U.S. patent application number 10/021279 was filed with the patent office on 2002-08-01 for efficient magnet system for magnetically-assisted surgery.
Invention is credited to Creighton, Francis M. IV, Hall, Andrew F., Hastings, Roger N., Ritter, Rogers C..
Application Number | 20020100486 10/021279 |
Document ID | / |
Family ID | 22381794 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020100486 |
Kind Code |
A1 |
Creighton, Francis M. IV ;
et al. |
August 1, 2002 |
Efficient magnet system for magnetically-assisted surgery
Abstract
A system for magnetically assisted surgery includes a magnetic
support structure, a patient support structure and a magnet having
at least four poles attached to the magnetic support structure so
that the magnet provides a near-field magnetic field in an
operating region of a patient supported by the patient support
structure. The magnet is moveable so that the direction of the
magnetic field lines in the operating region is adjustable. The
magnet may include a pair of essentially semicircular half-segments
permanently magnetized and joined in an extremely stable disk
configuration. The magnetic field and gradient field provided by
the magnet is such that movement of the disk in one plane combined
with rotation of the disk is sufficient to orient the magnetic
field during surgical use, thereby reducing interference to medical
imaging devices needed during surgery. An example of a medical
delivery device that may be used for surgery in conjunction with
this system is a flexible endoscope or catheter having a series of
magnetically permeable rings.
Inventors: |
Creighton, Francis M. IV;
(St. Louis, MO) ; Hall, Andrew F.; (St. Charles,
MO) ; Hastings, Roger N.; (Maple Grove, MN) ;
Ritter, Rogers C.; (Charlottesville, VA) |
Correspondence
Address: |
Bryan K. Wheelock
Harness, Dickey & Pierce, P.L.C.
Suite 400
7700 Bonhomme
St. Louis
MO
63105
US
|
Family ID: |
22381794 |
Appl. No.: |
10/021279 |
Filed: |
December 11, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10021279 |
Dec 11, 2001 |
|
|
|
09287397 |
Apr 6, 1999 |
|
|
|
6330467 |
|
|
|
|
60118959 |
Feb 4, 1999 |
|
|
|
Current U.S.
Class: |
128/899 |
Current CPC
Class: |
A61B 2034/742 20160201;
A61B 90/36 20160201; A61B 34/73 20160201; A61M 25/0127 20130101;
A61B 2034/733 20160201; A61B 2034/301 20160201; A61B 1/00158
20130101; A61B 34/70 20160201 |
Class at
Publication: |
128/899 |
International
Class: |
A61B 019/00 |
Claims
What is claimed is:
1. A method of controlling an element within a patient's body which
is responsive to a magnetic field, the method comprising applying
at least two different magnetic fields to the element within the
body to control the element, the magnetic fields having different
angular relationships between the field direction and the
gradient.
2. The method according to claim 1 wherein in one of the magnetic
fields applied to the element, the gradient is substantially
parallel to the field direction and wherein in another of the
magnetic fields applied to the element the gradient is
substantially perpendicular to the field direction.
3. The method according to claim 2 wherein one of the fields
applied to the element is an end field of a permanent magnet and
one of the fields applied to the element is a side field of a
permanent magnet.
4. The method according to claim 3 wherein the permanent magnet is
a multipole permanent magnet.
5. The method according to claim 4 wherein the multipole permanent
magnet is a quadrupole permanent magnet.
6. The method according to claim 1 wherein the magnet fields are
applied with at least one permanent magnet.
7. The method according to claim 1 wherein the magnetic fields are
applied with at least one permanent magnet.
8. The method according to claim 7 wherein the at least two fields
are applied to the element by changing at least one of the position
and orientation of the magnet with respect to the patient.
9. The method according to claim 1 wherein the magnetic fields are
applied with at least one electromagnetic coil.
10. The method according to claim 9 wherein the at least two fields
are applied to the element by changing at least one of the position
and orientation of the magnet with respect to the patient.
11. The method according to claim 10 wherein the magnetic fields
are applied with at least one superconducting electromagnetic
coil.
12. The method according to claim 11 wherein the at least two
fields are applied to the element by changing at least one of the
position and orientation of the magnet with respect to the
patient.
13. The method according to claim 11 where the superconductor coil
has a mechanical refrigerator associated with it for maintaining
the superconducting state of the superconducting magnet coil.
14. An improved method of controlling an element within a patient's
body which is responsive to a magnetic field through the controlled
application of magnetic fields, the improvement comprising
successively applying at least two different magnetic fields in
which the angle between the magnetic field direction and the
gradient are different.
15. A method of controlling an element within the human body which
is responsive to an applied magnetic field, the method comprising
applying a series of magnetic fields including fields in which the
magnetic gradient is negligible for orienting the element along the
field direction and fields in which the magnetic gradient is
non-negligible and oblique to the magnetic field direction for
pulling the element in a direction different from the orientation
of the element.
16. A method of controlling an element with the human body which is
responsive to an applied magnetic field, the method comprising
applying a series of magnetic fields to control the element
including fields in which the direction and strength of the
magnetic gradient is negligible for orienting the element along the
field direction and fields in which the magnetic gradient is
non-negligible and oblique to the magnetic field direction for
pulling the element in a direction different from the orientation
of the element.
17. A device for magnetically assisted surgery of a patient
comprising: a magnet support structure; a magnet having at least
four poles, the magnet attached to the magnet support structure so
that the magnet provides a near-field magnetic field in an
operating region within a patient, the magnet being moveable to
alter a direction of magnetic field lines in the operating region
within the patient.
18. The device of claim 17 wherein the magnet is a quadrupole
magnet.
19. The device of claim 18 wherein the magnet is a permanent
magnet.
20. The device of claim 19 wherein the magnet is generally
cylindrical and has a radius and an axis perpendicular to its
radius.
21. The device of claim 20 wherein the magnet comprises a pair of
essentially semicircular segments joined so that the segments
attract each other and provide, in a region proximate the magnet
disk, a magnetic field essentially parallel to the magnet disk
along the axis of the magnet.
22. The device of claim 20 wherein the magnet is mounted rotatably
on its axis so that a direction of magnetic field lines in the
operating region of the patient may be varied.
23. The device of claim 22 and wherein the magnet is mounted
translatably in at least one radial direction.
24. The device of claim 23 wherein the magnet is mounted so that it
is translatable in a plurality of radial directions.
25. The device of claim 24 and further comprising a medical imaging
system configured to provide a medical image of the operating
region of the patient.
26. The device of claim 25 wherein the medical imaging system
comprises an x-ray source and an x-ray imaging plate on opposite
sides of the operating region of the patient, and further wherein
the x-ray source and x-ray imaging plate are positioned in a region
entirely on one side of a face of the magnet.
27. The device of claim 18 wherein the magnet is a NdFeB maximum
energy product.
28. The device of claim 27 wherein the magnet has a 44 MgOe
composition.
29. The device of claim 28 wherein the magnet is disk-shaped and
has a radius of about 12.39 inches and a thickness of 6.20
inches.
30. The device of claim 29 wherein the magnet provides a field of
at least about 0.15 Tesla at 6 inches from its face.
31. The device of claim 17 wherein the magnet comprises at least
one electromagnetic coil.
32. The device of claim 31 wherein the magnet comprises a
continuously wound coil with a cross-over to provide a quadrupole
or higher-order magnetic field.
33. The device of claim 31 wherein the magnet comprises at least a
pair of separately wound electromagnetic coils.
34. The device of claim 33 wherein the coils are each shaped in the
form of a pie section and assembled into a circular
configuration.
35. The device of claim 34 wherein the pair of separately wound
electromagnetic coils are D-shaped, with a flat portion of each of
the D-shaped coils adjacent one another.
36. The device of claim 22 wherein the at least one coil is
superconducting.
37. The device according to claim 36 where the superconductor coil
has a mechanical refrigerator associated with it for maintaining
the superconducting state of the superconducting magnet coil.
38. A device for magnetically assisting surgical operations, the
device comprising: a magnetic delivery vehicle configured to be
introduced into a patient; a magnet support base; and a magnet
assembly adjustably supported on the support base and positionable
thereon to provide a magnetic field of specified direction and
having an transverse gradient at a location in which the magnetic
delivery vehicle is introduced into a patient supported by the
patient support structure.
39. The device of claim 38 wherein the magnet assembly comprises a
computer-controlled robotic arm having a magnetic effector.
40. The device of claim 37 and further comprising a medical imaging
device configured to provide a relative location and orientation of
the magnetic delivery vehicle, the magnet assembly, and the
operating region of the patient.
Description
FIELD OF THE INVENTION
[0001] This invention relates to systems for magnetically-assisted
surgery and more particularly to systems for producing the magnetic
fields required to guide surgically implanted magnetic medical
devices.
BACKGROUND OF THE INVENTION
[0002] Several magnet systems to provide guidance for magnetic
medical devices for navigation within a patient have been devised
or are under development. An example of such a system is disclosed
in commonly assigned application Ser. No. 09/189,633, "Articulated
Magnetic Guidance System," which is hereby incorporated by
reference in its entirety. A device disclosed therein includes a
bed, a bed articulation system, a pair of x-ray sources, a coil or
magnet articulation system, and an optional pair of additional
magnets. The magnet articulation system comprises an articulation
support, servo control mechanisms to provide movement of a coil or
a permanent magnet along an arcuate arm both through a polar angle
and in a radial direction. Optionally, the entire arm may also be
pivoted through an azimuthal angle. The arm itself may comprise a
track and gimbal assembly. Additional embodiments described in the
referenced application include one in which the arm itself is
moveable via an articulation support, another in which the magnet
or coil is mounted on a pivotable ring support, and another in
which the magnet or coil is mounted as an effector on a robotic
arm. In the latter embodiment, it is desirable for the effector and
all other parts of the robotic arm to be provided with exclusion
zones to prevent accidental contact with a patient, with medical
personnel, and, of course, with other items that might be damaged
by such contact.
[0003] Other magnetic systems that provide guidance for magnetic
medical devices within a patient are disclosed in commonly assigned
application Ser. No. 09/211,723, filed Dec. 14, 1998, "Open Field
System for Magnetic Surgery," which is also incorporated by
reference in its entirety. A plurality of magnets are configured
and arranged to provide a magnetic field effective within an
operating region of a patient to navigate a magnetic medical device
within the operating region while providing access to the patient
for imaging and other purposes. 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.
One or more magnets are arranged and configured to provide a
magnetic field along each of the other of the oblique axes. The
magnetic fields generated by the magnets are effective to
controllably navigate the magnetic medical device within
substantially the entirety of the operating region. A preferred
embodiment of the system described in this reference comprises
three magnets in three mutually perpendicular planes, arranged so
that their axes at least converge and more preferably intersect in
the operating region. The magnets are arranged in an open
configuration, so that the patient typically does not have to
extend through a magnet coil to reach the operating region. In a
preferred embodiment, the magnets comprise coils that are fixed
with respect to one another in a generally downwardly facing
hemispherical shell.
[0004] Still other magnetic systems providing guidance for magnetic
medical devices navigated within a patient are disclosed in
commonly assigned Provisional App. Ser. No. 60/095,710, filed Dec.
14, 1998, "Method and Apparatus for Magnetically Controlling
Catheters for body Lumens and Cavities," which is also incorporated
by reference in its entirety. The apparatus of the invention
disclosed therein generally comprises a magnet system for applying
a magnetic field to a magnet-tipped distal end of a medical device.
The magnetic field provides a field that can navigate, orient, and
hold the distal end of the medical device in the body. The
apparatus also includes a computer for controlling the magnet
system. Imaging devices connected to the computer provide images of
the body part through which the catheter is being navigated.
Displays are provided of these images. A controller connected to
the computer has a joystick and a trigger to enable a user to input
points on the displays for two-point and three-point navigation.
The magnet system itself is preferably a set of electromagnetic
coils that can be disposed around the body part to create a
magnetic field of variable direction and intensity. Magnet systems
suitable for such use are disclosed in U.S. Pat. No. 4,869,247,
issued Sep. 26, 1989, "Video Tumor Fighting System," and U.S. Pat.
No. 5,125,888, issued on Jun. 30, 1992, entitled "Magnetic
Stereotactic System for Treatment Delivery," the disclosures of
both of which are also incorporated by reference in their
entirety.
[0005] In the commonly assigned application entitled "Device and
Method for Specifying Magnetic Field for Surgical Applications,"
application Ser. No. 09/020,798, filed Feb. 9, 1998, and which is
hereby incorporated by reference in its entirety, six normally
conducting or superconducting coils are arranged in a rectangular
box or helmet. With the Z-axis defined in the direction of the
axial component of the head, the X- and Y-coil axes are rotated
45.degree. from the sagittal plane of the head. Biplanar
fluoroscopy cameras linked to a real-time host system are provided.
Both cameras are calibrated to the six-coil host helmet design, in
which three pairs of opposing coils on mutually perpendicular axes
are provided. X-ray generators are also provided for the
cameras.
[0006] In yet another commonly-assigned application entitled
"Method and Apparatus Using Shaped Field of Repositionable Magnet
to Guide Implant," application Ser. No. 09/020,934, filed Feb. 2,
1998, and which is herein incorporated by reference in its
entirety, an apparatus comprising a moveable magnet assembly having
a plurality of fiducial marks is disclosed. In an exemplary
embodiment, the magnet assembly may be a gantry supporting either a
strong permanent magnet or a superconducting electromagnet,
although a strong permanent magnet may require additional
articulation to compensate for its lack of current control and
magnitude. The magnet assembly may be automatically controlled to
provide the needed orientation, location and coil current required
to align its magnetic field with the desired motion of a magnetic
object to be guided. Localizers and camera-like sensors are
provided to detect the fiducial marks on the magnet assembly, and
additional fiducial markers may be placed on the patient's body.
Medical imaging devices are used to display the location of the
magnet relative to the volume of interest in the patient and the
location of the implant. Various means are provided for moving the
magnet.
[0007] Each of these devices and methods provides some success in
being able to provide magnetic field orientations in all directions
in sufficient strength for the intended applications. Nevertheless,
even with specially designed systems, it is still difficult to
completely avoid interference with the imaging system while
achieving full functionality of the magnetic guidance system. In
many of the above systems, this difficulty becomes apparent in the
requirement to provide limitations in the movements of one or more
large magnets or their supporting structures, or in limitations
imposed on movements and positioning of an imaging system relative
to the magnet system. In addition, the systems designed to date,
including many of the above, have been quite large and expensive,
or are restricted in purpose and application.
[0008] The magnets used in magnetic navigation are typically
superconducting electromagnets which provide controllable, strong
magnetic fields. One drawback of superconducting electromagnets is
the cryogen system required to keep the coil at the approximately
4.degree. K needed to safely maintain the superconducting state of
the coil. The size and weight of the cryogen system makes it
difficult to support and move the superconducting electromagnetic
coil and also restricts the orientations in which the coil can be
positioned. While substantial progress has been made in the design
of cryogenic systems, there are limits on the position and
orientation of the dewar for the cryogen, which limits the
orientations in which the associated coil may be placed. The size
of the cryogen system also restricts where the coil can be
positioned relative to the patient.
[0009] It would therefore be desirable to provide a relatively
inexpensive system for magnetically assisted surgery that could
produce a magnetic field in any orientation and at sufficient
strength for use in medical applications. It would also be
desirable if the system could provide field lines through a given
procedure point in space (i.e., the location of the magnetic
medical device) that could be easily and safely changed with a
minimum of articulation of the magnet, so that the effect of the
various exclusion zones in an operating region could be minimized.
It is also desirable to provide such a magnet system where the
magnet is compact and capable of being moved in any orientation
relative to the patient to maximize the freedom of navigation
within the patient.
SUMMARY OF THE INVENTION
[0010] According to the method of this invention an element that is
responsive to a magnetic field is controlled within a patient's
body by the application of at least two different magnetic fields,
each field having a different angular relationship between the
field direction and the gradient. This can be conveniently done by
translating or rotating a magnet, such as a permanent magnet or an
electromagnet, and in particular a multipole magnet such as a
quadrupole magnet. Relatively small translations or rotations of
multipole magnets can result in substantial changes in field
direction and/or the angular relationship between the field
direction and gradient.
[0011] The system for magnetically assisted surgery of a patient of
this invention comprises a magnet support structure, a patient
support structure, and a multipole magnet attached to the magnet
support structure so that the magnet provides a near-field magnetic
field in an operating region within a patient supported by the
patient support structure. The magnet is moveable to alter the
direction of magnetic field lines in the operating region of the
patient. The magnet is preferably a quadrupole magnet, and may be a
permanent magnet.
[0012] If the magnet is a permanent quadrupole magnet, it is
preferably cylindrical, comprising a pair of essentially
semicircular segments joined so that the segments attract each
other strongly in a highly stable arrangement. This arrangement
would provide, in a region near a face of the magnet disk, a
magnetic field essentially parallel to the face of the magnet disk,
along the axis of the magnet. The magnet may be mounted so that it
can be rotated on its axis and/or translated in one or more radial
directions. A medical imaging system may also be provided and
configured to provide a medical image of the operating region of a
patient.
[0013] In accordance with a second aspect of the invention, a
system for magnetically assisted surgery of a patient comprises a
magnetic medical device configured to be implanted in a patient, a
patient support structure, a magnet support base, and a magnet
assembly adjustably supported on the support base and positionable
thereon to provide a magnetic field of specified magnitude and
direction and having a transverse gradient at the location of the
magnetic medical device within the patient supported by the patient
support structure. The magnet assembly may comprise a
computer-controlled robotic arm having a magnetic effector, and the
system may further comprise a medical imaging device configured to
provide a relative location and orientation of the magnetic medical
device in the patient and of the magnet assembly. The magnet
assembly may itself comprise a permanent magnet, an electromagnet,
or a superconducting electromagnet.
[0014] In the case of a superconducting electromagnet, in
accordance with the present invention the superconducting coil
preferably includes a mechanical refrigeration system instead of a
conventional cryogen cooling system. The refrigeration system is
more compact, less expensive to operate, and allows greater
maneuverability of the superconducting coil relative to the
patient.
[0015] In some applications it is important to have a field in a
direction approximately perpendicular to the "pulling" direction,
i.e., the gradient direction. In some instances it would further be
desirable to controllably change the relationship between the
gradient direction and the field direction. One way of doing this
efficiently is to use a multipole magnet, such as a quadrupole
magnet. In such magnets, simple translation can change the field
direction 90.degree. while, since the gradient direction remains
unchanged, changing the relationship between the field direction
and the gradient direction. Another way of doing this efficiently
is to use a simple magnet, and rotate it to use the side field. A
simple magnet can be less expensive and stronger for a given weight
than a multipole magnet, but there are occasions where the rotation
required of a simple magnet might make the articulation more
interfering with imaging and other medical apparatus in the
surgical field.
[0016] The apparatus and method of this invention can thus provide
for applying a directing magnetic field at any desired angle to a
magnetic medical device within an operating region in a nearby
patient, while simultaneously applying a pulling gradient in an
essentially transverse direction to the orientation of the magnetic
field.
[0017] The apparatus and method of this invention can also provide
a method and apparatus for performing surgery on a patient by
directing a magnetic medical device, such as a catheter or
endoscope having a magnetic or magnetically permeable tip, in a
direction perpendicular to the magnetic field. Thus, the magnetic
medical device axis is easily oriented, even with modest or weak
magnetic fields.
[0018] The apparatus and method of this invention can also provide
an external magnet system for magnetically assisted surgery that
will provide an orienting field and transverse gradient for stable
and reliable movement of a magnet medical device.
[0019] The apparatus and method of the invention can also provide
an external magnet system for magnetically assisted surgery using a
magnetic medical device, in which the direction and strength of the
magnetic force on the magnetic medical device may readily be
controlled by a surgeon.
[0020] Finally, the apparatus and method of this invention can
provide a magnet system for magnetically assisted surgery that
minimizes the limiting effect of exclusion zones on the ability of
the magnet system to provide magnetic fields of selected direction
and strength within.
[0021] The manner in which these and other features of the
invention are achieved will become apparent to one skilled in the
art upon study of the accompanying figures and description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a perspective view of an embodiment of a system
for magnetically assisted surgery in accordance with the
invention;
[0023] FIG. 2 is a perspective view of the magnet assembly of FIG.
1;
[0024] FIG. 3A is a graph showing relationships of magnetic field
strength and distance along the axes of a cylindrical quadrupole
magnet;
[0025] FIG. 3B is a graph showing contours of equal field strength
when the magnet of FIG. 2 is viewed from the -X direction;
[0026] FIG. 3C is a graph showing contours of equal field strength
when the magnet of FIG. 2 is viewed from the +Y direction;
[0027] FIG. 4 is graph showing the relationship of the calculated
weight of the magnet of FIG. 2 to its calculated magnetic field at
a distance six inches from its face;
[0028] FIG. 5 is side view of the apparatus shown in FIG. 1,
showing some of the movements of both the magnet assembly and the
patient support relative to an operating region of a patient;
[0029] FIG. 6 is an illustration of a magnetic medical device that
may be introduced into a patient and used in conjunction with the
magnetic surgical systems of this invention;
[0030] FIG. 7 is an isometric, schematic illustration of an
embodiment of the system for magnetically assisted surgery
employing a quadrupole electromagnet;
[0031] FIG. 8A is an illustration of a pair of oppositely-wound
coils of a type suitable for use as the magnet of the system shown
in FIG. 7;
[0032] FIG. 8B is an illustration of a single, continuously-wound
coil having a cross-over, the coil being of a type suitable for use
as the magnet of the system shown in FIG. 7;
[0033] FIG. 9 is a perspective view of a superconducting coil and
refrigerator combination;
[0034] FIG. 10 is a top elevation view of the superconducting coil
and refrigerator combination;
[0035] FIG. 11 is a side elevation view of the superconducting coil
and refrigerator combination;
[0036] FIG. 12 is an end elevation view of the superconducting coil
and refrigerator combination;
[0037] FIG. 13 is a perspective view of a magnetic surgery system
including a superconducting coil and refrigerator combination;
and
[0038] FIG. 14 is a longitudinal cross sectional view of an
electromagnet coil showing the field lines and direction of
magnetic gradient.
[0039] Although the figures are intended to be illustrative, it
should not necessarily be assumed that the figures are drawn to
scale. Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0040] FIG. 1 is a drawing of a system 10 for magnetically-assisted
surgery. The system generally comprises two sections; a magnet
assembly 11A and a patient support 11B. Magnet assembly 11A
comprises a magnet 12 that is located or brought into proximity
with an operating support region 20 of patient support 11B.
[0041] Magnet assembly 11A comprises a magnet 12, preferably having
more than two poles, and which is preferably a quadrupole magnet in
the form of a disk or cylinder having two semi-cylindrical segments
14 and 16 joined magnetically at a seam 15 coincident with a
diameter of the cylinder. Each of the half segments 14 and 16 are
magnetized in different directions so that the two segments attract
each other with great force when assembled into a disk to thereby
form a very stable mechanical system. While other forms of
quadrupole magnets can provide similar results, the form of magnet
12 shown in FIG. 1 and which is described in more detail below
provides remarkable simplicity and efficiency. Although a
quadrupole magnet is believed preferable, magnets or assemblies of
magnets having more than four poles could be substituted for magnet
12 within the scope of the invention.
[0042] FIG. 2 shows how the half segments of the magnet cylinder 12
are magnetized to provide advantages in accordance with this
invention. The axis of the cylinder 12 is taken as the Z axis,
while the seam 70 that joins the half segments 14 and 16
arbitrarily defines a Y direction. The X direction is taken as
being perpendicular to the Y direction and the Z axis. On one side
of seam (15)70, half segment 14 of magnet disk 12 is magnetized in
the -Z direction, while half segment 16 of magnet 12 is magnetized
in the +Z direction. As indicated above, there is a considerable
magnetic force holding the two half segments 14 and 16 together
along seam (15)70, making magnet disk 12 a very stable
structure.
[0043] FIG. 2 also shows a few of the magnetic field lines 72, 74
of magnet 12, the arrangement of which provide special features of
the system. It is known that the distant field strength of a
quadrupole falls off with distance by one power greater than that
of the dipole. Therefore, one might expect that quadrupole magnets
would be less useful than dipole magnets in surgical applications,
where large magnetic fields are frequently required. However, for
medical and surgical applications, the system described herein
takes surprising advantage of the magnetic field lines in the near
and transition fields of the quadrupole magnet 12.
[0044] To provide an effective magnetic field for surgical
applications, quadrupole magnet 12 may preferably comprise a NdFeB
magnet of 44 MgOe maximum energy, having a radius of 12.39 inches
and a thickness of 6.20 inches. In this case, quadrupole magnet 12
would weigh about 800 pounds and could be permanently magnetized to
achieve a field strength along the Z axis of about 0.15 Tesla at 6
inches from its face 92. FIG. 3A is a graph of the magnetic field
strength in Tesla calculated for this cylindrical quadrupole magnet
12 along the three axes of the magnet; line 80 shows the strength
along the Z axis, and lines 82 and 84 show the strength along the X
and Y axes, respectively. Contours 86 of equal field strength when
viewing magnet 12 towards the -X direction are illustrated in FIG.
3B, while contours 88 of equal field strength when viewing magnet
12 towards the +Y direction are illustrated in FIG. 3C.
[0045] The multitude of small arrows 90 in FIG. 3C represents
magnetic field directions on a grid of points. The arrangement of
field line directions crossing the Y-Z plane (the plane of seam 70)
are parallel to face 92 of the magnet as seen in FIG. 2 Therefore,
a rotation of magnet 12 about the Z axis will change the magnetic
field direction at any point on the Z axis while maintaining the
same strength. It is thus possible to rotate the magnetic field
direction along the Z-axis by 360.degree. or any portion thereof
without an accompanying translation of quadrupole magnet 12. On the
other hand, translation of the quadrupole magnet 12 along the X
axis by slightly over half of its radius will turn the magnetic
field so that it is directed along the -Z direction. The same
translation along the -X axis will turn the field so that it is
oriented in the +Z direction. It will thus be apparent that
complete control of magnetic field direction in an operating region
of a body for medical and surgical applications can be achieved by,
at most, two translations and one rotation, or two rotations and
one translation of quadrupole magnet 12. Such an operating region
of a body could include a person's head, as for magnetically
assisted brain surgery. Although not shown in the figures, it may
be advantageous in some applications to mount magnet 12 so that its
Z axis may also be tilted. In use, the patient's operating region
will be in the near field of magnet 12.
[0046] Because cost and navigation efficiency are partly determined
by size and weight, FIG. 4 provides a plot showing the relationship
of the calculated weight of magnet 12 to its calculated magnetic
field at a distance 6 inches from its face. The plot has been
calculated for three different aspect ratios (i.e., the ratio of
radius to thickness). Line P is for an aspect ratio of 1.0; line Q
is for an aspect ratio of 2.0; and line R is for an aspect ratio of
4.0.
[0047] Referring again to FIG. 1, magnet 12 is preferably rotatably
mounted on a track 26. This mounting allows two independent
movements of magnet 12, one being a rotation on the axis of the
magnetic disk 12 shown by arrow A, and the other being translation
along track 26 as indicated by arrow B. Preferably, track 26 itself
is also rotatable about an axis as indicated by arrow C. This
additional rotation may be provided by mounting track 26 on a shaft
24 that is rotatably mounted on the support base 22 of magnet
assembly 11A. Shaft 24 may also be slidable along its axis to
thereby provide another direction of motion that permits magnet 12
to be withdrawn from proximity to the operating region of the
patient. This motion is indicated by arrow G in FIG. 1.
[0048] The embodiment of magnet assembly 11A in FIG. 1 thus
provides a quadrupolar magnet 12 that is or that may be brought
into close proximity with an operating region of a patient.
Quadrupole magnet 12 may be subject to a plurality of rotational
and translational movements to provide differing magnetic field
orientations in the operating region. Translation in three
dimensions (including withdrawal from the operating region) is
provided in the embodiment of FIG. 1. In other embodiments, it may
be possible to mechanically tilt the axis of the magnet with
respect to the operating region. Although tilting may be desirable
in some operating situations, it is not necessary to practice the
invention.
[0049] Magnet assembly 11A may comprise a robotic support
manipulator to provide the rotation and translation of magnet 12,
and may optionally also provide tilting of the Z axis of magnet 12.
Because of the weight of magnet 12 and for other reasons, as well,
robotic control is preferable to full manual movement of magnet 12,
although manual control is both possible and contemplated within
the scope of the invention. The movements required of the robotic
manipulator are those that are required to make possible the
movements of magnet 12 as described herein. Robotic manipulators
are well-known in the art, and the design of servo mechanisms to
provide the needed movements of magnet 12 would present no special
difficulties to one skilled in that art. Such servo mechanisms
could be manually controlled by a surgeon viewing real-time medical
images of the operating region of a patient, or could be
automatically controlled by a computer interpreting such images. If
manually controlled, a computer could provide assistance by
displaying medical images of the operating region of the patient,
showing the magnetic delivery vehicle (MDV) or magnetic seed in the
patient with other useful information superimposed or adjacent to
this image. This other information could include a desired path of
the MDV or magnetic seed and the magnetic field lines or gradient
of magnet 12.
[0050] FIG. 1 illustrates a patient support essentially identical
to that described in copending application Ser. No. 09/211,723,
filed Dec. 14, 1998, and incorporated by reference above. Patient
support 11B comprises a bed 18 that is supported at a convenient
operating level by a base support 19. Bed 18 includes a region 20
that is or can be brought into proximity with magnet 12. (Although
it is contemplated that the magnet 12 will be moveable, movement of
the operating region of a patient relative to magnet 12 may
alternately, in some circumstances, be accomplished by moving the
bed 18 supporting the patient.) Also provided is a rotating pivot
or swiveling support 30 on which is attached an imaging assembly
11C comprising a base frame 32, arcuate support 34, and arcuate
section 28. Part of imaging assembly 11C may comprise any suitable,
commercially available C-arm assemblies, such as those made by
General Electric Co. of Syracuse, N.Y., however, it is not required
that the "arcuate" section be in the shape of an arc. Because
commercially available C-arm assemblies usually are this shape,
however, it is convenient to use this terminology. Support 30 need
not be mounted or free-standing on a floor, as shown here. Some
other mounting possibilities include attachment of support 30 to an
extension of base support 19 of patient support 11B, or to an
extension of support base 22 of magnet assembly 11A. Mountings that
do not require movements of imaging assembly 11C that interfere
with the attached imaging apparatus described below when magnet 12
is repositioned are preferable.
[0051] Arcuate section 28 supports one or more X-ray or
fluoroscopic tubes 46A and 46B for use in providing a medical image
of the operating region of the patient supported at region 20 of
bed 18. Thus, each of the tubes 46A and 46B have their beams aimed
at corresponding imaging plates 44A and 44B through this region.
Preferably, imaging plates 44A and 44B are held in place by imaging
plate supports 42A and 42B, respectively, which are separate
supporting arms. The position of these plates may be adjusted
somewhat by moving blocks 40A and 40B, respectively, which are
configured to slide (such as on tracks, not shown in FIG. 1), over
surfaces 38A and 38B of a pie-shaped portion 36 of arcuate support
28.
[0052] Some of the pivoting and movement mechanisms of the C-arm
and imaging assembly 11C are not shown in FIG. 1, but are shown and
described in application Ser. No. 09/211,723. Briefly, arcuate
section 28 is configured to provide various views of an operating
region of a patient by pivoting at swivel support 30 (shown by
arrow D), partial rotation around another pivot (as shown by arrow
F, along an axis preferably perpendicular to the pivoting axis at
30), and by partial rotation of the entire arcuate section 28
around a central point, as indicated by arrow E. Each movement of
arcuate section 28 also causes the imaging tubes 46A and 46B and
their respective imaging plates to move correspondingly relative to
the operating region of the patient, which is not operatively
coupled to these C-arm movements. Thus, various views of the
operating region are available. Some of the movements of both
magnet assembly 11A and patient support 11B may also be seen in
FIG. 5, which also shows where an operating region 62 of a patient
60 would be situated in relation to the parts of the inventive
apparatus. It will be recognized that the views provided by the
imaging devices can provide the relative locations of magnet
assembly 11A, a medical delivery device in a patient 60, and an
operating region of the patient 62.
[0053] It will be observed that movement of the arcuate section 28
and the objects attached to it result in physical exclusion volumes
being created. These are regions of space that are or may be
occupied by the moving components, and that must therefore be
avoided by movements of the magnet 12 or magnet assembly 11A. If
the physical exclusion volumes are not respected, physical
interference between the components of the system occur. It may
also be useful to consider magnetic as well as physical exclusion
regions. Magnetic exclusion regions are regions from which, taking
into account the movement of magnet 12, magnetic objects or objects
that may be adversely affected by magnetic fields should be
excluded. Thus, it may be desirable to avoid placing some types of
imaging plates 44A and 44B within a region of high field strength
of magnet 12. However, because of the relatively small size of
quadrupole magnet 12 and the requirement of only limited rotational
and translational movement, both its physical and magnetic
exclusion zones are advantageously quite small. Additionally,
because magnet 12 is a quadrupole magnet, the magnetic exclusion
zone is smaller than might otherwise be the case, because the
magnetic field generally drops off more quickly with distance for
such magnets than with the dipole magnets and solenoids previously
used. (Similar advantages may be obtained with magnets having more
than four poles.)
[0054] The inventive system described herein is intended for use in
magnetically assisted surgery. For example, it may be used to guide
a tiny magnet on the end of a catheter or guide wire that is
magnetically navigated into an aneurysm in the brain. A magnetic
medical device 102, as illustrated in FIG. 6, may be introduced
into an operating region 62 of a patient 60 in accordance with this
invention. Magnetic medical device 102 may comprise a series of
magnetically permeable rings 104. These rings may be mounted on a
slightly flexible rod 106, such as a catheter or endoscope. The
individual moments of the rings are induced to be along the
direction of the magnetic field of magnet 12, and this orientation
is not altered by the gradient of the field. Instead, the gradient
and the direction of the field may be used in a complementary way
so that the axis 108 of the magnetic medical device is easily
oriented, even with the application of modest or weak magnetic
fields from the external magnet 12. At the same time, the
transverse gradient applies a transverse force TF on the moment of
the system.
[0055] Magnet assembly 11A and patient support 11B as shown and
described herein are physically separate assemblies, but it should
be clear that this is not a requirement of the invention. It is
also not necessary that patient support 11B be in the form shown
here. Any form of supporting structure suitable for holding or
supporting an operating region of a patient may be used, possibly
including a floor in an emergency, with suitable modification of
either or both magnet assembly 11A and imaging assembly 11C so that
the magnet may be appropriately positioned and the operating region
properly imaged. In the claims appended below, it should be
understood that a magnet support structure and a patient support
structure need not be physically separate assemblies, and that,
unless explicitly stated otherwise, the magnet support structure
and patient support structure may comprise different portions of a
single structure.
[0056] In alternate embodiments, a magnet may be attached to a
flexible or articulated arm that is attached to the ceiling, rather
than to a support structure such as shown in FIG. 1 that is
attached to or supported by the floor. A ceiling mounted assembly
would avoid congestion at the floor area of the patient. Moreover,
the flexible or articulated arm may be designed to allow easy
manual or adjustment of the position and angle of the magnet
assembly. Alternately, the ceiling supported assembly could be
robotically controlled.
[0057] In another alternative embodiment, the transverse magnitude
and gradient fields may be generated by an electromagnet rather
than a permanent magnet. It is a general characteristic of coil
systems having standard symmetries (i.e., that are symmetric about
the coil axis and symmetric with respect to a center, equatorial
plane of the coil) that in regions in and near the equatorial
plane, both inside and outside the coil, a magnetic field exists
that is parallel to the coil axis, while at the same time a
transverse gradient of the field is perpendicular to the axis. For
example, a single circular turn of wire in a plane has such a field
and gradient relationship. However, for such a coil, the region
inside or outside the coil at which this relationship occurs is too
narrow to be useful. Attempts to use such a coil to magnetically
assist a surgical procedure employing a magnetic medical device
will be subject to error due to operator inaccuracy.
[0058] Appreciable regions around a long solenoid coil (with either
normally conducting or superconducting turns) will have an
essentially transverse relationship of field and gradient. However,
the field and gradient will be relatively weak for a given number
of ampere-turns of the coil. However, upon recognizing the
advantages of providing the transverse field and gradient
relationship in accordance with this invention, one skilled in the
art would be able to optimize the design of a coil for use in
conjunction with the invention. Such a coil would have a
sufficiently large region in which the required relationship
exists, at a suitable distance from the coil for use in a desired
surgical application. Permanent magnets may also be designed with
similar characteristics, although different mathematical tools may
be required. The quadrupole magnet 12 described in detail above is
one particularly simple and advantageous permanent magnet design in
accordance with this invention.
[0059] Notwithstanding the above remarks, it is possible to
configure two or more (preferably superconducting) electromagnets
to achieve many of the advantages of the permanent quadrupole
magnet 12 discussed above, as well as some additional advantages.
Such a configuration is represented isometrically (and somewhat
schematically) in FIG. 7. Referring to FIG. 7, quadrupole magnet
12' comprises a pair of preferably D-shaped coils 112, 114 mounted
at an end of an articulated arm 116. The straight sections of coils
112 and 114 are preferably closely adjacent to one another, as
shown. Articulated arm 116 has a number of joints exemplified by
118, 120, 122, 124. The joints provide sufficient articulation to
position and rotate quadrupole magnet 12' around an operating
region of a patient placed on patient support 11B. An articulated
arm 116 suitable for this purpose will be found in commonly
assigned application Ser. No. 09/189,633, filed Nov. 10, 1998,
entitled "Articulated Magnetic Guidance Systems and Devices and
Methods for Using Same for Magnetically-Assisted Surgery," which is
hereby incorporated by reference in its entirety. Movement of
articulated arm 116 may be manually controlled, or more preferably,
robotically controlled, such as by computer-controlled servo
systems, which may preferably be coordinated with a medical imaging
system as well as one or more visual display systems and input
systems to assist a surgeon guiding a magnetic implant influenced
by quadrupole magnet 12'. Many of these systems are not shown in
FIG. 7, but it will be understood that at least a medical imaging
system such as one similar to that shown in FIG. 1 and described in
conjunction therewith would normally be present and would be used
during surgery.
[0060] Coils 112 and 114 are oppositely wound, as shown in FIG. 8A,
or a single, continuously-wound coil 112' with a cross-over, as
shown in FIG. 8B, may be provided instead. Either of these coil
arrangements will operate as a quadrupole magnet to generate
transverse gradients, i.e., gradients having a pulling direction
perpendicular to the direction of the magnetic field. The field and
gradient of the electromagnetic quadrupole magnet 12' are similar
in form to those of permanent magnet 12 shown in FIG. 1. An
advantage of the permanent magnet quadrupole over a superconducting
quadrupole electromagnet is that it is not necessary to provide
cryogens for a permanent magnet. However, superconducting coils can
have considerably greater strength for a given size and weight. If
magnet 12' in FIG. 7 were superconducting, a cryogenic system (not
shown) would have to be supplied. The design of a suitable
cryogenic system could be accomplished by one skilled in the art,
however, and is not considered part of the present invention.
[0061] Aside from the stronger magnetic fields obtainable from a
superconducting quadrupole electromagnet, another advantage of an
electromagnetic quadrupole magnet 12' is that the field strengths
produced in the operating region of a patient may be controlled not
only by repositioning magnet 12', but by controlling the currents
in its coil 112' or coils 112 and 114. This reduces somewhat the
need for movement of magnet 12' and possibly the need for certain
types of articulation of articulated arm 116.
[0062] Although articulated arm 116 is shown in FIG. 7 as being
suspended from a ceiling, it will be recognized that other mounting
configurations that provide for stable movement and positioning of
magnet 12' are also suitable. Also, it should be noted that other
configurations of electromagnets that are effective in producing or
emulating a multipolar magnetic field (i.e., one of more than 2
poles) may be used instead of the quadrupole example shown and
described here. For example, an eight-pole electromagnet could be
compactly formed from four coils wound in 90.degree. pie-shaped
sections assembled in a circular arrangement. However, absent
special circumstances, a quadrupolar field should suffice for
surgical applications. (It should be mentioned that a D-shaped
section may be considered as a 180.degree. pie-shaped section.)
[0063] As shown in FIGS. 9-13, a superconducting coil and
refrigerator combination 200 can be constructed for use in
magnetically assisted surgery. The combination 200 comprises a
superconducting electromagnetic coil 202 and a refrigerator 204.
The refrigerator 204 is more compact than the cryogen systems
typically used with superconducting magnets, making it possible to
bring the superconducting electromagnetic coil closer to the
patient without interference from the patient or surrounding
medical and imaging equipment. The refrigerator 204 is also not
restricted in the orientation in which it can be placed as were
prior cryogen systems, allowing more freedom to position and orient
the coil and refrigerator combination relative to the patient. A
suitable superconducting coil and refrigerator combination 200 may
be a Cryofree.TM. magnet system available from Oxford Instruments,
Concord, Mass.
[0064] The mechanical refrigerator 204 is preferably attached to
one side of the coil 202, with its axis perpendicular to the axis
of the coil. Because of the axial symmetry of the coil, its
magnetic field and gradients are identical on any circles about the
coil axis in planes perpendicular to the axis). At least
270.degree. of such a circle are free of the refrigerator 204, and
therefore useful in applying a field to the operating region of the
patient without the refrigerator interfering with the patient or
other medical or imaging equipment near the patient. Furthermore
because of this symmetry the field direction can be reversed or its
angle changes by rotation about an axis perpendicular to the axis
of the coil, without changing the current in the coil (and its
attendant ramp times).
[0065] In some applications it is desirable to be able to pull a
magnetic device perpendicular to its axis, for example a catheter
or electrode having a small cylindrical magnet attached to its
distal end. FIG. 14 shows the magnetic field lines surrounding an
electromagnetic coil 202, and the direction of the magnetic
gradient g. The field lines in the equatorial plane e of the coil
202 are parallel to the axis a of the coil, and thus would tend to
align a magnetic medical device in a direction parallel to the axis
of the magnet; but the gradient at the equatorial plane g.sub.e, is
perpendicular to this direction, and will pull a magnetic medical
device toward the coil axis. In contrast the gradient along the
axis g.sub.a is generally parallel to the field direction, and will
pull a magnetic medical device along the axis.
[0066] As shown in FIG. 13, a superconducting coil and refrigerator
combination 200 can be incorporated as part of a magnetic surgery
system 210. Magnetic surgery system 210 comprises a patient support
212 for supporting a patient thereon and a magnetic support 214 for
moveably supporting the coil and refrigerator combination.
[0067] The magnet support 214 is shown mounted on the ceiling, but
could also be mounted on the floor. The magnet support 214 has a
pivotally mounted articulated arm 216 which can extend and retract
to position the magnet coil 202 around the patient to create the
desired magnetic field within an operating region in the patient.
The magnet support 214 can either be manually operated by the
physician, or it can be automatically operated by a computer
control which operates one or more motors or actuators to
automatically position the magnet in a selected position, or to
automatically position the magnet to achieve a selected field or
gradient.
[0068] The superconducting electromagnetic coil and refrigerator
combination 200 is lightweight and compact to facilitate the
manipulation of the magnet with the articulated arm 216.
[0069] It will be understood that embodiments incorporating subsets
of the inventive concepts herein disclosed are possible that
provide some but not all of the advantages of the invention or that
meet or satisfy one or more but not all of the objects of the
invention. In addition, many modifications of the inventive
embodiments disclosed herein will be apparent to those of ordinary
skill in the art. Therefore, the scope of the invention should be
determined as provided by the claims below, including the full
range of equivalents provided under applicable laws.
* * * * *