  12  to assist in taking these tissue samples. The control module  12  controls and powers an MRI biopsy device  14  that is positioned and guided by a localization fixture  16  attached to a breast coil  18  that is placed upon a gantry (not shown) of the MRI machine. 
     The control module  12  is mechanically, electrically, and pneumatically coupled to the MRI biopsy device  14  so that components may be segregated that need to be spaced away from the strong magnetic field and the sensitive RF receiving components of the MRI machine. A cable management spool  20  is placed upon a cable management attachment saddle  22  that projects from a side of the control module  12 . Wound upon the cable management spool  20  is a paired electrical cable  24  and mechanical cable  26  for communicating control signals and cutter rotation/advancement motions respectively. In particular, electrical and mechanical cables  24 ,  26  each have one end connected to respective electrical and mechanical ports  28 ,  30  in the control module  12  and another end connected to a reusable holster portion  32  of the MRI biopsy device  14 . An MRI docking cup  34 , which may hold the holster portion  32  when not in use, is hooked to the control module  12  by a docking station mounting bracket  36 . 
     An interface lock box  38  mounted to a wall provides a tether  40  to a lockout port  42  on the control module  12 . The tether  40  is advantageously uniquely terminated and of short length to preclude inadvertent positioning of the control module  12  too close to the MRI machine. An in-line enclosure  44  may advantageously register the tether  40 , electrical cable  24  and mechanical cable  26  to their respective ports  42 ,  28 ,  30  on the control module  12 . 
     Vacuum assist is provided by a first vacuum line  46  that connects between the control module  12  and an outlet port  48  of a vacuum canister  50  that catches liquid and solid debris. A tubing kit  52  completes the pneumatic communication between the control module  12  and the MRI biopsy device  14 . In particular, a second vacuum line  54  is connected to an inlet port  56  of the vacuum canister  50 . The second vacuum line  54  divides into two vacuum lines  58 ,  60  that are attached to the MRI biopsy device  14 . With the MRI biopsy device  14  installed in the holster portion  32 , the control module  12  performs a functional check. Saline is manually injected into biopsy device  14  to serve as a lubricant and to assist in achieving a vacuum seal. The control module  12  actuates a cutter mechanism (not shown) in the MRI biopsy device  14 , monitoring full travel. Binding in the mechanical cable  26  or within the biopsy device  14  is monitored with reference to motor force exerted to turn the mechanical cable  26  and/or an amount of twist in the mechanical cable  26  sensed in comparing rotary speed or position at each end of the mechanical cable  26 . 
     A remote keypad  62 , which is detachable from the reusable holster portion  32 , communicates via the electrical cable  24  to the control panel  12  to enhance clinician control of the MRI biopsy device  14 , especially when controls that would otherwise be on the MRI biopsy device  14  itself are not readily accessible after insertion into the localization fixture  16  and/or placement of the control module  12  is inconveniently remote (e.g., 30 feet away). An aft end thumbwheel  63  on the reusable holster portion  32  is also readily accessible after insertion to rotate the side from which a tissue sample is to be taken. 
     Left and right parallel upper guides  64 ,  66  of a localization framework  68  are laterally adjustably received respectively within left and right parallel upper tracks  70 ,  72  attached to an under side  74  and to each side of a selected breast aperture  76  formed in a patient support platform  78  of the breast coil  18 . A base  80  of the breast coil  18  is connected by centerline pillars  82  that are attached to the patient support platform  78  between the breast apertures  76 . Also, a pair of outer vertical support pillars  84 ,  86  on each side spaced about a respective breast aperture  76  respectively define a lateral recess  88  within which the localization fixture  16  resides. 
     It should be appreciated that the patient&#39;s breasts hang pendulously respectively into the breast apertures  76  within the lateral recesses  88 . For convenience, herein a convention is used for locating a suspicious lesion by Cartesian coordinates within breast tissue referenced to the localization fixture  16  and to thereafter selectively position an instrument, such as a probe  90  ( FIG. 1 ) of a disposable probe assembly  91  that is engaged to the reusable holster portion  32  to form the MRI biopsy device  14 . To enhance hands off use of the biopsy system  10 , especially for repeated reimaging within the narrow confines of a closed bore MRI machine, the MRI compatible biopsy system  10  may also guide a trocar (“introducer”)  92  encompassed by a sleeve  94 . Depth of insertion is controlled by a depth stop device  95  longitudinally positioned on either the probe  90  or the sleeve  94 . 
     This guidance is specifically provided by a lateral fence, depicted as a grid plate  96 , which is received within a laterally adjustable outer three sided plate bracket  98  attached below the left and right parallel upper guides  64 ,  66 . Similarly, a medial fence with respect to a medial plane of the chest of the patient, depicted as a medial plate  100 , is received within an inner three-sided plate bracket  102  attached below the left and right parallel upper guides  64 ,  66  close to the centerline pillars  82  when installed in the breast coil  18 . To further refine the insertion point of the instrument (e.g., probe  90 , trocar/sleeve  92 ,  94 ), a guide cube  104  is inserted into the backside of the grid plate  96 . 
     The selected breast is compressed along an inner (medial) side by the medial plate  100  and on an outside (lateral) side of the breast by the grid plate  96 , the latter defining an X-Y plane. The X-axis is vertical (sagittal) with respect to a standing patient and corresponds to a left to right axis as viewed by a clinician facing the externally exposed portion of the localization fixture  16 . Perpendicular to this X-Y plane extending toward the medial side of the breast is the Z-axis, which typically corresponds to the orientation and depth of insertion of the probe  90  of the MRI biopsy device  14  or the trocar/sleeve  92 ,  94 . For clarity, the term Z-axis may be used interchangeably with “axis of penetration”, although the latter may or may not be orthogonal to the spatial coordinates used to locate an insertion point on the patient. Versions of the localization fixture  16  described herein allow a nonorthogonal axis of penetration to the X-Y axis to a lesion at a convenient or clinically beneficial angle. 
     In  FIG. 4 , guide cube  104  includes a central guide hole  106 , a corner guide hole  108 , and an off-center guide hole  110  that pass orthogonally to one another between respective opposite pairs of faces  112 ,  114 ,  116 . By selectively rotating the guide cube  104  in two axis, one of the pairs of faces  112 ,  114 ,  116  may be proximally aligned to an unturned position and then the selected proximal face  112 ,  114 ,  116  optionally rotated a quarter turn, half turn, or three quarter turn. Thereby, one of nine guide positions  118  (i.e., using central guide hole  106 ),  120   a - 120   d  (i.e., corner guide hole  108 ),  122   a - 122   d  (i.e., using off-center guide hole  110 ) may be proximally exposed as depicted in  FIG. 5 . 
     In  FIG. 6 , the two-axis rotatable guide cube  104  is sized for insertion from a proximal side into one of a plurality of square recesses  130  in the grid plate  96  formed by intersecting vertical bars  132  and horizontal bars  134 . The guide cube  104  is prevented from passing through the grid plate  96  by a backing substrate  136  attached to a front face of the grid plate  96 . The backing substrate  136  includes a respective square opening  138  centered within each square recess  130 , forming a lip  140  sufficient to capture the front face of the guide cube  104  but not so large as to obstruct the guide holes  104 ,  106 ,  108 . The depth of the square recesses  130  is less than the guide cube  104 , thereby exposing a proximal portion  142  of the guide cube  104  for seizing and extraction from the grid plate  96 . 
     In  FIGS. 7-9 , in the illustrative version, the trocar  92  is slid into the sleeve  94  and the combination is guided through the guide cube  104  ( FIG. 9 ) to the biopsy site within the breast tissue. The sleeve  94  includes a hollow shaft (or cannula)  196  that is proximally attached to a cylindrical hub  198  and has a lateral aperture  200  proximate to an open distal end  202 . The cylindrical hub  198  has an exteriorly presented thumbwheel  204  for rotating the lateral aperture  200 . The cylindrical hub  198  has an interior recess  206  that encompasses a duckbill seal  208 , wiper seal  210  and a seal retainer  212  to provide a fluid seal when the shaft  196  is empty and for sealing to the inserted introducer (trocar)  92 . Longitudinally spaced measurement indicia  213  along an outer surface of the hollow shaft  196  visually, and perhaps physically, provide a means to locate the depth stop device  95  of  FIG. 1 . 
     The trocar  92  advantageously incorporates a number of components with corresponding features. A hollow shaft  214  includes a fluid lumen  216  that communicates between an imagable side notch  218  and a proximal port  220 . The hollow shaft  214  is longitudinally sized to extend, when fully engaged, a piercing tip  222  out of the distal end  202  of the sleeve  94 . An obturator thumbwheel cap  224  encompasses the proximal port  220  and includes a locking feature  226 , which includes a visible angle indicator  228  ( FIG. 8 ), that engages the sleeve thumbwheel  204  to ensure that the imagable side notch  218  is registered to the lateral aperture  200  in the sleeve  94 . An obturator seal cap  230  may be engaged proximally into the obturator thumbwheel cap  224  to close the fluid lumen  216 . The obturator seal cap  230  includes a locking or locating feature  232  that includes a visible angle indicator  233  that corresponds with the visible angle indicator  228  on the obturator thumbwheel cap  224 , which may be fashioned from either a rigid, soft, or elastomeric material. In  FIG. 9 , the guide cube  104  has guided the trocar  92  and sleeve  94  through the grid plate  96 . 
     In  FIGS. 10-11 , an alternative guide cube  104   a  has rotation in two axes but is self grounding by means of an added rectangular prism  240  which has a shared edge with a cubic portion  242  of the guide cube  104   a . When viewed orthogonally to the shared cube edge, a larger square face  244  of the cubic portion  242  overlaps with a smaller square face  246  of the rectangular prism  240  to correspond with the desired size of an exposed proximal portion  248  of the inserted guide cube  104   a . The rectangular prism  240  allows proximal exposure of one of two adjacent faces  250 ,  252  of the guide cube  104   a  and then turning each to one of four quarter turn rotational positions. In the illustrative version, first face  250  has a central guide hole  106   a  and the second face  252  has a corner guide hole  108   a , and an off-center guide hole  110   a . A radial recess  254  is relieved into the rectangular prism  240  to allow grounding of the depth stop device  95  against the face  252  when the off-center guide hole  110   a  is used. 
     In  FIGS. 12-14 , another alternative guide cube  104   b  has a proximal enlarged hat portion  270  about a proximal face  271  that grounds against the selected square recess  130  in the grid plate  96  ( FIG. 6 ) and allows rotation about one axis to one of four quarter turn positions. Four angled guide holes  272   a ,  272   b ,  272   c ,  272   d  allow accessing not only an increased number of insertion points within the selected square recess  130  but also a desired angle of penetration rather than being constrained to a perpendicular insertion. 
     In  FIGS. 15-17 , an additional alternative guide cube  104   c  also has the proximal enlarged hat portion  270  about the proximal face  271  that grounds against the selected square recess  130  in the grid plate  96  ( FIG. 6 ) and allows rotation about one axis to one of four quarter turn positions. The guide holes are depicted as a first pair of converging angled through holes  310   a ,  310   b  having outwardly spaced proximal openings  311   a ,  311   b  ( FIG. 15 ), respectively, that communicate with partially intersecting distal openings  312   a ,  312   b , respectively. The guide holes are also depicted as a second pair of diverging angled through holes  310   c ,  310   d  having partially intersecting proximal openings  311   c ,  311   d , respectively, that communicate with outwardly spaced distal openings  312   c ,  312   d.    
     In  FIG. 18 , a further alternative two-hole guide cube  104   d  has two enlarged guide holes  330 ,  332  accessed through the proximal face  271  in the enlarged proximal hat portion  270 . Similarly, in  FIG. 19 , a one hole guide cube  104   e  has one enlarged guide hole  334  accessed through the proximal face  271  in the enlarged proximal hat portion  270 . Each guide cube  104   d ,  104   e  may receive a cylindrical rotating guide  336  ( FIG. 20 ) with an integral, proximal depth ring stop  338 . In  FIGS. 20, 21 , a through hole  340  in the cylindrical guide  336  is sized to receive a biopsy instrument cannula (e.g., probe  90 , sleeve  94 ) by being oval in cross section in the illustrative version. It should be appreciated that the cylindrical guide  336  may provide structural support to the guided portion of the biopsy instrument support as well as facilitate axial rotation thereof, especially for a non cylindrical biopsy instrument cannula. 
     It should be appreciated that the two-hole and one-hole guide cubes  104   d ,  104   e  and rotating guide  336  may comprise a guide cube set, perhaps with additional guide cubes (not shown) having uniquely positioned guide holes. With the enlarged guide holes  330 - 340  to accommodate the rotating guide  336 , too much overlap of guide holes (e.g.,  330 ,  332 ) may result in insufficient support by the rotating guide  336  for the inserted biopsy instrument cannula. Thus, fine positioning is accomplished by selecting one of the available guide cubes  104   d ,  104   e  for the desired position within a selected grid aperture. 
     In  FIGS. 22, 23 , a locking O-ring feature may be advantageously incorporated into a depth ring stop (rotating guide)  350 . Having to rely upon constant frictional engagement of the depth ring stop (rotating guide)  350  alone would result in difficulty in installing the ring stop  350  to the desired position or being too readily displaced to serve as a stopping structure. In the exemplary version, an outer circumference surface  351  of the ring stop  350  includes left and right outer longitudinal ridges  352 ,  354  that aid in gripping and orienting the depth ring stop  350  while turning for locking and unlocking. As viewed from behind, opposing inner longitudinal ridges  356 ,  358  formed in a generally cylindrical inner diameter  359  abut respectively at an upper left and lower right side of an oval cannula  360  ( FIG. 23 ) oriented with its elongate cross section vertically in an unlocked position. The inner longitudinal ridges  356 ,  358  allow a quarter turn clockwise of the oval cannula, depicted as  360 ′, to a locked position deforming an inner tangential locking rib  362 . 
     It should be appreciated that these orientations and geometry are illustrative. An amount of rotation to lock and unlock, for instance, may be less than or more than a quarter turn. In addition, noncircular features on an outer diameter of the depth ring stop  350  may be omitted. Other variations may be employed. For example, in  FIGS. 24-25 , a cylindrical rotating guide  380 , formed of a resilient polymer, has an elongate through hole  382  shaped to permit insertion of an oval biopsy cannula  384 . In  FIG. 26 , turning the cylindrical rotating guide  380  a quarter turn in either direction to a locked position, depicted at  380 ′, causes the cylindrical rotating guide  380 ′ to deform, binding onto the biopsy instrument cannula  384 , thereby serving as a depth stop. 
     Similarly, in  FIG. 27 , a rotating guide  400  is oval shaped with flattened elongate sides and with a corresponding elongate through hole  402 . The outer shape may be tactile, advantageous for gripping as well as for providing a visual indication of being locked or unlocked. A resilient tangential rib  404  crossing one inner corner of the elongate through hole  402  is positioned to bind against an inserted biopsy instrument cannula (not shown) when the rotating guide  400  is turned a quarter turn to a locking position. 
     In  FIG. 28 , a triangular clip depth stop  420  has a transverse front surface  422  with a proximally turned lower lip  424  and an upper lateral edge  426  attached to a downwardly and proximally ramped member  428  whose lower lateral edge  430  bends distally to form a horizontal locking actuator member  432  whose distal edge  434  rests upon the lower lip  424 . A front vertically elongate aperture  436  in the transverse front surface  422  is shaped to approximate the outer diameter of an inserted biopsy instrument cannula (not shown). An aft elongate aperture  438  formed in the downwardly and proximally ramped member  428  is a distal horizontal projection of the front vertically elongate aperture  436  when the locking actuator member  432  is upwardly raised, thus allowing insertion of the biopsy instrument cannula through both apertures  436 ,  438 . Upon release of the locking actuator member  432 , an upper inner surface  440  of the aft elongate aperture  438  lowers, binding upon the inserted biopsy instrument cannula, allowing the transverse front surface  422  to serve as a positive depth stop. 
     In  FIG. 29 , a scissor-like clip depth stop  450  is cut out of a layer of resilient material. In particular, an upper arm portion  452  and a lower arm portion  454  are attached to one radiating vertically away from each other toward the same lateral side (right as depicted) from a split cylindrical grasping portion  456  separated longitudinally on a lateral side opposite to the arm portions  452 ,  454  (left as depicted). In particular, an upper gripping half-cylindrical member  458  is attached at its right side to a lower portion  460  of the upper arm portion  452 . A lower gripping half-cylindrical member  462  is attached at its right side to an upper portion  464  of the lower arm portion  454 . An upper hemispheric portion  466  of the upper arm portion  452  includes an upper finger hole  468 . A lower hemispheric portion  470  of the lower arm portion  454  includes a lower finger hole  472 . A triangular recess  474  (opening rightward as depicted) formed by the arm portions  452 ,  454  and a longitudinal pin  476  inserted at the juncture between the arm portions  452 ,  454  predispose the arm portions  452 ,  454  to be resiliently drawn toward each other as the finger holes  468 ,  472  are gripped and moved together, thereby opening the upper and lower gripping half cylindrical members  458 ,  462 , widening the separation of their left ends. In this unlocked position, a biopsy instrument cannula (not shown) may be inserted and positioned to a desired depth. 
     In  FIG. 30-33  a shuttered depth stop  600  includes a resilient oval shell  602  with a corresponding oval aperture  604  with an upper right tab  606  projecting inwardly to the left and with a lower left tab  608  projecting inwardly to the right when viewed from behind ( FIG. 30 ). An upper resilient member  610  has a generally horseshoe-shaped outer surface  612  that conforms to an upper portion  614  of the oval aperture  604 . A lower resilient member  616  has a generally horseshoe-shaped outer surface  618  that conforms to a lower portion  620  of the oval aperture  604 . In the illustrative version, the upper and lower resilient members  610 ,  616  are identical but are rotated a half turn about a longitudinal axis with respect to each other. Moreover, the entire shuttered depth stop  600  is symmetric about its vertical axis defined by its longest dimension or about a horizontal axis defined by its second longest dimension. 
     A downwardly open rectangular prismatic recess  622  formed in the upper resilient member  610  is sized to receive an upper shutter  624  having an upper center tab  626  and a lower acute edge  628 . A top center rectangular slot  630  formed in the upper resilient member  610  communicates with the downwardly open rectangular prismatic recess  622  and receives the upper center tab  626 . An upwardly open rectangular prismatic recess  632  formed in the lower resilient member  616  is sized to receive a lower shutter  634  having a lower center tab  636  and an upper acute edge  638 . A bottom center rectangular slot  639  formed in the lower resilient member  616  communicates with the upwardly open rectangular prismatic recess  632  and receives the lower center tab  636 . An upper horizontal pin  640  attached horizontally as depicted across the upper shutter  624  is received for rotation onto opposite lateral sides of the downwardly open rectangular prismatic recess  622 . A lower horizontal pin  642  attached horizontally as depicted across the lower shutter  634  is received for rotation onto opposite lateral sides of the upwardly open rectangular prismatic recess  632 . 
     The right side of the upper resilient member  610  includes a right outward shoulder  644  that rests upon the upper right tab  606  of the resilient oval shell  602 . A laterally recessed downward arm  646  is attached to the right shoulder  644  and extends downwardly with its outer surface  648  vertically aligned with an innermost edge  650  of the right outward shoulder  644  and with its inner surface  652  defining the downwardly open generally rectangular prismatic recess  622 . The left side of the upper resilient member  610  includes a left inward shoulder  654  that is laterally aligned with and opposite of the upper right tab  606  of the resilient oval shell  602 . An outer downward arm  656  is attached to the left inward shoulder  654  and extends downwardly with its outer surface  658  against oval aperture  604  and an innermost edge  660  vertically aligned with an inner surface  662  of the lower left tab  608  upon which the outer downward arm  656  rests. 
     Similarly, the lower resilient member  616  includes a left outward shoulder  664  attached to a laterally recessed upward arm  666  and a right inward shoulder  668  attached to an outer upward arm  670  that abuts an underside of the upper right tab  606 . The laterally recessed downward arm  646  of the upper resilient member  610  extends downward past the longitudinal centerline of the shuttered depth stop  600  and an inserted biopsy instrument cannula  672 . A lower edge  674  of the laterally recessed downward arm  646  is spaced away from an upper surface  676  of the right inward shoulder  668 . In addition, an upper edge  678  of the laterally recessed upward arm  666  is spaced away from a lower surface  680  of the left inward shoulder  654 . When the resilient oval shell  602  is relaxed as in  FIGS. 30-32 , this spacing between the left inward shoulder  654  and the upper edge  678  of the laterally recessed upward arm  666  defines an upper left rectangular recess  682  communicating rightward into the downwardly open rectangular prismatic recess  622  and sized to allow unimpeded swinging of a leftward extension  684  of the upper shutter  624 . Spacing between the upper surface  676  of the right inward shoulder  668  and the lower edge  674  of the laterally recessed downward arm  646  defines a lower right rectangular recess  686  which communicates leftward into the upwardly open rectangular prismatic recess  632  which is sized to allow unimpeded swinging of a rightward extension  688  of the lower shutter  634 . 
     In  FIG. 31 , the shuttered depth stop  600  initially has closed upper and lower shutters  624 ,  634  due to restoring pressure from the top center rectangular slot  630  on the upper center tab  626  and from the bottom center rectangular slot  639  on the lower center tab  636  respectively. Insertion of a biopsy instrument cannula  672  from a selected side (thus the aft side) causes the upper and lower acute edges  628 ,  638  of the shutters  624 ,  634  to swing distally and outwardly but remain in contact due to the restoring pressure previously mentioned. Proximal retraction of the biopsy instrument cannula  672  frictionally rotates the acute edges  628 ,  638  proximally, and thus inwardly, binding upon the biopsy instrument cannula  672  preventing inadvertent retraction to serve as a depth stop. When retraction is desired, squeezing the resilient oval shell  602  to reduce the vertical height of the shutter depth stop  600  in  FIG. 33  causes the laterally recessed downward arm  646  to open the lower shutter  634  and the laterally recessed upward arm  666  to open the upper shutter  624 . 
     Alternatively, it should be appreciated that a single shutter may be employed in a shuttered depth stop consistent with aspects of the invention. As a further alternative or as an additional feature, grooves in the biopsy cannula may enhance engagement of one or two shutters to further avoid inadvertent proximal retraction of the positioned shuttered depth stop. Moreover, the grooves on the biopsy cannula may be ramped such that engagement is more prevalent against proximal retraction as compared to distal positioning. Further, such grooves may be along only a portion of the circumference of the biopsy cannula such that rotation of the shuttered depth stop also further unlocks from the biopsy cannula for positioning. 
     It should be appreciated with the benefit of the present disclosure that straight upper and lower acute edges  628 ,  638  of the two shutters  624 ,  634  may instead be contoured to closely approximate the transverse cross section of the encompassed shuttered depth stop  600  to increase the locking against inadvertent retraction. 
     While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art. 
     For example, other imaging modalities may benefit from aspects of the present invention. 
     It should be appreciated that a grid plate  96  with a backing lip  140  may be used such that a guide cube rotatable to each of the six faces with four quarter turn positions for each face may achieve a large number of possible insertion positions and angles of insertion. 
     It should be appreciated that any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material. 
     It should be appreciated that various directional terms such as horizontal, vertical, left, right, downward, upward, etc. have been used in conjunction with the orientation of depictions in the drawings. Applications consistent with the present invention may include usage of like components in other orientations. 
     It should be appreciated that biasing of the locking/unlocking components of various versions of a depth stop for a biopsy cannula described herein are advantageously formed out of an elastomeric material for economical manufacture. However, an assembly of rigid components biased by springs for biasing and/or actuating controls to move the locking surface out of engagement may be substituted to achieve similar results consistent with aspects of the present invention. 
     For example, the positioning and height of a central web of a breast coil may enable use of a medial grid plate used with a rotatable cube and penetrate from the medial side of the breast. For another example, a grid having a different geometric shape, such as hexagonal, may be employed. 
     As another example, each grid aperture of equilateral polygonal lateral cross section in a grid plate taper toward their distal opening to ground a similarly tapered guide block.