Magnetic microstructures for magnetic resonance imaging

1. A magnetic resonance contrast agent comprising a plurality of contrast structures, each contrast structure consisting of:

(a) a magnetic material arranged as a pair of disks defining a space between a circular surface of each disk, wherein the centers of the circular surfaces of the disks are arranged along a same axis normal to the circular surfaces, wherein the circular surfaces are parallel to each other, and wherein each disk consists of one or more layers of a material selected from the group consisting of a ferromagnetic material, a paramagnetic material, a superparamagnetic material, an alloy, a magnetic compound, and a combination thereof; and

(b) a non-magnetic spacer arranged between the disks, wherein the non-magnetic spacer consists of a material selected from the group consisting of a metal, a photo-epoxy, a hydrogel, a polymer, a ceramic, a plastic, a photoresist, and a combination thereof;

wherein each contrast structure has a maximum dimension between about 10 nm and about 100 μm, and

wherein the space creates a spatially extended region contained within a near-field region of the contrast structure over which an applied magnetic field results in a homogeneous field, such that nuclear magnetic moments of a second material when arranged within said spatially extended region precess at a characteristic Larmor frequency, whereby the magnetic resonance contrast agent is adapted to emit a characteristic magnetic resonance signal of the magnetic material.

2. The magnetic resonance contrast agent of claim 1 , wherein the non-magnetic spacer is configured to change in geometry in response to the environment of the magnetic resonance contrast agent, and wherein the change in geometry changes the spacing between the disks, thereby changing the magnitude of the homogeneous field.

3. The magnetic resonance contrast agent of claim 2 , wherein the geometry of non-magnetic material changes in response to pH, temperature, or solution salinity.

4. The magnetic resonance contrast agent of claim 3 , wherein the non-magnetic material expands or contracts in response to a change in temperature, thereby increasing or decreasing the spacing between the disk-shaped magnetic portions.

5. The magnetic resonance contrast agent of claim 3 , wherein the non-magnetic material expands or contracts in response to a change in pH, thereby increasing or decreasing the spacing between the disks.

6. The magnetic resonance contrast agent of claim 3 , wherein the non-magnetic material consists of a hydrogel.

7. The magnetic resonance contrast agent of claim 2 , wherein geometry of the non-magnetic spacer changes in response to pressure, vibration, orientation changes, or torque.

8. The magnetic resonance contrast agent of claim 2 , wherein the non-magnetic spacer decomposes or disconnects from at least one of the disks in response to the environment.

9. The magnetic resonance contrast agent of claim 8 , wherein the decomposition or disconnection of the non-magnetic spacer disrupts the arrangement of the disks, thereby eliminating the homogeneous field.

10. The magnetic resonance contrast of claim 2 , wherein the non-magnetic spacer disintegrates in response to the environment.

11. A method of performing magnetic resonance imaging, comprising:

(a) providing the magnetic resonance contrast agent of claim 1 dispersed in a medium;

(b) illuminating the magnetic resonance contrast agent with an excitatory electromagnetic pulse; and

(c) detecting electromagnetic radiation emitted from the magnetic resonance contrast agent with a detection system.

12. The method of claim 11 , wherein the medium is a liquid.