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

• US 7,778,687 B2
• Filed: 12/23/2003
• Issued: 08/17/2010
• 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): Winakur; Eric F
• Assistant Examiner(s): Rozanski; Michael T
• Application Number:
  US10/745,097
• Publication Number:
  US 20040138554A1
• Time in Patent Office: 2,429 Days
• Field of Search: 600/419, 600/423, 128/899, 340/572.5
• 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. A marker for localizing a target within a patient, comprising:

a ferromagnetic element and a plurality of windings around the ferromagnetic element for producing a magnetic field having a magnetic centroid; and

a casing around the ferromagnetic element and the windings, the casing being configured to be positioned relative to a target of the patient, and an element including a radiographic element of the marker having a radiographic centroid within the casing and substantially coincident with the magnetic centroid.

2. The marker of claim 1 wherein the ferromagnetic element and the windings define the magnetic centroid.

3. The marker of claim 1 wherein the radiographic element further comprises a capacitor electrically connected to the windings.

4. The marker of claim 1 further comprising:

the radiographic element having a capacitor electrically connected to the windings; and

the element further including a module having similar radiographic characteristics as the capacitor in a radiographic image.

5. The marker of claim 4 wherein the capacitor is located at one end of the ferromagnetic element and the module is located at another end of the ferromagnetic element.

6. The marker of claim 5 wherein the capacitor and the module have the same characteristics in X-ray images.

7. The marker of claim 5 wherein the capacitor and the module have the same characteristics in CT images.

8. The marker of claim 5 wherein the capacitor and the module are symmetrical relative the radiographic centroid.

9. The marker of claim 5 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.

10. A marker for localizing a target within a patient, comprising:

a ferromagnetic element;

a plurality of windings around the ferromagnetic element for producing a resonating magnetic field having a magnetic centroid; and

an element at a location relative to the ferromagnetic element, wherein the element is arranged so that a radiographic element of the marker has a radiographic centroid substantially coincident with the magnetic centroid.

11. The marker of claim 10 further comprising the radiographic element having a capacitor electrically connected to the windings, wherein the element comprises a module having similar radiographic characteristics as the capacitor.

12. The marker of claim 10 further comprising the radiographic element having a capacitor electrically connected to the windings and located at one end of the ferromagnetic element, and the element comprises a module having similar radiographic characteristics as the capacitor and located at another end of the ferromagnetic element.

13. The marker of claim 12 wherein the capacitor and the module are symmetrical relative to the radiographic centroid.

14. The marker of claim 10 wherein:

the ferromagnetic element comprises a ferrite rod having a diameter not greater than approximately 0.7 mm; and

the marker further comprises a casing around the ferromagnetic element and the windings that has an outer diameter not greater than approximately 2 mm.

15. The marker of claim 10 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.

16. The marker of claim 10 wherein the ferromagnetic element comprises a ferrite rod having a volume of approximately 0.5 mm³-19.0 mm³.

17. 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.

18. 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.

19. The marker of claim 10 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 marker further comprises a casing around the ferromagnetic element and the windings that has an outer diameter of approximately 1.5 mm-2.5 mm.

20. The marker of claim 10 wherein;

the ferromagnetic element comprises a ferrite rod having a diameter of approximately 0.3 mm-0.5 mm;

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 marker further comprises a casing around the ferromagnetic element and the windings that has an outer diameter of approximately 2 mm.

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

a ferromagnetic element, wherein the ferromagnetic element has a volume such that when the marker is in an imaging magnetic field having a 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;

a plurality of windings around the ferromagnetic element for producing a resonating magnetic field having a magnetic centroid; and

a casing around the ferromagnetic element and the windings, the casing being configured to be positioned relative to a target of the patient, and an element including a radiographic element of the marker having a radiographic centroid within the casing and substantially coincident with the magnetic centroid.

22. The marker of claim 21 wherein the ferromagnetic element and the windings define the radiographic centroid.

23. The marker of claim 21 further comprising the radiographic element having a capacitor electrically connected to the windings.

24. The marker of claim 21 further comprising:

the radiographic element having a capacitor electrically connected to the windings; and

the element including a module having similar radiographic characteristics as the capacitor in a radiographic image.

25. The marker of claim 24 wherein the capacitor is located at one end of the ferromagnetic element and the module is located at another end of the ferromagnetic element.

26. The marker of claim 25 wherein the capacitor and the module have the same characteristics in X-ray images.

27. The marker of claim 25 wherein the capacitor and the module have the same characteristics in CT images.

28. The marker of claim 25 wherein the capacitor and the module are symmetrical relative to the radiographic centroid.

29. A method of localizing a target of a patient, comprising:

imaging a radiographic element of a marker implanted in the patient using a radiographic imaging modality, the marker having an element at a location relative to a ferromagnetic core, the ferromagnetic core has a plurality of windings around the core capable of producing a resonating magnetic field having a magnetic centroid, and wherein the element is arranged so that the radiographic element of the marker further has a radiographic centroid configured to be within a casing and substantially coincident with the magnetic centroid;

generating a magnetic excitation field that causes the marker to produce the resonating magnetic field; and

sensing the resonating magnetic field to locate the marker.