Implantable Marker with a Leadless Signal Transmitter Compatible for Use in Magnetic Resonance Devices

• US 20080021308A1
• Filed: 09/27/2007
• Published: 01/24/2008
• 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: Hadford, Eric, Dimmer, Steven
• Granted Patent: US 8,857,043 B2
• Time in Patent Office: Days
• US Class Current: 600/424
• 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

1-40. -40. (canceled)

41. A method for imaging a target within a patient that has a marker implanted relative to the target, comprising:

subjecting the patient to a magnetic field in a magnetic resonance imaging device; and

providing a ferrite core in the marker having a volume such that force exerted on the marker by the magnetic field is less than gravitational force exerted on the marker.

42. The method of claim 41, wherein providing a ferrite core comprises placing a ferrite rod having a diameter not greater than approximately 0.5 mm in a coil having a plurality of turns, and inserting the ferrite rod and coil into a casing having an outer diameter not greater than approximately 2 mm.

43. The marker of claim 41 wherein providing a ferromagnetic core comprises placing a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm and a length of approximately 2 mm-12 mm in a coil.

44. The marker of claim 41 wherein providing a ferromagnetic core comprises placing a ferrite rod having a volume of approximately 0.5 mm3-19.0 mm3 into a coil.

45. A method of manufacturing a marker, comprising:

providing a ferromagnetic element;

positioning a coil of an inductor at least around a portion of the ferromagnetic element, wherein the coil comprises a plurality of windings of a conductor; and

encasing the ferromagnetic element and the coil in a casing, wherein the ferromagnetic element has a volume such that when the marker is in a magnetic resonance device 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 less than gravitational force exerted on the marker.

46. The method of claim 45 wherein the inductor further comprises a capacitor electrically coupled to the conductor and the casing comprising a barrier having an outer diameter of not greater than approximately 2.0 mm, and wherein providing the ferromagnetic element comprises providing a ferrite rod having a diameter not greater than approximately 0.5 mm.

47. The method of claim 45 wherein providing the ferromagnetic element comprises providing a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm and a length of approximately 2 mm-12 mm.

48. The method of claim 45 wherein providing the ferromagnetic element comprises providing a ferrite rod having a volume of approximately 0.5 mm3-19.0 mm3.

49. The method of claim 45 wherein providing the ferromagnetic element comprises providing a ferrite rod having a volume 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 with a field gradient of 3 T/m.

50. The method of claim 45 wherein providing the ferromagnetic element comprises providing a ferrite rod having a volume 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 with a field gradient of 3 T/m.

51. The method of claim 45 wherein 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 the casing has an outer diameter of approximately 1.5 mm-2.5 mm, and wherein providing the ferromagnetic element comprises providing a ferrite rod having a diameter of approximately 0.2 mm-0.7 mm.

52. The method of claim 45 wherein 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 the casing has an outer diameter of approximately 2 mm, and wherein providing the ferromagnetic element comprises providing a ferrite rod having a diameter of approximately 0.3 mm-0.5 mm,

53. (canceled)

54. A method of manufacturing a marker comprising:

providing a ferromagnetic element;

positioning a coil of an inductor at least around a portion of the ferromagnetic element, wherein the coil comprises a plurality of windings of a conductor; and

positioning the ferromagnetic element such that the radiographic and magnetic centroids of the marker are at least substantially coincident.