MR method for exciting the nuclear magnetization in a limited volume

• US 6,512,941 B1
• Filed: 11/22/2000
• Issued: 01/28/2003
• Est. Priority Date: 11/25/1999
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Lüdeke, Kai-Michael, Weiss, Steffen
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): Pass, Barry
• Application Number:
  US09/718,251
• Time in Patent Office: 797 Days
• Field of Search: 600/407, 600/411, 600/419-424, 324/318, 128/899
• US Class Current: 600/410
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/4838 using spatially selective suppression or saturation of MR signals

Abstract

The invention relates to a method of and a device for exciting the nuclear magnetization in a limited volume of an object to be examined, utilizing a microcoil (L) which is present in the volume and is attached, for example, to an interventional instrument during the formation of a magnetic resonance image of the object to be examined. The excitation of the nuclear magnetization is performed by at least one RF pulse whose frequency spectrum does not overlap the range of the spin resonance spectrum, so that no nuclear magnetization is excited outside the close range of the microcoil in the object to be examined. The microcoil, however, is provided with an active or passive circuit (for example, it is wired together with at least one capacitance (C) and a non-linear component (D1, D2) so as to form a non-linear resonant circuit) which locally generates an RF signal from the RF pulse. The RF signal overlaps the spin resonance frequency and causes excitation of the nuclear magnetization exclusively in the close range of the microcoil. After measurement and appropriate signal processing, this nuclear magnetization is used either to determine the position of the microcoil for reproduction in the MR image of the object to be examined or to form an MR image of the close range of the microcoil. The invention also relates to a medical instrument for use in conjunction with the method.

Claims

1. An MR method for exciting nuclear magnetization in a limited volume of an object to be examined, utilizing a microcoil which is present in said limited volume and is subject to at least one RF pulse, comprising:

generating the RF pulse with a frequency spectrum which does not overlap the Larmor frequency, so that a nuclear magnetization in the object to be examined is not excited thereby; and

generating an additional frequency spectrum by the microcoil under the influence of the RF pulse, wherein the additional frequency spectrum overlaps the Larmor frequency in such a manner that the nuclear magnetization is excited within a prescribed range of the microcoil present in said limited volume.

2. An MR method as claimed in claim 1, wherein the nuclear magnetization excited within the prescribed range of the microcoil is used to localize the microcoil.

3. An MR method as claimed in claim 2, further comprising:

generating a series of sequences to acquire an MR image of a volume of the object to be examined, wherein the volume of the object to be examined is larger than the prescribed range of the microcoil, wherein measurements required for the localization of the microcoil are performed so as to alternate with the excitation of the nuclear magnetization for the larger volume, wherein the localization is restricted to the prescribed range of the microcoil within the larger volume.

4. An MR method as claimed in claim 1, wherein the nuclear magnetization excited in the prescribed range of the microcoil is reproduced in an MR image.

5. An MR apparatus for carrying out the method in claim 1, including a magnet for generating a uniform, steady magnetic field whose strength defines the Larmor frequency, means for generating RF pulses, and means for receiving MR signals generated in the object to be examined, wherein the MR apparatus further includes a control device for controlling the frequency spectrum of the RF pulses in such a manner that no nuclear magnetization is excited thereby in the object to be examined, that the frequency spectrum of the RF pulse is modified, utilizing an active or passive circuit connected to the microcoil, in the prescribed range of the microcoil in such a manner that the modified frequency spectrum overlaps the Larmor frequency, and that MR signals arising in the prescribed range of the microcoil can be received by the receiving means.

6. An instrument for use in conjunction with a device as claimed in claim 5, wherein the microcoil is provided with non-linearly operating means.

7. An instrument as claimed in claim 6, wherein the microcoil is wired so as to form a non-linear resonant circuit.

8. An instrument as claimed in claim 7, wherein the resonant circuit includes two antiparallel connected diodes (D₁, D₂) which induce its non-linearity.

9. An instrument as claimed in claim 7, wherein the resonant circuit is attached to the instrument in the form of a miniaturized module.

10. An instrument for use in conjunction with a method as claimed in claim 1 wherein the instrument includes a microcoil provided with non-linearly operating means.

11. An instrument as claimed in claim 10, wherein the microcoil is wired so as to form a non-linear resonant circuit.

12. An instrument as claimed in claim 11, wherein the resonant circuit includes two antiparallel connected diodes (D₁, D₂) which induce its non-linearity.

13. An instrument as claimed in claim 11, wherein the resonant circuit is attached to the instrument in the form of a miniaturized module.