Abstract:
This document discusses, among other things, a fiducial markers capable of use in image guided surgery (IGS) procedures, such as neurosurgery, or other applications. One example includes a positioning instrument with a cap that mates directly to an imageable sphere to perform registration. Another example includes a jointed positioning instrument that, when placed in a base, pivots about a location defined by a center of the imageable sphere when it was in the base. Another example includes a fiducial marker with two imageable spheres defining a line intersecting a desired point on the base. Another example includes a base with a receptacle for receiving a positioning instrument. Another example includes an imageable sphere with a removable imageable portion to allow access to a center of the imageable sphere by a positioning instrument.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This patent application is a continuation-in-part of Mazzocchi et al. U.S. patent application Ser. No. 10/206,884, entitled “FIDUCIAL MARKER DEVICES, TOOLS, AND METHODS”, filed on Jul. 24, 2002, which is assigned to the assignee of the present patent application, and which is incorporated herein by reference in its entirety.  
         [0002]    This patent application is a continuation-in-part of Solar et al. U.S. patent application Ser. No. 10/374,677, entitled “FIDUCIAL MARKER DEVICES, TOOLS, AND METHODS,” filed on Feb. 25, 2003, which is assigned to the assignee of the present patent application, and which is incorporated herein by reference in its entirety.  
         [0003]    This patent application is also related to Mazzochi et al., U.S. patent application Ser. No. ______, entitled “Fiducial Marker Devices, Tools, and Methods,” filed on even date herewith (Attorney Docket No. 723.063US1), which is assigned to the assignee of the present patent application, and which is incorporated herein by reference in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0004]    This document relates generally to imaging a patient for performing surgical intervention, and more specifically, but not by way of limitation, to fiducial marker devices and associated tools and methods.  
         BACKGROUND  
         [0005]    Fiducial markers that can be located and recognized by an imaging system are useful in neurosurgery and other applications. For example, in one technique, multiple fiducial markers are screwed into the patient&#39;s skull to define recognizable landmarks that appear on a preoperative image of the patient&#39;s brain. Such a bone-anchored fiducial marker typically includes an externally threaded bone-screw portion, which is driven into the skull, and a threaded shaft that rises up and out of the skull from the bone-screw. The threaded shaft typically receives a screwed-on imageable sphere that is visible on a magnetic resonance imaging (MRI) image or computed tomography (CT) image. The multiple fiducial markers on the patient&#39;s skull define landmarks on preoperative images that are useful to the physician for planning entry coordinates and a trajectory to a target location in the brain. An image-guided workstation uses these preoperative images and planning to guide the neurosurgeon while actually performing the subsequent surgical procedure.  
           [0006]    After the preoperative planning phase, the patient is brought into the operating room so that the planned surgical procedure can be performed. On the operating table, the patient&#39;s skull is clamped in a head-frame or otherwise immobilized. In order to use the preoperative images provided by the image-guided workstation to guide the surgeon during the procedure, the patient&#39;s skull must first be “registered” to the preoperative images. The registration creates an association between (1) the actual physical location of the fiducial markers on the patient&#39;s skull in the operating room and (2) the locations of the images of the fiducial markers visible on the preoperatively-obtained images.  
           [0007]    According to one registration technique, a “wand” is used to perform the registration. The wand includes multiple light-emitting diode (LED) locators or reflective locators, which are visible to an infrared or other camera in the operating room. The camera is connected to the image-guided workstation. The locators define the position of the wand in the operating room, including the position of a sharp tip portion of the wand, which is in a known physical relationship to the locators. To register the patient, the imageable spheres are unscrewed from the fiducial marker shafts, and replaced by respective “divots” that are sized and shaped to receive the wand tip. These divots are screwed onto the fiducial marker shafts, such that the maximum depression point of the tip corresponds to the same location as the center of the imageable sphere when the imageable sphere was screwed onto the fiducial marker shaft. A reference divot is also present in the operating room at a known location, such as on the operating table or head-frame. During the patient registration process, the surgeon touches the wand tip to the reference divot, and then to each fiducial marker divot. This permits the image-guided workstation to correlate the actual physical location of the patient&#39;s skull to the preoperative images. The physician can then use the wand, in conjunction with the image-guided workstation, to locate an appropriate entry point and trajectory to the target in the brain. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.  
         [0009]    [0009]FIG. 1 is a schematic diagram illustrating generally one example of a fiducial marker and a positioning system including a positioning wand with a semispherical cap.  
         [0010]    [0010]FIG. 2 is a flow chart illustrating generally one example of using devices such as are shown in the example of FIG. 1.  
         [0011]    [0011]FIG. 3 is a schematic diagram illustrating generally an alternative example of a positioning wand that includes a ball and a socket or other joint.  
         [0012]    [0012]FIG. 4 is a flow chart illustrating generally one example of using the devices illustrated in FIG. 3 and FIG. 1.  
         [0013]    [0013]FIG. 5 is a schematic diagram illustrating generally an alternative example of a locator with two imageable spheres and a base with a built-in registration receptacle.  
         [0014]    [0014]FIG. 6 is a schematic diagram illustrating generally an alternative example of another locator, with an imageable sphere that includes a removable imageable cone.  
         [0015]    [0015]FIG. 7 is a schematic diagram illustrating generally a top view of the imageable sphere and included imageable cone of FIG. 6.  
         [0016]    [0016]FIG. 8 is a schematic diagram illustrating generally an alternative example of a locator including an imageable sphere with a removable imageable cone.  
         [0017]    [0017]FIG. 9 illustrates a top view of the cone of FIG. 8.  
         [0018]    [0018]FIG. 10 is a flow chart illustrating generally one example of a method for using the devices illustrated in FIGS.  6 - 9 .  
         [0019]    [0019]FIG. 11A, FIG. 11B, FIG. 11C, and FIG. 11D are schematic diagrams illustrating generally other examples of locators having imageable spheres that include removable imageable components.  
         [0020]    [0020]FIG. 12 is a schematic diagram illustrating generally an example of a fiducial marker assembly. 
     
    
     DETAILED DESCRIPTION  
       [0021]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as “examples,” are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.  
         [0022]    In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this documents and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.  
         [0023]    [0023]FIG. 1 is a schematic diagram illustrating generally one example of a fiducial marker  100  and a positioning system  102 . In this example, the fiducial marker  100  includes an assembly comprising a mounting base  104  and a locator  106 . The mounting base  104  includes a self-tapping or other externally threaded distal portion  108 . This permits the base  104  to be screwed into a patient&#39;s skull or another desired surface. A proximal portion  110  includes a male or female receptacle  112 . The receptacle  112  is sized and shaped to receive a complementary male or female receptacle  114  located on a distal portion of the locator  106 . In the example of FIG. 1, the receptacle  112  is an internally threaded or other orifice, and the receptacle  114  is an externally threaded or other prong.  
         [0024]    In the example of FIG. 1, the locator  106  includes a shaft  116  between the distal receptacle  114  and a proximal imageable sphere  118 . The imageable sphere  118  is made from, or contains, a material that provides good contrast on one or more imaging modalities. Examples of suitable imaging systems include, by way of example, but not by way of limitation, magnetic resonance (MR) imaging systems, computed tomography (CT), positron emission tomography (PET), and single photon emission computed tomography (SPECT), X-ray, fluoroscopy, or other radiographic imaging systems, ultrasonic imaging systems, and the like. These imaging modalities permit acquisition of an image of a volume of interest, such as a portion of a subject&#39;s brain. The acquired image includes a visible image of the imageable sphere  118 , providing a landmark that is located on the subject&#39;s skull.  
         [0025]    In the example of FIG. 1, the positioning system  102  includes a positioning instrument, which is also sometimes referred to as a positioning wand  120 . The wand  120  includes a distal cap  122 . The distal cap  122  includes a substantially semispherical orifice  124 . The orifice  124  is sized and shaped to fit snugly over the imageable sphere  118  such that a reference point  126  aligns with a center  128  of the imageable sphere  118 . The wand  120  includes a shaft  130  between the distal cap  122  and a proximal end  132 . The proximal end  132  of the wand  120  includes positioning locators  134 A-C that are remotely detectable by a detector portion of the positioning system  102 . In this example, the positioning system  102  is implemented as an optical positioning system and the detector is implemented as a camera  136 . The positioning locators  134 A-C are spherical or other reflectors (or, alternatively, an energy source, such as light-emitting diodes (LEDs)) that are illuminated by a light source  138  for detection by the camera  136 . The camera  136  feeds information about the location of the positioning locators  134 A-C to an image-guided surgical (IGS) computer workstation  138 .  
         [0026]    The positioning locators  134 A-C are located in a predetermined fixed arrangement with respect to each other and with respect to the reference point  126 . Therefore, recognizing the locations of the positioning locators  134 A-C using the positioning system  102  allows computation of the location of the reference point  126 . Therefore, when the cap  122  is placed upon the sphere  118 , this, in turn, permits computation of the location of the center point  128  of the sphere  118 . FIG. 1 illustrates the positioning locators  134 A-C in a very general conceptual way. One or more of the positioning locators will typically be individually mounted on one or more respective arms extending radially or otherwise from the proximal portion  132  of the wand  120 , such as illustrated in FIG. 5.  
         [0027]    [0027]FIG. 2 is a flow chart illustrating generally one example of using devices such as are shown in the example of FIG. 1. In the example of FIG. 2, at  200 , several bases (typically at least three or four) are screwed into the subject&#39;s skull or other desired surface, such as by using a socket that engages an externally faceted surface such as a hex head of the proximal portion  110  of the base  104 . At  202 , a locator  106  is attached to each one of the bases  104 . At  204 , at least one imaging modality is used to take one or more preoperative or other images of the subject&#39;s skull, or other desired volume of interest. Images of the locators  106  typically appear with good contrast on the images of the volume of interest. This image information is feed to the IGS workstation  138  for computing the locations, in the three-dimensional space of the images, of the centers  128  of the spheres  118 . The subject is then moved to the operating room. At  206 , the cap  122  of the wand  120  is placed over each of the spheres  118  to obtain the locations of their centers  128  to register the three dimensional space in which the patient is located to the three dimensional space of the preoperative images. This allows the preoperative images to be used for stereotactically guiding surgical operations on the subject in the operating room. Among other things, the devices shown in FIG. 1 avoid any need for replacing the locators  106  with a golf-tee-like “divot” or “localization cap” for receiving the wand  120 . This, in turn, reduces the complexity and cost of the stereotactic procedure.  
         [0028]    [0028]FIG. 3 is a schematic diagram illustrating generally an alternative example of a positioning wand  300 , with the base  104  and the locator  106 . The positioning wand  300  includes a ball  302  and socket  304  or otherjoint. The ball  302  and socket  304  pivot about a center reference point  306 . In this example, the ball  302  is the same size and shape as the sphere  118  of the locator  106 . Distal to the ball  302  is a shaft  308  that is the same size as the shaft  116  of the locator  106 . Distal to the shaft  116  is a prong (or other male or female receptacle)  310  that is the same length as the prong-like male receptacle  114  of the locator  106 . In this example, unlike the externally threaded prong-like receptacle  114  of the locator  106 , the prong  310  is not threaded. This permits the prong  310  to be easily inserted into and removed from the receptacle  112  of the base  104 .  
         [0029]    [0029]FIG. 4 is a flow chart illustrating generally one example of using the devices illustrated in FIG. 3 and FIG. 1. At  400 , the bases  104  are screwed in, such as discussed above. At  402 , the locators  106  are attached to respective bases  104 , such as discussed above. At  404 , the subject is imaged together with the locators  106 , such as discussed above. The subject is then moved into the operating room, such as discussed above. At  406 , the locators  106  are unscrewed or otherwise removed from the respective bases  104 . At  408 , the subject is registered to the images. This includes inserting the tip  310  of the positioning wand  300  into the receptacle  112  of each of the respective bases  104 . The positioning locators  134  on the wand  300  are in a known relationship to the pivoting center reference point  306 , which, in turn, occupies the same location as the center  128  of the sphere  118  when the locator  118  was inserted within the base  104 . In this manner, by using the positioning system  102  to determine the locations of the positioning locators  134  on the wand  300 , the center point  128  that was occupied by each of the locators  106  can be computed by the IGS workstation  138 . Again, among other things, this process avoids any need for replacing the locators  106  with a golf-tee-like “divot” or “localization cap” for receiving the wand  300 . This, in turn, reduces the complexity and cost of the stereotactic procedure.  
         [0030]    [0030]FIG. 5 is a schematic diagram illustrating generally an alternative example of a base  500 , a locator  502 , and a positioning wand  504 . The base  500  is similar, in certain respects, to the base  104 . However, in this example, the base  500  includes a receptacle  506  that includes a distal conical “divot”  508 , such as for receiving a pointed distal tip  510  of the positioning wand  504 . The locator  502  includes two imageable spheres  512 A-B. The imageable spheres  512 A-B are respectively located on middle and proximal portions of a shaft  513 . The spheres  512 A-B include respective centers  514 A-B that define a line therethrough. When a distal tip  515  of the locator  502  is threaded or otherwise inserted into the receptacle  506  of the base  500 , the line through the centers  514 A-B extends through the apex (point of maximum depression) of the conical divot  508 . In FIG. 5, the positioning wand  504  includes a shaft  518  extending proximally from the distal tip  510  and terminating at or near radial arms  520 A-C. The radial arms  520 A-C carry respective positioning locators  522 A-C.  
         [0031]    The method described with respect to FIG. 4 can also be used with the devices shown in FIG. 5. The images of the subject (or other volume of interest) with the locators  502  permit computation of each of the centers  514 A-B and of the line defined therebetween. The location of the apex of the divot  508  is located on this line at a known predetermined distance from the centers  514 A-B. During registration, at  408 , in which the tip  510  of the positioning wand is inserted into the divot  508  of each of the respective bases, the actual locations of the apexes of the divots  508  is computed, because the tip  510  of the positioning wand is in a known spatial relationship to the positioning locators  522 . These points of the apexes of the divots  508  are registered to corresponding points in the images that are extrapolated along the line defined by the centers  514  of the imageable spheres  512 A-B. Again, among other things, this process avoids any need for replacing the locators  106  with a golf-tee-like “divot” or “localization cap” for receiving the wand  504 . This, in turn, reduces the complexity and cost of the stereotactic procedure.  
         [0032]    [0032]FIG. 6 is a schematic diagram illustrating generally an alternative example of another locator  600  with the base  104 . In this example, the locator  600  includes an imageable sphere  602 . The imageable sphere  602  includes a removable cone  604  that forms an imageable portion of the imageable sphere  602 . Removing the cone  604  creates a conical orifice (also referred to as a divot)  606 . The conical orifice  606  has an apex located at a center  608  of the imaging sphere  602 . The conical orifice  606  is sized and shaped to permit a tip  510  of a positioning wand  504  to be received therein for performing registration. In one example, the cone  604  snap-fits into the conical orifice  606 , such as by a beveled proximal circumferential rim  609  that engages a lip  610  located circumferentially about the proximal base portion of the inverted conical orifice  606 , as illustrated in FIG. 1. In one example, the imageable cone  604  and/or the imageable sphere  602  includes a small orifice  700 , such as illustrated in the top view of FIG. 7, to facilitate prying the imageable cone  604  out of the imageable sphere  602 , such as by using a pick or like instrument to perform this removal.  
         [0033]    [0033]FIG. 8 is a schematic diagram illustrating generally an alternative example of a locator  800  including an imageable sphere  802  with a removable imageable cone  804 . In this example, a proximal portion of the cone  804  includes external threads  806  for engaging internal threads  808  of a conical orifice  810  providing a divot for receiving a tip  510  of a positioning wand  504 . An apex of the conical orifice  810  corresponds to the center  812  of the imageable sphere  802 . FIG. 9 illustrates a top view of the cone  804 , including an orifice  900  for receiving a pick or other instrument for unscrewing the cone  804  from the sphere  802  for removing it therefrom.  
         [0034]    [0034]FIG. 10 is a flow chart illustrating generally one example of a method for using the devices illustrated in FIGS.  6 - 9 . In FIG. 10, at  1000 , the bases  104  are screwed in, such as discussed above. At  1002 , the locators  600  or  800  are attached to respective bases  104 , such as discussed above. At  1004 , the subject is imaged together with the locators  600  or  800 , such as discussed above. The subject is then moved into the operating room, such as discussed above. At  1006 , the imageable cones  604  or  804  are pried, unscrewed, or otherwise removed from the respective bases  104 . At  1008 , the subject is registered to the images. In one example, this includes inserting the tip  510  of the positioning wand  504  into the orifice  610  or  810 , such that the tip  510  is located at the center of the imageable sphere  602  or  802 . The positioning locators  522  on the wand  504  are in a known relationship to the tip  510  located at the center  608  or  812  of the imageable sphere  602  or  802 . In this manner, by using the positioning system  102  to determine the locations of the positioning locators  522  on the wand  504 , the center point  608  or  812  can be computed by the IGS workstation  138 . Again, among other things, this process avoids any need for replacing the locators  600  or  800  with a golf-tee-like “divot” or “localization cap” for receiving the wand  504 . This, in turn, reduces the complexity and cost of the stereotactic procedure. Moreover, accuracy may be enhanced because the tip  510  is located at the actual center  608  or  812  of the imageable sphere  602  or  802 , rather than using an intermediate element such as a golf-tee-like “divot” or “localization cap” for receiving the wand  504 .  
         [0035]    FIGS.  11 A- 11 D are schematic diagrams illustrating generally other examples of locators  1100 A-D having imageable spheres  1102 A-D that include removable imageable components that allow direct access to the centers  1104 A-D of the respective imageable spheres  1102 A-D, such as for registration by touching a wand tip  510  thereto. FIG. 1A shows a removable imageable sphere  1106 A that is snap-fitted to an imageable inverted cone  1108 A on a proximal portion of the shaft  114 . FIG. 11B shows a removable imageable sphere  1106 B that is threaded onto an imageable inverted cone  1110 B on a proximal portion of the shaft  114 . The apexes of the inverted cones  1108 A and  1108 B respectively define the centers  1104 A and  1104 B of the imageable spheres  1102 A and  1102 B. FIG. 11C shows a removable imageable hemisphere  1110  that is snap-fitted to a complementary imageable hemisphere  1112  that is attached to a proximal portion of the shaft  114 . The snap-fitting provides a small male or female receptacle at the center of the imageable sphere  1102 C to which a wand tip can be touched during registration. FIG. 11D shows a removable imageable sphere  1114  that is snap-fitted to an imageable post  1116  extending from a proximal end of the shaft  114 . The snap-fitting provides a small male or female receptacle at the center of the imageable sphere  1102 C to which a wand tip can be touched during registration. The devices shown in FIGS.  1 A-C can be used with the method analogous to that described with respect to the flow chart of FIG. 10.  
         [0036]    [0036]FIG. 12 is a schematic diagram illustrating generally an example of a fiducial marker assembly  1200 . In this example, the fiducial marker assembly  1200  comprises a mounting base  1202 , which is attached to a skull  1204 , and an imageable fiducial marker locator  1206 . The locator  1206  includes an imageable sphere  1208 . A removable imageable cone  1210  portion of the imageable sphere  1208  permits access to the center  1212  of the imageable sphere  1208 , such as during registration.  
         [0037]    In the example of FIG. 12, the cone  1210  is threaded into the other portions of the sphere  1208 . The cone  1210  is attached to a protective cap  1214 . In the example of FIG. 12, the cap  1214  includes a proximal disk  1216 , tangentially extending radially from the removable imageable cone  1210  portion of the imageable sphere  1208 . A sleeve  1218  extends from the circumference of the disk  1216  toward the skull  1204 . The cap  1214  protects portions of the fiducial marker assembly  1200  from damage. The cap  1214  is either made of a material that is imageable (like the cone  1210  and the other portions of the sphere  1208 ) or of a different material that is not imageable, i.e., does not provide good contrast on an imaging modality. In a further example, the sleeve  1218  includes external threads that engage internal threads of a cylindrical skirt  1220 , which allows the protective cap  1214  to accommodate different scalp thicknesses.  
         [0038]    Although the above examples of positioning were illustrated in conjunction with optical positioning systems, certain aspects of such positioning wands can also be used with a wide variety of other remotely detectable positioning systems, such as electric or magnetic field type positioning systems using electric or magnetic positioning locators, articulated arm type positioning systems, etc.  
         [0039]    It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.