MRI superconductive magnet
An object of the present invention is to provide a MRI superconductive magnet enables sharp images representing patients' health states to be produced. [Means for Achieving the Object] A MRI superconductive magnet having a superconductive coil, a liquid vessel of liquid helium used to cool the superconductive coil, a heat shield to accommodate the liquid vessel therein, a vacuum chamber to accommodate the heat shield therein, a load supporting body for supporting the superconductive coil from the vacuum chamber and securing the superconductive coil, a second cold part of a multi-stage refrigerator for cooling a heat exchanger to condense evaporated helium gas, and a first cold part of the multi-stage refrigerator for cooling the heat shield, wherein a magnetic shield is provided from the first cold part of the multi-stage refrigerator to an outer periphery of the second cold part of the multi-stage refrigerator.
1. A MRI superconductive magnet having a superconductive coil, a liquid vessel containing the superconductive coil and liquid helium used to cool the superconductive coil, a heat shield to accommodate the liquid vessel therein, a vacuum chamber accommodating the heat shield therein, a load supporting body supporting the liquid vessel in the vacuum chamber, and a multi-stage refrigerator extending through said heat shield and into said liquid vessel, the multi-stage refrigerator having a first cold part and a second cold part for cooling a heat exchanger in the liquid vessel for condensing evaporated helium gas,
characterized in that:
a magnetic shield is provided inside of the heat shield extending from the first cold part of the multi-stage refrigerator to an outer periphery of the second cold part of the multi-stage refrigerator, and
a thermal anchor is provided, arranged to directly interconnect thermally the magnetic shield and the liquid helium in the liquid vessel,
wherein said magnetic shield is made of aluminum.
2. The MRI superconductive magnet according to claim 1 , wherein the magnetic shield is disposed in the heat shield through a joint made of different materials.
3. The MRI superconductive magnet according to claim 1 , wherein the magnetic shield is disposed between the heat shield and the superconductive coil.
4. The MRI superconductive magnet according to claim 1 , wherein the magnetic shield is thermally connected to the second cold part of the multi-stage refrigerator.
5. The MRI superconductive magnet according to claim 1 , wherein the multi-stage refrigerator is disposed at an end of the superconductive magnet, the magnetic shield extends from the first cold part of the multi-stage refrigerator and past the second cold part of the multi-stage refrigerator to the superconductive coil, and the magnetic shield is formed with a single fan-like plate or a plurality of fan-like plates.
6. The MRI superconductive magnet according to claim 1 , wherein the magnetic shield is accommodated in the vacuum chamber.