Magnetic resonance imaging apparatus

1. A magnetic resonance imaging apparatus comprising:

a static magnetic-field magnet configured to generate a static magnetic field in an imaging area in which a subject is to be placed;

a main coil that is provided on an inner side of the static magnetic-field magnet, and which is configured to apply a gradient magnetic field onto the subject when placed in the static magnetic field;

a shield coil that is provided between the static magnetic-field magnet and the main coil, and which is configured to shield the gradient magnetic field generated by the main coil;

a radio-frequency coil that is provided on an inner side of the main coil, and which is configured to apply a radio-frequency magnetic field onto the subject placed inside the static magnetic field;

a radio-frequency shield that is provided between the main coil and the radio-frequency coil, and which is configured to shield the radio-frequency magnetic field generated by the radio-frequency coil; and

an inner-layer cooling pipe that is provided on an inner side of the main coil and between the radio-frequency coil and the radio-frequency shield, and which is configured to pass a coolant in the inner-layer cooling pipe.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein the radio-frequency shield comprises an electrically conductive surface formed in a substantially drum shape, said shield being provided between the main coil and the radio-frequency coil, and including a slit that is formed at a position at which an eddy current would be produced by the main coil.

3. The magnetic resonance imaging apparatus according to claim 2 , wherein an insulating film formed from an insulating material is provided between the inner-layer cooling pipe and the radio-frequency shield.

4. The magnetic resonance imaging apparatus according to claim 2 , further comprising an outer-layer cooling pipe that is provided on an outer side of the main coil, and which is configured to pass a coolant in the inner-layer cooling pipe.

5. The magnetic resonance imaging apparatus according to claim 2 , wherein:

the inner-layer cooling pipe includes a plurality of cooling pipes arranged in parallel,

the inner-layer cooling pipe further includes a branching pipe that branches a coolant supplied from a chiller, and flows branched coolant into each of the cooling pipes, and

each of the cooling pipes and the branching pipe included in the inner-layer cooling pipe are connected to each other via a pipe that is formed from an insulating material.

6. The magnetic resonance imaging apparatus according claim 2 , wherein the inner-layer cooling pipe includes a first cooling pipe that passes a coolant in a first direction, and a second cooling pipe provided in parallel with the first cooling pipe, and

the second cooling pipe passes a coolant in a second direction opposite to the first direction in which the first cooling pipe passes the coolant.

7. The magnetic resonance imaging apparatus according to claim 1 , wherein an insulating film formed from an insulating material is provided between the inner-layer cooling pipe and the radio-frequency shield.

8. The magnetic resonance imaging apparatus according to claim 1 , further comprising an outer-layer cooling pipe that is provided on an outer side of the main coil, and which is configured to pass a coolant in the inner-layer cooling pipe.

9. The magnetic resonance imaging apparatus according to claim 8 , wherein the inner-layer cooling pipe is formed so as to have a pipe diameter smaller than a pipe diameter of the outer-layer cooling pipe.

10. The magnetic resonance imaging apparatus according to claim 8 , wherein:

the inner-layer cooling pipe and the outer-layer cooling pipe are each formed in a helical shape, and

the inner-layer cooling pipe is formed to have narrower intervals within its helical shape than the outer-layer cooling pipe.

11. The magnetic resonance imaging apparatus according to claim 8 , wherein:

the inner-layer cooling pipe and the outer-layer cooling pipe are each arranged in a helical shape, and

the inner-layer cooling pipe is formed so as to have a longer length in a direction along a helical axis than the outer-layer cooling pipe.

12. The magnetic resonance imaging apparatus according to claim 1 , wherein:

the inner-layer cooling pipe includes a plurality of cooling pipes arranged in parallel,

the inner-layer cooling pipe further includes a branching pipe that branches a coolant supplied from a chiller, and flows branched coolant into each of the cooling pipes, and

each of the cooling pipes and the branching pipe included in the inner-layer cooling pipe are connected to each other via a pipe that is formed from an insulating material.

13. The magnetic resonance imaging apparatus according to claim 12 , wherein a low dielectric substance is filled between each of the cooling pipes included in the inner-layer cooling pipe.

14. The magnetic resonance imaging apparatus according to claim 1 , wherein the inner-layer cooling pipe includes a first cooling pipe that respectively; and a coolant in a first direction, and a second cooling pipe provided in parallel with the first cooling pipe, and

the second cooling pipe respectively; and a coolant in a second direction opposite to the first direction in which the first cooling pipe respectively; and the coolant.

15. The magnetic resonance imaging apparatus according to claim 1 , wherein the inner-layer cooling pipe covers an inner surface of the radio-frequency shield.