U.S. patent number 7,305,263 [Application Number 10/801,062] was granted by the patent office on 2007-12-04 for magnetic navigation system and magnet system therefor.
This patent grant is currently assigned to Stereotaxis, Inc.. Invention is credited to Francis M. Creighton, IV.
United States Patent |
7,305,263 |
Creighton, IV |
December 4, 2007 |
**Please see images for:
( Certificate of Correction ) ** |
Magnetic navigation system and magnet system therefor
Abstract
A magnetic navigation system for orienting a magnetically
responsive medical device in a selected direction within an
operating region in a subject's body. The system includes a support
for supporting the subject, a magnet system a magnetic field to the
operating region, and an imaging system. The magnet system includes
at least two magnets disposed on opposite sides of the operating
region for applying a magnetic field of at least 0.08 Tesla in any
selected direction in the operating region by a change of the
position and/or orientation of the magnets within an exclusion zone
volume. The imaging system includes an imaging beam source and an
imaging beam detector disposed on opposite sides of the operating
region. The source and the detector being carried on a C-arm which
can pivot about an axis generally parallel to the longitudinal axis
of the subject to change the imaging angle. The magnets of the
magnet system being configured and positioned so that the C-arm can
pivot through at least about 60.degree. without impinging upon the
exclusion zone of the magnets.
Inventors: |
Creighton, IV; Francis M. (St.
Louis, MO) |
Assignee: |
Stereotaxis, Inc. (St. Louis,
MO)
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Family
ID: |
33493087 |
Appl.
No.: |
10/801,062 |
Filed: |
March 15, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040249263 A1 |
Dec 9, 2004 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60454410 |
Mar 13, 2003 |
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Current U.S.
Class: |
600/424; 378/11;
378/13; 378/205; 600/425; 600/427; 600/429; 606/130 |
Current CPC
Class: |
A61B
90/10 (20160201); A61B 34/73 (20160201); A61B
2034/732 (20160201); A61B 90/361 (20160201) |
Current International
Class: |
A61B
5/05 (20060101) |
Field of
Search: |
;600/424-427,429
;606/130 ;378/11,13,205 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mercader; Eleni Mantis
Assistant Examiner: Lauritzen; A.
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Parent Case Text
CROSS-REFERENCE TO PREVIOUSLY FILED APPLICATIONS
This invention claims priority of U.S. Patent Application Ser. No.
60/454,410, filed Mar. 13, 2003, the entire disclosure of which is
incorporated herein by reference.
Claims
What is claimed is:
1. A magnetic navigation system for orienting a magnetically
responsive medical device in a selected direction within an
operating region in a subject's body, the system comprising: a
support for supporting the subject; a magnet system for applying a
magnetic field to the operating region, the magnet system
comprising at least two magnets disposed on opposite sides of the
operating region for applying a magnetic field of at least 0.08
Tesla in any selected direction in the operating region by a change
of the position and/or orientation of the magnets within an
exclusion zone volume; an imaging system for imaging the operating
region, the imaging system comprising a imaging beam source and an
imaging beam detector disposed on opposite sides of the operating
region, the source and the detector being carried on a C-arm which
can pivot about an axis generally parallel to the longitudinal axis
of the subject to change the imaging angle; the magnets of the
magnet system being configured and positioned so that the C-arm can
pivot through at least about 60.degree. without impinging upon the
exclusion zone of the magnets.
2. The magnetic navigation system according to claim 1 wherein the
C-arm can pivot at least about 30.degree. in either direction from
the midsagittal plane of the subject.
3. The magnetic navigation system according to claim 1 wherein the
C-arm can pivot through at least about 75.degree. without impinging
upon the exclusion zone of the magnets.
4. The magnetic navigation system according to claim 3 wherein the
C-arm can pivot at least about 37.5.degree. in either direction
from the midsagittal plane of the subject.
5. The magnetic navigation system according to claim 1 wherein the
C-arm can pivot through at least about 80.degree. without impinging
upon the exclusion zone of the magnets.
6. The magnetic navigation system according to claim 5 wherein the
C-arm can pivot at least about 40.degree. in either direction from
the midsagittal plane of the subject.
7. The magnetic navigation system according to claim 1 wherein the
C-arm can pivot through at least about 120.degree. without
impinging upon the exclusion zone of the magnets.
8. The magnetic navigation system according to claim 7 wherein the
C-arm can pivot at least about 60.degree. in either direction from
the midsagittal plane of the subject.
9. The magnetic navigation system according to claim 1 wherein each
of the at least two magnets is translatable along a first axis that
extends radially outwardly from the center of the operating region,
is pivotable about a second axis, generally perpendicular to the
first axis, that extends through the center of mass of the magnet,
and is rotatable about the first axis.
10. The magnetic navigation system according to claim 9 wherein the
first axes of each of the at least two magnets are collinear.
11. The magnetic navigation system according to claim 9 wherein the
first axes of each of the at least two magnets form an angle of
between about 163.degree. and 178.degree..
12. The magnet navigation system according to claim 9 wherein the
at least two magnets are rotatable about the operating region in
fixed relation to move the exclusion zones out of the way of the
imaging system.
13. The magnetic navigation system according to claim 1 wherein the
imaging system has an imaging zone at least +/-15 centimeters on
either side of the centerline between the imaging source and
receiver, from the operating region to the receiver, that does not
impinge upon the exclusion zone of the at least two magnets.
14. The magnetic navigation system according to claim 1 wherein the
imaging system has an imaging zone at least +/-20 centimeters on
either side of the centerline between the imaging source and
receiver, from the operating region to the receiver, that does not
impinge upon the exclusion zone of the at least two magnets.
15. The magnetic navigation system according to claim 1 wherein the
exclusion zone of each of the at least two magnets is generally
cylindrical exclusion zone with a frustoconical face oriented
toward the operating region.
16. A magnet system for a magnetic navigation system for orienting
a magnetically responsive medical device in a selected direction
within an operating region in the body of a subject being supported
on a support, while the operating region is being imaged with an
imaging system including an imaging beam source and an imaging beam
detector disposed on opposite sides of the operating region, the
source and the detector being carried on a C-arm which can pivot
about an axis generally parallel to the longitudinal axis of the
subject to change the imaging angle, the imaging system having an
imaging zone at least +/-15 centimeters on either side of the
centerline between the imaging source and receiver, from the
operating region to the receiver, the magnet system comprising at
least two magnets disposed on opposite sides of the operating
region, the magnets configured so that by changing the position and
orientation of the magnets each within its own exclusion zone, the
magnets provide a navigating magnetic field in the operating region
of at least 0.08 T in any selected direction, such that the
exclusion zone permits the C-arm of the imaging system to pivot at
least 60.degree. without the imaging zone impinging on the
exclusion zone.
17. The magnet system according to claim 16 wherein the exclusion
zones are sized and shaped so that the C-arm can pivot at least
about 30.degree. in either direction from the midsagittal plane of
the subject.
18. The magnet system according to claim 16 wherein the C-arm can
pivot through at least about 75.degree. without impinging upon the
exclusion zone of the magnets.
19. The magnet system according to claim 18 wherein the C-arm can
pivot at least about 37.5.degree. in either direction from the
midsagittal plane of the subject.
20. The magnet system according to claim 16 wherein the exclusions
zones are shaped so that the C-arm can pivot through at least about
80.degree. without impinging upon the exclusion zone of the
magnets.
21. The magnet system according to claim 20 wherein the C-arm can
pivot at least about 40.degree. in either direction from the
midsagittal plane of the subject.
22. The magnet system according to claim 1 wherein the exclusion
zones are sized and shaped so that the C-arm can pivot through at
least about 120.degree. without impinging upon the exclusion zone
of the magnets.
23. The magnet system according to claim 22 wherein the C-arm can
pivot at least about 60.degree. in either direction from the
midsagittal plane of the subject.
24. The magnet system according to claim 16 wherein each of the at
least two magnets is translatable along a first axis that extends
radially outwardly from the center of the operating region, is
pivotable about a second axis, generally perpendicular to the first
axis, that extends through the center of mass of the magnet, and is
rotatable about the first axis.
25. The magnet system according to claim 24 wherein the first axes
of each of the at least two magnets are collinear.
26. The magnet system according to claim 24 wherein the first axes
of each of the at least two magnets form an angle of between about
163.degree. and 178.degree..
27. The magnet system according to claim 24 wherein the at least
two magnets are rotatable about the operating region in fixed
relation to move the exclusion zones out of the way of the imaging
system.
28. The magnet system according to claim 16 wherein the imaging
system has an imaging zone at least +/-20 centimeters on either
side of the centerline between the imaging source and receiver,
from the operating region to the receiver, that does not impinge
upon the exclusion zone of the at least two magnets.
29. The magnet system according to claim 16 wherein the exclusion
zone of each of the at least two magnets is generally cylindrical
exclusion zone with a frustoconical face oriented toward the
operating region.
30. The magnet system according to claim 16 wherein each of the at
least two magnets is comprised of a plurality of blocks each with a
magnetization direction that in one a plurality of predetermined
angular orientations that optimizes the magnetic field in a
particular direction and an operating point spaced from the magnet.
Description
BACKGROUND OF THE INVENTION
This invention relates to a magnetic navigation system for applying
a navigating magnetic field to an operating region inside a subject
while simultaneously imaging the operating region.
Magnetic navigation systems have been developed which apply a
navigating magnetic field in a selected direction to an operating
region in a subject to change the direction of a magnetically
responsive medical device in the operating region. Examples of such
systems are disclosed in U.S. Pat. No. 6,241,671, issued Jun. 5,
2001, for Open Field System for Magnetic Surgery; and U.S. Pat. No.
6,630,879, issued Oct. 7, 2003, An Efficient Magnet System for
Magnetically-Assisted Surgery, the disclosures of which are
incorporated herein by reference. However for many procedures it is
desirable to provide simultaneous or near simultaneous images of
the operating region either to confirm the position and orientation
of the medical device, or to otherwise control the medical
procedure being conducted with the medical device. Imaging can be
conveniently provided with a C-arm mounted x-ray imaging system,
employing an imaging beam source and detector disposed on opposite
sides of the operating region. However, the magnet systems employed
in magnetic navigation systems typically must be positioned in
close proximity to the subject in order to provide magnetic field
of sufficient strength to be useful in navigation. Thus the magnet
systems create an exclusion zone around the subject into which the
imaging system cannot impinge, and this exclusion zone restricts
the orientations at which the C-arm can be positioned for
imaging.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a
magnet navigation system for magnetically navigating within an
operating region is provided in which a C-arm based imaging system
can pivot at least about 60.degree. around the operating region,
and more preferably at least about 75.degree., still more
preferably at least about 80.degree., and in some embodiments as
much as 120.degree.. Generally, a preferred embodiment of a
magnetic navigation system in accordance with the principles of
this invention is adapted to orient a magnetically responsive
medical device in a selected direction within an operating region
in a subject's body. The system generally comprises a support for
supporting the subject, a magnet system for applying a magnetic
field to an operating region in the subject, and an imaging system
for imaging the operating region. The magnet system preferably
comprise at least two magnets disposed on opposite sides of the
operating region for applying a magnetic field of sufficient
navigating strength in any selected direction in the operating
region by a change of the position and/or orientation of the
magnets within separate exclusion zones. The imaging system
preferably comprises an imaging beam source and an imaging beam
detector disposed on opposite sides of the operating region. The
source and the detector are carried on a conventional C-arm which
can pivot about an axis generally parallel to the longitudinal axis
of the subject to change the angular position of the source and the
detector, and thus the angle at which the operating region is
imaged. The magnets of the magnet system are configured and
positioned so that the C-arm can pivot through at least about
60.degree. without impinging upon the exclusion zones of the
magnets.
The magnets can be sized and shaped, and the imaging system carried
on the C-arm can be selected so that pivoting ranges of as much as
about 120.degree. can be achieved. In some preferred embodiments
the at least two magnets are directly opposed at 180.degree. apart,
and in other embodiments the at least two magnets are oriented at
angles of between about 163.degree. to about and about 178.degree..
In some embodiments the at least two magnets can rotate around the
operating zone (preferably in fixed relation to each other) to
thereby move their exclusion zones to increase the pivot range of
the C-arm.
The systems of the present invention provide magnet navigation of
magnetically responsive devices in the body, while achieving an
extended range of imaging angles of the operating region, to
provide better information about the operating region for use in
navigating medical devices and/or using medical devices in the
operating region.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the arrangement of a first embodiment
of a magnet system constructed according to the principles of this
invention, showing a 60.degree. range of motion for an imaging
C-arm carrying a 30 cm.times.30 cm receiver plate;
FIG. 2 is a schematic view of the first embodiment of the magnet
system shown in FIG. 1, showing a 80.degree. range of motion for an
imaging C-arm carrying a 20 cm receiver;
FIG. 3 is a schematic view of a second embodiment of a magnet
system constructed according to the principles of this invention,
showing a 75.degree. range of motion for a C-arm carrying a 30 cm
receiver; and
FIG. 4A is a schematic view of an alternate implementation of the
second embodiment in which the magnets can rotate about the
operating region, showing a 120.degree. range of motion for a C-arm
carrying a 20 cm receiver, with the magnets rotated 22.5.degree. in
one direction from its normal position;
FIG. 4A is a schematic view of an alternate implementation of the
second embodiment in which the magnets can rotate about the
operating region, showing a 120.degree. range of motion for a C-arm
carrying a 20 cm receiver, with the magnets rotated 22.5.degree. in
the opposite direction from its normal position;
FIG. 5 is a perspective view of the magnet and its exclusion
zone;
FIG. 6 is an enlarged view of the magnet.
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of a magnetic navigation system constructed
according to the principles of this invention is shown
schematically in FIG. 1. The magnetic navigation system is adapted
for orienting a magnetically responsive medical device in a
selected direction within an operating region in a subject's body.
The first embodiment of the system comprises a support 22 for
supporting the subject, a magnet system 24 for applying a magnetic
field to the operating region 26, and an imaging system 28 for
imaging the operating region 26.
The subject support 22 is preferably a generally horizontal surface
for supporting a subject in a generally horizontal position so that
the operating region of the system is positioned within the
subject's body.
The magnet system 24 comprises at least two magnets 30 and 32
disposed on opposite sides of the operating region 26 for applying
a magnetic field sufficient for magnetic navigation in any selected
direction within the operating region. (Magnet 30 is shown in FIG.
1 with its magnetic field lines, but for clarity, magnet 32 is
shown without its magnetic field lines). Magnets 30 and 32 are
preferably identical in construction. The strength of the field
required for magnetic navigation depends in part upon the magnetic
responsiveness of the device that is in the operating region 26,
which is typically provided with a magnetically responsive element,
such as a permeable or permanent magnet, or an electromagnetic
device. In this preferred embodiment, the magnets 30 and 32
preferably can provide a navigating field of at least about 0.08
Tesla in any selected direction in the operating region, however in
other embodiments the magnets 30 and 32 might be designed to
provide a magnetic field of at least about 0.06 Tesla, or even
lower as advances are made in improving the magnetic responsiveness
of the medical devices deployed in the operating region 26. The
magnets 30 and 32 are shaped and configured so that a change of the
position and/or orientation of the magnets within an exclusion zone
34 permits the magnets to apply a magnetic field of the desired
strength in the operating region 26 in any selected direction. A
mechanism, not shown, is provided for repositioning and reorienting
the magnets 30 and 32 as required to provide the desired field in
the operating region. An example of one possible device is
disclosed in U.S. patent application Ser. No. 10/347,525, for
Magnetic Navigation System, incorporated herein by reference.
Each of the magnets is preferably made up of a plurality of blocks
of magnetic material each of which is magnetized in one of a
plurality of predetermined magnetization directions to maximize the
magnet field in a particular direction at an operating point spaced
from the front face of the magnet. It has been empirically
determined that increments of 30.degree. in magnetization direction
are usually adequate, and any gains in field strength by obtained
by smaller increments are usually not cost-effective. Details of
the construction of such magnets are disclosed in U.S. Pat. No.
6,630,879, issued Oct. 7, 2003, An Efficient Magnet System for
Magnetically-Assisted Surgery, and in U.S. patent application Ser.
No. 10/056,227 for Rotating And Pivoting Magnet For Magnetic
Navigation, the disclosures of which are incorporated herein by
reference. The design of such magnets is disclosed in U.S. patent
application Ser. No. 10/082,715 for Magnets With Varying
Magnetization Direction and Method of Designing Such Magnets,
incorporated herein by references. A possible method of
manufacturing such magnets is disclosed in U.S. patent application
Ser. No. 10/704,195, for Method of Making A Compound Magnet,
incorporated herein by reference.
Each of the magnets 30 and 32 is sized and shaped to so that by
translating the magnet along a first axis A extending radially from
the operating region 26, pivoting of the magnet about a second axis
B perpendicular to the first axis A and extending substantially
through the center of mass of the magnet, and rotation of the
magnet about the first axis A, permits the magnets 30 and 32 to
apply a magnetic field to the operating region 26 in any selected
direction. The translation, pivoting, and rotation of the magnets
required to achieve the desired range of directions in the
operating region define the exclusion zone 34 into which the
imaging system 28 must not impinge so as to not interfere with the
proper operation of the magnet system 24. In general the magnet is
translated and pivoted to follow a line of constant magnetic field
strength, e.g. the 0.08 Tesla line, at the operating point in the
operating region. The rotation of the magnet allows the direction
of the field to be changed. Pivoting the magnets at or near their
centers of mass helps reduce the size of the exclusion zones 34,
and also allows for more compact and less expensive mechanisms for
pivoting the magnets.
As shown in the Figures, the exclusion zone 34 is generally
cylindrical, with a frustoconical front face oriented toward the
operating region 26. The exclusion zone is preferably contained
within a protective shell, which protects the mechanism for moving
the magnet, and hides the movement from view.
The imaging system 28 comprises an imaging beam source 36 and an
imaging beam detector 38 disposed on opposite sides of the
operating region 26. The source 36 and the detector 38 are carried
on a C-arm 40 which can pivot about an axis generally parallel to
the longitudinal axis of the subject on the support 22, to change
the imaging angle of the operating region 26. (Two C-arms are shown
in FIG. 1 in order to illustrate the range of motion of the C-arm,
but there is preferably only one C-arm used for imaging the
operating region 26).
The detector 38 is preferably a solid state amorphous silicon x-ray
receiving plate 42, which is substantially unaffected by the
magnetic fields created by the magnet system 24. These solid state
receiving plates are presently available in 20 cm.times.20 cm and
30 cm.times.30 cm sizes, with the 30 cm.times.30 cm size being
shown in FIG. 1. Of course some other size imaging plate could be
used. The imaging plate is disposed in a cover 44, so that the
width of the imaging zone extends 15 cm on either side of the
centerline between the imaging source 36 and the imaging receiver
38 for a 20 cm.times.20 cm plate, and so that the width of the
imaging zone extends 20 cm on either side of the centerline between
the imaging source 36 and the imaging receiver 38 for a 30
cm.times.30 cm plate.
The receiving plate 42 is preferably mounted for translation toward
and away from the operating region 26, in order to change the
resolution of the images of the operating region. The movement of
the receiving plate 42 and cover 44 define an imaging zone 46
extending generally from the operating region 26, centered along
the line between the source 36 and the receiver 38 through the
center of the operating region 26. As described below the magnet
system, and in particular the exclusion zones of the magnet system,
preferably does not impinge upon this imaging zone 46.
The magnets 30 and 32 are configured and positioned so that the
C-arm 40 can pivot through at least about 60.degree. without
impinging upon the exclusion zone of the magnets, and more
specifically, so that the magnets 30 and 32 and their exclusions
zones 34 don't impinge upon the C-arm 40, the imaging beam source
36 and detector 38, or the imaging zone 46. Similarly, the C-arm
40, the imaging beam source 36 and detector 38, and the imaging
zone 46 do not impinge upon the magnets 30 and 32 and their
exclusions zones.
As shown in FIG. 1, rather than being in direct opposition,
180.degree. apart, the magnets 30 and 32, and more particularly the
first axes A of the magnets 30 and 32 intersect at an angle of
178.degree.. This additional 2.degree. permits the C-arm 40 to
travel a full 60.degree.. In the preferred embodiment, this travel
is preferably symmetric about the mid-sagittal plane, so that the
imaging system can provide left anterior oblique and right anterior
oblique images at 30.degree. from the mid-sagittal plane.
In some alternate constructions, the magnets 30 and 32 can be
mounted for movement (preferably in fixed relationship to each
other) about the operating region, to provide greater clearance for
the imaging system to thereby extend the pivot range of the C-arm
40.
As shown in FIG. 2, the imaging system can alternatively be
provided with a 20 cm.times.20 cm imaging plate. The smaller
imaging plate 42 results in a smaller imaging zone 46, and thus
permits a broader range of pivoting of the C-arm. Thus, as shown in
FIG. 2, the C-arm 40 can pivot over a range of 80.degree.,
preferably centered on the mid-sagittal plane.
A second embodiment of a magnetic navigation system constructed
according to the principles of this invention is shown
schematically in FIG. 3. The magnetic navigation system is adapted
for orienting a magnetically responsive medical device in a
selected direction within an operating region in a subject's body.
The second embodiment of the system comprises a support 122 for
supporting the subject, a magnet system 124 for applying a magnetic
field to the operating region 126, and an imaging system 128 for
imaging the operating region 126.
The subject support 122 is preferably a generally horizontal
surface for supporting a subject in a generally horizontal position
so that the operating region of the system is positioned within the
subject's body.
The magnet system 124 comprises at least two magnets 130 and 132
disposed on opposite sides of the operating region 126 for applying
a magnetic field sufficient for magnetic navigation in any selected
direction within the operating region. Magnets 130 and 132 are
preferably identical in construction. The strength of the field
required for magnetic navigation depends in part upon the magnetic
responsiveness of the device that is in the operating region 126,
which is typically provided with a magnetically responsive element,
such as a permeable or permanent magnet, or an electromagnetic
device. In this preferred embodiment, the magnets 130 and 132
preferably can provide a navigating field of at least about 0.08
Tesla in any selected direction in the operating region, however in
other embodiments the magnets 130 and 132 might be designed to
provide a magnetic field of at least about 0.06 Tesla, or even
lower as advances are made in improving the magnetic responsiveness
of the medical devices deployed in the operating region 126. The
magnets 130 and 132 are shaped and configured so that a change of
the position and/or orientation of the magnets within an exclusion
zone 134 permits the magnets to apply a magnetic field of the
desired strength in the operating region 126 in any selected
direction. A mechanism, not shown, is provided for repositioning
and reorienting the magnets 130 and 132 as required to provide the
desired field in the operating region. An example of one possible
device is disclosed in U.S. patent application Ser. No. 10/347,525,
for Magnetic Navigation System, incorporated herein by
reference.
Each of the magnets is preferably made up of a plurality of blocks
of magnetic material each of which is magnetized in one of a
plurality of predetermined magnetization directions to maximize the
magnet field in a particular direction at an operating point spaced
from the front face of the magnet. It has been empirically
determined that increments of 30.degree. in magnetization direction
are usually adequate, and any gains in field strength by obtained
by smaller increments are usually not cost-effective. Details of
the construction of such magnets are disclosed in U.S. Pat. No.
6,630,879, issued Oct. 7, 2003, An Efficient Magnet System for
Magnetically-Assisted Surgery, and in U.S. patent application Ser.
No. 10/056,227 for Rotating And Pivoting Magnet For Magnetic
Navigation, the disclosures of which are incorporated herein by
reference. The design of such magnets is disclosed in U.S. patent
application Ser. No. 10/082,715 for Magnets With Varying
Magnetization Direction and Method of Designing Such Magnets,
incorporated herein by references. A possible method of
manufacturing such magnets is disclosed in U.S. patent application
Ser. No. 10/704,195, for Method of Making A Compound Magnet,
incorporated herein by reference.
Each of the magnets 130 and 132 is sized and shaped to so that by
translating the magnet along a first axis A extending radially from
the operating region 26, pivoting of the magnet about a second axis
B perpendicular to the first axis A and extending substantially
through the center of mass of the magnet, and rotation of the
magnet about the first axis A, permits the magnets 130 and 132 to
apply a magnetic field to the operating region 126 in any selected
direction. The translation, pivoting, and rotation of the magnets
required to achieve the desired range of directions in the
operating region define the exclusion zone 134 into which the
imaging system 128 must not impinge so as to not interfere with the
proper operation of the magnet system 124. Pivoting the magnets at
or near their centers of mass helps reduce the size of the
exclusion zones 134, and also allows for more compact and less
expensive mechanisms for pivoting the magnets.
As shown in the Figures, the exclusion zone 134 is generally
cylindrical, with a frustoconical front face oriented toward the
operating region 126. The exclusion zone is preferably contained
within a protective shell, which protects the mechanism for moving
the magnet, and hides the movement from view.
The imaging system 128 comprises an imaging beam source 136 and an
imaging beam detector 138 disposed on opposite sides of the
operating region 126. The source 136 and the detector 38 are
carried on a C-arm 140 which can pivot about an axis generally
parallel to the longitudinal axis of the subject on the support
122, to change the imaging angle of the operating region 126. (Two
C-arms are shown in FIG. 3 in order to illustrate the range of
motion of the C-arm, but there is preferably only one C-arm used
for imaging the operating region 126).
The detector 138 is preferably a solid state amorphous silicon
x-ray receiving plate 142, which is substantially unaffected by the
magnetic fields created by the magnet system 124. These solid state
receiving plates are presently available in 20 cm.times.20 cm and
30 cm.times.30 cm sizes, with the 30 cm.times.30 cm size being
shown in FIG. 3. Of course some other size imaging plate could be
used. The imaging plate is disposed in a cover 144, so that the
width of the imaging zone extends 15 cm on either side of the
centerline between the imaging source 36 and the imaging receiver
138 for a 20 cm.times.20 cm plate, and so that the width of the
imaging zone extends 20 cm on either side of the centerline between
the imaging source 136 and the imaging receiver 38 for a 30
cm.times.30 cm plate.
The receiving plate 142 is preferably mounted for translation
toward and away from the operating region 126, in order to change
the resolution of the images of the operating region. The movement
of the receiving plate 142 and cover 144 define an imaging zone 146
extending generally from the operating region 126, centered along
the line between the source 136 and the receiver 138 through the
center of the operating region 126. As described below the magnet
system, and in particular the exclusion zones of the magnet system,
preferably does not impinge upon this imaging zone 146.
The magnets 130 and 132 are configured and positioned so that the
C-arm 140 can pivot through at least about 60.degree. without
impinging upon the exclusion zone of the magnets, and more
specifically, so that the magnets 130 and 132 and their exclusions
zones 134 don't impinge upon the C-arm 140, the imaging beam source
136 and detector 138, or the imaging zone 146. Similarly, the C-arm
140, the imaging beam source 136 and detector 138, and the imaging
zone 146 do not impinge upon the magnets 130 and 132 and their
exclusions zones.
As shown in FIG. 3, rather than being in direct opposition,
180.degree. apart, the magnets 130 and 132, and more particularly
the first axes A of the magnets 130 and 132 intersect at an angle
of 163.degree.. This additional 17.degree. permits the C-arm 140 to
travel a full 75.degree.. In the preferred embodiment, this travel
is preferably symmetric about the mid-sagittal plane, so that the
imaging system can provide left anterior oblique and right anterior
oblique images at 30.degree. from the mid-sagittal plane.
In some alternate constructions, the magnets 130 and 132 can be
mounted for movement (preferably in fixed relationship to each
other) about the operating region, to provide greater clearance for
the imaging system to thereby extend the pivot range of the C-arm
40. As shown in FIG. 4A and FIG. 4B, the imaging system can
alternatively be provided with a 20 cm.times.20 cm imaging plate.
The smaller imaging plate 142 results in a smaller imaging zone
146, and thus permits a broader range of pivoting of the C-arm.
Thus, as shown in FIGS. 4A and 4B, by permitting the magnets 130
and 132 to rotate (preferably in fixed relationship to each other)
+/-22.5.degree. about the operating region 126, the C-arm 40 can
pivot over a range of 120.degree., preferably centered on the
mid-sagittal plane. For simplicity, FIGS. 4A and 4B only show the
magnet 130, it being understood that magnet 132 moves in fixed
relationship with magnet 130, so that the angle between their
respective A axes remains 163.degree..
Magnet 30 is shown in more detail in FIG. 5. As shown in FIG. 5,
the magnet comprised of a plurality of sections or layers each
having a different magnetization direction than the adjacent
layers. As shown in FIG. 5, the magnet 30 has five layers 206, 208,
210, 212, and 214, each having a magnetization direction varying by
30.degree. from its adjacent layers. As shown in FIG. 6. the layers
206, 208, 210, 212, and 214 extend parallel to the axis B, which
extends through the center of mass 202 of the magnet 30. The magnet
has a flat, generally circular front face 200, surrounded by a
generally conical surface 204. The sides of the magnet 30 have a
plurality of flat faces to save the weight of material that does
not contribute significantly to the field strength of the
magnet.
The magnetization direction of the layers 206, 208, 210, 212, and
214 varies in a plane perpendicular to the axis B. The section 206
is magnetized in a direction downwardly and rearwardly as shown in
FIG. 6, at an angle of 60.degree. with respect to vertical. The
section 208 is magnetized in a direction downwardly and rearwardly
as shown in FIG. 6, at an angle of 30.degree. with respect to
vertical. The section 210 is magnetized in a direction downwardly
as shown in FIG. 1, at an angle of 0.degree. with respect to
vertical. The section 212 is magnetized in a direction downwardly
and forwardly as shown in FIG. 6, at an angle of 30.degree. with
respect to vertical. The section 214 is magnetized in a direction
downwardly and forwardly as shown in FIG. 6, at an angle of
60.degree. with respect to vertical.
The view of FIGS. 5 and 6 is an idealized design, and in actual
practice the magnet of substantially the desired shape could be
built up from smaller blocks of magnetic material approximating the
shape of the idealized design, as is known.
* * * * *