Open-type magnetic resonance imaging apparatus

1. An open-type magnetic resonance imaging apparatus comprising:

a pair of static magnetic field magnets opposed to each other with respect to an imaging region; and

a pair of gradient magnetic field coils opposed to each other with respect to the imaging region, wherein

each static magnetic field magnet includes

a discoid magnetic pole configured to generate a static magnetic field in a Z axis direction in which the pair of static magnetic field magnets are opposed each other, and

an annular magnetic pole configured to generate a static magnetic field on an X-Y plane perpendicular to the Z axis direction, and

each gradient magnetic field coil includes

a Z coil configured to provide a magnetic field being gradient in the Z axis direction in the imaging region,

a magnetic material block configured to shield the discoid magnetic pole from a magnetic flux generated from the Z coil, and

a correction coil configured to shield the annular magnetic pole from the magnetic flux generated from the Z coil.

2. The open-type magnetic resonance imaging apparatus according to claim 1 , wherein

the each static magnetic field magnet includes:

an annular main coil configured to generate the static magnetic field in the Z axis direction; and

a shield coil configured to reduce a magnetic field outside the open-type magnetic resonance imaging apparatus.

3. The open-type magnetic resonance imaging apparatus according to claim 2 , wherein

the shield coil is arranged radially outside of the main coil and configured to generate a magnetic field which has an opposite polarity to a polarity of the magnetic field in the imaging region.

4. The open-type magnetic resonance imaging apparatus according to claim 2 , wherein

the correction coil is arranged radially outside of the Z coil, and

the correction coil is arranged at the same height in the Z axis direction as the Z coil.

5. The open-type magnetic resonance imaging apparatus according to claim 1 , wherein

the each gradient magnetic field coil includes:

an X coil configured to provide a magnetic field being gradient in an X axis direction in the imaging region; and

a Y coil configured to provide a magnetic field being gradient in a Y axis direction in the imaging region.

6. The open-type magnetic resonance imaging apparatus according to claim 5 , wherein

the correction coil is arranged radially outside of the Z coil, and

the correction coil is arranged at the same height in the Z axis direction as the Z coil.

7. The open-type magnetic resonance imaging apparatus according to claim 5 , wherein

the each X coil includes two coils which are arranged in the X axis direction with the Z axis interposed between the two coils, and

the each Y coil includes two coils arranged in the Y axis direction with the Z axis interposed between the two coils.

8. The open-type magnetic resonance imaging apparatus according to claim 1 , further comprising:

an RF coil configured to apply a radiofrequency electromagnetic pulse to the static magnetic field in the imaging region.

9. The open-type magnetic resonance imaging apparatus according to claim 8 , further comprising:

a receiver coil configured to receive a magnetic resonance-related signal from a test subject in response to application of a radiofrequency electromagnetic pulse to the test subject by the RF coil.

10. The open-type magnetic resonance imaging apparatus according to claim 1 , further comprising:

a movable bed configured to convey a test subject into the imaging region of the open-type magnetic resonance imaging apparatus.

11. The open-type magnetic resonance imaging apparatus according to claim 1 , wherein

the correction coil is arranged radially outside of the Z coil, and

the correction coil is arranged at the same height in the Z axis direction as the Z coil.

12. The open-type magnetic resonance imaging apparatus according to claim 1 , wherein

the each magnetic material block includes sheet magnetic materials which are stacked on each other in the Z axis direction and arranged side by side in a tile-like formation in an X axis direction and in a Y axis direction perpendicular to the Z axis direction.

13. The open-type magnetic resonance imaging apparatus according to claim 12 , wherein

the sheet magnetic material of the magnetic material block includes a silicon steel plate.

14. The open-type magnetic resonance imaging apparatus according to claim 12 , wherein

the magnetic material block has a thickness of 20 mm or more.

15. The open-type magnetic resonance imaging apparatus according to claim 1 , wherein

the Z coil is formed in an annular shape about the Z axis.