MRI Radiation Shield Surface Structure Against Eddy Current Damage
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Solution Overview
Problem
The radiation shield in MRI apparatuses is susceptible to damage and deformation due to eddy currents induced by gradient-coil heating, leading to increased heat transfer and evaporation of liquid helium, which compromises the integrity and efficiency of the system.
Innovation Solution
The radiation shield is designed with multiple concavities and/or convexities on its surface, particularly on the gradient coil side, with a polygonal or circular cross-section to enhance strength and rigidity, using non-magnetic materials like aluminum or copper alloys to maintain high heat transfer performance and reduce eddy current effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the radiation shield is made with high electrical conductivity metal material, then radiation shielding performance is improved, but the shield becomes susceptible to damage from eddy currents and electromagnetic forces
Solution Approach 1:
The radiation shield is divided into multiple segments or panels that are electrically isolated from each other. This segmentation breaks the continuous conductive path, thereby reducing eddy current loops while maintaining radiation shielding effectiveness through the cumulative effect of multiple segments.
Solution Approach 2:
Different regions of the radiation shield have different electrical conductivity properties. High conductivity materials are used in areas where radiation shielding is critical, while regions prone to high eddy current exposure use materials with lower conductivity or include insulating features to reduce electromagnetic force damage.
2Stability of the object's composition
If the radiation shield rigidity is increased to prevent deformation, then structural stability is improved, but heat transfer to the helium vessel increases
Solution Approach 1:
The radiation shield incorporates a three-dimensional thermal isolation structure, such as thermal vacuum gaps or insulating support legs, that extend in the radial dimension between the shield and helium vessel. This dimensional approach provides mechanical support for rigidity while maintaining thermal isolation through the extended path.
Solution Approach 2:
The radiation shield assembly uses composite construction combining high-rigidity structural components with low thermal conductivity materials. For example, the shield may be supported by ceramic or composite insulators that provide both mechanical stability and thermal isolation, preventing heat transfer while maintaining structural integrity.
3Object-affected harmful factors
If the radiation shield is cooled more effectively to reduce helium evaporation, then radiation shielding performance is improved, but eddy current heating increases
Solution Approach 1:
The cooling system is designed to specifically target the inner surface of the radiation shield that faces the helium vessel, while the outer surface exposed to gradient coil heating is thermally isolated or actively heated. This differential temperature management converts the harmful temperature gradient into a beneficial configuration where the critical inner surface remains cold for radiation shielding while the outer surface can tolerate higher temperatures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively prevents radiation shield damage, reduces helium evaporation, and minimizes eddy current interference, ensuring stable operation and prolonged system efficiency.
Implementation Method 1
a radiation shield disposed between the helium vessel and the vacuum vessel... for reducing evaporation amount of liquid helium in the helium vessel caused by radiation
Implementation Method 2
a large eddy current I which is caused by gradient-coil induced heating (GCIH) attributable to operation of the gradient coil
Implementation Method 3
a large eddy current I which is caused by gradient-coil induced heating (GCIH) attributable to operation of the gradient coil
Implementation Method 4
gradient-coil induced heating (GCIH) attributable to operation of the gradient coil
Data Source
AI summary
A static magnetic field magnet according to any of embodiments includes: a superconducting coil generating a static magnetic field; and a radiation shield surrounding the superconducting coil. In the static magnetic field magnet, at least a surface on a gradient coil side of the radiation shield includes a peripheral portion that forms multiple concavity and/or convexity. Further, In the static magnetic field magnet, a shape of a cross-section perpendicular to a depth direction of each of the multiple concavity and/or convexity formed by the peripheral portion is polygonal or circular. It is preferable that the peripheral portion is configured to form the multiple concavity and/or convexity in a straight line.