Implantable marker with a leadless signal transmitter compatible for use in magnetic resonance devices

• US 7,289,839 B2
• Filed: 12/30/2002
• Issued: 10/30/2007
• Est. Priority Date: 12/30/2002
• Status: Active Grant

• Current Assignee: Varian Medical Systems Incorporated (Siemens AG)
• Original Assignee: Calypso Medical Technologies, Inc. (Siemens AG)
• Inventors: Dimmer, Steven C., Hadford, Eric
• Primary Examiner(s): Lacyk; John P.
• Application Number:
  US10/334,698
• Publication Number:
  US 20040127787A1
• Time in Patent Office: 1,765 Days
• Field of Search: 600/407, 600/410, 600/411, 340/572.4, 340/572.5, 340/573.1, 128897-898
• US Class Current: 600/407
• CPC Class Codes: A61B 2090/3975 active
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/06 Devices, other than using radiation, for detecting or locating foreign bodies for removing same A61B17/50 ; determining position of probes within or on the body of the patient
• CPC Class Codes: A61B 5/062 using magnetic field
• CPC Class Codes: Y10T 29/43 Electric condenser making
• CPC Class Codes: Y10T 29/4902 Electromagnet, transformer or inductor
• CPC Class Codes: Y10T 29/49073 by assembling coil and core
• CPC Class Codes: Y10T 29/49194 Assembling elongated conductors, e.g., splicing, etc.

Abstract

A leadless marker for localizing the position of a target within a patient. In one embodiment, the marker includes a casing, a resonating circuit, and a ferromagnetic element. The casing is configured to be positioned at a selected location relative to a target site in the patient; the casing, for example, can be configured to be permanently or semi-permanently implanted into the patient. The resonating circuit has an inductor within the casing comprising a plurality of windings of a conductor, but it does not have external electrical lead lines extending through the casing. The ferromagnetic element is at least partially within the inductor. The ferromagnetic element has a volume such that when the marker is in an imaging magnetic field having a field strength of 1.5 T and a gradient of 3 T/m, then the force exerted on the marker by the imaging magnetic field is not greater than gravitational force exerted on the marker.

Claims

1. A lead less marker for localizing the position of a target within a patient, comprising:

a casing configured to be positioned at a selected location relative to a target site in the patient;

a resonating circuit without external electrical lead lines extending through the casing, the resonating circuit having an inductor within the casing comprising a plurality of windings of a conductor; and

a ferromagnetic element at least partially within the inductor, the ferromagnetic element having a volume such that when the marker is in an imaging magnetic field having a field strength of 1.5 T and a gradient of 3 T/m, then force exerted on the marker by the imaging magnetic field is not greater than gravitational force exerted on the marker.

2. The marker of claim 1 wherein (a) the inductor further comprises a capacitor electrically coupled to the conductor, (b) the ferromagnetic element comprises a ferrite rod having a diameter not greater than approximately 0.5 mm, and (c) the casing has an outer diameter not greater than approximately 2 mm.

3. The marker of claim 1 wherein the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm and a length of approximately 2 mm-12 mm.

4. The marker of claim 1 wherein the ferromagnetic element comprises a ferrite rod having a volume of approximately 0.5 mm3-19.0 mm3.

5. The marker of claim 1 wherein the ferromagnetic element comprises a ferrite rod and the volume of the rod is less than a volume of ferrite that produces an artifact of 1500 mm2 in an image produced by a resonating magnetic field of approximately 1.5 T.

6. The marker of claim 1 wherein the ferromagnetic element comprises a ferrite rod and the volume of the rod is less than a volume of ferrite that produces an artifact of 400 mm2-1200 mm2 in an image produced by a resonating magnetic field of approximately 1.5 T.

7. The marker of claim 1 wherein (a) the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm, (b) the windings comprise a coil having an inner diameter of approximately 0.2 mm-0.8 mm and an outer diameter of approximately 0.8 mm-1.9 mm, and (c) the casing has an outer diameter of approximately 1.0 mm-2.5 mm.

8. The marker of claim 1 wherein (a) the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.3 mm-0.5 mm, (b) the windings comprise a coil having an inner diameter of approximately 0.3 mm-0.6 mm and an outer diameter of approximately 1.2 mm-1.9 mm, and (c) the casing has an outer diameter of approximately 2 mm.

9. The marker of claim 1 wherein (a) the inductor further comprises a capacitor at one end of the ferromagnetic element which is electrically coupled to the conductor, and (b) the marker further comprises a module at the other end of the capacitor which is symmetrical with respect to the capacitor.

41. The marker of claim 1 wherein the inductor further comprises a capacitor at one end of the ferromagnetic element which is electrically coupled to the conductor, and wherein the method further comprises providing a module at the other end of the ferromagnetic element which is symmetrical with respect to the capacitor.

10. A leadless implantable marker for localizing the position of a target within a patient, comprising:

a casing configured to be permanently implanted in the patient;

a ferromagnetic element in the casing, the ferromagnetic element having a volume such that when the marker is in an imaging magnetic field having a field strength of 1.5 T and a gradient of 3 T/m, then force exerted on the marker by the magnetic field is not greater than gravitational force exerted on the marker; and

a resonating circuit without external electrical lead lines extending through the casing, the resonating circuit having an inductor within the casing comprising a plurality of windings of a conductor around at least a portion of the ferromagnetic element, wherein the resonating circuit is configured to be energized by an excitation magnetic field and produce a response signal for identifying the position of the marker relative to a reference sensor assembly.

11. The marker of claim 10 wherein (a) the inductor further comprises a capacitor electrically coupled to the conductor, (b) the ferromagnetic element comprises a ferrite rod having a diameter not greater than approximately 0.5 mm, and (c) the casing has an outer diameter not greater than approximately 2 mm.

12. The marker of claim 10 wherein the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm and a length of approximately 2 mm-12 mm.

13. The marker of claim 10 wherein the ferromagnetic element comprises a ferrite rod and the volume of the rod is less than a volume of ferrite that produces an artifact of 1500 mm2 in an image produced by a resonating magnetic field of approximately 1.5 T.

14. The marker of claim 10 wherein the ferromagnetic element comprises a ferrite rod and the volume of the rod is less than a volume of ferrite that produces an artifact of 400 mm2-1200 mm2 in an image produced by a resonating magnetic field of approximately 1.5 T.

15. The marker of claim 10 wherein (a) the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm, (b) the windings comprise a coil having an inner diameter of approximately 0.2 mm-0.8 mm and an outer diameter of approximately 1.2 mm-1.9 mm, and (c) the casing has an outer diameter of approximately 1.5 mm-2.5 mm.

16. The marker of claim 10 wherein (a) the inductor further comprises a capacitor at one end of the ferromagnetic element which is electrically coupled to the conductor, and (b) the marker further comprises a module at the other end of the ferromagnetic element which is symmetrical with respect to the capacitor.

17. A wireless implantable marker for localizing the position of a target within a patient, comprising:

a ferromagnetic core having a length and a cross-sectional dimension normal to the length, wherein the cross-sectional dimension is not greater than 0.7 mm;

a resonating circuit comprising a conductive element having a plurality of windings surrounding at least a portion of the ferromagnetic core, wherein the resonating circuit is not coupled to external electrical leads; and

a casing around the ferromagnetic core and the resonating circuit.

18. The implantable marker of claim 17, wherein the casing has a cross-sectional dimension normal to the length of the ferromagnetic core not greater than approximately 2.5 mm.

19. The implantable marker of claim 17, wherein the ferromagnetic core has cross-sectional dimension defined by a diameter of approximately 0.25 mm to 0.65 mm.

20. The marker of claim 17 wherein (a) the resonating circuit further comprises a capacitor at one end of the ferromagnetic core which is electrically coupled to the conductive element, and (b) the marker further comprises a module at the other end of the ferromagnetic core which is symmetrical with respect to the capacitor.

21. A wireless implantable marker for localizing the position of a target within a patient, comprising:

a ferromagnetic core having an outer diameter not greater than approximately 0.7 mm;

a coil having windings positioned around at least a portion of the core; and

a casing around the core and the coil without external electrical leads projecting from the casing.

22. The marker of claim 21 wherein (a) a capacitor is electrically coupled to the coil, (b) the ferromagnetic core comprises a ferrite rod having a diameter not greater than approximately 0.5 mm, and (c) the casing has an outer diameter not greater than approximately 2 mm.

23. The marker of claim 21 wherein the ferromagnetic core comprises a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm and a length of approximately 2 mm-12 mm.

24. The marker of claim 21 wherein the ferromagnetic core comprises a ferrite rod and the volume of the rod is less than a volume of ferrite that produces an artifact of 1500 mm2 in an image produced by a magnetic resonance imager magnetic field of approximately 1.5 T.

25. The marker of claim 21 wherein (a) a capacitor is coupled to the coil and positioned at one end of the ferromagnetic core, and (b) the marker further comprises a module at the other end of the ferromagnetic core which is symmetrical with respect to the capacitor.

26. A leadless implantable marker for localizing the position of a target within a patient, comprising:

a ferromagnetic core having a volume that produces an image artifact not greater than 1500 mm2 in an image from a magnetic resonance device using a magnetic field strength of 1.5 T and a gradient of 3 T/m;

a resonating circuit comprising a conductive element having a plurality of windings surrounding at least a portion of the ferromagnetic core, wherein the resonating circuit is not coupled to external electrical leads; and

a casing enclosing the core and the resonating circuit.

27. The marker of claim 26 wherein (a) the resonating circuit further comprises a capacitor electrically coupled to the conducting element, (b) the ferromagnetic core comprises a ferrite rod having a diameter not greater than approximately 0.5 mm, and (c) the casing has an outer diameter not greater than approximately 2 mm.

28. The marker of claim 26 wherein the ferromagnetic core comprises a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm and a length of approximately 2 mm-12 mm.

29. The marker of claim 26 wherein the ferromagnetic core comprises a ferrite rod having a volume of approximately 0.5 mm3-19.0 mm3.

30. The marker of claim 26 wherein (a) the ferromagnetic core comprises a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm, (b) the windings comprise a coil having an inner diameter of approximately 0.2 mm-0.8 mm and an outer diameter of approximately 1.2 mm-1.9 mm, and (c) the casing has an outer diameter of approximately 1.5 mm-2.5 mm.

31. The marker of claim 26 wherein (a) the ferromagnetic core comprises a ferrite rod having a diameter of approximately 0.3 mm-0.5 mm, (b) the windings comprise a coil having an inner diameter of approximately 0.3 mm-0.6 mm and an outer diameter of approximately 1.2 mm-1.9 mm, and (c) the casing has an outer diameter of approximately 2 mm.

32. The marker of claim 26 wherein (a) the resonating circuit further comprises a capacitor at one end of the ferromagnetic core which is electrically coupled to the conductive element, and (b) the marker further comprises a module at the other end of the ferromagnetic core which is symmetrical with respect to the capacitor.

33. A leadless implantable marker for localizing the position of a target within a patient, comprising:

a ferromagnetic element having a first end and a second end;

a resonating circuit comprising an inductor having a plurality of windings of a conductor surrounding at least a portion of the ferromagnetic element and a capacitor at the first end of the ferromagnetic element;

a module at the second end of the ferromagnetic element, the module being symmetrical relative to the capacitor; and

a casing around the ferromagnetic element, the resonating circuit and the module.

34. The marker of claim 33 wherein (a) the ferromagnetic element comprises a ferrite rod having a diameter not greater than approximately 0.7 mm, and (b) the casing has an outer diameter not greater than approximately 2 mm.

35. The marker of claim 33 wherein the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.2 mm-0.5 mm and a length of approximately 2 mm-12 mm.

36. The marker of claim 33 wherein the ferromagnetic element comprises a ferrite rod having a volume of approximately 0.5 mm3-19.0 mm3.

37. The marker of claim 33 wherein the ferromagnetic element comprises a ferrite rod and the volume of the rod is less than a volume of ferrite that produces an artifact of 1500 mm2 in an image produced by a resonating magnetic field of approximately 1.5 T.

38. The marker of claim 33 wherein the ferromagnetic element comprises a ferrite rod and the volume of the rod is less than a volume of ferrite that produces an artifact of 400 mm2-1200 mm2 in an image produced by a resonating magnetic field of approximately 1.5 T.

39. The marker of claim 33 wherein (a) the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.2 mm-0.6 mm, (b) the windings comprise a coil having an inner diameter of approximately 0.2 mm-0.8 mm and an outer diameter of approximately 1.2 mm-1.9 mm, and (c) the casing has an outer diameter of approximately 1.5 mm-2.5 mm.

40. The marker of claim 33 wherein (a) the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.3 mm-0.5 mm, (b) the windings comprise a coil having an inner diameter of approximately 0.3 mm-0.6 mm and an outer diameter of approximately 1.2 mm-1.9 mm, and (c) the casing has an outer diameter of approximately 2 mm.