Abstract:
A method of registering an article having a surface to previously created scan data of the article includes the steps of providing a flexible substrate having multiple tracking points attached to the substrate, applying the substrate to the article to be registered, creating a model of the surface of the article from a location of each tracking point; and registering the model with the previously created scan data. A method of creating a model of a surface having a shape and an article to enable the creation of a model of a surface are also disclosed.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a flexible tracking article for use with a computer guided tracking system and a method of using the same. More particularly, this invention relates to a flexible tracking article for use with a computer guided surgical navigation system that can be registered with a preoperative or intraoperative scanned image with minimal patient discomfort.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are a wide variety of applications that require the identification and registration of a surface or shape with a previously created image. Certain manufacturing systems use the placement of tracking devices in predetermined locations to track the position of a work piece relative to an industrial process. Another use of this type of tracking system is in computer assisted or image guided surgical navigation systems.  
           [0003]    The use of surgical navigation systems for complex surgical procedures has become relatively widespread. These surgical navigation systems use specially developed tools that include tracking devices so that the surgeon can see the position of the surgical tool overlaid on a monitor showing a preoperative or intraoperative image. The preoperative images are typically prepared using well-known preoperative scanning techniques, such as MRI or CT scans. The intraoperative images can be prepared using a fluoroscope, a low level x-ray, and similar devices. Tracking devices typically include multiple optical emitters such as LED&#39;s that can be detected by the surgical navigation system. The surgical navigation system can determine the position and/or orientation of the surgical tool from the position of the emitters.  
           [0004]    In addition to tracking the surgical tool, the surgical navigation systems also must track or register the preoperative or intraoperative images to the patient in the operating arena so that the coordinate systems for the image files match the coordinate systems for the surgical navigation system. Typical registration procedures include placing fiducials or other markers at various locations on the anatomy of the patient. The preoperative or intraoperative scan is then performed with these markers in place and the markers then are either left in place until the surgery occurs or reapplied in the same position immediately prior to surgery. During the setup procedure before the surgical procedure, the scanned images in the computer are then registered to the patient by matching the location of these markers in the scanned images with the position of the actual markers on the patient in the surgical arena. Because the matching of the exact locations of these markers is critical to successful registration, the prior methods of attaching these markers usually involve an invasive procedure, such as attaching the markers themselves or a clamping device that carries the markers to bony areas of the patient. Alternatively, surgical personnel may use a permanent or semi-permanent marker to mark the patient at the locations where the markers or the clamping device are to be reapplied.  
           [0005]    It is well recognized that the prior techniques are uncomfortable for the patient and often leave permanent marks or scarring. As a result, there have been numerous attempts to create less invasive markers for use in the registration of scanned images to the coordinate system of the surgical navigation system at the time of surgery.  
           [0006]    In U.S. Pat. Nos. 6,122,541 and 6,248,900, a headband for frameless stereotatic registration is disclosed. This headband has markers, which can be visualized in the preoperative image scan and also includes LED&#39;s so that the headband can act both as a registration aid and as a tracking device for the patient during surgery. The system is registered during surgery by the standard registration practice of touching the tip of a tracking probe to each reference marker prior to beginning the surgical procedure.  
           [0007]    U.S. Pat. No. 5,676,673 discloses a headset to be mounted on the patient. The headset is used to mount a reference unit such as magnetic field generator to track a surgical instrument inside the patient relative to the preoperative image. Registration of the image to the patient is accomplished using conventional fiducial type markers attached to the patient&#39;s skin.  
         SUMMARY OF THE INVENTION  
         [0008]    According to one aspect of the present invention, a method of registering an article having a surface to previously created scan data of the article includes the steps of providing a flexible substrate having multiple tracking points attached to the substrate, applying the substrate to the article to be registered, creating a model of the surface of the article from a location of each tracking point, and registering the model with the previously created scan data.  
           [0009]    According to a further aspect of the present invention a method of creating a model of a surface having a shape includes the steps of providing a flexible substrate having multiple tracking points attached to the substrate, attaching the flexible substrate to the surface, determining a location for each tracking point, and calculating the shape of the surface from the location of each tracking point.  
           [0010]    According to an still further aspect of the present invention an article to enable the creation of a model of a surface includes a flexible substrate, multiple tracking points attached to the flexible substrate at predetermined locations, wherein the tracking points can be tracked by a tracking system, and a data link to enable communication from the flexible substrate to a tracking system.  
           [0011]    According to a yet further aspect of the present invention an article to enable the creation of a model of a surface includes a flexible substrate, multiple light emitting diodes attached to the flexible substrate at predetermined locations, wherein each light emitting diode is in a fixed relation to its neighboring light emitting diodes; and a data link to enable communication from the flexible substrate to an optical tracking system.  
           [0012]    Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic representation of the surgical navigation system using the flexible tracking device and method of the present invention;  
         [0014]    [0014]FIG. 2 is a block diagram of the surgical navigation system of FIG. 1;  
         [0015]    [0015]FIG. 3 is a plan view of one embodiment of the multiple tracking device of the present invention;  
         [0016]    [0016]FIG. 4 is an isometric view showing a flexible tracking device of the present invention adapted for ear, nose and throat surgery affixed to a patient;  
         [0017]    [0017]FIG. 5 is a cross section of the flexible tracking device taken generally along the lines  5 - 5  of FIG. 4;  
         [0018]    [0018]FIG. 6 is an enlarged plan view of a portion of the flexible tracking device of FIG. 4;  
         [0019]    [0019]FIG. 7 is a flow diagram of a computer program for creating a model embodying one aspect of the method of the present invention; and  
         [0020]    [0020]FIG. 8 is a flow diagram of computer program for registration of scan data embodying one aspect of the method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    [0021]FIGS. 1 and 2 are a schematic view and a block diagram of a surgical navigation system  50  adapted to track a surgical tool  52  having a tool tracking device  54  associated therewith. The surgical navigation system  50  includes a personal computer  56  that has an internal CPU  58 , a memory  60  and a storage device  62 . Also associated with the personal computer  56  are a pointing device or mouse  64 , a keyboard  66  and a monitor  68 .  
         [0022]    The surgical navigation system  50  also includes a camera  70 , which is comprised of three separate CCD camera arrays  72 ,  74  and  76 . These camera arrays  72 ,  74  and  76  are adapted to detect infrared signals generated by the tool tracking device  54  and also by a flexible tracking device  88 . The camera  70  can be conveniently mounted a cart (not shown) or can be physically mounted or attached to an operating room wall (not shown) or to a operating room light (not shown). The surgical navigation system  50  also includes a localizer  82  that cooperates with the camera  70  to identify the location of LED&#39;s on the flexible tracking device  88  and LED&#39;s  92  on the tool tracking device  54 , as well as any other tracking devices that may be within the field of the camera  70 . The CCD camera arrays  72 ,  74  and  76  contain their own calibration information and transmit the position data from the various LED&#39;s to the localizer  82 . The localizer  82  then converts the raw position data into position and orientation data using techniques well known to those of skill in the art. The localizer  82  communicates the position and orientation data to the personal computer  56  through a cable  112 . The camera  70  also includes two infrared transceivers (IR)  78  and  80  that are capable of communicating with the flexible tracking device  88 , the tool tracking device  54 , and any other suitable tracking devices within the view of the camera  70 . The transceivers  78  and  80  are directly connected to computer  56  through a separate circuit in a cable  84 . The flexible tracking device  88  has an IR transceiver  98  built into a battery pack  96 , which is attached to the flexible tracking device  88  by a cable  94 . Similarly, the tool tracking device  54  has an IR transceiver  100  also capable of communicating with the IR transceivers  78  and  80 . The tool tracking device  54  also includes a status light  102  and a plurality of buttons  104 ,  106  and  108  that are capable of being programmed to transmit certain signals through the IR transceiver  100  to the surgical navigation system  50 . The tool tracking device  54  also includes a battery  110 .  
         [0023]    With regard to FIG. 3, a second embodiment  120  of the flexible tracking device of the present invention is shown. The flexible tracking device  120  includes a flexible sheet  122  having a 6×8 array of LED&#39;s  124  affixed to the surface thereof. As shown in FIG. 3, the 6×8 array of LED&#39;s  124  are all powered by a power source such as a battery pack  128  which is attached to flexible sheet  122  by cable  126 . The battery pack  128  also includes an IR transceiver  130  similar to that discussed above. For simplicity, the wiring from the battery pack  128  to each of the LED&#39;s in the 6×8 array of LED&#39;s  124  is not shown, however each LED in the 6×8 array of LED&#39;s  124  is connected to the battery pack  128  and is capable of being independently illuminated so that surgical navigation system  50  can determine the position of each individual LED in the 6×8 array of LED&#39;s  124 . The flexible sheet  122  has a layer of light adhesive on one side and is stuck on to the patient  86  using this adhesive. The LED&#39;s in the 6×8 array of LED&#39;s  124  that are visible to camera  70  can be used by the surgical navigation system  50  for surface matching as well as patient tracking.  
         [0024]    The geometry of the sheet  122  can be initialized by tracking rigid tissues of the patient  86  after determining the spatial relationship of the 6×8 array of LED&#39;s  124  with the camera  70 . A second mode of initialization is to track soft tissue displacement or deformation over time. Using the first mode, the positional information of the flexible sheet  122  and the 6×8 array of LED&#39;s  124  can be used to register the tracked feature of the patient to an image data set, such as a CT scan, using, for example, surface matching techniques.  
         [0025]    With reference to FIG. 4, a third embodiment of the flexible sheet of the present invention is shown. In this embodiment, a flexible tracking device  140  is similar to the flexible tracking device  88  and has a flexible sheet  142  having an array of LED&#39;s  144  spaced at known intervals from each other. The array of LED&#39;s  144  differs from the 6×8 array of LED&#39;s  124  in that it is not a rectangular array. Nonetheless, each LED  152  in the array of LED&#39;s  144  is in known relationship to its neighbor LED&#39;s. In the embodiment of the flexible tracking device  140  shown in FIG. 4, the flexible tracking device  140  is attached to surgical navigation system  50  directly by cable  146 , which is attached to the flexible tracking device  140  by a flexible cable extension  148  of the flexible tracking device  140 . Flexible cable  148  is attached to cable  146  by a coupling  150 . The cable  146  includes a connection from an external power source (not shown) to each LED in the array of LED&#39;s  144  through the flexible cable extension  148 . As shown in FIG. 4, the entire flexible tracking device  140  is capable of being sold as a disposable item in a pre-sterilized condition. The flexible tracking device  140  can be coupled with cable  146  at a distance from the patient  86  such that a sterile field can be maintained during a surgical procedure. As shown in FIG. 4, the flexible array  140  conforms to the features of patient  86  including the bony structures of the nose, forehead and cheekbones to provide a suitably firm surface such that the array of LED&#39;s  144  can be used for surface matching to register with previously scanned data. The detail of the electric connection  149  from the coupling  150  to the array of LED&#39;s  144  is shown in FIGS. 5 and 6.  
         [0026]    With reference to FIG. 5, a cross sectional view of the flexible tracking device  140  is shown. As shown in FIG. 5 and also shown in FIG. 6, the electric connections  149  of the flexible tracking device  140  have a negative flexible conductive circuit  154  and a positive flexible conductive circuit  156  electrically connected to each LED  152  in the array of LED&#39;s  144 . The negative flexible conductive circuits  154  are sequentially connected to the negative terminals of each LED  152 . Similarly, the positive flexible conductive circuit  156  is connected to the positive terminal of each of the LED&#39;s  152 . As shown in FIGS. 4, 5, and  6 , the negative flexible conductive circuits  154  and the positive flexible conductive circuit  156  can be formed directly on the surface of flexible sheet  142 . The negative flexible conductive circuits  154  and the positive flexible conductive circuit  156  can formed from any suitable conductive material such as copper aluminum, silver, and the like. In addition, conductive inks can also be used to print the electric circuits  149  directly onto the flexible sheet  142 . Examples of conductive ink materials include conductive copper inks, conductive silver inks and any other suitable materials that can be applied to form a flexible circuit that will transmit electricity and also can be sterilized at least one time. The electric connections  149  can be formed on the flexible substrate by any conventional method such as standard chemical etching techniques where a solid plane of copper is etched to remove the copper from the non-conducting areas to reveal the conductive traces or screen or other conventional printing processes used to print conductive circuits.  
         [0027]    The LED  152  is bonded directly to flexible sheet  142  by soldering the LED directly to the negative flexible conductive circuits  154  and the positive flexible conductive circuit  156 . In addition, the LED  152  is coated with an essentially optically transparent coating to form an essentially transparent protective coating  160 . Suitable materials for this coating include transparent epoxy compounds conventionally used in the industry. Coating  160  protects the LED  152  from inadvertent movement. It is not necessary for coating  160  to completely cover the entire surface of flexible substrate  142 . However, while it is not shown in FIG. 5, it may be desirable for the coating  160  also to cover the negative flexible conductive circuits  154  and the positive flexible conductive circuit  156 . Typically this is not necessary because a protective coating is formed as part the normal flexible circuit manufacturing process that covers the negative flexible conductive circuits  154  and the positive flexible conductive circuit  156 . The protective coating formed during the manufacturing process is removed only where connections to the LED  152  are to be made.  
         [0028]    The flexible sheet  142  can be formed from any suitable surgically acceptable flexible insulating sheet material such as industry standard flexible FR4 sheet materials. These flexible sheet materials are available from a number of commercial sources. The base materials for most flexible FR4 sheets are polymeric materials such as polyimide, polyester, and the like.  
         [0029]    Lastly, as shown in FIG. 5, attached to the back of flexible sheet  142  is an adhesive  158 . The adhesive  158  can be any adhesive suitable for human contact. Also, it is preferable that the adhesive  158  be a contact adhesive which while reasonably tacky to a patient&#39;s skin is one that can be removed without damage to the patient&#39;s skin. Examples of suitable adhesives for use in the present invention include contact adhesives such as surgical adhesives, hairpiece adhesives or other similar adhesives that are suitable for use in contact with human skin.  
         [0030]    As shown in FIGS. 4, 5 and  6 , the flexible circuits  154  and  156  are arranged on the flexible tracking device  140  such that the flexible tracking device  140  can be trimmed to fit a particular situation without disabling any of the LED&#39;s  152  that remain after the flexible tracking device  140  has been trimmed.  
         [0031]    With reference to FIG. 7 that shows a flow diagram for creating a model of a surface for use in the method of the present invention. The method begins at a block  180  that initiates the formation of a model from the array of LED&#39;s on the flexible tracking device  140 . Control passes to a block  182  that determines if a minimum number of LED&#39;s on the flexible tracking device  140  are visible to the camera  70 . If insufficient LED&#39;s are visible, the control passes to a display block  190  that instructs the user to turn the object so more LED&#39;s will be visible. Based on the identity of the LED&#39;s that are visible, the block  190  will instruct the user as to which way to move the object. If sufficient LED&#39;s are visible, the block  182  will pass control to a block  184  that determines the identity of all visible LED&#39;s. After the identity of the visible LED&#39;s has been fully determined, a block  188  will determine the quality of the various LED&#39;s that are visible by comparing the location of the visible LED&#39;s with a database of relationships among the LED&#39;s within the array of LED&#39;s that has been stored in a block  186 . The quality of the LED image relates to the direction each particular LED is pointing. If an LED pointing directly at the camera  70 , the quality of that LED&#39;s image is considered good. However, if an LED is pointing in a direction that is not normal to the camera  70 , the positional data from that LED is not as reliable. If there are insufficient LED&#39;s pointing normal to the camera  70 , the block  188  will again pass control to the display block  190  that will instruct the user to move the object.  
         [0032]    If the block  188  determines that the image quality of the visible LED&#39;s is acceptable, control passes to a block  192  that constructs a model of the shape of the object from the LED&#39;s that are visible. The model is created by determining a series of planes from groups of visible LED&#39;s. Thereafter these planes are combined to create the model of the object. The more LED&#39;s that are visible, the more precise the model will be. If a previously created preliminary model has been created, the block  192  will combine the data from the preliminary model with the new position data for the additional LED&#39;s and create a more refined model. After the model has been constructed, control passes to a block  194  that determines if all LED&#39;s have been used to construct the model created by the block  192 . If less than all LED&#39;s have been used, then the block  194  will consider the model created by the block  192  as a preliminary model and control passes to the display block  190  that instructs the user to turn the object and the process is repeated until all LED&#39;s have been used to create the model. While the method has been described with a system that requires all LED&#39;s to be used to construct the model, if there are a large number of LED&#39;s on the flexible tracking device, the block  194  could be programmed to accept some number less that all LED&#39;s and consider the model complete. In this case, the system could update the model as more LED&#39;s become visible after registration as described below, in which case, the system would update the model with the newly created model created as the object is moved during a procedure. Once the block  194  determines that sufficient LED&#39;s have been used to create the model, that the model is sufficiently described and is complete. Control then will pass to a block  196  that stores the model in the memory  60  of the computer  56  for use in the registration process to be described below. Control then passes to a block  200  that begins the registration process.  
         [0033]    Turning now to FIG. 8 that shows a flow diagram of the registration process that as an aspect of the present invention. The method continues at the block  200  that initiates the registration procedure. Control passes to a block  202  that checks to see the number of registration procedures that have been planned and have not been executed. If the is only one remaining registration procedure planned, the system branches to a display and decision block  206 . If there is more than one unexecuted registration procedure, control passes to a display box  204  that displays a messaged that the user must select a particular registration procedure and the system also displays the unexecuted registration procedures that have been planned so that the user can select the next procedure to execute. After the user selects the next registration procedure, the system moves to the display and decision block  206 . The display and decision block  206  displays the following user selectable registration procedures: point matching, surface matching or auto registration.  
         [0034]    If the user chooses point matching at the display and decision block  206 , the system branches to a block  208  that determines how many reference sets are available. If the block  208  determines there are two or more reference sets, the system passes control to a block  210  that displays a message for the user to select a reference set. The system waits until a suitable set is selected. After one reference set is selected, the system moves to a block  212  that conducts a conventional point matching routine using well defined landmarks of the object, such as the tip of the nose or the inside of the ear. After the block  212  has conducted the point matching routine, the system moves to a block  214  that confirms success of the registration procedure. After the block  214  is executed, the system then determines by a block  216  if a further registration procedure has been planned. If the system determines there are no further registration procedures planned, the system moves to an exit block  218 . However, if the system determines there are further registration procedures planned the system loops back to the block  200  and the method is again conducted until there are no further unexecuted planned registration procedures.  
         [0035]    If the user chooses surface matching at the display and decision block  206 , the system branches to a block  220  that conducts an identical determination to that conducted by the block  208  previously described. If the block  220  determines there are two or more reference sets available, the system branches to a block  222  that conducts an identical determination to that conducted by the block  210  previously described. The system then passes to a block  224  that conducts a conventional point matching procedure. After the point matching procedure is concluded, the system moves to a block  226  that conducts a conventional surface matching procedure using the information generated by the point matching procedure. After the block  226  has conducted the surface matching routine, the system moves to a block  214  that confirms success of the registration procedure. After the block  214  is executed, the system then determines by a block  216  if a further registration procedure has been planned. If the system determines there are no further registration procedures planned, the system moves to an exit block  218 . However, if the system determines there are further registration procedures planned the system loops back to the block  200  and the method is again conducted until there are no further unexecuted planned registration procedures.  
         [0036]    If the user chooses auto registration at the decision and display block  206 , the system branches to a block  228  that determines if the flexible tracking device  140 , or a similar device, has been connected to the system. If the flexible tracking device  140  has not been connected, the system branches to a display block  230  that instructs the user to attach the flexible tracking device  140  to the system. The system then waits until the user either attaches the appropriate flexible tracking device or the user chooses to exit the procedure. After the system determines that the flexible tracking device  88  has been attached, the system moves on to an auto registration block  232 . The auto registration block  232  determines if a shape model has been constructed during the initialization procedure. If no model has been constructed, control passes to a display block  240  that instructs the user to initialize the system to create a model or exit. If a model has been constructed and has been stored in a block  235 , control passes to a block  236  that determines if the shape model from the block  235  matches the scanned image from a block  234  in the memory  60  of the computer  56  within a predetermined and prestored error level. If the image and the shape model are within the error level, a block  238  registers the location of the flexible tracking device to the scanned image and the system passes control to the block  214  that confirms success of the registration procedure and proceeds as described above. If the block  236  determines the scanned image and the shape model are not within the acceptable error level, the display block  240  instructs the user to reinitialize the model creation. Alternatively, the user can choose to exit the auto registration procedure and choose a different registration method.  
         [0037]    In addition, while the invention has been described with reference to a surgical system using scanned images of a patient, the method and flexible tracking device can be used to register the shape of any article to a scanned image, such as manufacturing work pieces, and the like.  
       Industrial Applicability  
       [0038]    The present invention is useful to quickly, easily and in a non-invasive enable a surgical system to track and register preoperative and intraoperative scanned images to a patient&#39;s anatomy without the need for invasive marking procedures.  
         [0039]    Numerous modifications to the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention and to teach the best mode of carrying out same. The exclusive rights to all modifications which come within the scope of the appended claims are reserved.