Rotating and pivoting magnet for magnetic navigation
A magnet assembly comprising a magnet mounted for pivoting about a first axis spaced from the magnet, and rotating about a second axis that is perpendicular to and intersects with the first axis. The magnet comprising a plurality of segments each with a magnetization direction such that through a combination of pivoting and rotating the magnet projects a magnetic field in any direction at an operating point spaced from the front of the assembly. The segmented construction with segments of different magnetization directions allows small changes in the orientation of the magnet to substantially change the magnet field direction at a system operating point.
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This application is a continuation of U.S. patent application Ser. No. 10/056,227, filed Jan. 23, 2002, now U.S. Pat. No. 6,975,197, issued Dec. 13, 2005, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTIONThis invention relates to magnet medical procedures, and in particular to a magnet useful in navigating magnetic medical devices in the body.
BACKGROUND OF THE INVENTIONElectromagnets and permanent magnets have been developed for moving magnet medical devices in the body. Some magnets used in medical applications apply a gradient to pull magnet medical devices within the body. Other magnets used in medical applications simply apply a magnetic field in a selected direction to align magnetic medical devices in the selected direction. Still other magnets apply both a magnetic field and a magnetic gradient to simultaneously orient and move a magnetic medical device.
There are a number of important competing design considerations for magnets used in medical procedures. First and foremost is providing sufficient field strength or gradient to orient or move the magnetic device. Electromagnets and in particular superconducting electromagnets can create strong magnet fields and gradients, but they are expensive to construct and operate. Until recently, it was difficult to construct a permanent magnet that could provide a sufficiently strong and universally directed magnetic field and gradient at a distance sufficiently far from the magnet to be useful in medical procedures. Recently, a focused permanent magnet has been developed which can create useful magnet fields at sufficient distances from the magnet to be employed in magnet surgery. The magnet is comprised of a plurality of segments each magnetized in a direction to contribute to the desired magnetic property, for example field strength at an operating point spaced in front of a magnet. This magnet and its method of design are disclosed in co-pending, co-owned, U.S. patent application Ser. No. 09/546,840, filed Apr. 11, 2000, U.S. patent application Ser. No. 09/497,467, filed Feb. 3, 2000, the disclosures of which are incorporated herein by reference. This magnet has other useful properties in that field direction could be changed by a simple translation of the magnet. However, these magnets still had relatively large exclusion zones to accommodate the movement of the magnet. The large exclusion zone made access to the patient, and positioning of other medical equipment (particularly imaging equipment) in the procedure room difficult. Thus a second design criteria is to minimize the exclusion zone, to provide greater access to the patient for medical staff and equipment.
A third design criteria is to minimize the degrees of freedom of magnet motion to provide a universally directed magnetic field. The fewer degrees of freedom of magnet motion needed, the simpler the navigation, and the less expensive the apparatus for moving the magnet.
SUMMARY OF THE INVENTIONThe present invention relates to a magnet, and to a magnet system that is capable of generating useful magnet fields in virtually any direction, at distances from the magnet sufficient to conduct medical procedures in the patient's body. The magnet is designed so that a magnetic field can be generated in virtually any direction with a minimum amount of movement so that the exclusion zone—the zone from which the patient and other medical equipment and personnel cannot be located—or the inclusion zone—the zone that the magnet occupies—is minimized.
Generally the magnet of the present invention comprises a plurality of magnet segments each magnetized in direction to optimize the magnetic field at an operating point spaced from the magnet. The magnet is adapted to pivot about a first axis spaced behind the magnet, and to rotate about a generally horizontal axis. Through a combination of pivoting and rotating the magnet can project a magnetic field at the operating point in virtually any direction of sufficient strength to be useful. The shape of the magnet is determined to minimize the inclusion zone, which in the preferred embodiment is a horizontal cylinder, with a beveled edge on the forward face.
BRIEF DESCRIPTION OF THE DRAWINGS
A magnet constructed according to the principles of this invention is indicated generally as 20 in
The magnet 20 is preferably mounted for pivoting about a first axis A1, generally parallel to the vertical axis of the magnet. As shown in
A housing 50 for containing the magnet and structure for pivoting and rotating the magnet is shown in
As described above, the magnet 20 is adapted to pivot about an axis A1 generally behind the magnet. The radius of curvature of the generally cylindrical front face 22 corresponds to the distance between the front face and the pivot axis (15 inches in this preferred embodiment). The back face of the magnet is shaped in accordance with a surface of constant contribution to the magnetic field at the operating point. Material on such a surface contributes equally to the magnetic field at the operating point, regardless of its position on the surface. By selecting the appropriate surface of constant contribution to achieve the desired magnet size and strength, an excluding material that would lie beyond the surface, the weight of the magnet can be optimized for its selected magnetic properties. A constant contribution force can be calculated or plotted by maximizing the contribution to a particular magnet property at the magnet's operating point, for example the transfer field at the magnet's operating point, and determining the surface of points that contribute equally to the selected magnetic property. The superposition of several such surfaces of constant contribution is shown in
An important design criteria for the magnet 20 is its inclusion volume, which represents the combination of all of the volumes that the magnet occupies throughout all of the desired possible orientations of the magnet, i.e., all of the desired pivots and rotations. The inclusion volume of a magnet constructed according to the principles of this invention is shown in
Two magnets 20 can be mounted in opposition, so that their magnetic fields add, to provide a useful magnetic field at greater distances, for example to conduct cardiac procedures in the chest, where the application point of the magnetic field is necessarily far away from the magnet.
As shown in
While it is possible with the magnet assembly of the present invention to project a field at the application point in any direction, at sufficient strength to be useful, it may not always be possible to move smoothly and continuously from one magnetic field direction to another in the plane containing both directions. Thus when changing the field from a first direction to the second direction, it is possible that a field direction will temporarily swing out of the plane—a phenomenon known as coning. However, amount of coning depends upon the distance from the magnet, and as shown in
A magnetic surgery system incorporating a magnet system constructed according to the principles of the present invention is indicated generally as 100 in
A magnetic surgery system incorporating two magnet systems constructed according to the principles of the present invention is indicated generally as 200 in
Claims
1.-10. (canceled)
11. A method of making a magnet assembly that generates a magnetic field which is optimized at a predetermined operating point spaced from the center of the magnet, comprising:
- providing a plurality of segments of permanent magnet material configured to be arranged in a parallel manner to form a magnet assembly;
- forming a radius of curvature on the top face of each of the plurality of segments, such that the segments when assembled form a generally curved top surface having a radius of curvature that corresponds to the distance between the top face and an intended pivot axis of the assembled magnet;
- forming a generally curved back face of each of the plurality of segments, such that the segments when assembled form a shape in accordance with at least one select surface of constant contribution to the predetermined operating point, such that the segments of permanent magnet material will each contribute to the magnetic field generated at the predetermined operating point spaced from the center of the assembled magnet.
12. The magnet assembly of claim 1 wherein the magnetization direction of each of the plurality of magnets is preferably selected to generally optimize the magnetic field at the magnet operating point spaced from the center of the magnet assembly.
13. The magnet assembly of claim 1 wherein the at least one select surface of constant contribution is that which provides sufficient permanent magnetic material for the assembled segments to achieve the desired field strength and field gradient product, and excludes permanent magnet material beyond the surface to keep the weight of the magnet assembly low.
14. The magnet assembly of claim 1, wherein the back side of the plurality of segments forming the magnet assembly comprises a supposition of one or more surfaces of constant contribution.
15. The magnet assembly of claim 1 wherein the generated magnetic field is at least 0.4 Tesla at an application point at least 13 inches from the top surface of the magnet assembly, or at least 0.1 Tesla at an application point 7.5 inches from the top surface of the magnet assembly.
16. The magnet assembly of claim 1 wherein the predetermined operating point is in the range of two to 15 inches from the top face of the assembled magnet assembly.
17. The magnet assembly of claim 1 wherein the intended pivot axis is approximately 15 inches from the top face of the assembled magnet assembly.
18. The magnet assembly of claim 1 wherein the plurality of segments comprise a plurality of parallel bands.
19. The magnet assembly of claim 1, wherein the permanent magnet material of any segment along the back surface contributes equally to the magnetic field at the operating point.
20. The magnet assembly of claim 1, wherein the back side of the plurality of segments forming the magnet assembly comprises a supposition of one or more surfaces of constant contribution.
21. A method of making a magnet assembly that generates a magnetic field which is optimized at a predetermined operating point spaced from the center of the magnet, comprising:
- providing a plurality of segments of permanent magnet material that extend from top to bottom of a magnet assembly that is formed when the segments are arranged in a parallel manner;
- forming a radius of curvature on the top face of each of the plurality of segments, such that the segments when assembled form a generally curved top surface having a radius of curvature that corresponds to the distance between the top face and an intended pivot axis of the assembled magnet;
- forming a generally curved back face of each of the plurality of segments, such that the segments when assembled form a shape in accordance with at least one select surface of constant contribution to the predetermined operating point, such that the segments of permanent magnet material will each contribute to the magnetic field generated at the predetermined operating point spaced from the center of the assembled magnet; and
- assembling the plurality of segments to form the magnet assembly.
22. The magnet assembly of claim 11 wherein the magnetization direction of each of the plurality of magnets is preferably selected to generally optimize the magnetic field at the magnet operating point spaced from the center of the magnet assembly.
23. The magnet assembly of claim 11 wherein the at least one select surface of constant contribution is that which provides sufficient permanent magnetic material for the assembled segments to achieve the desired field strength and field gradient product, and excludes permanent magnet material beyond the surface to keep the weight of the magnet assembly low.
24. The magnet assembly of claim 11, wherein the back side of the plurality of segments forming the magnet assembly comprises a supposition of one or more surfaces of constant contribution.
25. The magnet assembly of claim 11 wherein the generated magnetic field is at least 0.4 Tesla at an application point at least 13 inches from the top surface of the magnet assembly, or at least 0.1 Tesla at an application point 7.5 inches from the top surface of the magnet assembly.
26. The magnet assembly of claim 11 wherein the predetermined operating point is in the range of two to 15 inches from the top face of the assembled magnet assembly.
27. The magnet assembly of claim 11 wherein the intended pivot axis is approximately 15 inches from the top face of the assembled magnet assembly.
28. The magnet assembly of claim 11 wherein the plurality of segments comprise a plurality of parallel bands.
29. The magnet assembly of claim 11, wherein the permanent magnet material of any segment along the back surface contributes equally to the magnetic field at the operating point.
30. The magnet assembly of claim 11, wherein the back side of the plurality of segments forming the magnet assembly comprises a supposition of one or more surfaces of constant contribution.
Type: Application
Filed: Jan 8, 2007
Publication Date: Jan 24, 2008
Applicant:
Inventor: Francis Creighton (St. Louis, MO)
Application Number: 11/650,856
International Classification: H01F 7/02 (20060101);