Magnetic resonance imaging apparatus, static magnetic field homogeneity adjustment method, program, and computer

1. A static magnetic field homogeneity adjustment method for a magnetic resonance imaging apparatus in an imaging space of computing positions of a plurality of magnetic pieces separated from the imaging space through shimming computation with respect to a static magnetic field in the imaging space generated by a magnetic field generation device, and disposing the plurality of magnetic pieces at the positions obtained through the shimming computation, the method comprising:

an adjustment step of imposing restriction that a polarity of a magnetic field distribution generated in the imaging space by the magnetic pieces disposed at the positions is either positive or negative during the shimming computation, and adjusting the static magnetic field homogeneity,

wherein, in a case where a direction of magnetic moment of the magnetic pieces is parallel to a direction of the static magnetic field, positions of the magnetic pieces where the magnetic pieces generate a negative magnetic field distribution in the imaging space are selected.

2. A static magnetic field homogeneity adjustment method for a magnetic resonance imaging apparatus in an imaging space of computing positions of a plurality of magnetic pieces separated from the imaging space through shimming computation with respect to a static magnetic field in the imaging space generated by a magnetic field generation device, and disposing the plurality of magnetic pieces at the positions obtained through the shimming computation, the method comprising:

an adjustment step of imposing restriction that a polarity of a magnetic field distribution generated in the imaging space by the magnetic pieces disposed at the positions is either positive or negative during the shimming computation, and adjusting the static magnetic field homogeneity,

wherein, in a case where a direction of magnetic moment of the magnetic pieces is orthogonal to a direction of the static magnetic field, positions of the magnetic pieces where the magnetic pieces generate a positive magnetic field distribution in the imaging space are selected.

3. The static magnetic field homogeneity adjustment method for a magnetic resonance imaging apparatus according to claim 1 ,

wherein a boundary of selected positions of the magnetic pieces is a boundary at which positive and negative magnetic field distributions generated in the imaging space by the magnetic pieces satisfy the following equation:

3

⁢

M

⁢

⁢

z

·

Z

2

r

5

-

Mz

r

3

=.

where Z is a position in a static magnetic field direction (Z axis direction), r is a distance from magnetic moment, and Mz is magnetic moment [Am 2 ] in the static magnetic field direction (Z axis direction).

4. A static magnetic field homogeneity adjustment method for a magnetic resonance imaging apparatus in an imaging space of computing positions of a plurality of magnetic pieces separated from the imaging space through shimming computation with respect to a static magnetic field in the imaging space generated by a magnetic field generation device, and disposing the plurality of magnetic pieces at the positions obtained through the shimming computation, the method comprising:

an adjustment step of imposing restriction that a polarity of a magnetic field distribution generated in the imaging space by the magnetic pieces disposed at the positions is either positive or negative during the shimming computation, and adjusting the static magnetic field homogeneity,

wherein, in the adjustment step of disposing the magnetic pieces, each location from a bore opening of the magnetic field generation device is selected so that a magnetic piece is not disposed therein, and a negative region is estimated by evaluating magnetic field homogeneity predicted after the adjustment step is completed, and a magnetic piece amount used for the adjustment step is changed.

5. A magnetic resonance imaging apparatus comprising:

a magnetic field generation device that is provided with an electromagnet forming a static magnetic field in an imaging space; and

magnetic body holding members in which a plurality of depressions for accommodation of magnetic pieces for magnetic field adjustment are arranged on a surface portion of the electromagnet on the imaging space side,

wherein the density of an amount of magnetic pieces accommodated in a portion of each of the magnetic body holding members close to the imaging space is higher than the density of an amount of magnetic pieces in a portion thereof distant from the imaging space,

wherein the magnetic field generation device includes a cylindrical electromagnet forming the imaging space in a cylindrical inner space,

wherein the magnetic body holding members are distributed on an inner circumferential surface of the electromagnet, and each of the magnetic body holding members is provided with a plurality of depressions which are disposed in an axial direction and accommodate the magnetic pieces in a longitudinal direction, and

wherein the depressions are not formed over a set length from both ends in some of the magnetic body holding members.

6. The magnetic resonance imaging apparatus according to claim 5 ,

wherein, in some of the magnetic body holding members, at least a length of one end side where the depressions are not formed is shorter than a length of the other side.