Anisotropic nanoparticle amplification of magnetic resonance signals

• US 20060001423A1
• Filed: 06/03/2005
• Published: 01/05/2006
• Est. Priority Date: 06/07/2004
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Barbic, Mladen
• Granted Patent: US 7,202,667 B2
• Time in Patent Office: Days
• US Class Current: 324/300
• CPC Class Codes: G01R 33/20 involving magnetic resonance medical aspects A61B5/055; magnetic resonance gyrometers G01C19/60

Abstract

The reversible transverse susceptibility of magnetic nanoparticles is used to achieve magnetic flux amplification in magnetic resonance settings. Nanoparticles having substantially uniaxial or unidirectional magnetic anisotropy and a reversible transverse susceptibility in the presence of the high DC magnetic field provide either or both of an amplification of the generated signal of an inductive coil or the detected signal of an inductive coil.

Claims

1. A method for amplifying generated or detected alternating magnetic flux of an induction coil in the presence of a large DC magnetic field, the method comprising steps of:

disposing nanoparticles having substantially uniaxial or unidirectional magnetic anisotropy and a reversible transverse susceptibility at the level of the large DC magnetic field within the induction coil and with their nanoparticle magnetic easy axes substantially commonly aligned at an angle relative to the large DC magnetic field; and

establishing an alternating current within the induction coil.

2. The method of claim 1, wherein the nanoparticle easy axes are substantially commonly aligned relative to the large DC magnetic field at an angle to maximize amplification of the magnetic flux.

3. The method of claim 1, wherein the nanoparticles are carried by a substrate.

4. The method of claim 1, wherein the nanoparticles comprise γ

-Fe₂O₃ single magnetic domain nanoparticles.

5. The method of claim 1, wherein the nanoparticles comprise exchange biased nanoparticles having ferromagnetic cores and anti-ferromagnetic shells.

6. The method of claim 1, wherein the coil comprises an induction coil in a magnetic resonance system and the large DC magnetic field is the magnetic field of the magnetic resonance system.

7. In a magnetic resonance system having alternating current generation and detection in inductive coils disposed in the presence of a magnetic resonance DC bias field, an improvement comprising nanoparticles having substantially uniaxial or unidirectional magnetic anisotropy and a reversible transverse susceptibility at the level of the magnetic resonance DC bias field, the nanoparticles being disposed within the core of at least one of the inductive coils and positioned relative to the DC bias field to amplify magnetic flux in the at least one of the inductive coils.

8. The system of claim 7, wherein magnetic easy axes of the nanoparticles are substantially commonly aligned relative to the DC bias field at an angle to maximize amplification of the magnetic flux.

9. The system of claim 8, wherein the nanoparticles are carried by a substrate.

10. The system of claim 7, wherein the nanoparticles comprise γ

-Fe₂O₃ single magnetic domain nanoparticles.

11. The system of claim 7, wherein the nanoparticles comprise exchange biased nanoparticles having ferromagnetic cores and anti-ferromagnetic shells.

12. A magnetic resonance system, the system comprising:

DC magnetic generation means for generating a polarizing DC magnetic field;

inductive coil means for generating excitation time-dependent magnetic fields perpendicularly to the DC magnetic field and for detecting weak time-dependent sample generated magnetic fields; and

nanoparticle amplification means for amplifying at least one of the excitation time-dependent magnetic fields and the weak time-dependent sample generated magnetic fields.

13. The system of claim 12, wherein said nanoparticle amplification means amplifies both of the excitation time-dependent magnetic fields and the weak time-dependent sample generated magnetic fields.