Passive shim arrangement for nuclear magnetic resonance

• US 5,235,284 A
• Filed: 11/06/1992
• Issued: 08/10/1993
• Est. Priority Date: 07/07/1989
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Tahara, Yasuyuki, Ebihara, Keiichi, Takeuchi, Kazuaki, Yoshida, Naoji
• Primary Examiner(s): Tokar, Michael J.
• Application Number:
  US07/972,715
• Time in Patent Office: 277 Days
• Field of Search: 324/300, 324/307, 324/309, 324/318, 324/319, 324/320, 324/322, 128/653.3, 128/653.5, 335/301
• US Class Current: 324/320
• CPC Class Codes: G01R 33/3873 using ferromagnetic bodies ; Passive shimming

Abstract

A passive shim arrangement for a nuclear magnetic resonance apparatus has a plurality of nonmagnetic tubes disposed at predetermined positions around a common axis. Each tube is parallel to and uniformly distant from the axis. Magnetic shims are inserted into the tubes to correct components of the magnetic field.

Claims

1. A passive shim arrangement for increasing the uniformity of a magnetic field comprising:

a plurality of nonmagnetic shim holders disposed at a uniform distance from a first axis around a region in which a magnetic field is to be generated, the first axis coinciding with a central axis of the magnetic field; and

a plurality of pairs of magnetic shims, each pair of magnetic shims being detachably installable on one of the shim holders parallel to the first axis, each pair of shims comprising a first magnetic shim and a second magnetic shim disposed adjacent to and overlapping the first magnetic shim, the first and second magnetic shims having different dimensions.

2. A passive shim arrangement as claimed in claim 1, comprising a support cylinder coaxial with the first axis, wherein each of the shim holders is secured to the support cylinders.

3. A passive shim arrangement as claimed in claim 1, wherein each of the shim holders is a nonmagnetic tube extending parallel to the first axis and sized to receive a pair of shims.

4. A passive shim arrangement as claimed in claim 1, wherein the shim holders are installed at 16 locations about the first axis.

5. A passive shim arrangement as claimed in claim 4, wherein the shim holders are installed at angles of π

/2·

(±

1/2±

1/3±

1/4) and π

/2·

(±

1/2±

1/3±

1/4)+π

with respect to a second axis perpendicular and intersecting to the first axis.

6. A passive shim arrangement as claimed in claim 4, wherein a plurality of the shim holders is installed at each of the 16 locations.

7. A passive shim arrangement as claimed in claim 1, wherein each shim has a length and cross-sectional area and including a first group of pairs of shims comprising eight identical pairs of shims, and a second group of pairs of shims comprising eight identical pairs of shims, each pair of shims in the first and second groups comprising a first shim and a second shim disposed adjacent and overlapping the first shim, each of the first shims of the first group of shims having the same length as and a different cross-sectional area from the first shims of the second group of shims, and each of the second shims of the first group of shims having the same length as and a different cross-sectional area from the second shims of the second group of shims.

11. A passive shim arrangement as claimed in claim 1, wherein each of the first shims has a cross-sectional area S1 and each of the second shims has a cross-sectional area S2, each of the first shims has two end surfaces, the end surfaces of each of the first shims being respectively disposed at approximately 33.88°

and 146.12°

with respect to the first axis, each of the second shims has two end surfaces, the end surfaces of each of the first shims being respectively disposed at approximately 62.04° and

117.96°

with respect to the first axis, and S1/S2 is approximately 7.16.

12. A passive shim arrangement as claimed in claim 1, wherein each of the first shims has a cross-sectional area S1 and each of the second shims has a cross-sectional area S2, each of the first shims has two end surfaces, the two end surfaces of each of the first shims being respectively disposed at approximately 40.09°

and 106.57°

with respect to the first axis, each of the second shims has two end surfaces, the two end surfaces of each of the first shims being respectively disposed at approximately 40.09° and

73.43°

with respect to the first axis, and S1/S2 is approximately 1.25.

13. A passive shim arrangement as claimed in claim 1, wherein each of the first shims has a cross-sectional area S1 and each of the second shims has a cross-sectional area S2, each of the first shims having two end surfaces, the two end surfaces of each of the first shims being respectively disposed at approximately 39.69°

and 140.31°

with respect to the first axis, each of the second shims has two end surfaces respectively disposed at approximately 65.11° and

114.39°

with respect to the first axis, and S1/S2 is approximately 5.47.

8. A passive shim arrangement for increasing the uniformity of a magnetic field comprising:

a support cylinder surrounding a region in which a magnetic field is to be generated, the support cylinder having an axis coinciding with a central axis of the magnetic field;

a plurality of nonmagnetic shim holders secured to the support cylinder a uniform distance from the axis of the cylinder at angles of π

/2·

(±

1/2±

1/3±

1/4) and π

/2·

(±

1/2±

1/3±

1/4)+π

with respect to an axis perpendicular to and intersecting the axis of the cylinder; and

a plurality of pairs of magnetic shims, each pair of shims being detachably installable on each of the shim holders parallel to the axis of the support cylinder.

9. A passive shim arrangement as claimed in claim 8 wherein each of the shims has a length and each pair of shims comprises a first shim and a second shim having different lengths, the first and second shims in each pair being disposed adjacent each other.

10. A passive shim arrangement as claimed in claim 9, wherein each of the first shims is symmetric with respect to a single plane perpendicular to the axis of the support cylinder.