Abstract:
A magnetic navigation system for orienting a magnetically responsive device in an operating region in a subject has at least two magnet units and a support for mounting the at least two magnet units for movement relative to the subject, the support supporting the at least two magnet units adjacent the operating region in the subject at locations to apply a magnetic field to the operating region. Each magnet unit includes sing a magnet and a positioner for selectively changing the position of the magnet. The system also includes a control for operating the positioners of each magnet unit to selectively change the positions of the magnets to maintain the magnetic field direction applied to the operating region by the magnets as the locations of the magnet units relative to the operating region change. The system is adapted for implementing a method of navigating according to the present invention in which the magnets in the magnet units are selectively rotated and pivoted to maintain the appropriate magnetic field direction projected by the magnets to maintain the device direction as the magnet units move on the support about the operating region.

Description:
CROSS-REFERENCE TO PREVIOUSLY FILED APPLICATIONS  
       [0001]    This invention claims priority of U.S. Patent Application Ser. No. 60/454,410, filed Mar. 13, 2003, the entire disclosure of which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to methods and apparatus for magnetically navigating magnetically responsive medical devices in an operating region in a subject.  
           [0003]    Medicine is increasingly relying on the remote navigation of medical devices in the body to reduce patient trauma, speed recovery, and perform procedures that could not be performed with conventional surgical techniques. Magnetic navigation of medical devices provides fast, simple, and reliable navigation in a subject&#39;s body. With the reduced size and increase flexibility of magnetically responsive medical devices, magnetically navigated devices can reach parts of the subjects body that could not be reached with most previously available remote navigation techniques.  
           [0004]    Magnetic navigation relies upon external source magnets, either electromagnets, or more recently permanent magnets, to provide a controllable magnetic field in an operating region in a subject to orient a magnetically responsive device in the operating region. A challenge for magnetic navigation is to position the magnet sufficient close to the patient to provide a sufficiently strong field for magnetic navigation, while accommodating patients of varying sizes, leaving room for other medical equipment (particularly imaging equipment), and provide access to the patient.  
         SUMMARY OF THE INVENTION  
         [0005]    Generally, the apparatus and method of this invention employ at least two magnet units movably mounted adjacent (and preferably on opposite sides of) an operating region in a subject for coordinated movement about the operating region. Each magnet unit comprises a magnet and a positioner for changing the position of the magnet, and thus the direction of the magnetic field that the magnet applies to the operating region. The magnets are mounted for coordinated movement about the operating region, so that the magnet units can be positioned close to the operating region, yet be moved out of the way to positions where they still apply a magnetic field to the operating region, when necessary for example to accommodate imaging equipment. The system preferably includes a controller for operating the positioners to maintain the magnetic field direction as the magnet units are moved.  
           [0006]    Thus, the invention provides a simple, relatively inexpensive way of applying a magnetic field in a selected direction. The capability of positioning the magnet units close to the operating region allows the magnets to be made smaller and more compact, which in turn means that the positioners can be smaller and less expensive. The smaller, more compact size of the magnets means that they interfere less with access to the patient by medical equipment or personnel, and the ability to move the magnet unit around the operating region allows the magnets to moved out of the way when needed, while still maintaining a magnetic field in the operating region. These and other features and advantages will be in part apparent, and in part pointed out hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a front elevation view of a first embodiment of a magnetic navigation system constructed according to the principles of this invention;  
         [0008]    [0008]FIG. 2 is a rear elevation view of the magnetic navigation system of the first embodiment;  
         [0009]    [0009]FIG. 3 is a side elevation view of the magnetic navigation system of the first embodiment;  
         [0010]    [0010]FIG. 4 is a front perspective view of the magnetic navigation system of the first embodiment;  
         [0011]    [0011]FIG. 5 is a front elevation view of a second embodiment of a magnetic navigation system constructed according to the principles of this invention;  
         [0012]    [0012]FIG. 6 is a front perspective view of the magnetic navigation system of the second embodiment;  
         [0013]    [0013]FIG. 7 is a rear perspective view of the magnetic navigation system of the second embodiment;  
         [0014]    [0014]FIG. 8 is a front perspective view of the magnetic navigation system of the second embodiment, with the imaging C-arm rotated 28°;  
         [0015]    [0015]FIG. 9 is a front elevation view of the magnetic navigation system of the second embodiment, with the imaging C-arm rotated 30°, and the magnet units rotated to accommodate the C-arm;  
         [0016]    [0016]FIG. 10 is a perspective view of a magnet adapted for use in the magnet units of some embodiments of this invention;  
         [0017]    [0017]FIG. 11 is a perspective view of a backing plate for a the magnet;  
         [0018]    [0018]FIG. 12 is a top plan view of the magnet;  
         [0019]    [0019]FIG. 13A is a perspective view of a positioner adapted for use in the magnet units of some embodiments of this invention;  
         [0020]    [0020]FIG. 13B is a perspective view of the positioner;  
         [0021]    [0021]FIG. 13C is a plan view of the positioner;  
         [0022]    [0022]FIG. 14A is a diagram illustrating the positioning of magnets on opposites sides of a patient in the lateral plane;  
         [0023]    [0023]FIG. 14B is a diagram illustrating the positioning of magnets on opposite sides of a patient, rotated 30° in the transverse plane;  
         [0024]    [0024]FIG. 14C is a diagram illustrating the positioning of magnets on opposite sides of a patient, rotated 45° in the transverse plane; and  
         [0025]    [0025]FIG. 14D is a diagram illustrating the positioning of magnets on opposite sides of a patient, rotated 60° in the transverse plane. 
     
    
       [0026]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    A first embodiment of a magnetic navigation system constructed according to the principles of this invention is indicated generally as  20  in FIGS. 1-4. The system  20  is adapted to apply a magnetic field of selected direction to an operating region in subject on a subject support (not shown) in the magnetic navigation system. The system  20  broadly comprises at least two magnet units  22  and  24  mounted on a support  26  adjacent (and preferably on opposite sides of) the operating region, for coordinated rotational movement about the operating region. The system also includes an imaging system  28  for imaging the operating region.  
         [0028]    More specifically, the magnet units  22  and  24  each comprise a compound permanent magnet  30  comprising a plurality of segments of magnetic material with differing magnetization directions so that relatively small rotations or pivots change the magnetic field projected by the magnet at a specific point. Each of the magnet units  22  and  24  also comprise a positioner  32  for controlling the position of the magnet  30 , e.g. for rotating the magnet  30  about a first axis and pivoting the magnet  30  about a second axis, to selectively change the magnetic field applied by each magnet to the operating region in a subject on the subject support.  
         [0029]    In the preferred embodiments of this invention, the magnet units  22  and  24 , and thus their respective magnets  30 , are mounted on opposite sides of the operating region. The first axis of rotation of each magnet preferably extends through the respective magnet and the operating region, and preferably the first axes of rotation of the magnets are co-linear. The second axes of pivoting of each magnet is preferably perpendicular to the first axis, and also rotates about the first axis.  
         [0030]    Each magnet unit  22  and  24  comprises a cover  36 . The cover protects the patient and medical personnel and equipment from the movement of the magnets  30 , it hides the movement to prevent patient concern over the operation of the system, and it improves the aesthetics of the system.  
         [0031]    As described above, the magnet units  22  and  24  are mounted on opposite sides of the operating region on support  26 . This support can be any support that accommodates the coordinated movement of the magnet units  22  and  24  about the operating region. As will be described below in more detail with respect to FIGS. 14A through 14D, it is desirable that the magnets  22  and  24  each rotate through a arc of about 120° from about 60° above the plane of the patient to about 60° below the plane of the patient. Of course, some greater or lesser range of rotation of the magnet units could be provided. One possible configuration for support  26  is shown in FIGS. 1-4, where the support comprises two stanchions  38  and  40 , having arcuate surfaces  38  and  40  on which the magnet units  22  and  24  can travel as they rotate about the operating region. The surfaces  40  and  42  can be the arcs of a circle, but could take some other shape so that the distance between the magnet units and the operating region changes as the magnet units rotate about the operating region on the stanchions  38  and  40 . Specifically, the surfaces  42  and  44  could be shaped so that the magnet units are closer to the operating region when they are above the plane of the subject. Any drive mechanism can be used to move the magnet units  22  and  24  on the stanchions  38  and  40 . Of course, instead of moving the magnet units  22  and  24  on the support, the magnet units  22  and  24  could be fixed relative to the support, and it could be the support that moves to rotate the magnet units  22  and  24  about the operating. In still another alternate construction, the rotation of the magnet units about the operating region could be accomplished by a combination of movement of the magnet units relative to the support, and movement of the support relative to the subject.  
         [0032]    The system  20  also includes an imaging system  28  for imaging the operating region. The imaging system preferably includes some type of C-arm structure  50 , or some other movable support that allows the imaging equipment to be repositioned about the operating region to allow imaging from the most advantageously angle. For most procedures in the chest, medical personnel are used to have left anterior oblique (lao) and right anterior oblique (rao) images, and the support is preferably capable of moving the imaging equipment to provide these images. The imaging system  28  preferably also includes a imaging beam source  52  and an imaging beam receiver  44 , such as an amorphous silicon plate. The source  52  and receiver  54  are preferably constructed to be immune to, or are shielded from the effects of, the magnets  30  in the magnet units  22  and  24 .  
         [0033]    A control is preferably provided to control the positioners  32  of each magnet unit  22  and  24 , to cause the magnets  30  to move to provide a magnetic field in a selected direction in the operating region. An interface can be provided to allow the user to identify a selected magnet field direction, and the controller operates the positioners  32  to position the magnets to achieve the desired magnetic field direction. Alternatively, the interface might allow the user to select a desired medical device orientation, and the controller operates the positioners  32  to position the magnets to achieve the magnetic field direction to achieve the desired medical device orientation. In this latter case the controller may take into account the physically properties of the device, represented in either a look-up table or in a set of equations, or parameters for equations, to determine the field to cause the device to align in the selected direction. The controller might also take into account the field strength applied in the operating region. In many prior magnetic navigation systems, the field strength is relatively constant, however in some embodiments of the present invention, in order to reduce magnet size, and facilitate movement of the magnet units, the field strength might vary depending upon the position of the magnet units. Thus the desired field direction to attain a given device orientation might vary depending upon the position of the magnet units. In at least some embodiments of this invention, the controller determines and applies the field based upon the desired orientation of the medical device input by the user, and upon the strength of the field that the magnets apply in their current position. The controller could also indicate to the user that it would be advantageous to reposition the magnets to achieve a higher field strength.  
         [0034]    A second embodiment of a magnetic navigation system constructed according to the principles of this invention is indicated generally as  120  in FIGS. 5-8. The system  120  is adapted to apply a magnetic field of selected direction to an operating region in subject on a subject support (not shown) in the magnetic navigation system. The system  120  broadly comprises at least two magnet units  122  and  124  mounted on a support  126  on opposite sides of the operating region, for coordinated rotational movement about the operating region. The system also includes an imaging system  128  for imaging the operating region.  
         [0035]    More specifically, the magnet units  122  and  124  each comprise a compound permanent magnet  30  comprising a plurality of segments of magnetic material with differing magnetization directions so that relatively small rotations or pivots change the magnetic field projected by the magnet at a specific point. Each of the magnet units  122  and  124  also comprise a positioner  132  for controlling the position of the magnet  30 , e.g. for rotating the magnet  30  about a first axis and pivoting the magnet  30  about a second axis, to selectively change the magnetic field applied by each magnet to the operating region in a subject on the subject support.  
         [0036]    In the preferred embodiments of this invention, the magnet units  122  and  124 , and thus their respective magnets  30 , are mounted on opposite sides of the operating region. The first axis of rotation of each magnet preferably extend through the respective magnet and the operating region, and preferably the first axes of rotation of the magnets are co-linear. The second axes of pivoting of each magnet is preferably perpendicular to the first axis, and rotates about the first axis.  
         [0037]    Each magnet unit  122  and  124  comprises a cover  136 , the cover protects the patient and medical personnel and equipment from the movement of the magnets  130 , it hides the movement to prevent patient concern over the operation of the system, and it improves the aesthetics of the system.  
         [0038]    As described above, the magnet units  122  and  124  are mounted on opposite sides of the operating region on support  126 . This support can be any support that accommodates the coordinated movement of the magnet units  122  and  124  about the operating region. As will be described below in more detail with respect to FIGS. 14A through 14D, it is desirable that the magnets  122  and  124  each rotate through a arc of about 120° from about 60° above the plane of the patient to about 60° below the plane of the patient. Of course, some greater or lesser range of rotation of the magnet units could be provided. One possible configuration for support  126  is shown in FIGS. 5-9, where the support comprises two stanchions  138  and  140 , having arcuate surfaces  142  and  144  on which the magnet units  122  and  124  can travel as they rotate about the operating region. The surfaces  142  and  144  can be the arcs of a circle, but could take some other shape so that the distance between the magnet units and the operating region changes as the magnet units rotate about the operating region on the stanchions  138  and  140 . Specifically, the surfaces  142  and  144  could be shaped so that the magnet units  122  and  124  are closer to the operating region when they are above the plane of the subject. Any drive mechanism can be used to move the magnet units  122  and  124  on the stanchions  134  and  136 . Of course, instead of moving the magnet units  122  and  124  on the support, the magnet units  122  and  124  could be fixed relative to the support, and it could be the support that moves to rotate the magnet units  122  and  124  about the operating. In still another alternate construction, the rotation of the magnet units about the operating region could be accomplished by a combination of movement of the magnet units relative to the support, and movement of the support relative to the subject.  
         [0039]    The system  120  also includes an imaging system  128  for imaging the operating region. The imaging system preferably includes some type of C-arm structure  150 , or some other movable support that allows the imaging equipment to be repositioned about the operating region to allow imaging from the most advantageously angle. For most procedures in the chest, medical personnel are used to have left anterior oblique (lao) and right anterior oblique (rao) images, and the support is preferably capable of moving the imaging equipment to provide these images. The imaging system  128  preferably also includes a imaging beam source  152  and an imaging beam receiver  154 , such as an amorphous silicon plate. The source  152  and receiver  154  are preferably constructed to be immune to, or are shielded from the effects of, the magnets  30  in the magnet units  122  and  124 .  
         [0040]    A control is preferably provided to control the positioners  132  of each magnet unit  122  and  124 , to cause the magnets to move to provide a magnetic field in a selected direction. An interface can be provided to allow the users to identify a selected magnet field direction, and the controller operates the positioners  132  to position the magnets to achieve the desired magnetic field direction. Alternatively, the interface might allow the user to select a desired device orientation, and the controller operates the positioners  132  to position the magnets to achieve the desired magnetic field direction to achieve the desired device orientation. In this latter case the controller may take into account the physically properties of the device, represented in either a look-up table or in a set of equations, or parameters for equations, to determine the field to cause the device to align in the selected direction. The controller might also take into account the field strength applied in the operating region. In many prior magnetic navigation systems, the field strength is relatively constant, however in some embodiments of the present invention, in order to reduce magnet size, and facilitate movement of the magnet units, the field strength might vary depending upon the position of the magnet units. Thus the desired field direction to attain a given device orientation might vary depending upon the position of the magnet units. In at least some embodiments of this invention, the controller determines and applies the field based upon the desired orientation of the medical device input by the user, and upon the strength of the field that the magnets apply in their current position. The controller could also indicate to the user that it would be advantageous to reposition the magnets to achieve a higher field strength.  
         [0041]    As shown in FIGS. 10 and 12, the magnet used in the embodiments of this invention preferably comprises an aluminum backing plate  200 , having a plurality of spacer blocks  202  thereon (FIG. 11) for mounting blocks  204  of magnetic material. As described above the blocks  204  are sized, shaped, and positioned, and have a magnetization direction to control the magnetic field strength projected by the assembled magnet into the operating region. Actually, to save manufacturing effort and expense, compromises are made in the shape and magnetization direction of the blocks from the optimum design. The inventors have discovered that a reasonable balance is to provide blocks with five different magnetization directions. Thus, as shown in FIG. 12, the blocks  204   a  have a magnetization direction of +60° relative to the horizontal axis of the blocks, the blocks  204   b  have a magnetization direction of +30° relative to the horizontal axis of the blocks, the blocks  204   c  have a magnetization direction of 0° relative to the horizontal axis, blocks  204   d  have a magnetization direction of −30° relative to the horizontal axis of the blocks, the blocks  204   e  have a magnetization direction of −60° relative to the horizontal axis. The blocks are preferably sized, shaped and positioned generally as taught in co-pending application Ser. No. 10/056,227, filed Jan. 23, 2002, for Rotating and Pivoting Magnet for Magnetic Navigation; and application Ser. No. 10/082,715, filed Feb. 25, 2002; for Magnets with Varying Magnetization Direction and Method of Designing Such Magnets; and application Ser. No. 09/546,840, filed Apr. 11, 2000, for Magnets with Varying Magnetization Direction and Method of Designing Such Magnets, the disclosures of which are incorporated herein by reference.  
         [0042]    A positioner  132  adapted for use in some embodiments of the magnetic navigation system of this invention is shown in FIGS. 13A-13C. As shown in FIGS. 13A-13C, the magnet  30  is pivotally mounted between the legs of a generally U-shaped bracket  302 . A motor  304  is mounted on the base of the U-shaped bracket, to drive a gear box  306  also mounted on the base of the U-shaped bracket. The gear box  306  drives a cable  308  connected to the magnet  30 , so that the motor  304  can move the magnet about its pivotal mounting.  
         [0043]    A shaft  310  extends from the bottom of the U-shaped bracket  302 , and is rotatably mounted in a box-shaped frame  312 . A drive motor  314  drives a sheave  316  which drives a belt  318  that drives a sheave  320  on the shaft  310 , to rotate the shaft, and thus the magnet  30 . As shown and illustrated in FIGS. 13A-13C, in addition to rotating the magnet about a first axis, and pivoting the magnet about a second, perpendicular axis, the positioner  132  also translates the magnet in a direction generally parallel to the axis of rotation. Thus the positioner  132  includes a guide rod  322 , carriage  324  slidably mounted on the guide rod  322 , and driven by a lead screw  326 . The lead screw  326  has a sheave  328  thereon, and is driven by a belt  330  driven by sheave  332  on motor  334 . In other embodiments, the positioner need not be able to translate the magnet, and can merely rotate and pivot the magnet.  
         [0044]    As shown in FIGS. 14A-14D, in addition to providing better access to the subject by medical equipment and personnel, the rotating movement of the magnet units also allows the magnet units to be positioned closer to the operating region. As shown in FIG. 14A, when the magnets are disposed in the plane of the patient, the magnets must be spaced sufficiently to accommodate the entire width of the patient. To accommodate most patients, this distance would be a minimum of 27 inches (about 69 cm), which would mean the distance to the center of the patient is 13.5 inches (about 34 cm). If as shown in FIG. 14B, the magnet units are rotated in the transverse plane 30°, at least one of the magnets can be moved closer to the operating region. The magnet unit above the plane of the patient can be moved to a distance of about 11.38 inches (about 29 cm) from the center of the patient. If as shown in FIG. 14C, the magnet units are rotated in the transverse plane 45°, at least one of the magnets can be moved closer to the operating region. The magnet unit above the plane of the patient can be moved to a distance of about 9.57 inches (about 24 cm) from the center of the patient. If as shown in FIG. 14D, the magnet units are rotated in the transverse plane 60°, at least one of the magnets can be moved closer to the operating region. The magnet unit above the plane of the patient can be moved to a distance of about 7.60 inches (about 19 cm) from the center of the patient.  
         [0045]    Thus the ability to move the magnet units, allows the magnet units to be placed closer to the patient, allowing smaller magnets to be used. However, when the magnet units have to be moved to provide access to the patient by medical personnel or equipment (e.g. imaging equipment), the magnets can be moved out of the way, while maintaining the magnetic field in the same direction (or in some preferred embodiments, adjusting the magnetic field direction to accommodating the changing field strength in the operating region).