Abstract:
A trackable medical instrument for use in a computer assisted image guided medical and surgical navigation systems that generate images during medical and surgical procedures, includes a guide member having an emitter array for being tracked by the system and a drive shaft contained within the guide member having a proximal and a distal end, the drive shaft being rotatable within the guide member while being fixable axially inside the guide member, the proximal end of the drive shaft having a first connector for interchangeably receiving at least one drive source, and the distal end having a second connector for interchangeably receiving at least one instrument tip.

Description:
This application is a reissue of U.S. Pat. No. 6,021,343 issued on Feb. 1, 2000 and also claims benefit under 35 U.S.C. §120 as a continuation of issued U.S. Pat. No. Re. 43,328, filed on Jan. 31, 2002; which is also a reissue of U.S. Pat. No. 6,021,343 issued on Feb. 1, 2000. The disclosures of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to computer assisted image guided medical and surgical navigation systems that generate images during medical and surgical procedures indicating the relative position of various body parts, surgical implants, and instruments. In particular, the present invention relates to an instrument for use in an image guided surgery navigation system that enables the system to track both the depth and the trajectory of the instrument during surgery. 
     2. Background of Related Art 
     Computer assisted image guided medical and surgical navigation systems are known and used to generate images in order to guide a doctor during a surgical procedure. Such systems are disclosed, for example, in U.S. Pat. No. 5,383,454 to Bucholz; PCT application Ser. No. PCT/US94/04530 (Publication No. WO 94/24933) to Bucholz; and PCT application Ser. No. PCT/US95/12984 (Publication No. WO 96/11624) to Bucholz et al., incorporated herein by reference. 
     In general, these image guided systems use images of a body part, such as CT scans, taken before surgery to generate images on a display, such as a CRT monitor screen, during surgery for representing the position of a surgical instrument with respect to the body part. The systems typically include tracking devices such as, for example, an LED array mounted on a surgical instrument as well as a body part, a digitizer to track in real time the position of the body part and the instrument used during surgery, and a monitor screen to display images representing the body and the position of the instrument relative to the body part as the surgical procedure is performed. 
     There is a need in the art for a surgically navigable tool for use with these image guided systems that is simple to use and manipulate, that enables the computer tracking system to track both the trajectory of the instrument and the depth that the instrument is inserted into the body, and that is easily interchangeable with alternative drive sources such as a ratcheting handle or other instruments such as awls, taps, and screwdrivers. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an image guided medical instrument whose tip and trajectory can be simultaneously tracked. 
     It is a further object of the invention to provide an image guided medical instrument capable of generating a signal representing the trajectory and the depth of the tip of the instrument. 
     It is a still further object of the invention to provide an image guided medical instrument that may easily be used with any number of different tips and handles. 
     It is another object of the invention to provide an image guided medical instrument that is of relatively simple construction and relatively easy to use. 
     Additional objects and advantages of the invention will be set forth in the description which follows and, in part, will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a trackable medical instrument for use in a computer assisted image guided surgery system having a digitizer for tracking the position of the instrument in three dimensional space and a display providing an indication of the position of the instrument with respect to images of a body part taken preoperatively. The instrument includes a guide member having an emitter array mounted thereon for being tracked by the digitizer, and a drive shaft contained within the guide member, the drive shaft having a proximal and a distal end, the drive shaft being rotatable within the guide member while being fixable axially within the guide member, the proximal end of the drive shaft having a first connector for interchangeably receiving at least one drive source, and the distal end having a second connector for interchangeably receiving at least one instrument tip. The instrument may further include at least one instrument tip for connection to the distal end of the drive shaft and a drive handle for connection to the proximal end of the drive shaft for transmitting torque to the instrument tip to cause rotation of the instrument tip. 
     In another aspect of this invention, the instrument may further include a sensor which senses the removal and the connection of an instrument tip to the instrument. The sensor may be an electromechanical switch on the guide member. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic front view of a computer assisted image guided surgery system used with an instrument according to the present invention. 
         FIG. 2  is a perspective view of an instrument according to the present invention. 
         FIG. 3  is an exploded view of the instrument shown in  FIG. 2 . 
         FIG. 4  is a view of a portion of the instrument shown in  FIG. 2 . 
         FIG. 5  is an exploded view of the portion of the instrument shown in  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     The medical instrument of the present invention is shown generally at  10  in  FIG. 1 . Instrument  100  can be used in many known computer assisted image guided surgical navigation systems such the system shown in  FIG. 1  and disclosed in PCT application Ser. No. PCT/US95/12984 (Publication No. WO 96/11624) to Bucholz et al., incorporated herein by reference. A computer assisted image guided surgery system, shown at  10 , generates an image for display on a monitor  106  representing the real time position of a body part and the position of instrument  100  relative to the body part. 
     An image may be generated on monitor  106  from an image data set stored in a controller, such as computer  108 , usually generated preoperatively by some scanning technique such as by a CAT scanner or by magnetic resonance imaging. The image data set and the image generated have reference points for at least one body part. The reference points for the particularly body part have a fixed spatial relation to the particular body part. 
     System  10  also generally includes a processor for processing image data, shown as digitizer control unit  114 . Digitizer control unit  114  is connected to monitor  106 , under control of computer  108 , and to instrument  100 . Digitizer  114 , in conjunction with a reference frame arc  120  and a sensor array  110  or other known position sensing unit, tracks the real time position of a body part, such as a cranium shown at  119  clamped in reference frame  120 , and an instrument  100 . Reference frame  120  has emitters  122  or other tracking means that generate signals representing the position of the various body reference points. Reference frame  120  is fixed spatially in relation to a body part by a clamp assembly indicated generally at  124 , 125 , and  126 . Instrument  100  also has a tracking device shown as an emitter array  40  which generates signals representing the position of the instrument during the procedure. 
     Sensor array  110 , mounted on support  112 , receives and triangulates the signals generated by emitters  122  and emitter array  40  in order to identify during the procedure the relative position of each of the reference points and the instrument. Digitizer  114  and computer  108  may then modify the image date set according to the identified relative position of each of the reference points during the procedure. Computer  108  may then generate an image data set representing the position of the body elements and the instrument during the procedure. System  10  may also include a foot switch  116  connected to instrument  100  and digitizer  114  for controlling operation of the system. The structure and operation of an image guided surgery system is well known in the art and need not be discussed further here. 
     Referring to  FIGS. 2 and 3 , an instrument according to the present invention is shown at  100 . Instrument  100  includes a guide member  30 , an interchangeable instrument tip  15 , and an interchangeable driving handle  20 . 
     A drive shaft  35  is housed within guide member  30  and is removably connected to an end, here the proximal end  37 , to surgical instrument tip  15  and at the other end, here the distal end  38 , to driving handle  20  such that torque applied manually or by motorized means to drive handle  20  is transmitted to drive shaft  35  which in turn is transmitted to tip  15 . Drive shaft  35 , while it could be extractable such as for service, is fixable axially in relation to guide member  30 , but is rotatable within guide member  30 . As shown in  FIG. 5 , bushings  33  may be provided at each end of guide member  30  to ensure smooth motion between drive shaft  35  and guide member  30 . Guide member  30  is preferably made of stainless steel, but can also be made of titanium, aluminum or plastic. Shaft  35  is preferably made from stainless steel, titanium, or aluminum. 
     Instrument  100  further includes a tracking device such as emitter array  40  attached to guide member  30  for tracking the location and trajectory of instrument  100 . As shown in  FIG. 4 , array  40  is equipped with a plurality of emitters or tracking means  45 , preferably four emitters, for generating a signal representing the trajectory of instrument  100  and the depth of instrument tip  15 . Preferably emitters  45  are light emitting diodes; however, other tracking devices known in the art capable of being tracked by a corresponding sensor array are within the scope of the invention. For purposes of illustration, not limitation, the tracking device may generate signals actively such as with acoustic, magnetic, electromagnetic, radiologic, and micropulsed radar systems, or passively such as with reflective surfaces. 
     Drive handle  20  and instrument tip  15  are shown as modular units that can be attached to drive shaft  35  with corresponding and interlocking male and female socket joints. As shown in  FIGS. 3 and 4 , drive shaft  35  has a female socket joint  34  for connection with a male socket  14  on tip  15 , and drive shaft  35  has a male socket joint  36  for connection with a female socket joint  26  on drive handle  20 . With the use of male and female socket joints, various instrument tips and various type and sized drive handles can be easily interchangeable. Instrument tip  15  could be any of a variety of instruments used in surgery such as taps, awls, and shaped tools for interacting with a work piece, such as a screwdriver for driving screws. Drive handle  20  could be any number of existing or specially designed handles and could be ratcheting, nonratcheting or motorized. Instrument tip  15  and drive handle  20  could also be permanently attached to drive shaft  35 . Other suitable connection means are within the scope of the invention as well. 
     In operation, torque applied to drive handle  20  is transmitted through drive shaft  35  to instrument tip  15 . Because drive shaft  35  is fixed axially in relation to guide member  30 , guide member  30  can remain stationary while drive shaft  35  rotates without translating along the axis of drive shaft  35 . The relationship between array  40  and the axis of drive shaft  35 , therefore, remains constant. Instrument tip  15  is also fixed axially in relation guide member  30 . As a result, the relationship between array  40  and instrument tip  15  also remains constant. Because the relationship between array  40  and tip  15  is constant, the signals emitted by emitters  45  can be used by the computer assisted image guided surgical navigation system to inform the surgeon of the position of instrument  100 , indicating both the trajectory or orientation in three dimensional space of instrument  100  and the length of travel along the trajectory, i.e., the depth instrument tip  15  has been inserted into a body part. 
     It should be recognized that other variations or modifications may be made to provide an instrument that has an emitter array fixed axially relative to the instrument tip while allowing the instrument tip to rotate relative to the emitter array. For example, guide member  30  may also be integral with instrument tip  15  and/or drive handle  20 . The array could then be fixed axially relative to the instrument and means could be provided to allow rotation of the instrument relative to the array. 
     As discussed above, a variety of different instrument tips may be easily interchanged on instrument  100 . To use these different instrument tips, information concerning the dimensions of the different tips may be entered into computer  108 . As a result, computer  108  can process the various image data for the specific instrument tip being used so that system  10  tracks the depth of the tip being used or, in the case of a screwdriver, so that system  10  tracks the depth of the screw being inserted. 
     System  10  may also be provided with a mechanism to prevent the system from operating after a new tip has been connected until computer  108  has been recalibrated. For example, an electromechanical switch, or other suitable sensors, could be provided on instrument  100  to provide a signal to computer  108  indicating that instrument tip  15  has been removed from instrument  100  or that a new instrument tip  15  has been coupled to instrument  100 . The switch is preferably a micro switch but can be embodied by any suitable electrical or electromechanical device or sensing device capable of providing a signal in response to attachment or detachment at a particular point on guide member  30  or tip  15 . 
     The switch may be automatically actuated when tip  15  is removed or coupled to instrument  100 . Computer  108  may be operably connected to the switch, such as through cable  161 , and is responsive to the operation of the switch. Alternatively, if a wireless instrument is used such as one with passive reflective surfaces in place of LED emitters, any suitable form of communication known in the art can be used. An alarm or other indication of some type, such as a message or display on monitor  106 , may be generated by computer  108  indicating to the user that tip  15  has been changed. The computer  108  may further prevent the system from operating until the system has been recalibrated for the new instrument tip. Recalibration may be accomplished by touching the instrument tip to a known reference point. Recalibration of the instrument tip can be positively confirmed by means of a light emission from the emitter array  40  detected by sensor array  110  and triangulated to determine the position of the instrument tip. Alternatively, the dimensions of the instrument or tool type may be entered into computer  108  or selected from a pre-programmed list of tool dimensions or tool types. Further, recalibration could be accomplished by a fiber optic device for reading a bar code on the instrument tip, or by any other suitable recalibration technique. 
     It will also be apparent to those skilled in the art that various modifications and variations can be made to the structure and methodology of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.