Shim Assembly Stray Field Shielding in MR Systems
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Solution Overview
Problem
Magnetic resonance (MR) systems face issues with stray fields generated by gradient coils causing eddy currents in main magnets, leading to increased temperature and potential quench, which requires more cooling medium and power, limiting system utilization and efficiency.
Innovation Solution
Incorporating a shim assembly located outside the gradient coil assembly to shield stray fields, improving the shielding effect and reducing the need for increased cooling capacity and power, while maintaining the efficiency of the shim assembly's homogeneity compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the gradient coil assembly generates a gradient magnetic field, then the imaging function is enabled, but a stray field is generated causing eddy currents in the main magnet
Solution Approach 1:
The patent introduces a shim assembly as an intermediary component positioned between the gradient coil assembly and the main magnet. This shim assembly acts as a mediator that actively compensates for and reduces the stray field generated by the gradient coil, thereby preventing eddy currents in the main magnet while preserving the gradient field's imaging function.
Solution Approach 2:
The shim assembly performs preliminary anti-action by pre-compensating for the stray field before it can significantly impact the main magnet. The system proactively counteracts the harmful stray field effects through active shimming, preventing the development of problematic eddy currents rather than addressing them after they occur.
2Temperature
If cooling capacity is increased to handle heat from eddy currents, then temperature control is improved, but system complexity and power consumption increase
Solution Approach 1:
The patent converts the harmful stray field into a beneficial effect by using the shim assembly to transform it into a compensatory field. Instead of merely managing the thermal consequences through complex cooling systems, the system actively transforms the stray field problem into a solution that reduces eddy current generation at its source, thereby reducing heat generation and simplifying cooling requirements.
3Object-affected harmful factors
If the shim assembly is placed inside the gradient coil assembly, then shielding effect is enhanced, but temperature increases affect the shim assembly performance
Solution Approach 1:
The patent repositions the shim assembly in a different spatial dimension relative to the gradient coil assembly. Instead of placing it inside where it would be exposed to high temperatures, the shim assembly is positioned on the outer surface or in the bore region, creating a spatial separation that protects it from thermal effects while maintaining its field-compensating function through its strategic geometric positioning.
4Reliability
If cooling medium consumption is increased, then magnet cooling effectiveness is improved, but operational efficiency and cost increase
Solution Approach 1:
The shim assembly enables the system to self-regulate stray field effects without requiring additional cooling resources. By actively compensating for stray fields, the system reduces eddy current generation and heat production, allowing the existing cooling system to maintain effectiveness without increased medium consumption, thereby preserving operational efficiency.
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 configuration reduces the impact of temperature increases on the shim assembly, enhances the shielding effect, and allows for a larger utilization range and improved scanning efficiency by minimizing the size and mass restrictions of the shim assembly.
Implementation Method 1
The shim assembly may be configured to at least partially shield a stray field which is generated by the gradient coil assembly and to which the magnet is subjected
Implementation Method 2
The magnet assembly may include a superconducting coil unit and a cryostat configured to cool the superconducting coil unit located inside the cryostat
Implementation Method 3
The cryostat may include a thermosiphon or a material of thermal conductivity configured to cool the magnet
Implementation Method 4
The gradient coil assembly may be configured to generate a gradient magnetic field
Implementation Method 5
The magnet assembly may be configured to generate a main magnetic field
Implementation Method 6
the cryostat may include a thermal shield layer, and the magnet may be located in a chamber enclosed by the thermal shield layer
Data Source
AI summary
The present disclosure may provide a magnetic resonance (MR) system. The MR system may include a magnet assembly, a gradient coil assembly, and a shim assembly. The magnet assembly may be configured to generate a main magnetic field. The magnet assembly may include a magnet and a cryostat configured to cool the magnet located inside the cryostat. The cryostat may form a bore. The gradient coil assembly may be configured to generate a gradient magnetic field. The gradient coil assembly may be located inside the bore. The shim assembly may be configured to at least partially shield a stray field which is generated by the gradient coil assembly and to which the magnet is subjected. The shim assembly may be located outside the gradient coil assembly.