Abstract:
A device for gauging and verifying the precision of surgical instruments is provided. The device includes a holder, at least one instrument, and a carousel having at least one cavity configured and dimensioned in the shape of the at least one instrument. The carousel is rotatably coupled to the holder. Markers or sensors for emitting or receiving signals are fitted to at least two of the holder, the carousel and the instrument, and allow determination of spatial information thereof. The spatial information is calibrated by inserting the at least one instrument in its respective cavity in the carousel and determining any change in dimensions from the instrument&#39;s first set of dimensions upon manufacture and its new set of dimensions following use.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of the U.S. National Stage designation of co-pending International Patent Application PCT/CH98/00030, filed Jan. 27, 1998, the entire content of which is expressly incorporated herein by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device for gauging and verifying the precision of surgical instruments. More particularly, the present invention relates to a calibration system for computer-assisted surgery that accounts for deviations in surgical instrument dimensions from predetermined values. 
     BACKGROUND OF THE INVENTION 
     The medical sciences have been revolutionized through the widespread introduction of digital imaging technologies such as ultrasonography, computer-assisted tomography (CT scanning), and magnetic resonance imaging (MRI). Especially in orthopedic and traumatologic applications, three-dimensional visualization employing these image-acquisition systems has become an important tool for physicians. 
     Advances in three-dimensional imagery applications have now been deployed in pre-operative, operative, and post-operative settings, providing practitioners with a variety of tools for simulation and/or computer-assisted guidance of medical procedures tailored to the actual anatomy of a given patient. For example, computer-based rendering of bone geometry—such as contours and volume characteristics—as well as bone surface features can provide the surgeon with a visual representation of an injury to a bone or joint. Such renderings can provide valuable insight with respect to strategies for invasive surgery. Furthermore, the three-dimensional imaging systems can provide a means for simulating surgical procedures, such as the virtual manipulation of bone sections. The simulations may also be useful in the shaping of bone and joint implants, or other anatomical modeling applications. 
     Three-dimensional imaging technologies have been introduced primarily for pre-surgery simulation and for computer-assisted navigation of surgical instruments with respect to a patient during surgical procedures. Particularly in applications involving the latter, it is desirable to precisely determine the position and orientation of the surgical instrument relative to a spatial reference system. The introduction of an accurate surgical aid of this type to an operating room setting advantageously allows a surgeon to dynamically observe the position of a surgical instrument with respect to a patient. Through the use of a computer processor, monitor, and an appropriate software module, it is possible to predict and display intended trajectories for surgical instruments, in real time, as a function of the instruments&#39; current orientations. Thus, surgical instruments may be precisely positioned without extensive preoperative planning. However, the guidance software can also allow the surgeon to compare an instrument path that was planned prior to an operation with the current position of the instrument, as well as the path resulting from that instrument position and orientation at any given time. Thus, in practice, an instrument path planned prior to surgery may be followed during surgery to guide the movement of an instrument. 
     A vast array of surgical instruments can be adapted for computer-assisted surgery, including without restriction such common tools as drills, spoons, scissors, forceps, and probes. In order to facilitate the detection of an instrument&#39;s position in a three-dimensional coordinate measuring system, the instrument is provided with markers or sensors for emitting or receiving electromagnetic waves, sound waves or magnetic fields. Each of these approaches to registering positional data presents limitations or challenges to achieving repeatable and thus reliable accuracy. Ultrasound measurements, for example, may be undertaken in an air environment, and thus are subject to changes in the physical characteristics of air which show significant variation as a function of temperature, pressure and relative humidity. Thus, when using ultrasonic registration, such external factors must be constantly measured so that deviations in the measurements may be continuously compensated. Without this monitoring, significant positioning errors may occur. Such compensation for external factors that effect registration is also necessary for magnetic-field measurement. For example, adjustments may be required to account for interference fields emanating, for instance, from display monitors, computers or electric motors, as well as non-permeable materials in the magnetic field such as metal objects moving within the magnetic field. 
     Systems for medical diagnosis and treatment that use reference field transducers and medical probes with probe field transducers to detect the position, orientation, or both of the probe within the body of a subject are disclosed in WO 97/29683 to Acker et al. A device that incorporates a frame which can be firmly aligned with an operating table is provided with fiducial gauging receptacles for a surgical probe. Markers are attached to a probe and the frame, and the frame can be locked in position relative to a patient. Provisions are included for transmitting, for example, a magnetic field between the markers on the probe and those on the frame. Sensors are used to detect any such field, and a processor is used to process the detected-field data and determine the position of the probe relative to the markers on the frame. The frame includes catheter calibration receptacles, positioned in known locations relative to transducer mounts. Before a probe carrying catheter is inserted into the body of a subject, the catheter is calibrated by placing the distal tip thereof, which carried the probe, in each of the receptacles in turn, and comparing the respective known position of the receptacle with position information derived from signals generated by position information generating means in the catheter. The drawback of this earlier design lies in the fact that the gauging receptacles can be used for one single probe only. 
     There is a need for a device for the precise gauging and accuracy verification of surgical instruments. In particular, there is a need for a device that can detect any deformation or wear of surgical instruments by a comparison with factory calibration. More particularly, there is a need for a device that can detect my change in the length of a surgical instrument such as a needle or drill bit. 
     SUMMARY OF THE INVENTION 
     The invention relates to a device for gauging and verifying the precision of instruments comprising a holder, at least one instrument having a first set of dimensions upon manufacture and a new set of dimensions following use, and a carousel having at least one cavity configured and dimensioned in the shape of the at least one instrument. The carousel is rotatably coupled to the holder. At least two of the holder, the carousel and the instrument are fitted with markers or sensors for emitting or receiving signals for determining spatial information thereof. The spatial information is calibrated by inserting the at least one instrument in its respective cavity in the carousel and determining any change in dimensions from the first set of dimensions to the second set of dimensions. 
     Preferably, the carousel is rotatably coupled to the holder with a longitudinal member, and the device can include a computer processor for processing and calibrating the spatial information. The spatial information can be positional and orientational data. 
     In a preferred embodiment, the signals are electromagnetic waves. The signals can be generated by optical light sources, light emitting diodes, or infrared light emitting diodes. The signals also can be carried by fiber optics illuminated by a light source. In other preferred embodiments, the signals can be acoustic waves or magnetic fields. 
     The invention also relates to a method for gauging and verifying the precision of instruments, the method including the steps of: providing at least one of a holder and carousel, and at least one instrument with markers or sensors for emitting or receiving signals; inserting the at least one instrument in a carousel having at least one cavity, the cavity precisely configured and dimensioned in an as-manufactured shape of the at least one instrument so that the instrument in its as-manufactured shape is disposed at a first spatial location; rotatably coupling the carousel to a holder; determining a new spatial location for the at least one instrument in the cavity; comparing the first spatial location with the new spatial location to determine any change in dimensions of the instrument from the as-manufactured shape; and generating calibration data to account for the change in dimensions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein: 
     FIG. 1 shows an exploded perspective view of one embodiment of the calibration device according to the present invention; and 
     FIG. 2 shows a cross-sectional view of the calibration device of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A calibration device formed in accordance with the principles of the present invention is shown in FIGS. 1 and 2. Calibration device  10  includes a holder  12 , a carousel unit  14 , and a longitudinal member  16  for locating carousel unit  14  with respect to holder  12 . In a preferred embodiment, carousel unit  14  has a generally cylindrical shape, and includes a bore  18  having a longitudinal axis  20  and is configured to receive longitudinal member  16 . Bore  18  connects upper surface  22  and lower surface  24 . Preferably, longitudinal member  16  is a bolt that is configured to be received within bore  18 . Shaft portion  26  of longitudinal member  16  has longitudinal axis  27  and an outer diameter that closely matches the inner diameter of bore  18 , so that longitudinal member  16  provides a bearing surface along which carousel unit  14  rotates. Thus, a tight tolerance is preferably maintained between the outer diameter of longitudinal member  16  and the inner diameter of bore  18  so that there is a minimal radial clearance between them. 
     Holder  12  preferably includes a support  28  with brackets  30 ,  32  secured thereto having bores  34 ,  36  respectively. Bore  34  connects upper surface  38  and lower surface  40  of bracket  30 , while bore  36  of bracket  32  may only partially extend from upper surface  42  toward lower surface  44 , terminating at an intermediate surface  45 . Bores  34 , 36  are preferably coaxially disposed about longitudinal axis  46 . In a preferred embodiment, bore  36  includes internal threading  48 , as shown in FIG.  2 . Internal threading  48  advantageously has a profile designed to accommodate external threading, not shown, on lower portion  50  of longitudinal member  16 . In an alternate embodiment, bore  36  and lower portion  50  instead may have smooth surfaces with internal and external diameters, respectively, that have a minimal radial clearance between them. 
     When calibration device  10  is assembled, carousel unit  14  is placed between brackets  30 ,  32  of holder  12  such that longitudinal axes  20 , 46  are coaxial, and longitudinal member  16  is inserted through bores  34 ,  18 , and  36 . Thus, longitudinal axis  27  of longitudinal member  16  is also coaxially located with respect to longitudinal axes  20 ,  46 . To facilitate the assembly process, longitudinal member  16  preferably includes a knurled rim, screwdriver slot, and/or hex-socket on upper portion  51  to ease manipulation of longitudinal member  16 . These features also facilitate the use of a wrench or other tools for threading and unthreading longitudinal member  16  when inserted through the bores. 
     It will be appreciated that various carousel units  14  may be used with holder  12 . This is particularly advantageous, for example, because carousel units  14  may be loaded with selections of surgical tools that are appropriate for different surgical procedures. Thus, each surgeon using an operating room may choose to install a different carousel unit  14  in red holder  12  to accommodate the particular needs of the surgery to be performed. Alternatively, a surgeon may require that a diverse array of surgical tools be available during a given procedure, and a number of carousels may be available for the surgeon&#39;s use. The tight tolerance that is preferably maintained between the outer diameter of longitudinal member  16  and the inner diameter of bores  18  in carousels  14  permits the accurate use of many carousels  14  with the same holder  12 . Such an interchangeable arrangement facilitates efficient use of calibration device  10 , each holder potentially including different cavity configurations for housing surgical instruments as will be discussed below. 
     In a preferred embodiment, carousel unit  20  is provided with indentations  52  which are located in the vicinity of and correspond to each cavity  54 ,  56  in carousel unit  20 . The cavities  54 ,  56  can be precisely aligned relative to the calibration device  10 . Holder  12  is provided with a spring-loaded detent  58 , which extends from holder  12  to engage an indentation  52  in lower portion  53  of carousel unit  20 . Referring to FIG. 2, spring-loaded detent  58  is preferably a compression-spring unit  60  that has a cylindrical outer shape with threading. Unit  60  is installed in a like-threaded, tapped hole  62  in holder  12 , and includes a screw body  64 , a compression spring  66 , and a ball  68 . Ball  68  and spring  66  are mounted coaxially about axis  70  in a recess  72  formed in screw body  64 , such that ball  68  protrudes partway out of recess  72 . In an alternate embodiment, spring-loaded detent  58  includes a bevel-tip pin instead of ball  68 . 
     When carousel unit  20  is installed in holder  12  using longitudinal member  16 , the carousel unit may be rotated about axes  20 ,  27 ,  46 . Indentations  52  are aligned to intersect axis  70  on which ball  68  is disposed, such that ball  68  may seat in an indentation  52  when carousel unit  20  has been rotated to align ball  68  with indentation  52 . Because ball  68  is mounted on spring  66 , the spring  66  is naturally compressed as the ball is forced into recess  71  when an indentation  52  is not aligned with ball  68 . Although the amount of compression of spring  66  is decreased when ball  68  seats in an indentation  52 , spring  66  still provides enough force to maintain the engagement of ball  68  with an indentation  52  to releasably lock carousel unit  20  in a desired and precise orientation with respect to holder  12 . Advantageously, because spring-loaded detent  58  allows carousel unit  20  and its associated cavities to be precisely positioned by click-stop action, a number of surgical instruments may be housed in carousel unit  20  in a readily accessible fashion such that the calibration of each instrument&#39;s dimensions may be separately achieved. In addition, because carousel unit  20  can be precisely positioned, each surgical instrument housed in a cavity therein can be located at a precisely known, spatially defined position. 
     Cavities  54 ,  56  in carousel unit  20  are precisely machined to accommodate a surgical instrument of a given geometry. The contour of the cavities  54 ,  56  is formed so that it exactly mimics the shape of the surgical instrument to within a known, high tolerance. Each carousel unit  20  is provided on its outer surface with indentations  52  that each correspond to a cavity in carousel unit  20 , and further permit the click-stop detent on the holder, when engaged in an indentation  52 , to releasably hold the corresponding cavity in a precisely defined position and orientation relative to the calibration device  10 . Cavity  56 , for example, houses an instrument that fits into slot  74  in upper surface  22  of carousel unit  20 . Cavity  56  is open on side  76 , permitting a user to verify that an instrument inserted therein contacts the cavity bottom  78  and/or other surfaces of cavity  56 . Alternatively, a cavity  54  may be precisely machined in carousel unit  20  so that a surgical instrument may be housed therein by inserting the instrument into cavity  54  through a hole  80 . Cavities  54  may be open along a side  84  or  86  to permit a surgeon to verify that an instrument housed therein has been inserted properly. Access to other cavities machined into carousel unit  20 , not shown, may be provided by holes of other sizes and/or shapes, such as hole  88  in upper surface  22 . 
     Due to the instrument-matching contour of each cavity  54 ,  56 , each surgical instrument placed in its corresponding cavity  54 ,  56  is retained in a precisely defined position and orientation with respect to housing  12  and overall with respect to calibration unit  10 . Because of the precisely defined geometry of each cavity, surgical instruments housed in the cavities may be precisely gauged in terms of their position and orientation, even when such instruments do not have an unusual feature or a pointed end. 
     Each surgical instrument housed in a cavity  54 ,  56  is provided with markers or sensors for emitting or receiving signals such as electromagnetic waves, sound waves or magnetic fields. In a preferred embodiment, each surgical instrument, not shown, is provided with at least three light emitting diodes (LEDs). It is desirable to have at least three such markers or sensors so that triangulation principles may be used to gauge and verify dimensions and/or measurements, as is known in the art. Similarly, holder  12  is equipped with at least three LEDs  90  that permit the detection of the exact location and orientation of the device by means of a positional measuring system. Preferably, the light waves emitted by LEDs  90  are detected by at least two sensors that are part of an optical coordinate-measuring system (not shown). A positional measuring unit appropriate for this application is the three-dimensional motion-sensing system OPTOTRAK 3020, which is commercially available from Northern Digital Inc. The signals received by the optical sensors are processed by a computer, using techniques known in the art such as run-length measurements, interferometry, or videogrammetry, so that the measured values permit the determination of the exact location and orientation of calibration device  10  and particularly holder  12 . The LEDs provided on a surgical instrument are similarly utilized. In alternate embodiments, instead of utilizing the aforementioned optical light sources, other devices may be used such as reflectors illuminated by external light sources, infrared light emitting diodes (IREDs), or fiber optics illuminated by a light source. 
     Thus, alternate embodiments of calibration device  10  may employ other means for detecting location and orientation, such as transmitters emitting selected wavelengths of electromagnetic waves. While optical light sources may be used, other systems may be acoustic wave-based and rely upon transmitters emitting sound waves and receivers in the form of microphones. Induction coils may also be used in combination with Hall-effect detectors. The use of such transmitters and receivers facilitates the rapid and accurate gauging of different surgical instruments in terms of their spatial position and orientation, which in turn permits the rapid correction of measuring errors when using suitably equipped surgical instruments. Such correction may be made before, during, or after medical procedures that require the surgical instruments. 
     In a preferred embodiment, a plug connector  92  on computer interconnecting cable  94  contains an erasable electronic memory device  96  that stores the positional and orientational data for calibration device  10 . Preferably, electronic memory device  96  is an erasable programmable read-only memory (EPROM). Electronic memory device  96  may be used in conjunction with controller software operating on appropriate computer hardware. 
     While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein. 
     Further, it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. For example, only two transmitters and two receivers may be necessary for calibrating some devices. Furthermore, the rotation and alignment of the carousel unit about the holder may be achieved using an alternative mechanism that does not provide click-stop action, such as the formation of interlocking tongue and groove patterns on the carousel unit and holder. In addition, a holder that accommodates multiple carousels at one time may be provided. The calibration system may also be used in other industries that require the gauging and verification of instruments, such as the aerospace, microelectronics, automotive, and textile sectors. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is accordingly defined as set forth in the appended claims.