US20090216113A1 - Apparatus and Methods for Using an Electromagnetic Transponder in Orthopedic Procedures - Google Patents

Abstract

Electromagnetic transponders as markers are used to localize and guide orthopedic procedures including: knee replacement, hip replacement, shoulder replacement, damaged bone reconstruction, and spine surgery, and more particularly, to guide orthopedic surgical navigation and alignment techniques and instruments. For example, the marker could further be used in any number of guides or templates that attach to the bony anatomy, such as a surgical guide, cutting guide, cutting jig, resection block and/or resurfacing guide. Further, the marker could be incorporated into an existing intramedullary guide rod for a femur and an extramedullary guide rod for a tibia in a knee replacement surgery; or into an external surgical guide system, or the marker could eliminate the need for an external template altogether. According to yet another anticipated use of the tracking system, the marker could be used in conjunction with or replace an optical alignment system.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)
• The present application claims the benefit of U.S. Patent Application No. 60/737,907 filed on Nov. 17, 2005, which is incorporated herein in its entirety.
TECHNICAL FIELD
• Apparatus and methods for using one or more electromagnetic transponders as markers to localize and guide orthopedic procedures including: knee replacement, hip replacement, shoulder replacement, damaged bone reconstruction, and spine surgery, and more particularly, to methods and apparatus for orthopedic surgical navigation and alignment techniques and instruments.
BACKGROUND
• One of the main problems in orthopedics today is the lack of accurate position and orientation information during surgery that could be used for registration of implanted devices to bone as well as registering bone structures after diseased or damaged tissue, bone and/or marrow has been removed during a surgical procedure (e.g. knee replacement surgery). For example, the stem of a hip or knee replacement implant should fit within the intramedullary canal of a bone in a manner that approximates the bone structure of the patient. This can be difficult because the bone structure of each patient is slightly different (e.g., different curvature, size, radial orientation, etc.). Although X-rays are typically used to assess the bone structure of a patient, these images do not provide real-time, accurate information during surgery for positioning implants or registering bones in an orientation suited for a specific patient. Therefore, there is a need to provide accurate information to surgeons during a procedure.
BRIEF DESCRIPTION OF THE DRAWINGS
• In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.
• FIGS. 1A-1I schematically illustrate a spinal stabilization implant having a localization and tracking device in accordance with an embodiment of the invention.
• FIG. 2 schematically illustrates a intramedullary alignment guide having a localization and tracking device in accordance with an embodiment of the invention.
• FIGS. 3A and 3B schematically illustrates an alignment guide having a localization and tracking device in accordance with an embodiment of the invention.
• FIG. 4A schematically illustrate implant, guide and/or minimally invasive surgical instruments and a localization system in accordance with various embodiments of the invention.
• FIG. 4B is a flow chart illustrating another method of using instruments and localization systems in accordance with the invention.
• FIG. 5A is an isometric view of a marker for use with an instrument in accordance with an embodiment of the invention.
• FIG. 5B is a cross-sectional view of the marker ofFIG. 5A taken alongline5B-5B.
• FIG. 5C is an illustration of a radiographic image of the marker ofFIGS. 5A-B.
• FIG. 6A is an isometric view of a marker for use with an instrument in accordance with another embodiment of the invention.
• FIG. 6B is a cross-sectional view of the marker ofFIG. 6A taken alongline6B-6B.
• FIG. 7A is an isometric view of a marker for use with an instrument in accordance with another embodiment of the invention.
• FIG. 7B is a cross-sectional view of the marker ofFIG. 7A taken alongline7B-7B.
• FIG. 8 is an isometric view of a marker for use with an instrument in accordance with another embodiment of the invention.
• FIG. 9 is an isometric view of a marker for use with an instrument in accordance with yet another embodiment of the invention.
• FIG. 10 is a schematic block diagram of a localization system for use in locating an instrument in accordance with an embodiment of the invention.
• FIG. 11 is a schematic view of an array of coplanar source coils carrying electrical signals in a first combination of phases to generate a first excitation field.
• FIG. 12 is a schematic view of an array of coplanar source coils carrying electrical signals in a second combination of phases to generate a second excitation field.
• FIG. 13 is a schematic view of an array of coplanar source coils carrying electrical signals in a third combination of phases to generate a third excitation field.
• FIG. 14 is a schematic view of an array of coplanar source coils illustrating a magnetic excitation field for energizing markers in a first spatial orientation.
• FIG. 15 is a schematic view of an array of coplanar source coils illustrating a magnetic excitation field for energizing markers in a second spatial orientation.
• FIG. 16A is an exploded isometric view showing individual components of a sensor assembly for use with a localization system to localize an instrument in accordance with an embodiment of the invention.
• FIG. 16B is a top plan view of a sensing unit for use in the sensor assembly ofFIG. 16A.
• FIG. 17 is a schematic diagram of a preamplifier for use with the sensor assembly ofFIG. 16A.
DETAILED DESCRIPTIONA. Overview
• The following disclosure is directed toward surgical guides, prosthesis, implants, and/or instruments including localization markers that (a) are energized by a wirelessly transmitted excitation energy and (b) wirelessly transmit a location signal in response to the excitation energy. Additional aspects of the following description are directed toward methods of using and tracking such instruments implanted or affixed to bony anatomy of a patient, an implant or prosthesis, an intramedullary device, an extramedullary device or a guide, using non-ionizing energy.
• One embodiment of a surgical guide, prosthesis, implant and/or instrument in accordance with the invention comprises an elongated member having a distal section configured to be passed through an intramedullary canal of a femur or other passageway in a human. The instrument further includes a magnetic marker having a transponder at the distal section. The transponder includes a circuit configured to be energized by a wirelessly transmitted magnetic excitation energy and to wirelessly transmit a magnetic location signal in response to the excitation energy. The magnetic transponder of the marker includes a circuit configured to (a) be energized by a wirelessly transmitted pulsed magnetic field and (b) wirelessly transmit a pulsed magnetic location signal in response to the pulsed magnetic field. The magnetic marker, for example, can be attached to or otherwise integral with the elongated member.
• Another aspect of the following disclosure is directed toward systems for tracking an implant in a patient or guide associated with the bony anatomy of the patient. One embodiment of such a system includes an elongate member having an elongated rod with a distal section configured to be passed through an intramedullary canal in a human and a magnetic marker having a transponder at the distal section of the member. Another embodiment of such a system includes an orthopedic implant having a magnetic marker in, affixed to or in a substantially fixed relationship to the implant. Another embodiment of such a system includes a guide for use during orthopedic surgery, the marker in a substantially fixed relationship to the guide. The transponder has a circuit configured to (a) be energized by a wirelessly transmitted pulsed magnetic field and (b) wirelessly transmit a pulsed magnetic location signal in response to the pulsed magnetic field. The system further includes an excitation source comprising an energy storage device, a source coil, and a switching network coupled to the energy storage device and the source coil. The source coil is configured to wirelessly transmit the pulsed magnetic field to energize a transponder. The switching network is configured to alternately transfer (a) stored energy from the energy storage device to the source coil and (b) energy in the source coil back to the energy storage device.
• Another aspect for tracking an implant in a patient or guide associated with the bony anatomy of the patient includes an implant or guide as set forth above and a sensor assembly comprising a support member and a plurality of field sensors carried by the support member. The field sensors are at least substantially locally planar relative to one another to sense the pulsed magnetic location signal from the transponder. The field sensors can be responsive only to field components of the pulsed magnetic location signal normal to individual field sensors. In other embodiments, the field sensors are arranged in an array occupying an area having a maximum dimension of approximately 100% to 300% of a predetermined sensing distance between the marker and the sensing array.
• Additional aspects of the invention are directed toward methods for guiding the prosthesis, implant, guide or other instrument. One embodiment of such a method comprises implanting the prosthetic in a patient and tracking the implant as it is implanted. According to further aspects, the implant can include one or a plurality of markers. Alternatively, the implant may be implanted in a collapsed or unexpanded state and may be expanded after positioning the implant in the patient. According to aspects of this embodiment, the implant may be initially tracked for purposes of placement and may be further tracked to confirm appropriate expansion of the implant. The implant is tracked as is placed in the patient by (a) wirelessly delivering a pulsed magnetic field to energize the marker, (b) wirelessly transmitting a pulsed location signal from the marker, (c) sensing the pulsed location signal at a sensor located outside the patient, and (d) periodically calculating a three-dimensional location of the marker in a reference frame. The method can further include providing an output of the location of the marker in the reference frame at least every t_fsecond and within t_lsecond from sensing the pulsed location signal. In many embodiments, t_fand t_lare not greater than one second.
• According to other aspects of the invention, the radiographic center of a marker coincide with the magnetic center of a transponder of the marker. If the radiographic center coincides with the magnetic center of the transponder, the transponders can be localized on X-ray or CT prior to surgery. After X-ray or CT, the surgery can be planned using the preoperative X-rays. Next, the markers may be localized intraoperatively with electromagnetic tracking. Finally, the markers can be localized during physical therapy to monitor recovery as well as longer term follow-up activities.
• According to further aspects of the invention, a plurality of electromagnetic markers are used to provide three dimensional position information (X, Y and Z position) as location fiducials for implants, guides, prosthesis and the like. As additional markers are used, the dimensionality of localization, alignment and registration solutions increases. For example, a single marker defines a single position in localization space; two markers can be used to register the distance between two points. Furthermore, two independent sets of two rigidly mounted markers can be used to register and align two vectors relative to each other. And, three markers rigidly mounted relative to each other can be used to define a plane including rotational angles of the plane (i.e. pitch, yaw and roll). Suitable markers include, for example, the markers shown and described in U.S. Pat. Nos. 6,918,919 and 6,822,570; and U.S. application Ser. Nos. 10/334,700; 09/954,700; 10/679,801; 10/382,123; 10/745,097; 10/746,888; and 11/166,801, all of which are incorporated herein by reference.
B. Tracking Systems and Methods for Spinal Stabilization Devices
• FIG. 1A illustrates a spinal stabilization device in an unexpanded or collapsed state coupled to a cannula of the delivery system.FIG. 1B is an enlarged view of the spinal stabilization device ofFIG. 1A.FIGS. 1C and 1D illustrates the spinal stabilization device in an expanded state coupled to a cannula of the delivery system.FIG. 1D is an enlarged view of the spinal stabilization device ofFIG. 1A. The spinal stabilization device further includes amagnetic marker40 having a transponder with a circuit configured to be energized by a wirelessly transmitted magnetic excitation energy and to wirelessly transmit a magnetic location signal in response to the excitation energy. Themarker40 enables the spinal stabilization device to be tracked in the patient using a non-ionizing energy and without electrically coupling the marker to a sensor or excitation source. The spinal stabilization device, therefore, is expected to significantly improve the ability to implant or otherwise guide devices through patients in many medical procedures. As explained in more detail below, themarker40 can be attached to the implant and/or imbedded in the implant depending upon the particular application. According to further aspects of the invention, a plurality of magnetic markers can be attached to the implant and/or imbedded in the implant.
• A system of the present invention includes acannula device70 having anouter sheath72, aproximal hub78 and preferably at least twointerior lumens74,76 for the percutaneous delivery the device and other tools as are know in the art for implanting the spinal device.
• As shown inFIGS. 1A-1C, an exemplaryspinal stabilization device24 is illustrated in collapsed and expanded configurations, respectively. According to aspects of the invention, the spinal stabilization device can be tracked during implantation in the collapsed state to confirm the location of the device prior to expanding the device. Exemplaryspinal stabilization device24 includes anexpandable spacer body24 that has a size and shape when in the expanded condition for operative positioning between the spinous processes of adjacent superior and inferior vertebrae of the spinal motion segment being treated.
• Themarker40 illustrated inFIGS. 1A and 1B is a magnetic marker including atransponder42 having a core44, acoil46 around thecore44, and acapacitor48 electrically coupled to thecoil46. Thecore44 is typically composed of ferrite, and thecoil46 includes a plurality of windings of a wire around thecore44. Thetransponder42 can be contained in acapsule49. Thetransponder42 generally has a small cross-sectional dimension so that the collapsedspinal device24 can pass through small entry ports. For example, thetransponder42 can have a cylindrical portion with a diameter from approximately 0.5-3 mm, and desirably from 0.5-2 mm. Thetransponder42 is a resonating circuit that receives the wirelessly transmitted magnetic excitation energy and produces a wirelessly transmitted location signal in response to the excitation signal. Thetransponder42 accordingly has a resonant frequency at which the magnetic excitation energy energizes thetransponder42. Several embodiments of instruments with themarker40, as well as specific embodiments ofmarkers40, are described below with reference toFIGS. 2A-9.
• Spinal spacers can be made of an inflatable non-porous material, i.e., balloon type spacers are inflated with an inflation or expansion medium, such as air, saline, another biologically compatible fluid, or a flowable solid material, such as polyurethane, or a gel, which thickens or hardens substantially upon injection intoballoon34. Themarker40 is contained in acapsule49 and therefore can be contained within the balloon type spacer or affixed to the surface of the balloon type spacer as described further below in reference toFIGS. 1E and 1F. In one embodiment,balloon34 is initially inflated with air to provide some structure or rigidity to it to facilitate its optimum positioning and alignment between the spinous processes. Once positioned as desired,balloon34 is injected with a flowable solid material (the air therein being displaced possibly via a vent hole within port32). In certain embodiments, the expandable body is made of a non-compliant or semi-compliant material so as to maintain a substantially fixed shape or configuration and ensure proper, long-term retention within the implant site. In other embodiments, the expandable member may be made of a compliant material. In any embodiment, the compressibility and flexibility ofballoon34 can be selected to address the indications being treated. When unexpanded or deflated,expandable body34 has a low profile, such as a narrow, elongated shape, to be easily translated through adelivery cannula70. The shape ofexpandable body34, when in an expanded or inflated state, has larger profile which is generally H-shaped.
• According to aspects of the invention, the markers may be incorporated into other spinal stabilization devices, for example, the expandable spine stabilization system in U.S. Publication No. 2005/0171543 entitled Spine Stabilization Systems and Associated Devices, Assemblies and Methods; U.S. Publication No. 2006/0084988 entitled System and Methods for Posterior Dynamic Stabilization of the Spine; U.S. Publication No. 2006/0241614 entitled Implants and Methods for Posterior Dynamic Stabilization of a Spinal Motion Segment; U.S. Publication No. 2006/0241613 entitled Implants and Methods for Inter-Transverse Process Dynamic Stabilization of a Spinal Motion Segment; U.S. Publication No. 2006/0229608 entitled Apparatus and Methods for Spinal Implant with Dynamic Stabilization System; U.S. Publication No. 2006/0085069 entitled Systems and Methods for Posterior Dynamic Stabilization of the Spine; U.S. Publication No. 2006/0084987 entitled Systems and Methods for Posterior Dynamic Stabilization of the Spine; U.S. Publication No. 2006/0111715 entitled Dynamic Stabilization Assemblies, Tool Set and Method; U.S. Publication No. 2006/0084985 entitled Systems and Methods for Posterior Dynamic Stabilization of the Spine; U.S. Publication No. 2006/0084984 entitled Systems and Methods for Posterior Dynamic Stabilization of the Spine; U.S. Publication No. 2006/0084983 entitled Systems and Methods for Posterior Dynamic Stabilization of the Spine; U.S. Publication No. 2006/0084982 entitled Systems and Methods for Posterior Dynamic Stabilization of the Spine; U.S. Publication No. 2006/0079898 entitled Spinal Motion Preservation Assemblies; U.S. Publication No. 2006/0058800 entitled Methods and Apparatus for Provision of Therapy to Adjacent Motion Segments; U.S. Publication No. 2006/0036240 entitled System and Method for Dynamic Skeletal Stabilization.
• FIGS. 1E and 1F are cross-sectional views illustrating additional embodiments of the spinal device24 (FIG. 1A) in which themarker40 is attached to thespinal device24. In the embodiment shown inFIG. 1E, adistal section18 of the spinal device has aninner surface28adefining alumen19, anouter surface28b, and arecess30 in theouter surface28b. Therecess30 extends to an intermediate depth in the wall between theinner surface28aand theouter surface28b. At least a portion of themarker40 is attached to thespinal device24 using an adhesive, weld or fastener to adhere themarker40 to therecess30 in thespinal device24. Referring toFIG. 1F, this embodiment is similar to the embodiment shown inFIG. 1E, but thespinal device24 includes ahole32 through the wall between theinner surface28aand theouter surface28b. In this embodiment, themarker40 is attached to thehole32 using an adhesive or other material. One aspect of the embodiments illustrated inFIGS. 1E and 1F is that at least a portion of themarker40 resides within the wall of thespinal device24. This reduces the cross-sectional area of thelumen19 occupied by themarker40 and/or reduces the overall cross-sectional dimension of thedistal section18 of thespinal device24 where themarker40 is located.
• FIG. 1G is a cross-sectional view illustrating a distal section of an instrument in accordance with another embodiment of the invention, andFIG. 1H is an isometric view of an embodiment of a marker for use with the instrument illustrated inFIG. 1G. In this particular embodiment, themarker40 includes atubular core44 having a bore45 (FIG. 1H) configured to receive theouter surface28bof the spinal device24 (FIG. 1G). Thecoil46 is wrapped around thetubular core44, and thecapsule49 or other coating encases thetubular core44 and thecoil46. Themarker40 illustrated inFIGS. 1G and 1H can further include a capacitor as described above with reference to themarker40 illustrated inFIG. 1.
• FIG. 1I is a cross-sectional view illustrating an instrument in accordance with another embodiment of the invention. The instrument in this embodiment can be used in any of the minimally invasive surgical techniques used in spine, joint, or other orthopedic surgeries. In this embodiment, the instrument has abody14ahaving adistal section18 that is configured to be inserted into a patient. Thebody14acan be a rigid or flexible member depending on whether the instrument is a probe, catheter, electrode, ablation tool, welding tool, sensor, or other diagnostic or therapeutic tool. In the case of a catheter, a significant portion of thebody14ais flexible and has alumen19. The instrument may further include a therapeutic ordiagnostic device20 at thedistal section18.
• The instrument illustrated inFIG. 1I has twomarkers40aand40bpositioned apart from one another along thebody14a. Themarkers40a-bcan be any of the markers illustrated above with respect to the Figures. For example, themarker40 illustrated inFIGS. 1G and 1H can be positioned on the outer wall of thebody14a(shown inFIG. 1E) or the inner wall of the lumen19 (not shown). Themarkers40a-bare aligned along a longitudinal axis of thebody14a. Themarkers40a-b, more specifically, are typically aligned with the central axis of thebody14a, but in other embodiments themarkers40a-bcan be aligned with each other along an off-center axis. In still other embodiments, themarkers40a-bcan be axially offset from each other along different axes of thebody14a. When thebody14ais flexible, the instrument can further include arigid support43 in the region of themarkers40a-b. Therigid support43 can be a sleeve on the inner wall or outer wall of thebody14a. Therigid support43 can alternatively be a thickened portion of thebody14a. Thedistal section18 of the instrument accordingly has afirst portion47aand asecond portion47b. Thefirst portion47ais rigid to maintain the relative orientation between themarkers40a-b, but thesecond portion47bcan be rigid or flexible depending upon the particular application. For example, thesecond portion47bof thedistal section18 may be a flexible tip to make it easier to pass the instrument through small or torturous passageways in a patient.
• The instrument shown inFIG. 1I provides a directional vector indicative of the location and angular orientation of thedistal section18 as the instrument is guided through the patient. Therigid support43 maintains the distance and axially alignment between themarkers40a-b. As a result, by knowing the three-dimensional coordinates of eachmarker40a-bin a reference frame and the relative positions between themarkers40a-b, a vector can be established that defines the position and orientation of thedistal section18 of the instrument with two degrees of orientation. The projection of the vector defined by themarkers40a-bcan be used to localize the tip of thedistal section18 that houses the therapeutic ordiagnostic device20. As a result, the instrument illustrated inFIG. 1I is expected to enhance the ease and accuracy with which a therapeutic or diagnostic device is positioned within a patient.
C. Tracking Systems and Methods Used for Other Implant Devices or in Bony Anatomy
• According to further aspects of the invention, electromagnetic markers could be used in orthopedic surgical applications such as a marker affixed to in-situ bone or to an implant; in a fixed relationship with a surgical guide to provide objective, real-time location information to allow more accurate surgical cuts of existing bone, length, rotation; during surgery to assure alignment and/or post surgery to confirm implant positioning and range of motion; in a bone screw to guide positioning of the screw, guide removal of the screw, or monitor implanted position of the screw.
• The marker could further be used in any number of guides or templates that attach to the bony anatomy, such as a surgical guide, cutting guide, cutting jig, resection block and/or resurfacing guide. For example, the marker could be incorporated into an existing intramedullary guide rod for a femur and an extramedullary guide rod for a tibia in a knee replacement surgery; or into an external surgical guide system, or the marker could eliminate the need for an external template altogether. According to yet another anticipated use of the tracking system, the marker could be used in conjunction with or replace an optical alignment system. Templates or guides are commonly used in orthopedic surgery of the spine, joints (e.g. knee or hip), and trauma.
• FIG. 2 shows, in cross-section, anintramedullary alignment guide2 having a handle, afemur4 having a tubular shaft of cortical bone surroundingintramedullary canal5 and having areas ofspongy bone6 at both ends of the shaft. The intramedullary alignment guide can further includemarkers40 such as the electromagnetic markers disclosed herein, in combination with a sensor assembly, controller and excitation source, in order to track the position of the intramedullary device. Themarkers40 may be integrally formed with the intramedullary alignment guide, may be contained on a cap or extension (not shown) of the intramedullary alignment guide, or may be otherwise contained in a substantially fixed relationship to the alignment guide. One example of a suitable intramedullary alignment guide is found in U.S. Pat. No. 4,474,177 entitled Method and Apparatus for Shaping a Distal Femoral Surface. Other suitable alignment guides are found in U.S. Pat. Nos. 4,718,413; 4,892,093; 5,454,816; 5,474,559; 5,601,563; 5,653,714, 6,712,824; 6,558,391; and U.S. Patent Publication Nos. 2002/0133163, 2005/0021039 and 2003/0100907 each of which are incorporated herein.
• According to aspects of the invention, a tracking system for use in orthopedic surgeries and other procedures provides objective internal alignment data (inflection, flexure, rotation, overall mechanical alignment) from bone (registration problem) for clinical confidence (need to take acquisition reference points away from cut). According to further aspects of the invention, relative position of remaining bone components can be confirmed once an initial cut has been made so that the completed replacement joint maintains correct position and rotation of bone components relative to each other (e.g. tibia and femur bone components in knee replacement surgery). Poor initial placement is the primary reason for replacement joints to fail in patients.
• According to further aspects of the invention, an easier way to integrate image data into a computer guided cutting and implantation surgical process is provided. For example, as detailed further below with, the system can provide data for use in treatment planning to increase the accuracy of the surgery, for a patient communication tool, and to reduce the duration of the surgery. In addition, orthopedic surgery is generally trending toward minimally invasive surgery (MIS), a surgical technique that allows the surgeon to see less of the surgery site. The tracking system of the present invention will provide significant benefits in a surgery technique that increases the risk of misalignment due to reduced visibility. By providing objective tracking and alignment data, minimally invasive knee replacement surgery and other minimally invasive surgeries will be practical for mainstream surgeons.
• One expected advantage of a tracking system for implants, guides and other orthopedic devices used in surgeries is the ability to rely on objective internal alignment data for bone increasing confidence for first cut. Additional advantages of obtaining objective internal alignment data includes confirmation of the relative position once an initial cut has been made. A further advantage is the ability to integrate image data into computer guided surgery. Yet another advantage is the enablement of treatment planning with preoperative x-ray or CT. Still another advantage is the enablement of accurate and precise image guided surgery for alignment of bone components during surgery.
• According to further aspects of the invention, the markers can be implanted in or relative to bone components of interest and used after surgery to monitor healing and/or physical therapy progress without any detrimental effects to the patient such as x-ray radiation
• According to aspects of the invention, the electromagnetic tracking system may be combined with an optical system to provide increased accuracy and ease of use. The combination system is advantageous over standard optical tracking for at least the following reasons: there are no line of sight issues; the electromagnetic markers can resonate at different frequencies and are distinguishable from each other by the system, the electromagnetic markers are a better proxy for the location of the implant than just the implant.
• As shown inFIG. 3,markers40 are used in combination with guide systems to provide tracking. Themarkers40 may be implanted in the bone or may be contained in a fixed relationship with the guide system or may be integrated with the guide system or may be a combination of one or more of these.
• Examplary Work Flow for a Knee Replacement Surgery:
• Pre-Surgery
• 1. X-Ray (diagnostic+markers) (image overlay)
• 1a. Treatment planning tool
• Surgery
• 2. Pre-registration. Localization framework (template or temporary guidance rod)
• 3. Data acquisition
• 4. Tibia/Femur planning pre-cut
• 5. Cut
• 5a. Remove intramedullary guide rod
• 6. Implant Placement
• 7. Ligament balancing
D. Systems and Procedures of a Localization and Tracking System
• FIG. 4A is a schematic view illustrating an embodiment of a localization system for use with any of the embodiments of theinstrument10 illustrated and/or described above with reference toFIGS. 1-3B. In this particular embodiment, theinstrument10 includes a plurality of markers40 (identified individually as afirst marker40a, asecond marker40band athird marker40c). Themarkers40a-care used to determine the location and configuration of the implant, guide or minimally invasivesurgical instrument10 as it is being inserted into the patient and/or after the implant, guide orinstrument10 has been located at the target site.
• The localization system includes an excitation source60 (e.g., a pulsed magnetic field generator), asensor assembly70, and a controller80 coupled to both the excitation source60 and thesensor assembly70. The excitation source60 generates an excitation energy to energize at least one of themarkers40a-con theinstrument10. The embodiment of the excitation source60 shown inFIG. 4A produces a pulsed magnetic field at different frequencies. For example, the excitation source60 can frequency multiplex the magnetic field at a first frequency E₁to energize thefirst marker40a, a second frequency E₂to energize thesecond marker40b, and a third frequency E₃to energize thethird marker40c. In response to the excitation energy, themarkers40a-cgenerate location signals L_1-3, respectively, at unique response frequencies. More specifically, thefirst marker40agenerates a first location signal L₁at a first frequency in response to the excitation energy at the first frequency E₁, thesecond marker40bgenerates a second location signal L₂at a second frequency in response to the excitation energy at the second frequency E₂, and thethird marker40cgenerates a third location signal L₃at a third frequency in response to the excitation energy at the third frequency E₃.
• Thesensor assembly70 can include a plurality of coils to sense the location signals L_1-3from themarkers40a-c. Thesensor assembly70 can be a flat panel having a plurality of coils that are at least substantially coplanar relative to each other. In other embodiments, thesensor assembly70 may be a nonplanar array of coils.
• The controller80 includes hardware, software or other computer-operable media containing instructions that operate the excitation source60 to multiplex the excitation energy at the different frequencies E_1-3. For example, the controller80 causes the excitation source60 to generate the excitation energy at the first frequency E₁for a first excitation period, and then the controller80 causes the excitation source60 to terminate the excitation energy at the first frequency E₁for a first sensing phase during which thesensor assembly70 senses the first location signal L₁from thefirst marker40awithout the presence of the excitation energy at the first frequency E₁. The controller80 also causes the excitation source60 to (a) generate the second excitation energy at the second frequency E₂for a second excitation period and (b) terminate the excitation energy at the second frequency E₂for a second sensing phase during which thesensor assembly70 senses the second location signal L₂from thesecond marker40bwithout the presence of the second excitation energy at the second frequency E₂. The controller80 replicates this operation with the third excitation energy at the third frequency E₃such that thethird marker40ctransmits the third location signal L₃to thesensor assembly70 during a third sensing phase. As such, the excitation source60 wirelessly transmits the excitation energy in the form of pulsed magnetic fields at the resonant frequencies of themarkers40a-cduring excitation periods, and themarkers40a-cwirelessly transmit the location signals L_1-3to thesensor assembly70 during sensing phases.
• The computer-operable media in the controller80, or in a separate signal processor, also includes instructions to determine the absolute positions of each of themarkers40a-cin a three-dimensional reference frame. Based on signals provided by thesensor assembly70 that correspond to the magnitude of each of the location signals L_1-3, the controller80 and/or a separate signal processor calculate the absolute coordinates of each of themarkers40a-cin the three-dimensional reference frame.
• One procedure for tracking the prosthesis, guide and/orinstrument10 through the patient includes attachingreference markers40d-fto the patient and acquiring reference images showing the position of thereference markers40d-frelative to the target site using MRI images, CT images, radiographic images or other suitable types of images. Thereference markers40d-fcan be adhered to the patient using an external patch, implanted in tissue, or otherwise anchored to the bone structure of the patient. Theinstrument10 is then implanted in the patient by moving thedistal section18 of thespinal device24 through a desired vessel or other passageway. As theinstrument10 is inserted into the patient, themarkers40a-fare individually energized by the excitation source60 at six different frequencies, and thesensor assembly70 receives independent location signals from each of themarkers40a-f. The controller80 and/or a separate signal processor then calculates the absolute position of each marker in a three-dimensional reference frame. The controller80 can also calculate (a) the location of thedevice20 using the absolute locations of themarkers40a-cand (b) the location of the target site using the absolute locations of thereference markers40d-f. Based on the calculated locations of themarkers40a-cand the target site, the controller80 can further calculate the relative offset between these items in real time.
• Theinstrument10 and localization system enable a practitioner to track the location of theinstrument10 relative to the target site as it is being implanted into the patient and at any time after implantation. The location system illustrated inFIG. 4A can calculate the absolute position of eachindividual marker40 at a frequency of approximately 1 ms to 1.0 second. Additionally, the location system can provide the absolute locations of themarkers40, thedevice20 carried by theinstrument10, and/or the target site either individually or relative to one another within a latency of 10 ms to 2 seconds from the time the localization signals were transmitted from themarkers40. The location system accordingly provides real-time tracking to an operator to ensure that theinstrument10 and/or thedevice20 pass through the desired passageway and are positioned accurately within the patient without ionizing radiation.
• FIG. 4D is a flow chart illustrating amethod450 of using an instrument in accordance with an embodiment of the invention, andFIG. 3 is a schematic view illustrating aspects of an embodiment of themethod450. Themethod450 for performing a diagnostic or therapeutic procedure on a patient includes afirst stage452 in whichreference markers40d-f(FIG. 3) are attached to a patient P. Themethod450 further includes asecond stage454 that includes obtaining one or more reference images showing the position of thereference markers40d-frelative to the target T using MRI images, CT images, radiographic images, ultrasonic images, or other suitable types of images as explained above with reference toFIG. 4A. Thereference markers40d-fcan be adhered to the patient using an external patch, implanted in tissue, or otherwise anchored to the bone structure of the patient. One aspect of the first andsecond stages452 and454 is that themarkers40d-fcan be attached to the patient during a diagnostic stage of treating the patient before obtaining the reference images. The markers can then be left in the patient for a long period of time because they are not hard-wired to any external excitation or sensing devices. The patient can accordingly be moved for further diagnostic procedures or therapeutic procedures at a later time or in a different location.
• Themethod450 continues with athird stage456 in which thereference markers40d-fanddevice markers40a-b(FIG. 3) are located during a diagnostic and/or therapeutic procedure. Thereference markers40d-fanddevice markers40a-bshown inFIG. 3 can be located simultaneously, or at least substantially simultaneously, in real time during the procedure as described above with reference toFIG. 4A. Themethod450 further includes afourth stage458 in which the location of the cuttingdevice20 is mapped or otherwise presented relative to the target T by superimposing a representation of the instrument on a display of a reference image that was previously obtained.
• Thefourth stage458 of themethod450 can have several different embodiments. Referring toFIG. 3, for example, the system can further include adisplay460 that provides animage462 that has been registered to the proper orientation using the reference images that were obtained in the earlier stages of the method and a reference frame defined by thereference markers40d-f(shown in phantom in the image462). The position of thedistal section18 of the cuttingdevice20 can be mapped (e.g., superimposed) onto the registeredimage462 to illustrate the relative orientation between the instrument and the target T. Thedisplay460 can further includealphanumeric indicators464 illustrating the relative displacement between thedistal section18 of the instrument and the target T. U.S. Pat. Nos. 5,729,129 and 6,161,032, which are herein incorporated by reference, disclose processes for displaying the position of the cuttingdevice20 on thedisplay460 by superimposing a representation of the device on previously acquired images of the patient.
• The systems and methods set forth above with respect toFIGS. 4A-4D that use wireless markers provide several advantages over conventional systems using wired transponders. For example, U.S. Pat. Nos. 5,729,129 and 6,161,032 disclose “wired” systems in which magnetic field sensors attached to the patient or a probe are hard-wired to a receiver to detect the position and orientation of medical probes within the body of a patient. U.S. Pat. No. 6,161,032 discloses a system having a wired field transmitter attached to the end of a probe (e.g., a catheter), three wired reference assemblies that can be attached to the patient, and a calibration array that is separate from the patient. In a typical application, it appears that a patient initially undergoes a diagnostic procedure in which the target (e.g., a soft tissue lesion) is imaged. The patient then proceeds to a therapeutic procedure at a later point in time during which the wired reference assemblies are attached to desired locations on the patient. The system is then calibrated with the patient in position for the therapy by locating the wired reference assemblies using either a calibration array or a probe that is manually placed on the reference assemblies. The image of the patient is then registered with respect to the external reference frame defined by the three reference assemblies. At this point, the patient is then ready to actually undergo the therapeutic procedure in which the probe is located relative to the reference transducers. The position of the probe is then mapped to the image to provide the practitioner a visual representation of the relative position between the probe and the target.
• One problem with such wired systems is that the reference assemblies are attached to the patient after obtaining the diagnostic images. The system is thus manually calibrated before performing the therapeutic procedure. This is a relatively time consuming aspect of the procedure that reduces the utilization of expensive equipment and facilities associated with surgical or therapeutic procedures. Another problem with such systems is that the reference assemblies may not be accurately positioned relative to the target such that the external reference frame defined by the reference assemblies introduces systemic errors that decrease the accuracy of the measurements. Therefore, wired magnetic tracking systems are not expected to provide satisfactory results for many applications.
• In contrast to the wired systems, the systems and methods set forth inFIGS. 4A and 4B that use wireless markers increase the utilization of expensive facilities and accurately localize the instrument. Thereference markers40d-fof the system illustrated inFIG. 3 are accurately imaged and localized during an initial diagnostic stage of a therapy. This eliminates having to calibrate the system and determine the reference frame while a patient is positioned at a treatment site immediately before a treatment as required in U.S. Pat. No. 6,161,032. As a result, the inventive systems and methods increase the utilization of expensive operating rooms or other equipment. The inventive systems and methods also reduce systemic errors caused by inaccurately positioning reference assemblies on the patient or inaccurately placing a probe tip on a reference assembly as disclosed in U.S. Pat. No. 6,161,032.
• The systems and methods described above with reference toFIGS. 4D and 3 also provide more accurate measurements because thereference markers40d-finherently move with the patient to enhance the accuracy with which the instrument is positioned relative to the target. For example, thereference markers40d-fcan be implanted very close to soft tissue targets or dynamic organs (e.g., the heart or lungs) so that the reference frame defined by the markers moves with the target. Additionally, because the reference markers and the device markers are located concurrently during a procedure, the dynamic measurement of the reference frame automatically compensates for patient movement. This eliminates having to calibrate the reference frame defined by the markers and having to re-register or re-map images relative to the markers. As a result, the systems and methods described above with reference toFIG. 3 andFIG. 4D provide greater accuracy and enable faster processing times for diagnostic and/or therapeutic procedures.
• The systems set forth inFIGS. 3 and 4D further provide additional comfort to the patient throughout the diagnostic and therapeutic procedures. Because thereference markers40d-fare wireless, they can remain in the patient after implantation for an indefinite period of time without having any leads or markers external to the patient. This allows the patient to go about normal daily functions without complications caused by external lead wires, which is particularly beneficial for treatments that involve one or more procedures over a number of days or weeks. Themarkers40d-f, moreover, do not generate a significant amount of heat and they are relatively small. Thus, they do not cause uncomfortable sensations or pain.
E. Methods in Accordance with the System
• According to methods of the invention, implanting an electromagnetic marker within in a bone to define a reference point relative to the bone structure; localizing the position of the bone during reconstructive surgery relative to either a prosthesis or another bone structure. According to aspects of the invention, the localization can be in real-time during a procedure with a person in the operating room.
• According to further methods of the invention, positioning an electromagnetic marker on a device relative to a bone to define a reference point relative to the bone structure, and the reference point localizes the position of the bone element during reconstructive surgery relative to either a prosthesis or another bone element. In further aspects of this example, the device can have one or more of the following characteristics: the device being a template of known mechanical dimensions temporarily used during surgery; the device being a prosthetic device of known mechanical dimensions and permanently implanted; and/or the device being a bone screw or similar device and permanently implanted.
• A method for using implanted an electromagnetic transponder to localize bone components. This method can further include on or more of the following: localization bone components using one or more electromagnetic transponders pre-operatively with X-ray; localization bone components using one or more electromagnetic transponders during surgery electromagnetically; localization bone components using one or more electromagnetic transponders following surgery electromagnetically.
• A method for using implanted an electromagnetic transponder to localize bone components relative to prosthetic devices during surgery. According to this method, a marker is directly implanted into the bone of a patient to provide a fixed reference point for use during orthopedic surgery. Alternatively, the marker can be substantially fixed relative to the bony anatomy of a patient to be used as a reference point during orthopedic surgery.
F. Specific Embodiments of Markers and Localization Systems
• The following specific embodiments of markers, excitation sources, sensors and controllers provide additional details to implement the systems and processes described above with reference toFIGS. 1-4C. The present inventors overcame many challenges to develop markers and localization systems that accurately determine the location of a marker which (a) produces a wirelessly transmitted location signal in response to a wirelessly transmitted excitation energy, and (b) has a cross-section small enough to be passed through narrow lumens in the patient. The following specific embodiments are described in sufficient detail to enable a person skilled in the art to make and use such a localization system for tracking catheters and other instruments through the patient, but the invention is not limited to the following embodiments of markers, excitation sources, sensor assemblies and/or controllers.
• 1. Markers
• FIG. 5A is an isometric view of amarker100 for use with the instrument10 (FIGS. 1-3B). The embodiment of themarker100 shown in FIG.5A includes acasing110 and a magnetic transponder120 (e.g., a resonating circuit) in thecasing110. Thecasing110 is a barrier configured to be implanted in the patient, or attached to theinstrument10 as described above. Thecasing110 can alternatively be configured to be adhered to the skin of the patient, or otherwise attached to the patient. Thecasing110 can have barbs or other features to anchor thecasing110 in soft tissue or an adhesive for attaching thecasing110 externally to the skin of a patient. Suitable anchoring mechanisms for securing themarker100 to a patient are disclosed in International Publication No. WO 02/39917 A1, which designates the United States and is incorporated herein by reference. In one embodiment, thecasing110 includes (a) a capsule or shell112 having aclosed end114 and anopen end116, and (b) asealant118 in theopen end116 of theshell112. Thecasing110 and thesealant118 can be made from plastics, ceramics, glass or other suitable biocompatible materials.
• Themagnetic transponder120 can include a resonating circuit that wirelessly transmits a location signal in response to a wirelessly transmitted excitation field as described above. In this embodiment, themagnetic transponder120 comprises acoil122 defined by a plurality of windings of aconductor124. Many embodiments of themagnetic transponder120 also include acapacitor126 coupled to thecoil122. Thecoil122 resonates at a selected resonant frequency. Thecoil122 can resonate at a resonant frequency solely using the parasitic capacitance of the windings without having a capacitor, or the resonant frequency can be produced using the combination of thecoil122 and thecapacitor126. Thecoil122 accordingly generates an alternating magnetic field at the selected resonant frequency in response to the excitation energy either by itself or in combination with thecapacitor126. Theconductor124 of the illustrated embodiment can be hot air or alcohol bonded wire having a gauge of approximately 45-52. Thecoil122 can have 800-1000 turns, and the windings are preferably wound in a tightly layered coil. Themagnetic transponder120 can further include acore128 composed of a material having a suitable magnetic permeability. For example, thecore128 can be a ferromagnetic element composed of ferrite or another material. Themagnetic transponder120 can be secured to thecasing110 by an adhesive129 (FIG. 5B).
• Themarker100 also includes an imaging element that enhances the radiographic image of the marker to make the marker more discernible in radiographic images. The imaging element also has a radiographic profile in a radiographic image such that the marker has a radiographic centroid at least approximately coincident with the magnetic centroid of themagnetic transponder120. As explained in more detail below, the radiographic and magnetic centroids do not need to be exactly coincident with each other, but rather can be within an acceptable range.
• FIG. 5B is a cross-sectional view of themarker100 alongline5B-5B ofFIG. 5A that illustrates animaging element130 in accordance with an embodiment of the invention. Theimaging element130 illustrated inFIGS. 5A-B includes afirst contrast element132 andsecond contrast element134. The first andsecond contrast elements132 and134 are generally configured with respect to themagnetic transponder120 so that themarker100 has a radiographic centroid R_cthat is at least substantially coincident with the magnetic centroid M_cof themagnetic transponder120. For example, when theimaging element130 includes two contrast elements, the contrast elements can be arranged symmetrically with respect to themagnetic transponder120 and/or each other. The contrast elements can also be radiographically distinct from themagnetic transponder120. In such an embodiment, the symmetrical arrangement of distinct contrast elements enhances the ability to accurately determine the radiographic centroid of themarker100 in a radiographic image.
• The first andsecond contrast elements132 and134 illustrated inFIGS. 5A-B are continuous rings positioned at opposing ends of thecore128. Thefirst contrast element132 can be at or around afirst end136aof thecore128, and thesecond contrast element134 can be at or around asecond end136bof thecore128. The continuous rings shown inFIGS. 5A-B have substantially the same diameter and thickness. The first andsecond contrast elements132 and134, however, can have other configurations and/or be in other locations relative to thecore128 in other embodiments. For example, the first andsecond contrast elements132 and134 can be rings with different diameters and/or thicknesses.
• The radiographic centroid of the image produced by theimaging element130 does not need to be absolutely coincident with the magnetic centroid M_c, but rather the radiographic centroid and the magnetic centroid should be within an acceptable range. For example, the radiographic centroid R_ccan be considered to be at least approximately coincident with the magnetic centroid M_cwhen the offset between the centroids is less than approximately 5 mm. In more stringent applications, the magnetic centroid M_cand the radiographic centroid R_care considered to be at least substantially coincident with each other when the offset between the centroids is 2 mm or less. In other applications, the magnetic centroid M_cis at least approximately coincident with the radiographic centroid R_cwhen the centroids are spaced apart by a distance not greater than half the length of themagnetic transponder120 and/or themarker100.
• Theimaging element130 can be made from a material and configured appropriately to absorb a high fraction of incident photons of a radiation beam used for producing the radiographic image. For example, when the imaging radiation has high-acceleration voltages in the megavoltage range, theimaging element130 is made from, at least in part, high-density materials with sufficient thickness and cross-sectional area to absorb enough of the photon fluence incident on the imaging element to be visible in the resulting radiograph. Many high-energy beams used for therapy have acceleration voltages of 6 MV-25 MV, and these beams are often used to produce radiographic images in the 5 MV-10 MV range, or more specifically in the 6 MV-8 MV range. As such, theimaging element130 can be made from a material that is sufficiently absorbent of incident photon fluence to be visible in an image produced using a beam with an acceleration voltage of 5 MV-10 MV, or more specifically an acceleration voltage of 6 MV-8 MV.
• Several specific embodiments ofimaging elements130 can be made from gold, tungsten, platinum and/or other high-density metals. In these embodiments theimaging element130 can be composed of materials having a density of 19.25 g/cm³(density of tungsten) and/or a density of approximately 21.4 g/cm³(density of platinum). Many embodiments of theimaging element130 accordingly have a density not less than 19 g/cm³. In other embodiments, however, the material(s) of theimaging element130 can have a substantially lower density. For example, imaging elements with lower-density materials are suitable for applications that use lower-energy radiation to produce radiographic images. Moreover, the first andsecond contrast elements132 and134 can be composed of different materials such that thefirst contrast element132 can be made from a first material and thesecond contrast element134 can be made from a second material.
• Referring toFIG. 5B, themarker100 can further include amodule140 at an opposite end of the core128 from thecapacitor126. In the embodiment of themarker100 shown inFIG. 5B, themodule140 is configured to be symmetrical with respect to thecapacitor126 to enhance the symmetry of the radiographic image. As with the first andsecond contrast elements132 and134, themodule140 and thecapacitor126 are arranged such that the magnetic centroid of themarker100 is at least approximately coincident with the radiographic centroid of themarker100. Themodule140 can be another capacitor that is identical to thecapacitor126, or themodule140 can be an electrically inactive element. Suitable electrically inactive modules include ceramic blocks shaped like thecapacitor126 and located with respect to thecoil122, thecore128 and theimaging element130 to be symmetrical with each other. In still other embodiments themodule140 can be a different type of electrically active element electrically coupled to themagnetic transponder120.
• One specific process of using the marker involves imaging the marker using a first modality and then tracking the target of the patient and/or the marker using a second modality. For example, the location of the marker relative to the target can be determined by imaging the marker and the target using radiation. The marker and/or the target can then be localized and tracked using the magnetic field generated by the marker in response to an excitation energy in a non-ionizing environment.
• Themarker100 shown inFIGS. 5A-B is expected to provide an enhanced radiographic image compared to conventional magnetic markers for more accurately determining the relative position between the marker and the target of a patient.FIG. 5C, for example, illustrates aradiographic image150 of themarker100 and a target T of the patient. The first andsecond contrast elements132 and134 are expected to be more distinct in theradiographic image150 because they can be composed of higher density materials than the components of themagnetic transponder120. The first andsecond contrast elements132 and134 can accordingly appear as bulbous ends of a dumbbell shape in applications in which the components of themagnetic transponder120 are visible in the image. In certain megavolt applications, the components of themagnetic transponder120 may not appear at all on theradiographic image150 such that the first andsecond contrast elements132 and134 will appear as distinct regions that are separate from each other. In either embodiment, the first andsecond contrast elements132 and134 provide a reference frame in which the radiographic centroid R_cof themarker100 can be located in theimage150. Moreover, because theimaging element130 is configured so that the radiographic centroid R_cis at least approximately coincident with the magnetic centroid M_c, the relative offset or position between the target T and the magnetic centroid M_ccan be accurately determined using themarker100. The embodiment of themarker100 illustrated inFIGS. 5A-C, therefore, is expected to mitigate errors caused by incorrectly estimating the radiographic and magnetic centroids of markers in radiographic images.
• FIG. 6A is an isometric view of amarker200 with a cutaway portion to illustrate internal components, andFIG. 6B is a cross-sectional view of themarker200 taken alongline6B-6B ofFIG. 6A. Themarker200 is similar to themarker100 shown above inFIG. 5A, and thus like reference numbers refer to like components. Themarker200 differs from themarker100 in that themarker200 includes animaging element230 defined by a single contrast element. Theimaging element230 is generally configured relative to themagnetic transponder120 so that the radiographic centroid of themarker200 is at least approximately coincident with the magnetic centroid of themagnetic transponder120. Theimaging element230, more specifically, is a ring extending around thecoil122 at a medial region of themagnetic transponder120. Theimaging element230 can be composed of the same materials described above with respect to theimaging element130 inFIGS. 5A-B. Theimaging element230 can have an inner diameter approximately equal to the outer diameter of thecoil122, and an outer diameter within thecasing110. As shown inFIG. 6B, however, aspacer231 can be between the inner diameter of theimaging element230 and the outer diameter of thecoil122.
• Themarker200 is expected to operate in a manner similar to themarker100 described above. Themarker200, however, does not have two separate contrast elements that provide two distinct, separate points in a radiographic image. Theimaging element230 is still highly useful in that it identifies the radiographic centroid of themarker200 in a radiographic image, and it can be configured so that the radiographic centroid of themarker200 is at least approximately coincident with the magnetic centroid of themagnetic transponder120.
• FIG. 7A is an isometric view of amarker300 with a cutaway portion, andFIG. 7B is a cross-sectional view of themarker300 taken alongline7B-7B ofFIG. 7A. Themarker300 is substantially similar to themarker200 shown inFIGS. 6A-B, and thus like reference numbers refer to like components inFIGS. 5A-7B. Theimaging element330 can be a high-density ring configured relative to themagnetic transponder120 so that the radiographic centroid of themarker300 is at least approximately coincident with the magnetic centroid of themagnetic transponder120. Themarker300, more specifically, includes animaging element330 around thecasing110. Themarker300 is expected to operate in much the same manner as themarker200 shown inFIGS. 6A-B.
• FIG. 8 is an isometric view with a cutaway portion illustrating amarker400 in accordance with another embodiment of the invention. Themarker400 is similar to themarker100 shown inFIGS. 5A-C, and thus like reference numbers refer to like components in these Figures. Themarker400 has animaging element430 including afirst contrast element432 at one end of themagnetic transponder120 and asecond contrast element434 at another end of themagnetic transponder120. The first andsecond contrast elements432 and434 are spheres composed of suitable high-density materials. Thecontrast elements432 and434, for example, can be composed of gold, tungsten, platinum or other suitable high-density materials for use in radiographic imaging. Themarker400 is expected to operate in a manner similar to themarker100, as described above.
• FIG. 9 is an isometric view with a cutaway portion of amarker500 in accordance with yet another embodiment of the invention. Themarker500 is substantially similar to themarkers100 and400 shown inFIGS. 5A and 8, and thus like reference numbers refer to like components in these Figures. Themarker500 includes animaging element530 including afirst contrast element532 and asecond contrast element534. The first andsecond contrast elements532 and534 can be positioned proximate to opposing ends of themagnetic transponder120. The first andsecond contrast elements532 and534 can be discontinuous rings having agap535 to mitigate eddy currents. Thecontrast elements532 and534 can be composed of the same materials as described above with respect to the contrast elements of other imaging elements in accordance with other embodiments of the invention.
• Additional embodiments of markers in accordance with the invention can include imaging elements incorporated into or otherwise integrated with thecasing110, the core128 (FIG. 5B) of themagnetic transponder120, and/or the adhesive129 (FIG. 5B) in the casing. For example, particles of a high-density material can be mixed with ferrite and extruded to form thecore128. Alternative embodiments can mix particles of a high-density material with glass or another material to form thecasing110, or coat thecasing110 with a high-density material. In still other embodiments, a high-density material can be mixed with the adhesive129 and injected into thecasing110. Any of these embodiments can incorporate the high-density material into a combination of thecasing110, thecore128 and/or the adhesive129. Suitable high-density materials can include tungsten, gold and/or platinum as described above.
• The markers described above with reference toFIGS. 5A-9 can be used for themarkers40 in the instrument10 (FIGS. 1-4C). Theinstrument10 can have several markers with the same type of imaging elements, or markers with different imaging elements can be used with the same instrument. Several additional details of these markers and other embodiments of markers are described in U.S. application Ser. Nos. 10/334,698 and 10/746,888, which are incorporated herein by reference. For example, the markers may not have any imaging elements for applications with lower-energy radiation, or the markers may have reduced volumes of ferrite and metals to mitigate issues with MRI imaging as set forth in U.S. application Ser. No. 10/334,698.
• 2. Localization Systems
• FIG. 10 is a schematic block diagram of alocalization system1000 for determining the absolute location of the markers40 (shown schematically) relative to a reference frame. Thelocalization system1000 includes anexcitation source1010, asensor assembly1012, asignal processor1014 operatively coupled to thesensor assembly1012, and acontroller1016 operatively coupled to theexcitation source1010 and thesignal processor1014. Theexcitation source1010 is one embodiment of the excitation source60 described above with reference toFIG. 4A; thesensor assembly1012 is one embodiment of thesensor assembly70 described above with reference toFIG. 4A; and thecontroller1016 is one embodiment of the controller80 described above with reference toFIG. 4A.
• Theexcitation source1010 is adjustable to generate a magnetic field having a waveform with energy at selected frequencies to match the resonant frequencies of themarkers40. The magnetic field generated by theexcitation source1010 energizes the markers at their respective frequencies. After themarkers40 have been energized, theexcitation source1010 is momentarily switched to an “off” position so that the pulsed magnetic excitation field is terminated while the markers wirelessly transmit the location signals. This allows thesensor assembly1012 to sense the location signals from themarkers40 without measurable interference from the significantly more powerful magnetic field from theexcitation source1010. Theexcitation source1010 accordingly allows thesensor assembly1012 to measure the location signals from themarkers40 at a sufficient signal-to-noise ratio so that thesignal processor1014 or thecontroller1016 can accurately calculate the absolute location of themarkers40 relative to a reference frame.
• a. Excitation Sources
• Referring still toFIG. 10, theexcitation source1010 includes a high-voltage power supply1040, anenergy storage device1042 coupled to thepower supply1040, and aswitching network1044 coupled to theenergy storage device1042. Theexcitation source1010 also includes acoil assembly1046 coupled to theswitching network1044. In one embodiment, thepower supply1040 is a 500 volt power supply, although other power supplies with higher or lower voltages can be used. Theenergy storage device1042 in one embodiment is a high-voltage capacitor that can be charged and maintained at a relatively constant charge by thepower supply1040. Theenergy storage device1042 alternately provides energy to and receives energy from the coils in thecoil assembly1046.
• Theenergy storage device1042 is capable of storing adequate energy to reduce voltage drop in the energy storage device while having a low series resistance to reduce power losses. Theenergy storage device1042 also has a low series inductance to more effectively drive thecoil assembly1046. Suitable capacitors for theenergy storage device1042 include aluminum electrolytic capacitors used in flash energy applications. Alternative energy storage devices can also include NiCd and lead acid batteries, as well as alternative capacitor types, such as tantalum, film, or the like.
• Theswitching network1044 includes individual H-bridge switches1050 (identified individually by reference numbers1050a-d), and thecoil assembly1046 includes individual source coils1052 (identified individually by reference numbers1052a-d). Each H-bridge switch1050 controls the energy flow between theenergy storage device1042 and one of the source coils1052. For example, H-bridge switch #11050aindependently controls the flow of the energy to/fromsource coil #11052a, H-bridge switch #21050bindependently controls the flow of the energy to/fromsource coil #21052b, H-bridge switch #31050cindependently controls the flow of the energy to/fromsource coil #31052c, and H-bridge switch #41050dindependently controls the flow of the energy to/fromsource coil #41052d. Theswitching network1044 accordingly controls the phase of the magnetic field generated by each of the source coils1052a-dindependently. The H-bridges1050 can be configured so that the electrical signals for all the source coils1052 are in phase, or the H-bridges1050 can be configured so that one or more of the source coils1052 are 180° out of phase. Furthermore, the H-bridge switches1050 can be configured so that the electrical signals for one or more of the source coils1052 are between 0 and 180° out of phase to simultaneously provide magnetic fields with different phases.
• The source coils1052 can be arranged in a coplanar array fixed relative to the reference frame. Each source coil1052 can be a square, planar winding arranged to form a flat, substantially rectilinear coil. The source coils1052 can have other shapes and other configurations in different embodiments. In one embodiment, the source coils1052 are individual conductive lines formed in a stratum of a printed circuit board, or windings of a wire in a foam frame. Alternatively, the source coils1052 can be formed in different substrates or arranged so that two or more of the source coils are not planar with each other. Additionally, alternate embodiments of the invention may have fewer or more source coils than illustrated inFIG. 10.
• The selected magnetic fields from the source coils1052 combine to form an adjustable excitation field that can have different three-dimensional shapes to excite themarkers40 at any spatial orientation within an excitation volume. When the planar array of the source coils1052 is generally horizontal, the excitation volume is positioned above an area approximately corresponding to the central region of thecoil assembly1046. The excitation volume is the three-dimensional space adjacent to thecoil assembly1046 in which the strength of the magnetic field is sufficient to adequately energize themarkers40.
• FIGS. 11-13 are schematic views of a planar array of the source coils1052 with the alternating electrical signals provided to the source coils in different combinations of phases to generate excitation fields about different axes relative to the illustrated XYZ coordinate system. Each source coil1052 has twoouter sides1112 and twoinner sides1114. Eachinner side1114 of one source coil1052 is immediately adjacent to aninner side1114 of another source coil1052, but theouter sides1112 of all the source coils1052 are not adjacent to any other source coil1052.
• In the embodiment ofFIG. 11, all the source coils1052a-dsimultaneously receive alternating electrical signals in the same phase. As a result, the electrical current flows in the same direction through all the source coils1052a-dsuch that adirection1113 of the current flowing along theinner sides1114 of one source coil (e.g.,source coil1052a) is opposite to thedirection1113 of the current flowing along theinner sides1114 of the two adjacent source coils (e.g., source coils1052cand1052d). The magnetic fields generated along theinner sides1114 accordingly cancel each other out so that the magnetic field is effectively generated from the current flowing along theouter sides1112 of the source coils. The resulting excitation field formed by the combination of the magnetic fields from the source coils1052a-dshown inFIG. 11 has amagnetic moment1115 generally in the Z direction within anexcitation volume1109. This excitation field energizes markers parallel to the Z-axis or markers positioned with an angular component along the Z-axis (i.e., not orthogonal to the Z-axis).
• FIG. 12 is a schematic view of the source coils1052a-dwith the alternating electrical signals provided in a second combination of phases to generate a second excitation field with a different spatial orientation. In this embodiment, source coils1052aand1052care in phase with each other, andsource coils1052band1052dare in phase with each other. However, source coils1052aand1052care 180 degrees out of phase withsource coils1052band1052d. The magnetic fields from the source coils1052a-dcombine to generate an excitation field having amagnetic moment1217 generally in the Y direction within theexcitation volume1109. Accordingly, this excitation field energizes markers parallel to the Y-axis or markers positioned with an angular component along the Y-axis.
• FIG. 13 is a schematic view of the source coils1052a-dwith the alternating electrical signals provided in a third combination of phases to generate a third excitation field with a different spatial orientation. In this embodiment, source coils1052aand1052bare in phase with each other, andsource coils1052cand1052dare in phase with each other. However, source coils1052aand1052bare 180 degrees out of phase withsource coils1052cand1052d. The magnetic fields from the source coils1052a-dcombine to generate an excitation field having amagnetic moment1319 in theexcitation volume1109 generally in the direction of the X-axis. Accordingly, this excitation field energizes markers parallel to the X-axis or markers positioned with an angular component along the X-axis.
• FIG. 14 is a schematic view of the source coils1052a-dillustrating the current flow to generate anexcitation field1424 for energizingmarkers40 with longitudinal axes parallel to the Y-axis. The switching network1044 (FIG. 10) is configured so that the phases of the alternating electrical signals provided to the source coils1052a-dare similar to the configuration ofFIG. 12. This generates theexcitation field1424 with a magnetic moment in the Y direction to energize themarkers40.
• FIG. 15 further illustrates the ability to spatially adjust the excitation field in a manner that energizes any of themarkers40 at different spatial orientations. In this embodiment, the switching network1044 (FIG. 10) is configured so that the phases of the alternating electrical signals provided to the source coils1052a-dare similar to the configuration shown inFIG. 11. This produces an excitation field with a magnetic moment in the Z direction that energizesmarkers40 with longitudinal axes parallel to the Z-axis.
• The spatial configuration of the excitation field in theexcitation volume1109 can be quickly adjusted by manipulating the switching network to change the phases of the electrical signals provided to the source coils1052a-d. As a result, the overall magnetic excitation field can be changed to be oriented in either the X, Y or Z directions within theexcitation volume1109. This adjustment of the spatial orientation of the excitation field reduces or eliminates blind spots in theexcitation volume1109. Therefore, themarkers40 within theexcitation volume1109 can be energized by the source coils1052a-dregardless of the spatial orientations of the leadless markers.
• In one embodiment, theexcitation source1010 is coupled to thesensor assembly1012 so that the switching network1044 (FIG. 10) adjusts orientation of the pulsed generation of the excitation field along the X, Y, and Z axes depending upon the strength of the signal received by thesensor assembly1012. If the location signal from amarker40 is insufficient, theswitching network1044 can automatically change the spatial orientation of the excitation field during a subsequent pulsing of the source coils1052a-dto generate an excitation field with a moment in the direction of a different axis or between axes. Theswitching network1044 can be manipulated until thesensor assembly1012 receives a sufficient location signal from the marker.
• Theexcitation source1010 illustrated inFIG. 10 alternately energizes the source coils1052a-dduring an excitation phase to power themarkers40, and then actively de-energizes the source coils1052a-dduring a sensing phase in which thesensor assembly1012 senses the decaying location signals wirelessly transmitted by themarkers40. To actively energize and de-energize the source coils1052a-d, theswitching network1044 is configured to alternatively transfer stored energy from theenergy storage device1042 to the source coils1052a-d, and to then “re-transfer” energy from the source coils1052a-dback to theenergy storage device1042. Theswitching network1044 alternates between first and second “on” positions so that the voltage across the source coils1052 alternates between positive and negative polarities. For example, when theswitching network1044 is switched to the first “on” position, the energy in theenergy storage device1042 flows to the source coils1052a-d. When theswitching network1044 is switched to the second “on” position, the polarity is reversed such that the energy in the source coils1052a-dis actively drawn from the source coils1052a-dand directed back to theenergy storage device1042. As a result, the energy in the source coils1052a-dis quickly transferred back to theenergy storage device1042 to abruptly terminate the excitation field transmitted from the source coils1052a-dand to conserve power consumed by theenergy storage device1042. This removes the excitation energy from the environment so that thesensor assembly1012 can sense the location signals from themarkers40 without interference from the significantly larger excitation energy from theexcitation source1010. Several additional details of theexcitation source1010 and alternate embodiments are disclosed in U.S. patent application Ser. No. 10/213,980 filed on Aug. 7, 2002, which is incorporated by reference herein in its entirety.
• b. Sensor Assemblies
• FIG. 16A is an exploded isometric view showing several components of thesensor assembly1012 for use in the localization system1000 (FIG. 10). Thesensor assembly1012 includes asensing unit1601 having a plurality ofcoils1602 formed on or carried by apanel1604. Thecoils1602 can be field sensors or magnetic flux sensors arranged in asensor array1605.
• Thepanel1604 may be a substantially nonconductive material, such as a sheet of KAPTON® produced by DuPont. KAPTON® is particularly useful when an extremely stable, tough, and thin film is required (such as to avoid radiation beam contamination), but thepanel1604 may be made from other materials and have other configurations. For example, FR4 (epoxy-glass substrates), GETEK or other Teflon-based substrates, and other commercially available materials can be used for thepanel1604. Additionally, although thepanel1604 may be a flat, highly planar structure, in other embodiments, the panel may be curved along at least one axis. In either embodiment, the field sensors (e.g., coils) are arranged in a locally planar array in which the plane of one field sensor is at least substantially coplanar with the planes of adjacent field sensors. For example, the angle between the plane defined by one coil relative to the planes defined by adjacent coils can be from approximately 0° to 10°, and more generally is less than 5°. In some circumstances, however, one or more of the coils may be at an angle greater than 10° relative to other coils in the array.
• Thesensor assembly1012 shown inFIG. 16A can optionally include acore1620 laminated to thepanel1604. Thecore1620 can be a support member made from a rigid material, or thecore1620 can be a low-density foam (e.g., closed-cell Rohacell foam). Thecore1620 is preferably a stable layer that has a low coefficient of thermal expansion so that the shape of thesensor assembly1012 and the relative orientation between thecoils1602 remain within a defined range over an operating temperature range.
• Thesensor assembly1012 can further include a first exterior cover1630aon one side of the sensing subsystem and asecond exterior cover1630bon an opposing side. The first and second exterior covers1630a-bcan be thin, thermally stable layers, such as Kevlar or Thermount films. Each of the first and second exterior covers1630a-bcan includeelectric shielding1632 to block undesirable external electric fields from reaching thecoils1602. Theelectric shielding1632, for example, prevents or minimizes the presence of eddy currents caused by thecoils1602 or external magnetic fields. Theelectric shielding1632 can be a plurality of parallel legs of gold-plated copper strips to define a comb-shaped shield in a configuration commonly called a Faraday shield. It will be appreciated that theelectrical shielding1632 can be formed from other materials that are suitable for shielding. Theelectric shielding1632 can be formed on the first and second exterior covers1630a-busing printed circuit board manufacturing technology or other techniques.
• Thepanel1604 with thecoils1602 is laminated to thecore1620 using a pressure sensitive adhesive or another type of adhesive. The first and second exterior covers1630a-bare similarly laminated to the assembly of thepanel1604 and thecore1620. The laminated assembly forms a rigid structure that fixedly retains the arrangement of thecoils1602 in a defined configuration over a large operating temperature range. As such, thesensor assembly1012 does not substantially deflect across its surface during operation. Thesensor assembly1012, for example, can retain the array ofcoils1602 in the fixed position with a deflection of no greater than ±0.5 mm, and in some cases no more than ±0.3 mm. The stiffness of the sensing subsystem provides very accurate and repeatable monitoring of the precise location of leadless markers in real time.
• In still another embodiment, thesensor assembly1012 can further include a plurality of source coils that are a component of theexcitation source1010. One suitable array combining thesensor assembly1012 with source coils is disclosed in U.S. patent application Ser. No. 10/334,700. entitled PANEL-TYPF SENSOR/SOURCE ARRAY ASSEMBLY, filed on Dec. 30, 2002, which is herein incorporated by reference.
• FIG. 16B further illustrates an embodiment of thesensing unit1601. In this embodiment, thesensing unit1601 includes 32sensor coils1602; eachcoil1602 is associated with a separate output port (channel)1606 (shown individually as channels “Ch 0” through “Ch 31”). The overall dimension of thepanel1604 can be approximately 40 cm by 54 cm, but thearray1605 has a first dimension D₁of approximately 40 cm and a second dimension D₂of approximately 40 cm. Thearray1605 can have other sizes or other configurations (e.g., circular) in alternative embodiments. Additionally, thearray1605 can have more or fewer coils, such as 8-64 coils; the number of coils may moreover be a power of 2.
• Thecoils1602 may be conductive traces or depositions of copper or another suitably conductive metal formed on thepanel1604. Eachcoil1602 has a trace with a width of approximately 0.15 mm and a spacing between adjacent turns within each coil of approximately 0.13 mm. Thecoils1602 can have approximately 15 to 90 turns, and in specific applications each coil has approximately 40 turns. Coils with less than 15 turns may not be sensitive enough for some applications, and coils with more than 90 turns may lead to excessive voltage from the source signal during excitation and excessive settling times resulting from the coil's lower self-resonant frequency. In other applications, however, thecoils1602 can have less than 15 turns or more than 90 turns.
• As shown inFIG. 16B, thecoils1602 are arranged as square spirals, although other configurations may be employed, such as arrays of circles, interlocking hexagons, triangles, etc. Such square spirals utilize a large percentage of the surface area to improve the signal-to-noise ratio. Square coils also simplify design layout and modeling of the array compared to circular coils; for example, circular coils could waste surface area for linking magnetic flux from themarkers40. Thecoils1602 have an inner dimension of approximately 40 mm, and an outer dimension of approximately 62 mm, although other dimensions are possible depending upon applications. Sensitivity may be improved with an inner dimension as close to an outer dimension as possible given manufacturing tolerances. In several embodiments, thecoils1602 are identical to each other or at least configured substantially similarly.
• The pitch of thecoils1602 in thearray1605 is a function of, at least in part, the minimum distance between the marker and the coil array. In one embodiment, the coils are arranged at a pitch of approximately 67 mm. This specific arrangement is particularly suitable when themarkers40 are positioned approximately 7-27 cm from thesensor assembly1012. If the markers are closer than 7 cm, then the sensing subsystem may include sensor coils arranged at a smaller pitch. In general, a smaller pitch is desirable when wireless markers are to be sensed at a relatively short distance from the array of coils. The pitch of thecoils1602, for example, is approximately 50%-200% of the minimum distance between the marker and the array.
• In general, the size and configuration of thearray1605 and thecoils1602 in the array depend on the frequency range in which they are to operate, the distance from themarkers40 to the array, the signal strength of the markers, and several other factors. Those skilled in the art will readily recognize that other dimensions and configurations may be employed depending, at least in part, on a desired frequency range and distance from the markers to the coils.
• Thearray1605 is sized to provide a large aperture to measure the magnetic field emitted by the markers. It can be particularly challenging to accurately measure the signal emitted by an implantable marker that wirelessly transmits a marker signal in response to a wirelessly transmitted energy source because the marker signal is much smaller than the source signal and other magnetic fields in a room (e.g., magnetic fields from CRTs, etc.). The size of thearray1605 can be selected to preferentially measure the near field of the marker while mitigating interference from far field sources. In one embodiment, thearray1605 is sized to have a maximum dimension D₁or D₂across the surface of the area occupied by the coils that is approximately 100% to 300% of a predetermined maximum sensing distance that the markers are to be spaced from the plane of the coils. Thus, the size of thearray1605 is determined by identifying the distance that the marker is to be spaced apart from the array to accurately measure the marker signal, and then arrange the coils so that the maximum dimension of the array is approximately 100% to 300% of that distance. The maximum dimension of thearray1605, for example, can be approximately 200% of the sensing distance at which a marker is to be placed from thearray1605. In one specific embodiment, themarker40 has a sensing distance of 20 cm and the maximum dimension of the array ofcoils1602 is between 20 cm and 60 cm, and more specifically 40 cm.
• A coil array with a maximum dimension as set forth above is particularly useful because it inherently provides a filter that mitigates interference from far field sources. As such, one aspect of several embodiments of the invention is to size the array based on the signal from the marker so that the array preferentially measures near field sources (i.e., the field generated by the marker) and filters interference from far field sources.
• Thecoils1602 are electromagnetic field sensors that receive magnetic flux produced by themarkers40 and in turn produce a current signal representing or proportional to an amount or magnitude of a component of the magnetic field through an inner portion or area of each coil. The field component is also perpendicular to the plane of eachcoil1602. Each coil represents a separate channel, and thus each coil outputs signals to one of 32output ports1606. A preamplifier, described below, may be provided at eachoutput port1606. Placing preamplifiers (or impedance buffers) close to the coils minimizes capacitive loading on the coils, as described herein. Although not shown, thesensing unit1601 also includes conductive traces or conductive paths routing signals from eachcoil1602 to itscorresponding output port1606 to thereby define a separate channel. The ports in turn are coupled to aconnector1608 formed on thepanel1604 to which an appropriately configured plug and associated cable may be attached.
• Thesensing unit1601 may also include an onboard memory or other circuitry, such as shown by electrically erasable programmable read-only memory (EEPROM)1610. TheEEPROM1610 may store manufacturing information such as a serial number, revision number, date of manufacture, and the like. TheEEPROM1610 may also store per-channel calibration data, as well as a record of run-time. The run-time will give an indication of the total radiation dose to which the array has been exposed, which can alert the system when a replacement sensing subsystem is required.
• Although shown in one plane only, additional coils or electromagnetic field sensors may be arranged perpendicular to thepanel1604 to help determine a three-dimensional location of themarkers40. Adding coils or sensors in other dimensions could increase the total energy received from themarkers40, but the complexity of such an array would increase disproportionately. The inventors have found that three-dimensional coordinates of themarkers40 may be found using the planar array shown inFIGS. 16A-B.
• Implementing thesensor assembly1012 may involve several considerations. First, thecoils1602 may not be presented with an ideal open circuit. Instead, they may well be loaded by parasitic capacitance due largely to traces or conductive paths connecting thecoils1602 to the preamplifiers, as well as a damping network (described below) and an input impedance of the preamplifiers (although a low input impedance is preferred). These combined loads result in current flow when thecoils1602 link with a changing magnetic flux. Any onesensor coil1602, then, links magnetic flux not only from themarker40, but also from all the other sensor coils as well. These current flows should be accounted for in downstream signal processing.
• A second consideration is the capacitive loading on thecoils1602. In general, it is desirable to minimize the capacitive loading on thecoils1602. Capacitive loading forms a resonant circuit with the coils themselves, which leads to excessive voltage overshoot when theexcitation source1010 is energized. Such a voltage overshoot should be limited or attenuated with a damping or “snubbing” network across thecoils1602. A greater capacitive loading requires a lower impedance damping network, which can result in substantial power dissipation and heating in the damping network.
• Another consideration is to employ preamplifiers that are low noise. The preamplification can also be radiation tolerant because one application for thesensor assembly1012 is with radiation therapy systems that use linear accelerators (LINAC). As a result, PNP bipolar transistors and discrete elements may be preferred. Further, a DC coupled circuit may be preferred if good settling times cannot be achieved with an AC circuit or output, particularly if analog to digital converters are unable to handle wide swings in an AC output signal.
• FIG. 17, for example, illustrates an embodiment of asnubbing network1702 having adifferential amplifier1704. Thesnubbing network1702 includes two pairs of series coupled resistors and a capacitor bridging therebetween. Abiasing circuit1706 allows for adjustment of the differential amplifier, while acalibration input1708 allows both input legs of the differential amplifier to be balanced. Thecoil1602 is coupled to an input of thedifferential amplifier1704, followed by a pair of high-voltage protection diodes1710. DC offset may be adjusted by a pair of resistors coupled to bases of the input transistors for the differential amplifier1704 (shown as having a zero value). Additional protection circuitry is provided, such asESD protection diodes1712 at the output, as well as filtering capacitors (shown as having a 10 nF value).
• c. Signal Processors and Controllers
• Thesignal processor1014 and thecontroller1016 illustrated inFIG. 10 receive the signals from thesensor assembly1012 and calculate the absolute positions of themarkers40 within the reference frame. Suitable signal processing systems and algorithms are set forth in U.S. application Ser. Nos. 10/679,801; 10/749,478; 10/750,456; 10/750,164; 10/750,165; 10/749,860; and 10/750,453, all of which are incorporated herein by reference.
G. Conclusion
• The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those skilled in the relevant art. The teachings provided herein of the invention can be applied to target locating and tracking systems, not necessarily the exemplary system generally described above.
• The various embodiments described above can be combined to provide further embodiments. All the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the invention can be modified, if necessary, to employ systems, devices, and concepts of the various patents, applications, and publications to provide yet further embodiments of the invention, for example, the markers can be implanted in bone, can be implanted in an intramedullary device, can be affixed to a minimally invasive surgical device and/or can be affixed to a surgical guide.
• These and other changes can be made to the invention in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all target locating and monitoring systems that operate in accordance with the claims to provide apparatus and methods for locating, monitoring, and/or tracking the position of a selected target within a body. Accordingly, the invention is not limited, except as by the appended claims.

Claims (37)

1. An electromagnetic marker for use in orthopedic procedures, comprising:

a template of known mechanical dimensions temporarily used during surgery; and

a marker fixed to the template in a substantially fixed relationship.

2. An electromagnetic marker for use in orthopedic procedures, comprising:

a prosthetic device configured for implantation in a patient; and

a marker fixed to the prosthetic device in a substantially fixed relationship.

3. An electromagnetic marker for use in orthopedic procedures, comprising:

a bone screw or similar device; and

a marker fixed to the bone screw or similar device in a substantially fixed relationship.

4. The apparatus ofclaim 1 wherein the marker comprises a wireless transponder configured to wirelessly transmit a location signal in response to a wirelessly transmitted excitation energy.

5. The apparatus ofclaim 1 wherein the marker comprises a casing affixed in or on the template and a magnetic transponder in the casing, and wherein the magnetic transponder comprises a coil and a capacitor coupled to the coil.

6. The apparatus ofclaim 1 wherein the template comprises a cutting guide, and wherein the apparatus further comprises a plurality of markers attached to the cutting guide.

7. The apparatus ofclaim 6 wherein the markers comprise wireless transponders configured to wirelessly transmit location signals in response to wirelessly transmitted excitation energy.

8. The apparatus ofclaim 6 wherein the markers comprise a first magnetic transponder having a first resonant frequency and a second magnetic transponder having a second resonant frequency different than the first resonant frequency.

9. The apparatus ofclaim 7 wherein the markers comprise radiopaque elements.

10. The apparatus ofclaim 7 wherein the markers comprise magnetic transponders and/or radiographic fiducials.

11. The apparatus ofclaim 10 wherein the transponders and the fiducials are in a fixed relationship and/or orientation to one another.

12. The apparatus ofclaim 4 wherein the transponder comprises an alternating magnetic circuit having a ferrite core and a coil with a plurality of windings around the ferrite core.

13. The apparatus ofclaim 4 wherein the transponder comprises a ferrite core and a coil around the ferrite core, and wherein the marker further comprises a capsule encasing the transponder, the capsule having a longitudinal axis and a cross-sectional dimension normal to the longitudinal axis of not greater than 2 mm.

14. The apparatus ofclaim 2 wherein the prosthetic device further comprises a first marker in a first portion of the member and a second marker in a second portion of the member spaced apart from the first marker, wherein the first and the second markers are orthogonally oriented with respect to each other.

15. The apparatus ofclaim 2 wherein the marker comprises an alternating magnetic circuit and wherein the marker has a radiographic centroid and the alternating magnetic circuit has a magnetic centroid at least approximately coincident with the radiographic centroid.

16. A system for localizing and/or tracking a device contained in a bony anatomy of a patient, comprising:

a transponder affixed to the bone of a patient, wherein the transponder has a circuit configured to be energized by a wirelessly transmitted pulsed magnetic field and to wirelessly transmit a pulsed magnetic location signal in response to the pulsed magnetic field;

an alignment device for aligning the bone of a patient during localizing and/or tracking of the transponder; and

an excitation source comprising an energy storage device, a source coil, and a switching network coupled to the energy storage device and the source coil, the source coil being configured to wirelessly transmit the pulsed magnetic field to energize the transponder, and the switching network being configured to alternately transfer (a) stored energy from the energy storage device to the source coil and (b) energy in the source coil back to the energy storage device.

17. The system ofclaim 16 wherein the switching network comprises an H-bridge switch.

18. The system ofclaim 16 wherein the switching network is configured to have a first on position in which the stored energy is transferred from the energy storage device to the source coil and a second on position in which energy in the source coil is transferred back to the energy storage device.

19. The system ofclaim 18 wherein the first on position has a first polarity and the second on position has a second polarity opposite the first polarity.

20. The system ofclaim 16 wherein the source coil comprises an array having a plurality of coplanar source coils.

21. The system ofclaim 20 wherein the switching network is configured to selectively energize the coplanar source coils to change a spatial configuration of the pulsed magnetic field.

22. The system ofclaim 16 wherein the transponder comprises an alternating magnetic circuit having a ferrite core and a coil with a plurality of windings around the ferrite core.

23. The system ofclaim 16 wherein the transponder is not electrically coupled to external leads outside the body.

24. A system for tracking a body contained in an implanted prosthesis of a human, comprising:

a prosthesis configured to be received in a cavity of a human and a magnetic transponder contained in or on the body, wherein the transponder has a circuit configured to be energized by a wirelessly transmitted pulsed magnetic field and to wirelessly transmit a pulsed magnetic location signal in response to the pulsed magnetic field; and

a sensor assembly comprising a support member and a plurality of field sensors carried by the support member configured to sense the pulsed magnetic location signal from the transponder.

25. The system ofclaim 24 wherein the field sensors are responsive only to field components of the pulsed magnetic location signal normal to individual field sensors.

26. The system ofclaim 24 wherein the field sensors are arranged in an array occupying an area having a maximum dimension of approximately 100% to 300% of a predetermined sensing distance between the marker and the sensing array.

27. The system ofclaim 24 wherein the transponder comprises an alternating magnetic circuit having a ferrite core and a coil with a plurality of windings around the ferrite core.

28. A method for using implanted an electromagnetic transponder to localize bone components, comprising:

implanting one or more electromagnetic transponder pre-operatively;

localizing bone components using one or more electromagnetic transponders pre-operatively; and

localizing bone components using one or more electromagnetic transponders during surgery electromagnetically.

29. The method ofclaim 28 further comprising:

localizating bone components using one or more electromagnetic transponders following surgery electromagnetically.

30. A method for using implanted an electromagnetic transponder to localize a prosthesis relative to bony anatomy during surgery, comprising:

localizing bone components using one or more electromagnetic transponders pre-operatively; and

localizing bone components using one or more electromagnetic transponders during surgery.

31. A method for using an electromagnetic transponder to localize a cutting guide during surgery, comprising:

localizing the cutting guide using one or more electromagnetic transponders pre-operatively; and

localizing the cutting guide using one or more electromagnetic transponders during surgery electromagnetically.

32. The method ofclaim 28 wherein localizing the marker comprises (a) wirelessly delivering a pulsed magnetic field to energize the marker, (b) wirelessly transmitting a pulsed location signal from the marker to a location outside the patient, (c) sensing the pulsed location signal at a sensor located outside the patient, and (d) periodically calculating a three-dimensional location of the marker in a reference frame.

33. The method ofclaim 32 further comprising providing an output of the location of the marker in the reference frame at least every t_fsecond and within t_lsecond from sensing the pulsed location signal, wherein t_fand t_lare not greater than 1 second.

34. The method ofclaim 33 wherein t_fand t_lare from approximately 10 ms to approximately 500 ms.

35. The method ofclaim 32 wherein providing an output of the location of the marker further comprises referencing the three-dimensional location of the marker with an image of the marker relative to a target.

36. The method ofclaim 32 wherein localizing the marker comprises determining whether the marker has moved from a desired location.

37. The method ofclaim 32 wherein localizing the marker occurs during surgery.

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