Abstract:
The invention relates generally to apparatus and devices for neuronavigation. A non-invasive dental based fiducial array is disclosed. The fiducial array has a base support member, one or more removable and repositionable marker bases supported by the base support member and a stopper spaced from and supported by the base support member that engages a part of the head of a patient or an animal and cooperates with the base support member to immobilize the fiducial array relative to a location of the head, such as maxillary teeth. An anchoring site is formed on the base support member to accept a custom made dental impression to precisely position the base support member relative to the location of the head.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Application No. 61/251,967 filed on Oct. 15, 2009, hereby incorporated by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates generally to apparatus and devices for neuronavigation. More particularly, a non-invasive dental based fiducial array is disclosed. 
       BACKGROUND OF INVENTION 
       [0003]    It is known to use fiducial arrays to provide fiducial points for neuronavigation. Markers attached to a fiducial array provide the required reference points in an image scan. While fiducial arrays may be attached to a head by employing anchoring holes drilled in the skull, non-invasive fiducial arrays are often preferred. 
         [0004]    For example, there are known dental based non-invasive fiducial array such as those described in U.S. Pat. Nos. 6,096,048 and 6,223,067 and United States Patent Application Publication No. US2004/0015176. However, often, it is desirable that a dental based fiducial array can be removed from a patient&#39;s mouth (or an animal&#39;s mouth) and re-installed later very accurately to the original position in the mouth. The accuracy is crucial to the precision of image scan and for registration of the imaged anatomy to the scanned images. Further, structural members of a fiducial array may not always be suitably positioned for patients of all ages. Similarly, different geometries of animals of different species may also cause interferences with part of the geometries or require re-positioning of fiducial markers to different locations to closely follow the location of brain regions. 
         [0005]    The forgoing creates challenges and constraints for a fiducial array for providing easily locatable fiducial points for neuronavigation and other similar procedures. There is therefore a need for a fiducial array as compared to the existing art. It is an object of the present invention to mitigate or obviate at least one of the above mentioned disadvantages. 
       SUMMARY OF INVENTION 
       [0006]    The invention relates generally to apparatus and devices for neuronavigation. More particularly, a non-invasive dental based fiducial array is disclosed. One aspect of the present invention involves a fiducial array that includes a base support member, one or more removable and repositionable hubs supported by the base support member and a stopper spaced from and supported by the base support member that engages a part of the head of a patient or an animal and cooperates with the base support member to immobilize the fiducial array relative to maxillary teeth. An anchoring site is formed on the base support member to accept a custom made dental impression to precisely position the base support member relative to the maxillary teeth. The hubs have removable marker base attached thereto for supporting fiducial markers. 
         [0007]    In an aspect of the invention, a non-invasive, dental-based fiducial array is provided. The fiducial array includes a base support member, a support arm, and one or more marker bases removably and re-positionably mounted to the support arm, each of said one or more marker bases being adapted for mounting a fiducial marker. The base support member is shaped to be received in oral cavity of a person or an animal and includes an anchoring site for accepting a customized dental impression. The support arm is pivotally secured to the base support member. 
         [0008]    One feature of the aspect of the invention provides a fiducial array that further includes a stopper spaced from and re-positionably mounted to the base support member. The stopper is sized to engage the head of the person or the animal and cooperating with the base support member to immobilize the base support member relative to the head. As a further feature, the fiducial array also includes a mounting post slidably coupled to the base support member and a mounting block releasably secured to the mounting post, the stopper being re-positionably secured to the mounting block. 
         [0009]    According to another feature of the aspect of the invention, the fiducial array further includes a removable hub mounted on the support arm, the one or more marker bases being mounted to the support arm through the removable hub. 
         [0010]    According to yet another feature of the aspect of the invention, the fiducial array further includes a connection member that pivotally connects the support arm to the base support member. According to, a further feature, the connection member includes two pivot connections and the two pivot connections have non-parallel pivot axes. 
         [0011]    In other aspects the invention provides various combinations and subsets of the aspects described above. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    For the purposes of description, but not of limitation, the foregoing and other aspects of the invention are explained in greater detail with reference to the accompanying drawings, in which: 
           [0013]      FIG. 1  is a perspective view showing a dental based fiducial array; 
           [0014]      FIG. 2  is a cross-sectional view showing a connection link that pivotally connects support arm of the fiducial array of  FIG. 1  to its base support member; 
           [0015]      FIG. 3  illustrates in a perspective view a base support member of the fiducial array shown in  FIG. 1 ; 
           [0016]      FIG. 4  shows in a perspective view an upright post; 
           [0017]      FIG. 5  shows in a perspective view a support arm; 
           [0018]      FIG. 6  shows in a perspective view an alternative support arm; 
           [0019]      FIG. 7  shows in a perspective view a removable hub (with some spokes and fiducial marker discs removed for better illustration) pivotally supported on a base plate of the fiducial array shown in  FIG. 1 ; 
           [0020]      FIG. 8  is a perspective view showing a dental based fiducial array that includes a stopper; 
           [0021]      FIG. 9  is a perspective view a stopper of the fiducial array of  FIG. 8 ; 
           [0022]      FIG. 10  shows in a cross-sectional view a stopper that includes a slide mount secured to a mounting post which is in turn secured to a base plate; 
           [0023]      FIG. 11  shows in a perspective view another construction of a dental-based fiducial array; and 
           [0024]      FIG. 12  shows in an exploded view the dental-based fiducial array of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0025]    The description which follows and the embodiments described therein are provided by way of illustration of an example, or examples, of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation, and not limitation, of those principles and of the invention. In the description which follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals. 
         [0026]    Referring to  FIG. 1 , there is shown an embodiment of a dental based fiducial array, generally indicated by reference number  20 . Fiducial array  20  has a base support member such as a base plate  22 . Base plate  22  may have a general U-shape, or some other shapes to be received in oral cavity of a person or an animal so that the person or animal may bite part of the base plate to immobilize the base plate with respect to a location of head, such as upper or lower jaw, or maxillary teeth or upper palate, while some other part of the base plate can be exposed for supporting other components of the fiducial array, without interfering with the anatomy of the oral cavity or the head. Base plate can be sized to fit human and/or animal mouth sizes. It will be appreciated, however, that the base plate may also take other shapes, such as an arc, a plate having an inner curved edge to accommodate the jaw anatomy, among others. As will be described in detail later, base plate provides an anchor point for precise positioning of the fiducial array relative to a location of the head, such as maxillary teeth of a person or animal. The exposed portion of the base plate can also be used for positioning the person or the animal&#39;s head relative to other medical instrument where needed. 
         [0027]    The base plate  22  has an anchoring site  70  for receiving a custom made dental impression. The anchoring site  70  has a plurality of slots  72  (or holes or other anchoring arrangements) formed in the base plate  22 . A dental impression of maxillary teeth (and if desired, upper palate) of a patient or an animal is formed from a thermo-moldable dental plastic and includes a plurality of projections to be received in the plurality of slots  72 . Conveniently, the thermo-moldable dental plastic may be placed on the base plate  22  with the maxillary teeth pressed against the base plate to make the dental impression. The pressure applied tends to create a plurality of projections that extend into and match the shape and location of the plurality of slots, thus providing desirable fitting between the dental impression and the base plate. 
         [0028]    One or more removable marker support, such as marker discs  24  are removably and pivotally joined to and supported by the base plate  22 . As will be described in detail later, each marker disc  24  is adapted for mounting a marker, which provides locatable fiducial points for neuronavigation. A support arm  42  may be provided for mounting the marker discs. A connection member, such as connection link  102  that includes a pivot connection or connections  30 , pivotally joins the support arm  42  to the base plate. Pivot connections allow the marker discs to be repositioned relative to the base plate, when required.  FIG. 1  shows a U-shaped base plate. Connection link is mounted to the base plate  22  at the distal ends  26  of the legs  28  of the U. This allows the markers to be placed as close to the brain region as possible, often of interest to a neurosurgeon. 
         [0029]    Connection link  102  shown in  FIG. 1  and  FIG. 2  has two pivot connections  30 , each pivot connection having a pivot axis A, B, and pivot axes A, B being non-parallel. Referring to  FIGS. 1 to 5 , an upright post  32  is pivotally joined to the base plate adjacent its distal end  26 . The upright post  32  has a toothed connection surface  34  to mate with a corresponding toothed connection surface  34  formed on the base plate  22  ( FIG. 3 ). A securing screw  36  or such other appropriate fasteners can be used to pass through a throughhole  38  formed in the base plate and threaded into a threaded hole  40  formed in the upright post to releasably secure the upright post to the base plate  22 . As can be more clearly seen in  FIG. 2 , upright post  32  is pivotable about rotational axis A of the securing screw  36 . Thus, connection between the upright post to base plate provided by the securing screw  36  allows the upright post  32  to pivot about the pivot axis A and provides the first pivot connection  30 . Tightening the securing screw  36  urges the toothed connection surfaces  34  toward each other until stopped and thereby fixes the orientation of the upright post  32  about its pivot axis. The toothed connection surfaces  34  define a series of pre-selected angular positions and facilitate precise angular positioning of the upright post. 
         [0030]    A support arm  42  is pivotally joined to the upright post  32  at a location spaced from the base plate. A securing screw  36  is used to provide a second pivot axis B and to secure the support arm  42  to the upright post  32 . Similarly, matching toothed connection surfaces  34  may be formed on support arm  42  and upright post  32 , as shown in  FIGS. 4 and 5 , for precise angular positioning of support arm  42  relative to upright post  32 . Throughhole  38  formed in support arm  42  and threaded hole  40  in upright post  32  allow a securing screw  36  to pass through and secure the support arm to the upright post. The connection between support arm  42  and upright post  32  provides the second pivot connection  30 , i.e., a pivot connection pivotable about pivot axis B. Of course, a threaded hole may also be formed in support arm  42  and a throughhole formed in upright post  32 , or throughholes be formed in both support arm  42  and upright post  32 , in which case a nut and a bolt will be required. 
         [0031]    Support arm  42  may be adapted for direct attachment of fiducial marker discs  86 .  FIG. 5  illustrates a support arm  42  that has a series of spoke holes  80  formed along one of its sides, each of which is suitably sized for accepting a spoke  84  that supports a fiducial disc  86  thereon. Support arm may be straight or suitably curved as seen in  FIG. 1 . One support arm  42  shown in  FIG. 1  is suitably curved so that the markers can be positioned as close to the head of a patient or animal as possible.  FIG. 6  illustrates another example of a support arm for direct attachment of fiducial marker discs. Support arm  42 ′ shown in  FIG. 6  has a round terminal end  104 . A series of spoke holes  80  are formed on the periphery side  106  of the terminal end  104  for accepting spokes  84  to mount fiducial marker discs  86  thereon. 
         [0032]    As yet another alternative, instead of forming a round terminal end at the distal end of support arm, one or more removable hubs  24  may be provided. As the pivot axes A, B of the two pivot connections  30  are in different planes and oriented differently, removable hub  24  attached to support arm also has at least two degrees of freedom. Referring to  FIGS. 7 and 8 , a removable hub  24  can be attached to support arm  42 ″ by way of a short arm  44 . A screw  46  or pin secures the removable hub  24  to the short arm  44 . Each removable hub  24  has a generally cylindrical body  74 , with a central hole  76  for receiving a short arm  44  of support arm  42 ″ and a plurality of spoke holes  80  formed on and angularly spaced along the side surface  82  of the cylinder. A spoke  84  is received in a spoke hole  80  and supports a fiducial marker base  86 . Spoke holes  80  may be formed along a generally radial direction and transverse to the longitudinal axis of the cylinder. They may also be at an angle different from 90° with the longitudinal axis of the cylinder. For example, the angle may be between 60° and 90°. 
         [0033]    The orientation of the removable hub  24  relative to the support arm  42 ″ may be adjusted by turning it around short arm  44  prior to tightening the securing screw  36 . Alternatively, short arm  44  may have a non-circular cross-section, with the hub having a hole of matching cross-sectional shape for receiving the short arm. For example, the cross section may be a hexagon, or some other polygon. The non-cylindrical cross-section allows accurate orientation of the hub relative to the support arm and any subsequent repositioning. With a cross-sectional shape such as hexagon that has rotational symmetry, stepped adjustment of relative orientation of the hub will also be possible. Of course, other means may be provided for accurate repositioning, such as markings on the hub and the short arm or the support arm. 
         [0034]    As noted, a fiducial marker base  86  is supported at the top end  90  of a spoke  84 . Fiducial marker base  86  and spoke  84  may be individually formed and then joined together, or integrally formed as one piece. Fiducial marker base shown in  FIG. 1  and  FIG. 7  has the shape of a disc, though other shapes are also possible. The fiducial marker disc  86  is secured to the spoke. The top end of the spoke has a supporting surface  92 . The orientation of supporting surface  92 , i.e., the normal of the surface, may not be aligned with the longitudinal axis of the spoke  84 . Instead, the supporting surface may be inclined, with the normal and the longitudinal axis of the spoke  84  forming a non-zero inclination angle. With markers positioned on supporting surfaces at such an inclination angle, the markers will not be co-planar, which may be desirable for certain applications. The inclination angle may be conveniently selected to be 30°, though it may be an angle up to 45°, or zero (i.e., not inclined). 
         [0035]    A fiducial marker disc  86  is adapted for accepting fiducial markers (not shown). At the center of the fiducial marker disc  86  there may be provided a small nipple  94 , for fitting a self-adhesive multi-modality marker. A receiving hole may be formed in spoke  84  as shown in  FIG. 6  for receiving the small nipple. The nipple may have a nipple hole  96  (about 1.5 mm), into which the distal tip of a neuronavigation pointer (not shown) can be touched to co-register the location of the supported fiducial marker to scan imaging data. 
         [0036]    Conveniently, a stopper  50  is provided for immobilizing the base plate relative to a location of the head, such as upper or lower jaw. Referring to  FIG. 8 , a base plate may be configured for supporting the stopper  50 , for example, by integrally forming an extended leg  48  at the bottom segment of U for mounting the stopper thereon. A stopper may be in the form of an eye bar  52  or a set of eye bars  52 . Stopper  50  engages a region of the head of the patient or the animal. Eye bar  52  is spaced from base plate. Its height relative to the base plate  22  is adjustable so that appropriate pressure can be applied by the cooperating stopper and base plate  22  to increase the position retaining power of the fiducial array. As will be appreciated, with an extended leg  48  integrally formed with base plate  22 , the extended leg  48  may also be used for supporting other instruments on the base plate, or for attaching the base plate to a support structure or surface to immobilize head during imaging or surgery procedure, where desirable or required. 
         [0037]    Referring to  FIGS. 8 ,  9  and  10 , a mounting post  54  is secured to the extended leg  48  by a securing bolt  56 . Eye bar  52  (or set of eye bars) is supported by a slide mount  58  that is slidably attached to the mounting post for adjusting height of the eye bar  52  relative to the base plate  22 . A slot  60  is formed in the extended leg  48 . A bolt hole  62  is formed in the mounting post  54 . A securing bolt  56  passes through the slot  60  and is threaded into the bolt hole  62  of the mounting post to secure the mounting post to the base plate. The slot  60  allows the mounting post  54  to be positioned at any location along the slot as may be desired. Thus, both height of eye bar  52  and distance of eye bar  52  along extended leg  48  can be adjusted and eye bar  52  can be re-positioned by adjusting its height and distance as desired or needed. 
         [0038]    The transverse cross section of mounting post  54  may have any suitable shape.  FIGS. 8 and 9  show an example that has a trapezoidal shape. The slide mount  58  has a corresponding trapezoidal through hole  64  for the trapezoidal shaped mounting post  54  to pass therethrough. A tightening screw  66 , or other suitable engagement means, is provided for pulling the mounting post towards the slide mount, along a direction from the longer side to the shorter side of the trapezoidal. Eye bar  52  has an eye bar slot  68  for a tightening screw  66  to pass through and to secure the eye bar to the slide mount  58 . The eye bar slot allows the eye bar to be positioned differently as the eye bar slides relative to the slide mount  58 . 
         [0039]    Of course, although a stopper in the form of a height-adjustable eye bar is described, the stopper may take any other suitable form. For example, a strap system (or even much simpler surgical tape) can be used to replace the eye bar for immobilizing the base plate relative to the maxillary teeth (or upper palette). 
         [0040]    The device described herein allows it to be applied to patients of different ages and also to animals of different species. To use the device for a patient (or an animal), a suitably sized base plate  22  is selected and placed in the mouth of the patient or animal. A suitable mass of thermo-moldable dental plastic, already appropriately heated, can be placed on the base plate for making a customized dental impression. Once solidified, the dental impression tends to be securely attached to the base plate, which will provide accurate anchor points when the fiducial array is reinstalled in the mouth of the patient or animal, from whom the dental impression is made. 
         [0041]    One or more marker discs are installed for mounting fiducial markers. Position of the marker discs, or fiducial markers, can be adjusted by rotating (i.e., pivoting) the upright post  32  and the support arm  42 . The pivot connections  30  provided by the upright post and the support arm allow the marker discs, or removable hubs if used for supporting marker discs, to be placed as close to patient&#39;s head (or the animal&#39;s head) as possible and close to the brain area which is of interest to a neurosurgeon. Once the marker discs or the removal hubs are suitably positioned, the securing screws  36  can be tightened. It is possible that one or more of the spokes  84  or fiducial marker discs  86  may interfere with some parts of the patient&#39;s (or the animal&#39;s) anatomy. The interfering fiducial marker disc or discs can be removed or the interfering spoke(s) be removed to avoid interference. The position of the removable hub or hubs and the fiducial marker discs may be recorded or left unchanged for future use. 
         [0042]    When the fiducial array needs to be reinstalled, the custom made dental impression is matched with the dental structures of the patient or animal, such as formation of maxillary teeth or upper palate, to ensure accurate positioning of the base plate  22  and the fiducial marker discs  86  carried by the base plate. The positions of fiducial marker discs may be further fine tuned should there be any relocation of these marker discs since last image scan. The height and position of stoppers  50  can be suitably adjusted to immobilize the fiducial array  20  during the surgical, imaging or other medical procedures. 
         [0043]      FIGS. 11 and 12  show in a perspective view and an exploded view another construction of a dental-based fiducial array  20 ″. Fiducial array  20 ″ is similar in construction to fiducial array  20  shown in  FIG. 1 . Unlike the single-piece construction of support arm  42  of fiducial array  20 , support arm  100  has a multi-section construction. As shown in  FIGS. 11 and 12 , support arm  100  has a first section  102  and a second section  108 , pivotally joined to each other. Toothed connection surfaces  34  can be provided at each pivot connections to define a series of pre-selected angular positions and facilitate angular positioning of neighboring sections. Although only two sections are shown in  FIGS. 11 and 12 , it will be understood that more sections may be used where appropriate and feasible. The distal section, or the second section  104  in this case, is shown to be the same as the short support arm  42  that has a round terminal end for mounting fiducial marker discs as described in connection with fiducial array  20  and illustrated in  FIG. 6 . Support arm  100  may also include holes  80 , similar to that shown in  FIG. 1 , or hubs  24  similar to that shown in  FIG. 7 , for mounting fiducial marker discs. 
         [0044]    Fiducial array  20 ″ also includes an attachment  102  which has a throughhole  104  defined therein. The attachment is shown to be secured to base plate  22  by threaded nuts, though it may also be secured using any other suitable fasteners. The attachment may also be integrally formed with base plate  22 . When the fiducial array is placed in the mouth of a patient or animal, the attachment provides support so that the mouth may remain open for longer duration without causing excessive fatigue. The throughhole  108  can be used to accommodate endotrached tube (“ET tube”) or other tubing during surgery. Tubings that pass through the throughhole  108  thus are protected and the mouth of the patient or the animal would not be closed so as to squeeze the ET tube or other catheters or probes in the mouth. The attachment  102  can also be used together with a strap to keep the fiducial array  20 ″ in position in the mouth of an animal. For example, the fiducial array  20 ″ may be placed in an animal&#39;s mouth so that the lower jaw and the maxillary teeth can close on the attachment  104  and the dental impression secured to base plate  22 . A strap may be provided to help keep the mouth closed. 
         [0045]    Various embodiments of the invention have now been described in detail. Those skilled in the art will appreciate that numerous modifications, adaptations and variations may be made to the embodiments without departing from the scope of the invention. Since changes in and or additions to the above-described best mode may be made without departing from the scope of the invention, the invention is not to be limited to those details but only by the appended claims.