Methods and apparatus for compensating field inhomogeneities in magnetic resonance studies

1. A method of determining locations at which at least two magnetic articles are to be positioned during a magnetic resonance imaging procedure of at least one subject, the method comprising:

A) using a magnetic resonance imaging system, applying a magnetic field B 0 to a region that includes the at least one subject and does not include the at least two magnetic articles;

B) receiving first magnetic resonance information about the region in response to the applied magnetic field B 0 , the first magnetic resonance information relating at least in part to one or more magnetic field inhomogeneities in the region;

C) determining, based at least in part on the first magnetic resonance information, at least one first location proximate the at least one subject at which at least one paramagnetic article is to be positioned so as to at least partially compensate for the one or more magnetic field inhomogeneities;

D) determining, based at least in part on the first magnetic resonance information, at least one second location proximate the at least one subject at which at least one diamagnetic article is to be positioned so as to at least partially compensate for the one or more magnetic field inhomogeneities;

E) prior to steps C) and D), determining a plurality of magnetic induction fields U induced in the region by a plurality of reference magnetic articles each having a reference magnetic susceptibility, the plurality of reference magnetic articles being placed at a plurality of different positions N proximate to the at least one subject, wherein the steps C) and D) are performed based at least in part on the first magnetic resonance information and the plurality of magnetic induction fields U;

F) determining inhomogeneous magnetic field information T by comparing the static magnetic field B 0 and the first magnetic resonance information; and

G) determining, for the plurality of different positions N proximate to the at least one subject, a plurality of scaling values η which, when respectively multiplied by the reference magnetic susceptibility, represent a plurality of actual magnetic susceptibilities at the plurality of different positions N that facilitate compensation of the one or more magnetic field inhomogeneities,

wherein i is a first index, j is a second index, M is a number of positions r within the region, and determining the plurality of scaling values comprises finding η that minimizes

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2. The method of claim 1 , wherein determining the plurality of scaling values ηcomprises solving a matrix equation T=Uη for η.

3. The method of claim 1 , further comprising determining, for each of the plurality of different positions N corresponding to a non-zero value for η, an integer number of diamagnetic and/or paramagnetic elements that equals or most closely approximates a corresponding one of the plurality of actual magnetic susceptibilities.

4. The method of claim 3 , wherein the first location determined in the step C) is a first position of the N positions corresponding to a first non-zero value for η, and the second location determined in the step D) is a second position of the N positions corresponding to a second non-zero value for η.

5. The method of claim 1 , wherein the at least one subject comprises a rodent.

6. The method of claim 1 , wherein the at least one subject comprises a plurality of rodents.

7. The method of claim 1 , further comprising:

placing the at least one paramagnetic article in the at least one first location;

placing the at least one diamagnetic article in the at least one second location; and

performing magnetic resonance imaging of the at least one subject with the at least one paramagnetic article in the at least one first location and the at least one diamagnetic article in the at least one second location.