[0001]    This invention relates to a surgical tool for use in MR imaging. 
       BACKGROUND OF THE INVENTION 
       [0002]    Traditional surgery relies on the physician&#39;s surgical skills and dexterity and ability to localize structures in the body. Surgical robots have recently been developed to address the physical human issues such as fatigue and tremor in procedures. These systems were specifically developed for Minimally Invasive Surgery (MIS) or “key-hole” general surgery, orthopaedics and stereotactic neurosurgery. 
         [0003]    Surgical robots have the potential to increase the consistency and quality of neurosurgery, and when used in conjunction with the advanced diagnostic imaging capabilities of MRI, can offer dramatic improvements. The Intuitive Surgical Inc. da Vinci and Computer Motion ZEUS robots are examples of MIS robots. 
         [0004]    Unfortunately, there are no surgical robots that uses updated or real time MRI patient data to achieve accurate image-guided surgery. MR provides excellent soft tissue contrast for brain surgery and angiography. However MR can be expensive; can be slow to image; limits the tools that can be used which must be MR compatible; requires RF quiet environment; line of sight limits for in-bore use; and mounts a large object in the OR. 
         [0005]    Given the superior tissue contrast provided by MR, there is clinical motivation to use MR images to guide surgical actions. 
         [0006]    Note that: “The interventional MRI safety issues that exist for a surgical instrument include unwanted movement caused by magnetic field interactions (i.e., the missile effect), heating generated by radiofrequency (RE) power deposition, and artifacts associated with the use of the instrument, if it is in the imaging area of interest during its intended use.” See Shellock—JOURNAL OF MAGNETIC RESONANCE IMAGING 13:152-157 (2001). 
         [0007]    Uses of neurosurgical tools, such as those used in the present invention, include: dissecting/tissue manipulation, cutting, ablation/cauterizing, biopsy, aspiration. For example, biopsies acquire a small portion of tissue of interest from a specific region in a patient. The biopsy procedure is termed stereotactic due to the precise localization with which the sample is obtained. Multiple biopsies may be taken from a single patient. 
         [0008]    In U.S. Pat. No. 7,156,316 (Sutherland et al) issued Dec. 26, 2006 discloses a surgical tool for use in an MR imaging system but discloses that the tool should be manufactured of titanium which is well known for use in the high magnetic field and high RF field associated with MR. This tool is particularly designed for use in relation to a Robotic surgical device. The disclosure of this patent is hereby incorporated herein by reference. 
         [0009]    The present invention relates to a tool for use in an MR imaging system and may be used in a robotic surgical system of the type disclosed in the above patent or may be used in a manual system where the tool is manipulated by the surgeon, often using guidance systems. 
         [0010]    In U.S. Pat. No. 7,391,173 (Schena) issued Jun. 24, 2008 and assigned to Intuitive Surgical is disclosed an actuation system for a surgical tool which includes first and second motor driven capstans for operating a cable drive to the tool head. 
         [0011]    In US published application 2008/0009838 (Schena) published Jan. 10, 2008 and assigned to Intuitive Surgical is disclosed an actuation system for a surgical tool which includes a compact capstan system. 
         [0012]    In US published application 2010/0082041 (Prisco) published Apr. 1, 2010 and assigned to Intuitive Surgical is disclosed an actuation system for a surgical tool which includes a motor driven capstan system with a tendon driven by the capstan and having an end attached to a passive pre-load system. 
       SUMMARY OF THE INVENTION 
       [0013]    It is one object of the invention to provide a surgical tool for use in MR imaging. 
         [0014]    According to one aspect of the invention there is provided a surgical tool for use on a patient in an MR Imaging system comprising: 
         [0015]    a tool support member; 
         [0016]    the tool support member having a first end carrying an operating device for carrying out a procedure on a part of the patient; 
         [0017]    the tool support member having a second end including an actuation device for actuating the operating device; 
         [0018]    the tool being formed of a material which:
       has a minimal impact on MR images due to the lack of MR spin signal in the material;   is non-ferromagnetic so as to be unresponsive to a magnetic field of the MR imaging system;   is non-conductive of electric current so as to be unresponsive to an RF field of the MR imaging system so as to avoid heating of the tool by the RF field;   has selected components having a magnetic susceptibility which is substantially equal to that of human tissue.       
 
         [0023]    In one arrangement, the actuation device is arranged to be actuated by an end effector of a robot. However the actuation device can also be arranged to be actuated manually. 
         [0024]    Preferably there is provided a force limiting component arranged to limit force applied to the operating device by the actuation device to a predetermined maximum force. 
         [0025]    Preferably the force limiting component includes a drive transfer member which allows slippage of drive from the actuation device to the operating device. 
         [0026]    Preferably the drive transfer member comprises an elongate band movable along its length by the actuation device, wherein the band is arranged to slip on a drive coupling around which it is wrapped. 
         [0027]    Preferably the drive coupling is connected to the operating device for movement thereof between different positions thereof for carrying out the procedure on the part of the patient. 
         [0028]    Preferably the elongate member is driven along its length by rotary capstan member at the actuation device around which the band is wrapped where the capstan member is rotated by a crank driven by movement of an engagement device longitudinally of the tool support member. 
         [0029]    Preferably the crank engages one of inner and outer coaxial members with the capstan member housed within a housing connected to the other of the inner and outer coaxial members. 
         [0030]    Preferably the capstan member is biased along the tool head relative to the housing by a pair of springs engaged between the housing and an axle of the capstan member. 
         [0031]    Preferably the capstan member is driven by an actuation method that does not depend on electricity. 
         [0032]    Preferably the tool support member is carried on a tool holder and wherein there is provided a force limiting component arranged to limit bending force applied to the tool support member by the tool holder to a predetermined maximum force. 
         [0033]    Preferably the joint in the tool support member is pulled into engagement of the parts in the straight position by a band extending along the tool support member which extends against a spring tension to allow longitudinal movement of the parts into the bent position. 
         [0034]    Preferably movement of the band operates the operating device. 
         [0035]    Preferably the band extends along a hollow interior of the tool support member. 
         [0036]    Preferably the tool support member and the operating device are formed at least in part of a ceramic material. 
         [0037]    Preferably the ceramic material comprises a material selected from the group consisting of Yttrium zirconia, types of alumina, silicon nitride, and alloys thereof and which have a magnetic susceptibility substantially equal to that of human tissue. 
         [0038]    Preferably the magnetic susceptibility of the material of the tool support member adjacent to and touching human tissue is substantially equal to that of human tissue 
         [0039]    Preferably the operating device is driven by the actuation device through an actuation method that does not depend on electricity that could pose a safety hazard to the patient or that might introduce RF noise. 
         [0040]    Preferably the biopsy tool includes a biopsy sample acquisition method that does not rely on sharp edges of a jaw. 
         [0041]    Preferably the biopsy tool the operating device comprises a biopsy tool which includes cooperating jaws having a fixed jaw and a movable jaw, one of the jaws having a raised contact area fully surrounding a cup for receiving a biopsy sample with the contact area arranged to engage a cooperating surface of the other of the jaws, the jaws being arranged to provide an even application of closing force around the contact area between the jaws. 
         [0042]    Preferably said raised contact area arranged to engage a planar cooperating surface of the other of the jaws so that the raised contact area forms a cutting edge on the planar surface. 
         [0043]    Preferably the planar surface includes a cup facing the cup of said one jaw. 
         [0044]    The arrangement described herein is primarily for use as a biopsy tool for use in a MRI scanner. However the features described herein can be applied to other surgical robotic instruments. 
         [0045]    According to a second aspect of the invention there is provided a surgical tool for use on a patient in an MR Imaging system comprising: 
         [0046]    a tool support member; 
         [0047]    the tool support member having a first end carrying an operating device for carrying out a procedure on a part of the patient; 
         [0048]    the tool support member having a second end including an actuation device for actuating the operating device; 
         [0049]    the tool being formed of a material which:
       has a minimal impact on MR images due to the lack of MR spin signal in the material;   is non-ferromagnetic so as to be unresponsive to a magnetic field of the MR imaging system;   is non-conductive of electric current so as to be unresponsive to an RF field of the MR imaging system so as to avoid heating of the tool by the RF field;       
 
         [0053]    the operating device being driven by an elongate band movable along its length by the actuation device; 
         [0054]    wherein the band is arranged to slip on a drive coupling around which it is wrapped to provide a force limiting component arranged to limit force applied to the operating device by the actuation device to a predetermined maximum force; 
         [0055]    wherein the drive coupling is connected to the operating device for movement thereof between different positions thereof for carrying out the procedure on the part of the patient. 
         [0056]    According to a third aspect of the invention there is provided surgical tool for use on a patient in an MR Imaging system comprising: 
         [0057]    a tool support member; 
         [0058]    the tool support member having a first end carrying an operating device for carrying out a procedure on a part of the patient; 
         [0059]    the tool support member having a second end including an actuation device for actuating the operating device; 
         [0060]    the tool being formed of a material which:
       has a minimal impact on MR images due to the lack of MR spin signal in the material;   is non-ferromagnetic so as to be unresponsive to a magnetic field of the MR imaging system;   is non-conductive of electric current so as to be unresponsive to an RF field of the MR imaging system so as to avoid heating of the tool by the RF field;       
 
         [0064]    wherein the tool support member is carried on a tool holder and wherein there is provided a force limiting component arranged to limit bending force applied to the tool support member by the tool holder to a predetermined maximum force; 
         [0065]    wherein the force limiting component comprises a joint between two parts of the tool support member which move from an aligned position to a bent position in response to a bending force on the tool support member greater than said predetermined maximum. 
         [0066]    According to a fourth aspect of the invention there is provided surgical tool for use on a patient in an MR Imaging system comprising: 
         [0067]    a tool support member; 
         [0068]    the tool support member having a first end carrying an operating device for carrying out a procedure on a part of the patient; 
         [0069]    the tool support member having a second end including an actuation device for actuating the operating device; 
         [0070]    the tool being formed of a material which:
       has a minimal impact on MR images due to the lack of MR spin signal in the material;   is non-ferromagnetic so as to be unresponsive to a magnetic field of the MR imaging system;   is non-conductive of electric current so as to be unresponsive to an RF field of the MR imaging system so as to avoid heating of the tool by the RF field;       
 
         [0074]    wherein the operating device comprises a biopsy tool which includes cooperating jaws having a fixed jaw and a movable jaw, one of the jaws having a raised contact area fully surrounding a cup for receiving a biopsy sample with the contact area arranged to engage a cooperating surface of the other of the jaws, the jaws being arranged to provide an even application of closing force around the contact area between the jaws. 
         [0075]    A control system enables the biopsy tool to acquire a tissue sample in an automated manner. 
         [0076]    If the tool is not used in a robotic operating system, a patient stabilizing system can be used that provides rigid support of the patient relative to the biopsy tool. 
         [0077]    The biopsy tool does not degrade the performance of the imaging system in relation to image quality by its proximity to the tissue of interest. 
         [0078]    The biopsy tool does not degrade image quality of MRI through mechanisms of magnetic susceptibility artefacts. This is accomplished by selecting materials that have similar values of magnetic susceptibility to that of tissue. 
         [0079]    The biopsy tool position/orientation can be registered with an imaging system (common coordinate spaces for planning, monitoring, action). Registration maps physical patient-space and the image-space. This can be accomplished through knowledge of the robotic articulated joints and the robotic anchorage position relative to the patient. Real-time targeting may be accomplished by: selectively imaging thin volumes near the tip of the tool; optimizing a segmentation algorithm to isolate the fiducials in the instrument; registering the physical coordinates of the fiducials to their image coordinates; tracing a planned trajectory to the region of interest avoiding specified areas; coordinating instrument movement during the MRI scanner acquisition stage so as to not interfere with image quality. 
         [0080]    An instrument and imaging system that maintains an updated image volume set of multi-parametric images (T1, T2, DTI etc) over the course of the procedure. Procedures include: biopsy, tumor resection. Reasons to update the image set include: patient movement, removal of tumor, brain shift. 
         [0081]    The tool is invisible in the MR image after the point of contact with the robot end-effector. This is accomplished by material selection (e.g. ceramics) and modification to match magnetic susceptibility of human tissue. 
         [0082]    The tool is robust for clinical use despite being made of brittle materials such as ceramics. 
         [0083]    The surgeon has full control of biopsy tool when it is in the go/no-go zone. 
         [0084]    The biopsy tool force is limited to that necessary to acquire a specimen. 
         [0085]    Full movement of the effector shall be greater than the full movement of the tip. This ensures that the tip can be fully closed after positioning. Full stop possible in one direction. This tool allows the friction actuation to be re-set (this is not a calibration). 
         [0086]    The tool is designed to be easy to manufacture, assemble, and re-furbish; the tool accommodates fluid flushing for cleaning by a hole in the PEEK tube that connects to the ceramic tube. The tool can be flushed with air or a cleaning solution; The tool is heat sterilizable as per normal hospital sterilization procedures. The tool is designed to be robust for extended use as a re-usable/sterilized surgical instrument. 
         [0087]    It is intended for use with a robotic surgery device which provides a movable support with at least 6 degrees of freedom. It has a means for retention of a biopsy specimen, that is a closed-mouth capture. 
         [0088]    The cable actuation method is suitable for use in the MRI scanner and is (MR compatible based on the use of a cable material such as Kevlar/Vectran) and a spring material such as titanium, that does not interfere with imaging quality in that it is RF quiet and has a safety mechanism by using a high cable tension which causes slip by design to prevent shattering of the ceramic hollow cylinder of the tool support. 
         [0089]    The biopsy sample acquisition method does not rely on sharp edges of the jaw. The even application of closing force on the jaw and the complete mating/sealing of the upper and lower jaw contact areas ensures sample. This feature reduces manufacturing/refurbishing costs and increases tool robustness/reliability. 
         [0090]    The tool provides a means for retention of a biopsy specimen as well as for cutting/dissecting tissue. Mechanical activation of the device opens and closes a mouth on the end of the shaft. It is an effective cutter/dissector. 
         [0091]    The tool does not introduce imaging artefacts by its presence in the image (e.g. magnetic susceptibility artefacts). This is of particular importance for the biopsy tool tip which is positioned close to the point of sample acquisition 
         [0092]    The tool is integrated with the robotic system to localize its position in physical space via known geometry, joint orientations, and relative position offsets from the robot base. Biopsy sample location is stored in system memory as a virtual landmark. Further clinical actions can be taken with precise reference to where the biopsy sample was taken. 
         [0093]    The tool is part of a complete system for planning, analysis (pathology type), treatment selection, treatment and assessment. 
         [0094]    Used in conjunction with MRI images, the images are spatially registered to the tool and the biopsy tool can be precisely moved to the location of the desired sample. This ensures an industry standard stereotactic accuracy of approximately 1-2 mm. 
         [0095]    The biopsy tool can be used in two modes of operation at the discretion of the surgeon. One is manual, the other is automated and depends on integration of the surgical robot, tool and MR imaging system. 
         [0096]    Mode A: mouth is closed on entering cavity. Surgeon opens mouth, moves it forward and closes it to acquire sample. 
         [0097]    Mode B: Auto-biopsy. Robotic automated control of mouth and forward motion once the surgeon positions the tool initially. Benefit is smooth controlled motion. 
         [0098]    It therefore has designed slip couplings and bend joints to prevent overloading and a sample collection device which avoids excessive force. It has cleaning ports integrated into the design so that sterility can be obtained by flushing the device interior with a cleaning fluid. A novel spring-loaded capstan ensures proper cable tension. A unique jaw shape enables a cutting pressure to be applied simultaneously around the desired tissue and does not depend on sharp edges to obtain the sample. Springs in the main casing provide cable tensioning to keep the jaws in a default closed position for movement of the biopsy device along a trajectory to the sample to be acquired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0099]    One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: 
           [0100]      FIG. 1  is a schematic side elevational view of a microsurgical robot system operating with the bore of an MR magnet and including a tool according to the present invention. 
           [0101]      FIG. 2  is a schematic side elevational view of one robot arm of the system of  FIG. 1  with the tool according to the present invention. 
           [0102]      FIG. 3  is a side elevational view of the arm of  FIG. 2  on an enlarged scale with the tool according to the present invention. 
           [0103]      FIG. 4  is a schematic illustration of an MR image and visual image controlled micro-surgery system. 
           [0104]      FIG. 5  is an isometric view of the tool of  FIG. 1 . 
           [0105]      FIG. 6  is an isometric view of the actuation portion only of the tool of  FIG. 5  shown sectioned along a vertical center line. 
           [0106]      FIG. 7  is an isometric view of the actuation portion only of the tool of  FIG. 5  shown sectioned along a horizontal center line. 
           [0107]      FIG. 8  is a longitudinal cross-sectional view of the operating portion only of the tool of  FIG. 5 . 
       
    
    
       [0108]    In the drawings like characters of reference indicate corresponding parts in the different figures. 
       DETAILED DESCRIPTION 
       [0109]    An overview of the system is shown in  FIGS. 1 to 4  which comprises a robot manipulator  10 , a work station  11  and a controller  12  which communicates between the robot manipulator and the work station. As an input to the work station is also provided a stereo microscope  13 , an MRI imaging system  14  and a registration system  15 . 
         [0110]    The work station includes a number of displays including at first display  16  for the MRI image, a second display  17  for the microscope image and a third display  18  for the system status. Further the work station includes two hand controllers schematically indicated at  19  and an input interface or control panel  20  allowing the surgeon to control the systems from the work station while reviewing the displays. The work station further includes a computer or processor  21 , a data recording system  22  and a power supply  23 . 
         [0111]    The display  17  includes a stereoscopic display  17 A which provides a simulated microscope for viewing the images generated by the stereo-microscope system  13 . Further the display  17  includes a monitor  17 B which displays a two dimensional screen image from the microscope system  13 . 
         [0112]    The robot manipulator  10  includes a field camera  24  which provides an image on a monitor  25  at the work station. 
         [0113]    The magnetic resonance imaging system  14  is of a conventional construction and systems are available from a number of manufacturers. The systems are of course highly complicated and include their own control systems so that the present workstation requires only the display of the image on the monitor  16  where that image is correlated to the position of the tool using known registration systems. 
         [0114]    The hand controllers  19  are also of a commercially available construction available from a number of different sources and comprise 6 degrees of freedom movable arms which can be carefully manipulated by the surgeon including end shafts which can be rotated by the surgeon to simulate the rotation of the tool as described hereinafter. An actuator switch on the tool allows the surgeon to operate the actuation of the tool on the robot as described hereinafter. 
         [0115]    The robot manipulator comprises a cabinet  101  and two arms  102  and  103  which are mounted on the cabinet together with the field camera  24  which is also located on the cabinet. The field camera is mounted at the back of the cabinet viewing past the arms of the front of the cabinet toward the patient and the site of operation to give a general overview field of the situation for viewing on the display  25 . 
         [0116]    The control system  12  for communication between the work station and the robot manipulator and for controlling the operation of each of those components includes a force sensor sub system  121  and a motion control sub system  122  together with power supplies and further components as indicated schematically at  123 . The force sensor sub system controls the feed back forces as detected at the end effector of the robot arm to the hand control systems  19 . The motion control subsystem  122  converts the motion control sensors from the hand-control system  19  into individual operating instructions to the various components of the arms. The motion control sub system also provides an output which is communicated to the work station for display on the MRI imaging monitor  16  of the location of the tip of the tool relative to the image displayed on the screen  16 , as generated by the registration system  15 . 
         [0117]    The structure of the arms is shown in  FIG. 2 , where the arms are mounted with their base  111  for attachment to the cabinet support. Each of the arms  102  and  103  includes a number of joints which allow operation of a tool schematically indicated at  26 . Thus each arm includes a first joint defining a shoulder yaw pivot  131  defining a vertical axis of rotation. On the vertical axis is mounted a second joint  132  forming a shoulder roll joint which provides rotation around a horizontal axis. The shoulder yaw axis extends through the joint  132 . A rigid link  135  extends from the joint  132  to an elbow joint  136  which is cantilevered from the shoulder roll joint  132 . The elbow joint includes an elbow yaw joint  137  and an elbow roll joint  138 . The yaw joint  137  is connected to the outer end of the link  135  and provides rotation about a vertical axis. The roll joint  138  is located on the axis and provides a horizontal axis. A link  141  lies on the horizontal axis and extends outwardly from the joint  138  to a wrist joint generally indicated at  142 . The wrist joint  142  includes a wrist yaw joint and wrist roll joint. The wrist yaw joint provides a vertical axis about which a link can pivot which carries the roll joint. The roll joint provides a horizontal axis which allows the tool  26  to rotate around that horizontal axis. The tool  26  includes a roll joint  148  including a gear drive  150  which provides rotation of the tool  26  around its longitudinal axis by driving a gear of the tool. The tool further includes a tool actuator  149  which is grasped by one jaw  149 A of the actuator of the robot and can move longitudinally along the tool relative to the joint  148  which is grasped by a jaw  148 A of the robot to provide actuation of the tool using various known tool designs. That is the jaws  148 A and  149 A of the robot move longitudinally of the tool to effect the operation of the tool. 
         [0118]    Thus the forces required to provide rotation around the various axes are minimized and the forces required to maintain the position when stationary against gravity are minimized. This minimization of the forces on the system allows the use of MRI compatible motors to drive rotation of one joint component relative to the other around the respective axes. 
         [0119]    The arrangement described above allows the use of piezoelectric motors to drive the joints. Such piezoelectric motors are commercially available and utilize the reciprocation effect generated by a piezoelectric crystal to rotate by a ratchet effect a drive disc which is connected by gear coupling to the components of the joint to effect the necessary relative rotation. 
         [0120]    The robot therefore can be used in the two arm arrangement for microsurgery in an unrestricted area outside of the closed bore magnet or for microsurgery within an open bore of a magnet where the arrangement of the magnet can be suitable to provide the field of operation necessary for the two arms to operate. The two arms therefore can be used with separate tools to effect surgical procedures as described above. In some cases a single arm can be used to effect stereotactic procedures including the insertion of a probe or cannula into a required location within the brain of the patient using the real time magnetic resonance images to direct the location and direction of the tool. 
         [0121]    In  FIG. 1 , the system is shown schematically in operation within the bore of a magnet  30  of the MRI system  14 . The bore  31  is relatively small allowing a commercially available patient table  32  to carry the required portion of the patient into the bore to the required location within the bore. The field camera  24  is used within the bore for observing the operation of the robot  10  and particularly the tool  26 . 
         [0122]    In  FIGS. 5 to 8  is shown the tool  26  of  FIG. 1  which provides a surgical tool for use on a patient in an MR Imaging system. This comprises a tool support member or shaft  201  having a first end  202  carrying an operating device  203  for carrying out a procedure such as a biopsy on a part of the patient. A second end  204  of the tool support member includes the actuation device  205  including a first actuation portion  205 A for engaging the jaw  149 A of  FIG. 3  and a second actuation portion  205 B for engaging the jaw  148 A of  FIG. 3  of the robot for actuating the operating device  203 . The portion  205 B carries the gear  205 C for cooperation with the gear  150  of the robot. 
         [0123]    In order to be operable during imaging within the bore of the magnet, the tool itself is formed of materials which are non-ferromagnetic so as to be unresponsive to a magnetic field of the MR imaging system, are non-conductive of electric current so as to be unresponsive to an RF field of the MR imaging system so as to avoid heating of the tool by the RF field and have a magnetic susceptibility which is substantially equal to that of human tissue. 
         [0124]    The materials selected for manufacture of the part of the tool include a ceramic material. Thus those parts which lie immediately adjacent the human tissue are not formed of titanium since that material has been found to have a magnetic susceptibility which is sufficiently different from that of the human tissue that the MR image includes unacceptable artefacts at the interface with the human tissue, which is of course in many cases the area of most interest. 
         [0125]    The ceramic material selected can be Yttrium zirconia, types of alumina, silicon nitride, and alloys thereof. 
         [0126]    The tool comprises an axial tube  220  which is carried inside an outer axial tube  221  by bearings  222  and  223  allowing longitudinal sliding movement of the outer tube  221  on the outside surface of the tube  220 . The outer tube  221  is connected to the actuation portion  205 A so that longitudinal movement of the portion  205 A drives the outer tube  221  axially. 
         [0127]    The portion  205 B and the gear  205 C surround the outer tube  221  and are connected to a housing  225  which holds the inner tube  220 . Thus the housing  225  is connected to the jaw  148 A to hold the tool and the tube  220  at a position determined by the jaw. The tool is rotated by the gear  150  which drives the gear  205 C to rotate the housing  225  and thus the tube  220  about the longitudinal axis of the tool. This rotation takes place relative to the portions  205 A and  205 B which remain stationary on bearings  224  located between the portion  205 B and the housing  225  and on bearings  224 A located between the portion  205 A and the housing outer tube  221 . In this way the jaws hold the portions fixed from rotation and allow the gear to rotate the tool including the housing around the axis. 
         [0128]    Movement of the jaw  149 A longitudinally of the of the tool toward and away from the housing  225  acts to move the outer tube  221  axially which connects to a crank  226  which drives rotation of a rotary capstan member  227  within the housing  225  relative to a transverse shaft or axle  228  at right angles to the longitudinal axis. 
         [0129]    The drive system to the operating tool  203  also includes a band or tendon  230  with two longitudinally extending runs  230  and  231  along the inner tube  220 . 
         [0130]    Thus the tendon or band  230  is driven along its length by the rotary capstan member  227  at the actuation device around which the band is wrapped in two loops each applied into a respective one of two grooves  250  and  251  around the outer surface of the capstan member. 
         [0131]    The capstan member is rotated by the crank  226  driven by movement longitudinally of the tool support member. The crank engages one of inner and outer coaxial members  220 ,  221 . The capstan member is housed within the housing  225  connected to the other of the inner and outer coaxial members  220  and  221 . Thus the relative longitudinal movement between the tubes  220 ,  221  driven by the actuators moving the engagement members  205 A and  205 B drives rotation of the single capstan member around its axis to actuate movement of the tendon  230 . 
         [0132]    The capstan member is biased along the tool head relative to the housing by a pair of springs  252 ,  253  each engaged between an inner end face of the housing  225  and the axle  228  of the capstan member  227 . Thus the axle  228  is pushed inside the housing along the housing away from the end face of the housing to tension the tendon 
         [0133]    The capstan member is driven by an actuation method using the actuators  205 A and  205 E that does not depend on electricity. 
         [0134]    The components described above are formed from different materials of PEEK, titanium. Thus, as well as the ceramic material which is used for the inner axial rod and bearings); the PEEK is used for the outer axial rod  220 ; titanium is used for the set screws  233  and tension spring); Kevlar/Vectran is used for the tendon  230 . 
         [0135]    As the tool and particularly the tool support member and the operating device are formed of a material which can crack if subjected to a force greater than said predetermined maximum, it is necessary to provide systems which ensure that the forces applied do not exceed a predetermined maximum. 
         [0136]    As shown in  FIG. 8  there is provided a force limiting component arranged to limit force applied to the operating device by the actuation device to a predetermined maximum force. Thus the force limiting component includes a drive transfer member defined by a wrap  208  of the elongate tendon  230  movable along its length which slips on a pulley  209  around which it is wrapped. This allows slippage of drive from the actuation device  149 A to jaws  206  and  207  of the operating device  203 . 
         [0137]    The pulley  209  is connected to the movable jaw  206  to move it in respective direction depending on the direction of movement of the tendon  230  and thus on the pulling action on the tendon  230  effected by the actuator  149 . The jaw  206  rotates around a bearing shaft  210  carried on the stationary jaw  207  which is fixed to the shaft  202 . Precise control is translated from full travel of the effector  149  into ⅛″ of tip movement of the jaws. This is implemented using the co-axial construction of the inner and outer tubes. Pull-back on the effector  149  causes a rotation on the pulley  209 . The pulley  209  has a wedge-shape so that motion scaling or reduction occurs. Essentially, linear axial movement of the effector  149  turns the pulley  209 . The pulley  209  interacts with the pin  210  as a lever effect. The effective pulley diameter on the actuation tendon  230  is optimal. A 60 degree rotation maps to the effective surface area. The two wedge and half-pulleys arrangement maintain a rigid pulley structure. 
         [0138]    Thus the drive transfer member comprises the elongate band or tendon  230  movable along its length by the actuation device provided by the portions  148 ,  149  of the robot end effector which operate through the portions  205 A and  205 B. The band is arranged to slip on the drive coupling  209  around which it is wrapped so that as soon as a pre-determined maximum force between the jaws  206  and  207  is reached, the tendon  230  slips and the jaws move no further regardless of additional forces being applied by the end effector of the robot. 
         [0139]    The tendon  230  runs are driven along their length by the rotary member  227  which is rotated around the transverse axis by the  226  crank driven by movement of the outer tube  221  longitudinally of the tool support member. 
         [0140]    Thus the friction pulley has just enough force to acquire the biopsy sample. This is accomplished by the torque limiting tendon  230  arrangement which will slip by design after a threshold is exceeded. 
         [0141]    As shown in  FIGS. 6 and 7 , the tool support member or shaft  201  includes a force limiting component  240  located between the end  241  of the shaft  202  and the end  242  of the inner tube  220 . The joint or component  240  is arranged to limit bending force applied to the tool support member by the tool holder to a predetermined maximum force. That is, if the force applied by movement of the robot arm to the shaft  202  exceeds a predetermined level beyond which cracking or shattering of the shaft  202  and jaw  206  can occur if forced against a stationary object, the joint  240  in the tool support member  202  moves to a bent position in response to a bending force on the tool support member greater than said predetermined maximum. 
         [0142]    A second break-away joint  244  is also located at the tip of the shaft  201  and can protect the tool  203  from damage by a similar break away action. 
         [0143]    Each break-away joint  240 ,  244  includes two components  245  and  246  where one provides a convex surface sitting inside a concave surface defined by the other. These surfaces will allow rotation one on the other when the torque between them exceeds the required value. The surfaces are held against one another in frictional contact by the tension in the tendon  230 . Thus a deflection of the shaft will elongate the tendon  230 . The cable is on the pre-tensioned spring  232 . As such, a lateral stiffness of the shaft  202  at the joints  240  and  244  can be defined and configured. The joint  244  at the tip and the joint  240  at the ceramic/body junction include a specific geometry defined by the portions  245  and  246  which is used to support 90 degree snap-back. This geometry provides a joint between ceramic tube and rest of body in which initially this joint has a high load; but after 10 degrees of deflection, the spring compression rate is significantly reduced. The benefit is that a shorter spring  232  may be used since travel is reduced. This leads to a more compact design. 
         [0144]    Thus the two joints  240  and  244  in the tool support member are pulled into engagement of the parts in the straight position by the tendon  230  extending along the tool support member, which operates the operating device, where the tendon  230  stretches in length either along its length by a controlled elasticity or at the spring  232  to allow longitudinal movement of the parts into the bent position. 
         [0145]    The operating device is driven by the actuation device through an actuation method that does not depend on electricity that could pose a safety hazard to the patient or that might introduce RF noise. The wrap  208  loops around the jaw pulley  209  twice (or more). Both ends of the cable  229  are attached to the actuation pulley  227  of the actuator at the far end as shown in  FIG. 6  and are preloaded to accomplish the following: 
         [0146]    1. The pulley section  209  of the moveable jaw is held laterally inside fixed jaw tension of tendon  230  provides a seating force to hold the pin in place (as a result of smaller diameter of pin interfacing with the pulley bore; 
         [0147]    2. The tendon  230  tension provides enough friction on the jaw to achieve adequate closing force; 
         [0148]    3. The friction actuation provides enough slip so the tendon  230  is never over-tensioned. 
         [0149]    The operating device comprises a biopsy tool which includes the cooperating jaws  206  and  207  having a fixed jaw  207  attached to the member  201  and a movable jaw  206 . One of the jaws  206  has a raised contact area  260  fully surrounding a cup  261  for receiving a biopsy sample. The contact area defined by the raised lip  260  is arranged to engage a cooperating surface  262  of the other of the jaws which lies in a flat face plane  263  of the jaw  207 . The jaws  20   c  and  207  and the pivot pin are arranged to provide an even application of closing force around the contact area  260  onto the plane  263  between the jaws around the cup  261 . 
         [0150]    Thus the raised contact area  261  which is circular or oval and defines the edge of the cup  261  when it is closed engages the planar cooperating surface  263  of the other of the jaws  207  so that the raised contact area forms a cutting surface on the planar surface  263  which cuts by pinching around the full periphery of the up rather than by a shearing action. The cutting action thus avoids sharp cutting edges. The planar surface  263  also includes a cup  264  facing and matching the cup  261  of the jaw  206 . 
         [0151]    The biopsy tool includes a biopsy sample acquisition method that does not rely on sharp edges of a fixed jaw but instead the jaws  206 ,  207  have a movable jaw  206  which has even application of closing force on the jaw  207  and the complete mating/sealing of the jaw contact area  212 ,  213 . The jaw is closed by the friction pulley  209 . The pulley is designed to have a maximum diameter for greatest torque using minimal cable tension. This ensures that the jaw has sufficient closing force to acquire a tissue sample. Minimum cable tension allows the use of a thin cable. The tool implements a torque limit as a safety feature such that the cable will slip by design after a threshold force is exceeded. In this way the friction pulley avoids over-extensions and over-stressing tip and other components. A design feature is that an nominal 90 degree rotation of the pulley maps to a nominal 45 degrees jaw opening angle. 
         [0152]    The tip jaw pivot has a large diameter at both ends end but is smaller diameter in the centre where the jaw rotates. Pulley tension keeps the pivot pin correctly positioned. 
         [0153]    The pivot construction enables vertical movement of the jaw during closure. This results in a rolling contact of the jaw clipping area due to the back of the jaw closing first, and then the angle of the cable acting on the jaw pulley in such a way as to draw the jaw upward at full closing force. This rolling contact of the jaw ensures that full contact is made around the perimeter of the bite so that full clipping contact is ensured. This full contact enables sample acquisition without relying on sharp edges of the jaw. The ability to acquire a sample from a fairly blunt edge reduces manufacturing cost and is a factor in reliability/durability. 
         [0154]    The components are arranged for ease of assembly and disassembly in that the pivot pin  209  has a large diameter at its end  215  but is small in the centre  210  where the jaw rotates. This is not a press fit but rather relies on pulley tension. The benefit is that pivot is kept centred. There is a rolling contact of the two jaws and total contact is made around the perimeter of the bite  212 ,  213  so that full clipping contact is ensured. This full contact enables sample acquisition but does not rely on sharp edges of the jaw. The ability to acquire a sample from a fairly blunt edge reduces manufacturing cost and is a factor in reliability/durability. 
         [0155]    The tension system  232  for the actuation cable  229  is easy to assemble. The cable  229  pulls through a bore defined by a cross bore to the set screw  233 . In order to assemble, the process involves compressing the spring  232 ; 
         [0156]    turning until the cable engages and cutting cable so that this results in clean and secure cable attachment. In regard to the housing this has a cap which splits in two which allows easier access for install and servicing. 
         [0157]    The biopsy tool does not degrade image quality of MRI through mechanisms of magnetic susceptibility artefacts. This is accomplished by selecting materials that have similar values of magnetic susceptibility to that of tissue. 
         [0158]    The biopsy tool can be used in two modes of operation at the discretion of the surgeon. One is manual, the other is automated and depends on integration of the surgical robot, tool and MR imaging system. 
         [0159]    Mode A: mouth is closed on entering cavity. Surgeon opens mouth, moves it forward and closes it to acquire sample. 
         [0160]    Mode B: Auto-biopsy. Robotic automated control of mouth and forward motion once the surgeon positions the tool initially. The benefit is smooth controlled motion.
A biopsy tool for MR imaging for operation by a robot arm is formed of relatively brittle ceramic materials which have a magnetic susceptibility which is substantially equal to that of human tissue. The tool has designed slip couplings and bend joints to prevent overloading of forces on the sampling jaws. Cleaning ports are integrated into the design so that sterility can be obtained by flushing the device interior with a cleaning fluid. A novel spring-loaded capstan operated by a crank movable longitudinally of the tool ensures proper cable tension. A unique jaw shape enables a cutting pressure to be applied simultaneously around the desired tissue and does not depend on sharp edges to obtain the sample. Springs in the main casing provide cable tensioning to keep the jaws in a default closed position for movement of the biopsy device along a trajectory to the sample to be acquired.