Dynamic Magnetic Field Shield for MRI Superconducting Magnet

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing MRI systems with regenerative refrigerants face challenges in maintaining a stable static magnetic field due to magnetization and reciprocating motions, leading to distortion and unevenness, which current shielding technologies struggle to address effectively, particularly in miniaturized designs.

Innovation Solution

A superconducting magnet system incorporating a vacuum container, radiation shield, and a dynamic magnetic field shield with an electric good conductor arranged along the motion axis of the regenerative refrigerant, aligned with the magnetic force lines, to limit eddy currents and prevent concentration at the upper and lower ends of the shield, thereby maintaining a stable magnetic field without increasing the shield's axial size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a regenerative refrigerant is used for cooling the superconducting coil, then the cooling function is improved, but the static magnetic field becomes distorted and uneven due to magnetization and reciprocating motions

Engineering Contradiction:

Improvecooling temperatureVSAvoidmagnetic field stability

Core Design Contradiction:

TemperatureVSStability of the object's composition

Solution Approach 1:

A dynamic magnetic field shield made of electric good conductor is introduced as an intermediary between the regenerative refrigerant and the static magnetic field. This shield intercepts and dissipates dynamic magnetic fields generated by the reciprocating refrigerant through eddy currents, preventing magnetic field distortion while allowing the refrigerant to perform its cooling function effectively

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If a dynamic magnetic field shield is added to shield the regenerative refrigerant, then magnetic field stability is improved, but the device complexity increases

Engineering Contradiction:

Improvemagnetic field stabilityVSAvoidshield structure complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

Instead of providing complete 360-degree shielding, the dynamic magnetic field shield is strategically positioned only at locations where dynamic magnetic fields are generated by the reciprocating refrigerant. This localized shielding approach reduces the overall shield volume and structural complexity while maintaining magnetic field stability in the critical imaging region

Inventive Principle:

Principle #3Local quality

3Volume of moving object

If the shield size is reduced for miniaturization, then the device size is decreased, but the shielding effectiveness may be compromised

Engineering Contradiction:

Improveshield volumeVSAvoidmagnetic field homogeneity

Core Design Contradiction:

Volume of moving objectVSStability of the object's composition

Solution Approach 1:

The shield design utilizes the axial dimension along the reciprocation path of the regenerative refrigerant, positioning the shield to intercept dynamic magnetic fields in this specific dimension. This dimensional targeting allows effective shielding with reduced overall shield volume, enabling miniaturization while maintaining magnetic field homogeneity in the imaging region

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 ensures a stable and homogeneous static magnetic field with reduced shield size, enhancing the miniaturization of MRI systems while maintaining high-quality imaging capabilities.

Implementation Method 1

a superconducting coil for circulating a persistent current to generate a static magnetic field

Methodology Applied

Scientific EffectSuperconductivity: Superconductivity

Implementation Method 2

a first regenerative refrigerant for reciprocating between the outer surface of the refrigerant container and an inner surface of the radiation shield to cool a vaporized refrigerant

Methodology Applied

Scientific EffectAdiabatic expansion: Adiabatic Cooling

Implementation Method 3

a dynamic magnetic field shield that is an electric good conductor and arranged around the first regenerative refrigerant along a motion axis of the first regenerative refrigerant

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Data Source

PatentUS7714574B2Superconducting magnet with refrigerator and magnetic resonance imaging apparatus using the same

Publication Date: 2010.05.11 HITACHI HIGH TECH CORP

AI summary

A superconducting magnet includes: a superconducting coil for generating a static magnetic field; a refrigerant container for containing the superconducting coil and a refrigerant; a vacuum container for holding the refrigerant container in a vacuum state; a radiation shield between the refrigerant container and the vacuum container; a refrigerator for re-liquidfying the refrigerant; and a dynamic magnetic field shield. The refrigerator includes: first and second regenerative refrigerants. The dynamic magnetic field shield is an electric good conductor and arranged around the first regenerative refrigerant along a motion axis of the first regenerative refrigerant, wherein a direction of the motion axis is aligned with a direction of a magnetic force line of the static magnetic field at the first regenerative refrigerant.