Open field system for magnetic surgery

A system of navigating a magnetic medical device within that part of a patient located within an operating region of the system, the system comprising magnets, and preferably electromagnets, arranged to provide a magnetic field sufficient to navigate the magnetic medical device within the operating region. There are preferably three magnetic coils arranged in mutually perpendicular planes such that their axes intersect in the operating region. The magnetic coils are sized and arranged so that a patient can easily access the operating region to allow virtually any portion of the patient to be positioned within the operating region. The openness of the magnetic system allows access to the operating region by a bi-planer imaging system.

FIELD OF THE INVENTION
 This invention relates to a magnetic surgery system, and in particular to
 an open magnetic surgery system that provides greater access to the
 patient for imaging and other purposes.
 BACKGROUND OF THE INVENTION
 A wide variety of minimally invasive surgical procedures have been
 developed which employ catheters, endoscopes, or other similar devices
 that can be navigated remotely from their distal ends. The catheter,
 endoscope or other medical device is manipulated through the tissue or
 through an existing body lumen or cavity using a guide wire or other
 mechanical means. Examples of such procedures include the treatment of
 aneurysms, arterial ventricular malformations, atrial fibrillation,
 ureteral stones, and investigations of lumen such as sigmoidoscopies and
 colonoscopies, ERCP's; and biliary duct examinations. While these
 procedures are highly beneficial to the patient, they are difficult and
 time consuming for the physician. Some procedures can only be performed by
 the most skilled surgeons.
 Several attempts have been made to use magnets to assist in such surgeries,
 as documented in "A New Magnet System for "Intravascular Navigation`,"
 Shyam B. Yodh et al., Med. And Biol. Engrg., Vol. 6, pp. 143-147 (1968);
 "Magnetically Controlled Intravascular Catheter," John Alksne, Surgery,
 Vol. 61, no. 1, 339-345 (1968); "The `Pod`, a New Magnetic Device for
 Medical Applications," E. H. Frei et al., in Proceedings of 16th Ann.
 Conference on Engineering in Medicine and Biology, Vol. 5, Nov. 18-20,
 1963, pp. 156-157; "Magnetic Propulsion of Diagnostic or Therapeutic
 Elements Through the Body Ducts of Animal or Human Patients," U.S. Pat.
 No. 3,358,676, issued Dec. 19, 1967 to E. H. Frei et al.; "Selective
 Angiography with a Catheter Guided by a Magnet," H. Tillander, IEEE
 Transactions on Magnetics, Vol. Mag-6, No. 2, 355-375 (1970); and
 "Cerebral Arterioveneous Malformations Treated with Magnetically Guided
 Emboli," Jack Driller et al., in Proc. of 25th Ann. Conf. On Engineering
 and Biology, Vol. 14 (1972), p. 306.
 For various reasons these previous attempts at magnetically assisted
 surgery have not proven to be successful, nor are they widely used. One
 reason has been the inability of the previous systems to adequately guide
 the probes within the vessels, partly for mechanical and hydrodynamic
 reasons, partly from the lack of adequate computer and control technology,
 and partly because of an inability to provide adequate real time imaging
 for the procedures. Because of the small size of the vessels to be
 navigated, extremely high resolution and flexibly moveable fluoroscopes
 are needed to provide adequate imaging. These fluoroscopes are large
 instruments. Even now, accessibility of adequate imaging in the presence
 of the large magnets needed to move small magnetic guiding "seeds" on
 medical devices is difficult.
 Systems have been disclosed for magnetic guidance of catheters and
 guidewires to facilitate navigation of difficult vascular turns. An
 example of such a system is provided in U.S. utility patent application
 Ser. No. 09/020,934, filed Feb. 9, 1998, entitled "Method and Apparatus
 Using Shaped Field of Repositionable Magnet to Guide Implant,"
 incorporated by reference herein in its entirety. Other effective magnetic
 surgical systems have required relatively large magnets. Often,
 superconducting magnets with associated cooling systems are used to
 generate the most effective magnetic fields, and two magnets for each
 spatial direction have been provided for a total of six magnets, each
 having an associated cooling system. Such a system is disclosed in U.S.
 patent application Ser. No. 08/920,446, filed Aug. 29, 1997, entitled
 "Method and Apparatus for Magnetically Controlling Motion Direction of a
 Mechanically Pushed Catheter," incorporated by reference herein in its
 entirety.
 Imaging means can be used in conjunction with magnetically guided surgery.
 An example of such a system is described in U.S. utility patent
 application Ser. No. 09/020,798, filed Feb. 9, 1998, entitled "Device and
 Method for Specifying Magnetic Field for Surgical Applications,"
 incorporated by reference herein in its entirety. While magnetically
 guided surgery with such systems is practical, the sheer bulk and size of
 their magnetic systems results in less accessibility of the operating
 region of the patient than a surgeon might prefer. Also, imaging equipment
 (such as X-ray equipment) for observing the operating region has been
 fixed to the magnetic system assembly, or otherwise been immobile or of
 limited mobility relative to the magnets and/or the patient. This relative
 immobility tends to reduce the ability of the surgeons to see the medical
 operating device in the patient, making the operation somewhat more
 difficult for the surgeon and somewhat riskier for the patient than might
 otherwise be the case. Another difficulty with using magnetic systems for
 these purposes is that the conventional fluoroscopes cannot be used in
 magnetic fields of any significant magnitude. It would therefore be
 desirable to provide an apparatus for magnetically-assisted surgery that
 provides flexibility of both the imaging and of the magnetic field
 application.
 A difficulty associated with magnetic guidance is that relatively large
 magnetic fields are needed to guide the small magnets that can fit within
 the small vessels and body lumens. The large superconducting coils
 employed in previous systems to provide these relatively large magnetic
 fields put huge amounts of energy into the fields. Because of the tendency
 for the coils to quench if ramped (powered) up or down too rapidly, the
 rate at which current can be applied or removed from the coils is limited,
 even with advantageous ramping methods such as the "constant power ramp."
 See U.S. patent application Ser. No. 08/921,298, filed Aug. 29, 1997,
 entitled "Method and Apparatus for Rapidly Changing a Magnetic Field
 Produced by Electromagnets," incorporated by reference herein in its
 entirety. The distance between the coil and the operating region is also a
 factor in ramping time, and thus it is desirable to provide a system
 having coils located and sized so as to optimize both the "openness"
 described above in terms of the accessibility to the surgeon of an
 operating region of a patient, and the rapidity of field directional
 changes.
 Unless otherwise noted, all referenced issued patents, patent applications,
 and other documents are hereby incorporated by reference in their
 entirety.
 SUMMARY OF THE INVENTION
 The present invention provides an open system for navigating a magnetic
 medical device within that part of a patient located within an operating
 region of the system. Generally, the system comprises a plurality of
 magnets configured and arranged to provide a magnetic field effective
 within the operating region to navigate the magnetic medical device within
 the operating region, while providing access to the patent for imaging and
 other purpose.
 The magnets are preferably electromagnetic coils, and more preferably
 superconducting electromagnetic coils. The magnets are preferably capable
 of generating a magnetic field of at least about 0.1 Tesla in an operating
 region of at least about two inches by two inches by two inches, and more
 preferably in an operating region of at least about five inches by five
 inches by five inches. In a preferred embodiment, the magnets can generate
 a field of about 0.3 Tesla in any direction within the operating region.
 The operating region is preferably at least about twelve inches from each
 of the magnets, such that the system can accommodate a sphere having a
 radius of about twelve inches to provide sufficient room for a patient and
 imaging apparatus.
 Generally, a single magnet is arranged and configured to provide a magnetic
 field along at least one of a plurality of oblique axes extending through
 the operating region, and one or more magnets are arranged and configured
 to provide a magnetic field along each of the other of said oblique axes,
 said magnetic fields being effective to controllably navigate the magnetic
 medical device within substantially the entirety of the operating region.
 Preferably there are three magnets in three mutually perpendicular planes,
 arranged such that their axes converge in the operating region, and more
 preferably they are arranged so that their axes intersect in the operating
 region. The magnets are arranged in an open configuration, i.e., the
 patient typically does not have to extend through a magnet coil to reach
 the operating region, as was required in previous magnetic surgery
 systems. The coils are sized and positioned so that their respective near
 field lines are substantially straight within the operating region.
 The coils are preferably fixed relative to each other, but may be moveable
 relative to the patient. The magnets are preferably enclosed within a
 concave housing sufficiently large to accommodate the patient and imaging
 devices, yet small enough to fit within the conventional supports for
 imaging devices. In the most preferred embodiment, the shell has a
 generally hemispherical shape, with an inner diameter of at least about
 twenty-four inches and an outer diameter of no more than about fifty
 inches. The generally hemispherical shell is mounted so that its axis is
 at an angle between vertical and horizontal and thus faces generally
 downwardly, but so that the shell can be rotated about a generally
 vertical axis.
 To increase the flexibility of the system, there is preferably an opening
 in the housing, aligned with one of the coils, through which a portion of
 the patient's body can extend to bring another portion of the patient's
 body into the system's operating region. The system can include a patient
 support for supporting and for moving the patient relative to the
 operating region of the system.
 The system further comprises an imaging system for providing images of the
 operating region. The imaging system comprises at least one, and
 preferably two imaging devices. Each imaging device comprises an imaging
 plate and an x-ray imaging source. The imaging plates are preferably ones
 that are minimally affected by magnetic fields, such as amorphous silicon
 imaging plates. The imaging devices are preferably fixedly mounted with
 respect to each other, in mutually perpendicular directions to provide
 perpendicular bi-planar imaging of the operating region.
 The imaging devices are mounted on a movable support, independently of the
 magnet coils. The support allows the imaging devices to be moved about
 three axes, and may be, for example a conventional C-arm support. This
 allows the imaging devices to be moved relative to the operating region,
 to provide the surgeon the most advantageous view of the procedure. The
 three axes of movement of the imaging devices preferably intersect, and
 more preferably they intersect in the operating region, and most
 preferably they intersect at the same point where the axes of the magnets
 coils intersect. This provides the greatest flexibility of imaging in the
 operating region.
 More specifically, the system of this invention provides for navigating a
 magnetic medical device within that portion of a patient within an
 operating region of the system. The system includes a support for at least
 a portion of the patient. The system also includes a magnet assembly
 including electromagnetic coils arranged and configured so that the axes
 of the coils converge, and a magnet mount holding the magnet assembly so
 that the center of the operating region (i.e., the convergence of the
 axes) is within the desired portion of the patient on the patient support.
 An imaging assembly for providing an image of the operating region
 comprises at least one imaging plate and an imaging beam source mounted on
 an imaging support to be on opposite sides of the operating region, and a
 mechanism for selectively pivoting the support about three mutually
 perpendicular axes.
 In the preferred embodiment, a total of three super conducting magnets
 coils are configured so that each of their central axes lies generally
 along an axis of an orthogonal coordinate system having its origin
 approximately centered within the operating region. The magnets are
 supported by a generally hemispherical housing and each magnet is of
 sufficient strength to provide a magnetic field in the direction of its
 respective central axis having a generally consistent strength of about
 0.3 Tesla throughout substantially the entirety of the operating region. A
 control adjusts the strength of the magnetic field of each of said magnet
 coils to thereby controllably navigate the magnetic medical device within
 that part of a patient within the operating region.
 The method of navigating according to this invention includes applying a
 magnetic field to the magnetic medical device in the operating region with
 at least three electromagnetic coils contained within a magnet housing to
 navigate the medical device within the operating region; and providing an
 image of the magnetic medical device in the operating region with an
 imaging apparatus comprising at least one imaging plate and an imaging
 beam source, the imaging plate and imaging beam source being on opposite
 sides of the operating region, with the imaging plate being positioned
 between the operating region and the magnet housing. The imaging plate and
 imaging beam source are movable about three mutually perpendicular axes
 which extend through the operating region. These axes preferably extend
 through the point of intersection of the axes of the magnets.
 The present invention also includes a method of determining a distribution
 of ramping times for the electromagnetic coils in the system. This method
 includes calculating for a selected magnetic field magnitude and
 direction, the currents needed in each coil to provide the selected
 magnetic field magnitude and direction at a point in an operating region;
 estimating, for each of the calculated currents, a ramping time required
 to reach the calculated current; and repeating the current calculating
 step and the ramping time estimating step for a plurality of different
 points in the operating region, and for selected magnetic field magnitudes
 and directions to obtain a distribution of ramping times as a function of
 selected magnetic field magnitude and direction for the system.
 The present invention also includes a method of optimizing the design of
 the system, comprising selecting a maximum ramping time not to be exceeded
 by a selected percentage of navigational direction changes of the magnetic
 medical device; determining a distribution of ramping times; determining a
 percentage of ramping times in the distribution of ramping times that the
 selected maximum ramping time is exceeded; and modifying at least one
 property of at least one of the electromagnetic coils, the at least one
 property including at least one property selected from the group
 consisting of coil radius, coil cross-sectional area, coil distance from
 the operating region, and coil aspect ratio; and repeating the computing,
 determining, and modifying steps until the percentage of ramping times in
 the distribution of ramping times that the selected minimum ramping time
 is exceeded is not more than the selected percentage of navigational
 direction changes.
 A magnetic resonance imaging system comprising an electromagnet for
 generating a magnetic field in the vicinity of the a body for making a
 magnetic resonance image of a portion of the body and an x-ray image
 apparatus, comprising an x-ray image source and an x-ray image plate, for
 making an image of the portion of the body, at least the x-ray image plate
 being within the magnetic field generated by the electromagnet.
 Thus the system of the present invention provides for effective magnetic
 guidance of magnetic medical devices within the body for performing
 medical procedures. The system is capable of providing magnetic fields of
 sufficient strength for orientation and even movement of magnetic medical
 devices, within a sufficiently large operating region to allow practical
 medical procedures to be completed with magnetic assistance. However, the
 magnets are arranged so that the operating region of the system can be
 positioned in any portion of the body. The system provides open access so
 that imaging plates can be interposed between the patient and the magnets
 to provide high-quality images of the operating region. The imaging
 apparatus can be moved independently of the magnets to provide the best
 possible views of the operating region.
 These and other features and advantages will be in part apparent and in
 part pointed out hereinafter.

Corresponding reference numerals indicate corresponding parts throughout
 the several views of the drawings.
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The First Embodiment
 A first embodiment of an inventive open field magnetic surgical system
 constructed according to the principles of this invention is indicated
 generally as 50 in FIG. 1. The system 50 comprises a patient support 52, a
 magnet assembly 54 on a moveable magnet support 56, and an imaging
 assembly 58.
 The patient support 52 preferably comprises an elongate bed 60 mounted on a
 pedestal 62. The foot of bed 60 is oriented toward the front of system and
 the head of the bed is oriented toward the rear of the system. The head of
 the bed 60 is narrower than foot of the bed so that it can fit inside the
 magnet assembly 54 and accommodate the imaging devices of the imaging
 assembly 58. The bed 60 is preferably movable with respect to the pedestal
 62, to allow the patient to be moved relative to the magnet assembly 54.
 The bed 60 can preferably be moved longitudinally forwardly and rearwardly
 and vertically upwardly and downwardly, and it can be rotated about its
 longitudinal axis.
 The magnet assembly 54 comprises a housing 64 containing three magnets 66,
 68, and 70. The magnets 66, 68, and 70 are preferably electromagnet coils
 and more preferably superconducting electromagnet coils 72, 74, and 76.
 Suitable power and cooling conduits are provided within the housing 64, as
 is known.
 The magnet coils 72, 74, and 76 are arranged to provide a magnetic force
 within an operating region sufficient to move a magnetic medical device
 within that portion of a patient inside the operating region. This
 magnetic medical device may be, for example a magnet-tipped catheter,
 endoscope, or other elongate medical device or a magnet-tipped guidance
 for guiding an elongate medical device.
 As best shown in FIGS. 7-10, coil 72 is arranged in a transverse plane with
 its axis 72' extending generally longitudinally, parallel to the axis of
 the patient support in this preferred embodiment, the coil 72 has an
 26.090 inch outer diameter, a 19.010 inch inner diameter, and is 2.620
 inches thick, carrying up to 100 amperes at 11.7 kA/cm.sup.2. Coils 74 and
 76 are similar in construction and preferably oriented in mutually
 perpendicular planes that are perpendicular to the plane of coil 72. Each
 of the coils 74 and 76 has an outside diameter of 21.826 inches, an inside
 diameter of 15.750 inches, and is 2.850 inches thick, carrying up to 100
 amperes at 11.7 kA/cm.sup.2. The faces of the coils 74 and 76 are spaced
 11.9 inches from the axis of the coil 72, and the face of the coil 72 is
 spaced 12.75 inches from the axes 74' and 76' of the coils 74 and 76. The
 edges of coils 74 and 76 are spaced 1.88 inches from the edge of coil 72,
 and coils 74 and 76 are 1.45 inches apart at their closest points. The
 sizing and spacing of the magnet coils is described below.
 The magnet coils 72, 74, and 76 are preferably arranged in mutually
 perpendicular planes such that the axes 72', 74', and 76' of the coils
 intersect at a point in the center of the operating region.
 The magnet assembly 54 is preferably mounted on a moveable magnet support
 56 with an arm 78, such that the magnet assembly can rotate about a
 longitudinal axis parallel to the longitudinal axis of the bed 60. The
 magnet assembly can preferably turn about 20.degree. in either direction.
 This movement helps prevent shading of the imaging beam in certain
 circumstances. Of course, the magnet assembly could be fixedly mounted, if
 desired, and further could be fixedly mounted in a different orientation
 from that shown in the figures, for example below the patient support 52
 to facilitate urological and GI uses of the system.
 The magnet support 56 contains power supply and coolant for the coils 72,
 74, and 76. Power and coolant are communicated to the coils in housing 64
 through arm 78. As shown in FIG. 3, the magnet support 56 is slidably
 mounted on tracks 80 to move forwardly and rearwardly (toward and away
 from the patient support). Stops 82 on the tracks 80 restrict forward
 motion of the magnet support 56. There are a plurality of holes 84
 longitudinally spaced along the tracks 80. The magnet support 56 has
 locking pins (not shown) controlled by locking handles 86 to engage the
 holes 84 and lock the magnet in accurately located positions. Instead of,
 or in addition to, this locking mechanism, some other positioning
 mechanism such as a motorized or servo-controlled mechanism can be
 provided. This allows the position of the magnet assembly 54 to be
 automatically controlled by an external controller or computer.
 The housing 64 preferably has an opening 88 aligned with the central
 opening of the coil 72, so that a portion of the patient support and/or
 the patient thereon can extend through the housing so that the desired
 portion of the patient's body can be positioned within the operating
 region of the magnet assembly 54.
 The imaging assembly 58 comprises at least one imaging device, and in the
 preferred embodiment two imaging devices 90 and 92, mounted on a C-arm
 support 100 of C-arm 94. Such supports are made, for example, by General
 Electric Co. of Syracuse, N.Y. The imaging devices 90 and 92 are
 preferably arranged perpendicular to each other to provide bi-planar
 imaging in mutually perpendicular planes. Each of the imaging devices 90
 and 92 comprises an imaging plate 96 and an imaging beam source 98. In
 this preferred embodiment the imaging plates 98 are amorphous silicon
 imaging plates, known as LAST plates available from Varian, Palo Alto,
 Calif. These plates 96 are not affected by the presence of magnetic
 fields, such as those caused by the magnet coils 70, 72, and 74. The
 imaging beam sources 98 are preferably X-ray sources. Of course some other
 imaging beam and imaging plate could be used if desired.
 As shown in the Figures, C-arm 94 comprises a C-shaped support 100 on which
 the X-ray sources 98 of the imaging devices 90 and 92 are mounted. The
 C-shaped support 100 has a wedge shaped block 102 having perpendicular
 faces 104 and 106 which arms 108, each mounting one of the imaging plates
 96, extend. The arms 108 are hollow, providing a protected path for
 electrical wiring to the imaging plates 96. The arms 108 are preferably
 attached to blocks 110 that can move on their respective faces 104 and
 106, to permit adjustment of the positions of the imaging plates 96.
 The C-shaped support 100 is mounted on body 112, and moves about its
 circumference relative thereto so that the C-shaped support turns about
 its central axis. The body 112 is rotably mounted to the vertical leg 114
 of a generally L-shaped bracket 116. The body 112 can rotate relative to
 the L-shaped bracket 116 about a generally horizontal axis. The horizontal
 leg 118 of the generally L-shaped bracket 116 is pivotally mounted to the
 base 120 of the system so that the generally L-shaped bracket pivots about
 a generally vertical axis.
 The C-arm 94 thus allows the imaging devices 90 and 92 to be rotated about
 three mutually perpendicular axes. These axes preferably intersect, and
 their intersection is preferably in the operating region of the magnet
 assembly 54, and more preferably their intersection coincides with the
 intersection of the axes 72', 74', and 76' of the magnet coils 72, 74, and
 76. The imaging devices 90 and 92 rotate about a first axis when the
 C-shaped support 100 turns relative to the body 112 (see FIG. 6). The
 C-shaped support 100 can preferably rotate clockwise and counter clockwise
 over a range of about 90.degree.. The imaging devices 90 and 92 rotate
 about a second generally horizontal axis when the body 112 rotates
 relative to the L-shaped bracket 116 (see FIG. 4). The body 112 can
 preferably rotate about 30.degree. forwardly and rearwardly with respect
 to the L-shaped bracket 116. The imaging devices 90 and 92 rotate about a
 third generally vertical axis when the L-shaped bracket 116 rotates
 relative to the base 120 (see FIG. 5). The L-shaped bracket 116 can
 preferably rotate about 30.degree. forwardly and rearwardly with respect
 to the base 120.
 As best shown in FIG. 2A the imaging apparatus 58 provides bi-planar
 imaging of the portion of the patient's body inside the operating region
 of the magnet assembly 54. The support arms 108 are configured to clear
 the patient and the head of the bed, and support the imaging plates 96 in
 the space between the operating region and the magnet coils 72, 74, and
 76, of the magnet assembly 54 while maintaining the imaging plates aligned
 with their respective imaging beam sources 98. The imaging devices 90 and
 92 can be moved around the operating region to accommodate movement of the
 magnet assembly 54 and to provide the most advantageous views of the
 operating region so that the surgeon can see the navigation of the
 magnetic medical device.
 The magnet coils 72, 74, and 76 provide a controllable magnetic field
 inside that portion of a patient within the operating region of the magnet
 assembly 54. The coils 72, 74, and 76 provide a magnetic field of at least
 about 0.1 Tesla, and in the preferred embodiment at least about 0.3 Tesla.
 The imaging devices 90 and 92 provide bi-planar imaging of the operating
 region. The imaging plate 96 and the imaging beam source 98 are positioned
 on opposite sides of the operating region, with the imaging plates
 disposed between the operating region and the magnet coils 72, 74, and 76.
 FIG. 11 is a partial representation of the apparatus shown in FIGS. 1-5,
 with portions omitted to show the operational relationship between the
 electromagnetic coils 72, 74, 76, the imaging tubes 98, the imaging plate
 supports 108, and the imaging plates 96. Also shown is the passageway 88
 through which a physician has access to an operating region R in which the
 surgical procedure is taking place in patient P. As explained above, the
 passageway 88 allows portions of the patient to extend through the magnet
 assembly in order to bring selected portions of the patient into the
 operating region. Although FIG. 11 is not drawn to scale, a comparison of
 FIG. 11 shows that arcuate support 100, on which the imaging devices 90
 and 92 are mechanically coupled, may reorient those mechanically-coupled
 apparatuses about the various axes with three degrees of freedom to
 provide different medically useful views of operating region R within the
 patient P.
 Sizing and Locating the Electromagnet Coils
 The method by which the size and location of the coils can be selected is
 as follows: It is to be understood that use of the same method, with
 different compromises or initial assumptions, may result in a system
 having coils of somewhat different sizes and locations, but still within
 the principles of this invention.
 Using the Biot-Savart Law, it is possible to calculate the magnetic field
 everywhere for a coil having a given shape, size, and total number of
 ampere-turns. To arrive at the particular combination of size and location
 described above, the inventors started with the assumption that three
 coils would provide the best compromise between being too large and too
 close to provide a needed internal exclusion volume for imaging equipment
 and beams, while not being too weak to provide the needed strength in a
 given operating region or procedure volume inside the patient. The three
 coil choice follows from experience with six coil systems, and, in
 accordance with the invention, provides much more freedom for physicians
 and imaging.
 The inventors also intended for the body-axis coil (coil 72 in the first
 embodiment), to be larger and to have a free air bore large enough for the
 patient's head, with clearance for tubes, etc., so that the patient's
 chest can be positioned within the operating region. It is also most
 convenient and economical for construction purposes and for calculating
 operating currents to have the three coils be orthogonal, and for the two
 transverse coils to be alike. Other non-orthogonal arrangements could be
 calculated, but would result in less efficient structural designs.
 These qualitative requirements dictate the approximate size and shape of
 the three coils. If the coils are huge, they would provide great freedom
 for the imaging devices and for the surgeon, but the coil would be heavy,
 expensive and have long ramping times for field changes. If the coils are
 too small, they would interfere with the location and motion of the
 imaging plates 96. That is, the coils must be far enough from a central
 convergence point, the intersection of the three coil axes approximately
 centered in the operating region, that a pair of orthogonal imaging plates
 can move about the portion of the patient in the operating region, and not
 touch the coils, nor shadow each other's imaging x-ray beams. The
 dimensional details of the imaging equipment and beams, of the trial coil
 sizes and shapes, of the patient and the bed, etc., are put into a
 three-dimensional CAD program for interactive decision-making magnetic
 field determinations.
 Added to this, the coils must be large enough, individually, that their
 near field lines do not bend severely in the operating region, which is
 centered near the intersection of their axes. Otherwise, it becomes
 difficult to attain the field strengths needed at the needed distances
 from the coils, for certain directions of the field.
 An exact determination of the coil sizes and locations is achieved by
 iterative computer modeling in conjunction with the CAD plots. On a
 computer, a first trial size is chosen for the three coils of the set, and
 the fields are calculated at various angles and distances from the coil,
 assuming a current density (e.g., 14,000 Amperes per square cm) that is
 suitable for the superconducting coils of these strengths. From this
 choice, field lines and lines of equal field strength at full current for
 one coil (e.g., the axial coil, 72 in the first embodiment) are plotted to
 scale on a CAD drawing of the system with assumed coil location and with
 patient and imaging equipment in place.
 FIG. 12 is an illustration of such a CAD drawing. The operating region R
 within a patient P is shown, as are magnetic field lines .function.
 generated by coil 72. Lines F representing contours of equal magnetic
 field strength are also shown. Locations of imaging plates 96 are also
 represented. The axial coil (72 in the first embodiment) is also shown in
 FIG. 12, although its magnetic field is not represented. (The orientation
 of coil 74 as shown in FIG. 12 is not the same as that shown in FIG. 1 and
 other figures.) The axes 72' and 74' and of coils 72 and 74, respectively,
 are also represented in FIG. 12.
 Given a target field strength requirement, e.g., 0.3 Tesla, it can be
 determined, from the iterative computer modeling or by some other method,
 whether the individual coils have sufficient strength to cover, or nearly
 cover, the operating region, when appropriately combined. If the coils are
 too strong, the ramp time and weight will be too great, and their cross
 section can be reduced.
 Each coil supplies most of the field strength for the direction along its
 axis. The general requirement of small field curvature for the field lines
 leads to the fact that the coils act predominantly independently for each
 axis. That is, orthogonal coils do not contribute an operatively
 significant field component along the direction of the axis of the other
 coils in the operating region. And, curved lines fail to achieve
 sufficient strength along bisecting planes between coils. The total field
 at any location in the operating region, and at any required angle,
 therefore, will be, for purposes of magnetically-assisted surgery, the sum
 of the individual fields from each of the three coils. While this "vector
 sum" model which assumes straight field lines is only approximately
 correct, a computer can make accurate, detailed calculations of the total
 fields of the system with any given set of currents. A final determination
 of meeting field requirements in the operating region involves only modest
 changes from the trials just described. The final determination of coil
 sizes and locations, subject to the general considerations stated above,
 uses a computer program to calculate the magnetic fields and resultant
 ramping times as follows.
 The operating region can be broken into small segments or "nodes," for
 example, of about 20 along each side, so that a cubical-shaped operating
 region would have about 8,000 nodes. For about 20 random directions, in
 each node, the computer calculates the three coil currents needed to
 provide the required magnetic field strength at each direction, should the
 operating point be in the center of that node. Consequently, a total of
 20.times.8,000 calculations are made to provide this sampling of the total
 operating region. (Only two angles are needed to specify any direction in
 space, for example, a polar and an azimuthal angle. Therefore, there are
 only three unknown currents in each calculation, and the magnetic field
 strength and direction constitute three unknowns, so the calculation is a
 simple matrix solution. Information about such matrix calculations is
 provided in patent application Ser. No. 08/920,446, filed Aug. 29, 1997,
 on "Method and Apparatus for Magnetically Controlling Motion Direction of
 a Mechanically Pushed Catheter," incorporated by reference herein in its
 entirety.
 In using these calculations, it is often important to the physician in a
 particular application to be able to make use of a statistical statement
 about the distribution of coil currents, and consequently, the ramping
 time. For the purpose of determining the time needed for ramping, the
 maximum current of each set, is chosen in a sequence of turns in
 navigating to a target, and a model of the ramping needs is used. In one
 application, the essential ramping sequence has the following steps: (1)
 determine the previous field direction at the magnetic object location,
 (2) determine the desired new direction and the angle of the change, (3)
 using knowledge of the field needed to make a turn of this magnitude, set
 the new field direction and magnitude, (4) execute the new ramp, and (5)
 upon completion of the ramp and turn, ramp the current down.
 Each of these five-step sequences can be evaluated for the total ramp-up,
 ramp-down time. The computer can do the estimates for each of the
 above-stated 160,000 cases, and perform plots of either the overall
 probability distribution of ramp times, or it can plot binned
 probabilities for turns of 0-10.degree., 10-20.degree., etc. Such plots
 can inform the surgeon of the time needed for a given angle of turn. And,
 with an intuitive display, such as a thermometer type representation on a
 screen, the surgeon can quickly decide whether magnetic assist is
 necessary or useful on any given turn, thereby increasing the efficiency
 and effectiveness of the overall procedure.
 When the optimum compromise of coil size, location and coil power is
 determined, the dimensions and magnetic requirements are met, the design
 goes to a succeeding stage. From mechanical application of the Biot-Savart
 law, it is possible to calculate the stresses on each coil due to the
 interaction of currents in it and in the other coils. Textbooks (e.g.,
 Foundations of Electromagnetic Theory, Reitz, Milford, and Crysty,
 3.sup.rd Ed., page 166) give equations that may be used to calculate the
 vector differential interaction force d.sup.2 F between a differential
 length of a first coil, dl.sub.1, carrying current I.sub.1, and a
 differential length of a second coil, dl.sub.2, carrying current I.sub.2.
 These can be integrated or approximately summed. In the latter case,
 subtended angles of ten degrees might, for example, be chosen for each
 coil and the appropriate interactions vector summed. It would be useful in
 such a case to find the total force dF on each segment subtending 10
 degrees of the first coil from the complete 360 degrees of each of the
 other two coils (the second coil and a third coil). This complete
 procedure is able to handle any given cross section of these circular
 coils, when used in a typical finite element program such as "Maxwell EM"
 by Ansoft Corporation of Pittsburgh, Pa.
 Then the three components of dF are entered into a finite element analysis
 program "FEA" dealing with stresses and forces, e.g. "pro/MECHANICA".RTM.,
 Parametric Technology Corp., Waltham, Mass., which can be used by one
 skilled in the art on any inputted structure supporting the three coils.
 An individual coil force is transmitted from its surround, a "bobbin," to
 the supporting structure. In one simple but not preferred embodiment,
 three plates are welded together, each supporting one of the coils in the
 appropriate location. The results of calculation are often plotted as
 colored graphs, where regions of different stresses in the support
 structure (responding to the magnetic forces) are shown in different
 color. In addition, the program can determine deflections by summing
 reaction deflection to the stresses in individual elements of the
 structures. Then the designer tries different support struts which can
 alleviate excessive stresses or deflections in the first, simpler trial
 design. By an iterative process, and standard experience in mechanical
 design, the designer arrives at design shapes and/or structure details
 that minimize the overall weight of the structure, while exhibiting no
 excessive stresses and deflections.
 In addition to the structural support and strength, the coil mounting
 system for superconducting systems must consider the cryogenic materials
 and transfer of heat and cryogens. Those skilled in the art have methods
 and programs to calculate heat transfer. They also have methods for most
 efficiently arranging insulation, vacuum spaces, intermediate heat
 shields, and ducting for liquid cryogen transfer, as well as cold gas
 exit, if the system is not recondensing and recirculating.
 Several overall cryogenic systems in common practice are suitable for the
 practice of this invention. One such system simply uses liquid helium to
 cool the superconducting coils. The liquid helium evaporates and goes out
 as a gas. This system usually employs a 77.degree. Kelvin shield attached
 to a liquid nitrogen reservoir. Another method uses a cryogenic cooler
 that cools an object down to the approximately 4.5.degree. Kelvin needed
 to maintain superconducting wires in the superconducting state. This
 cryogenic cooler may either be attached solidly to the coil bobbin or it
 may, for flexibility, be coupled with liquid helium, which may either be
 totally enclosed or may need occasional replenishing. A cryogenic cooler
 may be used to cool a shield to intermediate temperatures. The cryogenic
 cooler may be attached solidly to the shield, or with a gas coupling, such
 as liquid neon. Cryogenic coolers have been designed to have two or more
 stages so as to supply more heat removing power at the higher,
 intermediate temperatures, and a lower cooling rate at the liquid helium
 temperatures. The selection of which system to use depends upon both
 economical and technical features, because cryocoolers are, at present,
 relatively expensive. Liquid helium is also expensive, however, and both
 space and weight are important considerations. Therefore, recirculating
 systems, which can be smaller and lighter, may be preferred.
 As is known, the coils may have a split or two piece construction to better
 accommodate thermal contraction upon cooling, and to facilitate coolant.
 The Second Embodiment
 A second embodiment of an inventive open field magnetic surgical system
 constructed according to the principles of this invention is indicated
 generally as 200 in FIGS. 13-24. The system 200 is similar in construction
 to the system 50, and comprises a patient support 202, a magnet assembly
 204 on a moveable magnet support 206, and an imaging assembly 208.
 The patient support 202 preferably comprises an elongate bed 210 mounted on
 a pedestal 212. The foot of the bed 210 is oriented toward the front of
 the system and the head of the bed is oriented toward the rear of the
 system. The head of the bed 210 is narrower than the foot of the bed so
 that it can fit inside the magnet assembly 204 and accommodate the imaging
 devices of the imaging assembly 208. The bed 210, is preferably moveable
 with respect to the pedestal 212 to allow the patient to be moved relative
 to the magnet assembly. The bed can be moved into and out of the system;
 raised and lowered, and rotated about its longitudinal axis. Other
 movements can be provided to facilitate positioning the patient relative
 to the operating volume of the magnet assembly.
 The magnet assembly 204 comprises a housing 214 containing three magnets
 216, 218, and 220. The magnets 216, 218, and 220 are preferably
 electromagnetic coils, and more preferably superconducting electromagnetic
 coils 222, 224, and 226. The housing 214 includes a jacket 228 containing
 suitable power and cooling apparatus to operate the superconducting coils.
 The magnet coils 222, 224, and 226 are arranged to provide a magnetic force
 within the operating volume sufficient to move a magnetic medical device
 within that portion of a patient inside an operating region.
 As best shown in FIGS. 29-33 the magnet coils 222, 224, and 226 are
 preferably arranged in three mutually perpendicular planes such that the
 axes of the three coils intersect generally in the center of the operating
 region. Coil 222 is arranged in a transverse plane with its axis extending
 generally longitudinally, parallel to the longitudinal axis of the patient
 support 202. The coil 222 is wound around a bobbin 230 that is secured to
 a plate 232. In this preferred embodiment, the coil 222 has a 28.2 inch
 outer diameter, a 21.06 inch inner diameter, and is 4.47 inches thick.
 Coils 224 and 226 are similar in construction and are preferably oriented
 in mutually perpendicular planes that are perpendicular to the plane of
 coil 222. Each of the coils 224 and 226 has an outside diameter of 26.48
 inches, an inside diameter of 20.23 inches, and is 5.69 inches thick. The
 faces of the coils 224 and 226 are spaced 13.81 inches from the axis of
 the coil 222, and the face of the coil 222 is spaced 13.78 inches from the
 axes of the coils 224 and 226. Coil 224 is wound around a bobbin 234 that
 is secured to plate 236. Coil 226 is wound around bobbin 238 that is
 secured to plate 240. The plates 232, 236 and 240 are secured together to
 form a self-supporting structure capable of withstanding the forces
 generated by the magnetic fields of the coils. The housing 214 preferably
 has an opening 242 therein aligned with the central opening in coil 222 so
 that a portion of the patient support and/or the patient can extend
 therethrough, to bring the desired portion of the patient within the
 operating region of the magnet assembly 204.
 The housing 214 is preferably mounted on a stanchion 244, which in this
 second embodiment forms the magnet support 206. The housing 214 preferably
 can pivot relative to the stanchion 244 about a longitudinal (front to
 back) horizontal axis. The housing 214 can preferably pivot 20.degree.
 from the center (See FIG. 24) toward the left (See FIG. 21A) and the right
 (See FIG. 23). The bottom of the stanchion 244 is slidably mounted in
 tracks 246 in the base 248 of the system 200. Thus the stanchion 244 (and
 the housing 214) can be moved forward (toward the patient support 202) and
 rearward (away from the patient support).
 The imaging assembly 208 is identical in construction to imaging assembly
 58 (shown best in FIG. 2A), and corresponding parts are identified with
 corresponding reference numerals. The imaging devices 90 and 92 can be
 pivoted about a horizontal transverse axis as the body 112 tilts
 rearwardly (FIG. 21A) and forwardly (FIG. 21B) relative to the vertical
 leg 114 of the generally L-shaped bracket 116. The body 112 can pivot
 about 30.degree. rearwardly and forwardly. The imaging devices 90 and 92
 can be pivoted about a generally vertical axis as the horizontal leg 118
 of generally L-shaped bracket 116 pivots rearwardly (FIG. 22A) and
 forwardly (FIG. 22B). The L-shaped bracket 116 can pivot about 30.degree.
 rearwardly and forwardly. The imaging devices 90 and 92 can be rotated
 about a third axis as support 100 rotates relative to body 112 clockwise
 (FIG. 23) and counterclockwise (FIG. 19). The c-shaped support 100 can
 rotate 90.degree. relative to body 112.
 The imaging devices 90 and 92 provide bi-planar imaging of the portion of a
 patient's body inside the operating region of the magnet assembly 204. The
 support arms 108 are configured to clear the patient and the head of the
 bed, and support the imaging plates 96 in the space between the operating
 volume and magnet coils 222, 224 and 226 of the magnet assembly 204, while
 maintaining the imaging plates 96 aligned with their respective imaging
 beam sources 98. The imaging devices 90 and 92 can be moved around the
 operating region to accommodate movement of the magnet assembly 204 and to
 provide the most advantageous views of the operating region so that the
 surgeon can see the navigation of the medical device.
 The Third Embodiment
 A third embodiment of an inventive open field magnetic surgery system
 constructed according to the principles of this invention is indicated
 generally as 300 in FIGS. 34-36. The system 300 is similar in construction
 to systems 50 and 200, and comprises a patient support 302, a magnet
 assembly 304 on a moveable magnet support 306, and an imaging assembly
 308.
 The patient support 302 preferably comprises an elongate bed 310 mounted on
 a pedestal 312. The foot of the bed 310 is oriented toward the front of
 the system and the head of the bed is oriented toward the rear of the
 system. The head of the bed 310 is narrower than the foot of the bed so
 that it can fit inside the magnet assembly 304 and accommodate the imaging
 devices of the imaging assembly 308. The bed 310, is preferably moveable
 with respect to the pedestal 312 to allow the patient to be moved relative
 to the magnet assembly. The bed can be moved into and out of the system;
 raised and lowered, and rotated about its longitudinal axis. Other
 movements can be provided to facilitate positioning the patient relative
 to the operating volume of the magnet assembly.
 The magnet assembly 304 comprises a generally hemispherical housing 314
 containing three magnets 316, 318 and 320. The magnets 316, 318 and 320
 are preferably magnet coils, and more preferably superconducting
 electromagnet coils 322, 324 and 326. The housing 314 contains suitable
 power and cooling apparatus to operate the superconducting coils.
 The magnet coils 322, 324 and 326 are sized and arranged to provide a
 magnetic force within an operating region sufficient to move a magnetic
 medical device within that portion of a patient inside the operating
 region.
 As best shown in FIGS. 41 and 42 the coils 322, 324 and 326 are preferably
 arranged in three mutually perpendicular planes such that the axes of the
 three coils intersect generally in the center of the operating region.
 Coil 322 is arranged so that it is normally in a vertical transverse
 plane, with its axis extending generally longitudinally, parallel to the
 longitudinal axis of the patient support 302. In this third preferred
 embodiment, the coil 322 has 26.09 inch outer diameter, a 19.01 inch inner
 diameter, and a thickness of 2.62 inches.
 Coils 324 and 326 are similar in construction and are preferably oriented
 in mutually perpendicular planes that are perpendicular to the plane of
 coil 322. Each of the coils 324 and 326 has an outside diameter of 21.83
 inches, an inside diameter of 15.75 inches, and a thickness of 2.85
 inches. The faces of the coils 324 and 326 are spaced 11.90 inches from
 the axis of coil 322, and the face of coil 322 is spaced 12.75 inches from
 the axes of the coils 324 and 326.
 The housing 314 preferably has an opening 328 therein aligned with the
 central opening of coil 322 so that a portion of the patient support
 and/or the patient can extend therethrough, to bring the desired portion
 of the patient within the operating volume.
 An alternate construction of the magnet assembly of this third embodiment
 is indicated generally as 304' in FIGS. 43-46. The magnet assembly 304'
 comprises a generally hemispherical housing 314'. The housing has a cold
 head mounting assembly 315 for connecting the magnet assembly 304 to a
 cooling system. Inside the housing 314' the three magnets 322', 324', and
 326'. The coils 322', 324' and 326' are preferably arranged in three
 mutually perpendicular planes such that the axes of the three coils
 intersect generally in the center of the operating region. Coil 322' is
 arranged so that it is normally in a vertical transverse plane, with its
 axis extending generally longitudinally, parallel to the longitudinal axis
 of the patient support 302. In this third preferred embodiment, the coil
 322' has 24.22 inch outer diameter, a 17.4 inch inner diameter, and a
 thickness of 2.62 inches.
 Coils 324' and 326' are similar in construction and are preferably oriented
 in mutually perpendicular planes that are perpendicular to the plane of
 coil 322'. Each of the coils 324' and 326' has an outside diameter of
 22.56 inches, an inside diameter of 16.14 inches, and a thickness of 3.05
 inches. The faces of the coils 324' and 326 are spaced 11.94 inches from
 the axis of coil 322', and the face of coil 322' is spaced 12.81 inches
 from the axes of the coils 324' and 326'.
 The housing 314' preferably has an opening 328' therein aligned with the
 central opening of coil 322' so that a portion of the patient support
 and/or the patient can extend therethrough, to bring the desired portion
 of the patient within the operating volume.
 The housing 314 has trunions 330 and 332 projecting from its exterior.
 These trunions 330 and 332 are connected to a band 334, that is mounted on
 an inverted "J" shaped support 336. The band 334 and the support 336
 suspend the housing 314 so that the axis of the generally hemispherical
 housing 314 extends at an angle with respect to vertical and horizontal,
 so that the housing faces generally downwardly. The axis preferably forms
 an angle of about 45.degree. with respect to horizontal. The support 336
 is mounted to a platform 338 which is slidably mounted in tracks 340 in
 base 342. Thus the support 336 (and the housing 314) can be moved forward
 (toward the patient support as shown in FIG. 35) and rearward (away from
 the patient support as shown in FIG. 36). The support 336 has a circular
 bottom 344 which can slide relative to the platform 338 so that the
 housing 314 pivots, preferably about a vertical axis that extends through
 the point of an intersection of the axes of the three magnet coils 322,
 324 and 326. In this third preferred embodiment, the housing 314 can pivot
 30.degree. toward each side.
 The imaging assembly 308 is identical to the imaging assembly 208 of the
 second embodiment and the imaging assembly 58 of the first embodiment, and
 corresponding parts are identified with corresponding reference numerals.
 The imaging devices 90 and 92 can be pivoted about a horizontal transverse
 axis as the body 112 tilts rearwardly and forwardly relative to the
 vertical leg 114 of the generally L-shaped bracket 116. The body 112 can
 pivot about 30.degree. rearwardly and forwardly. The imaging devices 90
 and 92 can be pivoted about a generally vertical axis as the horizontal
 leg 118 of generally L-shaped bracket 116 pivots rearwardly and forwardly.
 The L-shaped bracket 116 can pivot about 30.degree. rearwardly and
 forwardly. The imaging devices 90 and 92 can be rotated about a third axis
 as support 100 rotates relative to body 112 clockwise and
 counterclockwise. The C-shaped support 100 can rotate 90.degree. relative
 to body 112.
 The Fourth Embodiment
 A fourth embodiment of an inventive open field magnetic surgery system
 constructed according to the principles of this invention is indicated
 generally as 400 in FIGS. 47-50. The system 400 comprises a patient
 support 402, a magnet assembly 404, and a CT imaging assembly 406.
 The patient support 402 preferably comprises an elongate bed 410 mounted on
 a pedestal 412. The foot of the bed 410 is oriented toward the front of
 the system and the head of the bed is oriented toward the rear of the
 system. The head of the bed 410 is narrower than the foot of the bed so
 that it can fit inside the magnet assembly 404 and accommodate the imaging
 devices of the imaging assembly 406. The bed 410, is preferably moveable
 with respect to the pedestal 412 to allow the patient to be moved relative
 to the magnet assembly. The bed can be moved into and out of the system;
 raised and lowered, and rotated about its longitudinal axis. Other
 movements can be provided to facilitate positioning the patient relative
 to the operating volume of the magnet assembly.
 The magnet assembly 404 comprises a plurality (in this fourth preferred
 embodiment four) magnet coils 414 arranged on planar support 416, on a
 base 418. The magnet coils 414 are capable of generating a magnetic field
 in an operating region of sufficient strength to navigate a magnetic
 medical in the portion of the patient within the operating region. The
 coils may all have parallel axes, but this is not essential and some or
 all of the coils may be oriented out of the plane of planar support 416.
 The imaging assembly 406 comprises a compact CT imaging device 420 adapted
 to provide real time or near real time CT images of the operating region.
 The CT imaging device 420 has an opening 422 through which a portion of
 the patient support 402 and/or the patient can extend to allow the surgeon
 to bring virtually any portion of the patient's body within the operating
 region of magnet assembly 404. The CT imaging device is one that is not
 significantly affected by the proximity of the magnets 414.
 It should be noted that the same or a very similar magnetic and imaging
 equipment and arrangement may be used to provide for parenchymal
 navigation for neurosurgical procedures in brain tissue, such as for
 implanting catheters or introducing tubes in curved paths. See Werp et
 al., "Method of and apparatus for intraparenchymal positioning of medical
 devices," app. Ser. No. 08/969,165, filed Nov. 12, 1997; "Apparatus for
 and Method of Controlling an Electromagnetic Coil System," app. Ser. No.
 08/682,867, filed Jul. 8, 1996; Ritter et al., "Control Method for
 Magnetic Stereotaxis System," U.S. Pat. No. 5,654,864, issued Aug. 5,
 1997; Howard et al., "Magnetic Stereotactic System for Treatment
 Delivery," U.S. Pat. No. 5,125,888, issued Jun. 30, 1992; Howard et al.,
 "Magnetic Stereotactic System for Treatment Delivery," U.S. Pat. No.
 5,707,335, issued Jan. 13, 1998; Howard et al., "Video Tumor Fighting
 System," U.S. Pat. No. 4,869,247, issued Sep. 26, 1989; Howard et al.,
 "Magnetic Stereotactic System for Treatment Delivery," U.S. Pat. No.
 5,779,694, issued Jul. 14, 1998; Howard et al., "Magnetic Stereotactic
 System for Treatment Delivery," app. Ser. No. 09/114,414, filed Jul. 13,
 1998; "Method and Apparatus for Magnetically Controlling Motion Direction
 of a Mechanically Pushed Catheter," app. Ser. No. 08, 920,446, filed Aug.
 29, 1997; and Ritter et al., "Method and Apparatus for Rapidly Changing a
 Magnetic Field Produced by Electromagnets," app. Ser. No. 08/921,298,
 filed Aug. 29, 1997. Further applications of the inventive apparatus
 include the introduction of biopsy tools, electrodes for palidotomy, or
 stimulators for other treatment of Parkinson's disease, and the
 introduction of drug infusion apparatus.
 A combination of a magnetic resonance imaging device and a bi-planar
 imaging device is shown in FIGS. 51-54. The combination includes a
 conventional magnetic resonance imaging device 500 and a bi-planar imaging
 assembly 502, which is preferably identical to imaging assembly 58, shown
 best in FIG. 2A. This allows the patient to be imaged with the MRI and
 then imaged with the bi-planar imaging assembly close in time, without
 having to transport the patient from place to place to obtain the images.
 This facilitates calibration of the MRI and the bi-planar x-ray images
 used during magnetic surgery. The combination includes a patient support
 504, which is similar in construction to patient support 52, described
 above. This allows the patient to be moved into and out of the MRI 500 and
 into and out of the bi-planar imaging assembly 502. The close proximity of
 the MRI 500 and the bi-planar imaging assembly 502 is permitted in part by
 the use of amorphous silicon imaging plates, or some other imaging
 receptor, that is minimally affected by the significant magnetic fields
 adjacent the MRI 500.
 It will be recognized by one skilled in the art that the various
 embodiments shown and described herein are intended to be exemplary, that
 many modifications may be made within the spirit and scope of the
 invention. It should also be clear that embodiments are possible that
 incorporate some, but not all, of the features of the invention, such as,
 by way of example only, providing fewer directions of motion for a C-arm.
 Such embodiments may still fall within the scope and spirit of the
 invention, even though achieving only some of the objectives and
 advantages thereof. The scope of the invention should therefore be
 determined from the claims, including all legal equivalents thereto, with
 reference to the specification and the examples and figures provided
 therein.