Conductive Refrigerator Shield for MRI Magnetic Field Stability

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Solution Overview

Problem

Cryogenic MRI magnet systems face challenges in maintaining a stable, homogeneous magnetic field due to moving magnetic materials in refrigerators, which cause interference and degrade MRI images, especially since conventional shielding methods are ineffective for components within the vacuum jacket.

Innovation Solution

An electrically conductive shield is placed in the vacuum space surrounding the moving magnetic parts of the refrigerator to reduce magnetic field disturbances by utilizing eddy currents that oppose changes in the magnetic flux, thereby minimizing the impact of moving magnetic materials on the magnetic field.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional shielding methods (Faraday cage, magnetically soft steel cage) are used, then high frequency and low frequency magnetic interference is reduced, but these methods are ineffective for components within the vacuum jacket where the refrigerator is situated

Engineering Contradiction:

Improvemagnetic field interferenceVSAvoidshielding effectiveness for internal components

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The patent introduces an electrically conductive shield as an intermediary component placed within the vacuum jacket surrounding the refrigerator. This shield mediates the magnetic field disturbances by conducting eddy currents that oppose the changing magnetic flux from moving magnetic parts, thereby protecting the MRI magnet from interference while being positioned where conventional shields cannot reach

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces conventional magnetic shielding materials (Faraday cage, magnetically soft steel) with an electrically conductive shield that operates on electromagnetic induction principles. Instead of using magnetic materials to redirect flux, the system uses electrical conductivity to generate opposing eddy currents, substituting a mechanical/magnetic shielding approach with an electromagnetic one

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If moving magnetic materials are used in refrigerator heat exchangers, then refrigeration function is achieved, but magnetic field disturbances degrade MRI image quality

Engineering Contradiction:

Improverefrigeration functionVSAvoidmagnetic field homogeneity

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The patent converts the harmful effect of moving magnetic materials into a beneficial one by surrounding them with an electrically conductive shield. The moving magnetic materials continue to perform their refrigeration function, but their magnetic field disturbances are now harnessed to induce eddy currents in the shield, which in turn create opposing fields that cancel out the disturbances, effectively converting the source of interference into a self-regulating shielding mechanism

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Temperature

If the refrigerator is placed within the vacuum jacket for effective cooling, then thermal contact is improved, but magnetic interference cannot be shielded by conventional means

Engineering Contradiction:

Improvethermal contact efficiencyVSAvoidmagnetic field interference

Core Design Contradiction:

TemperatureVSObject-affected harmful factors

Solution Approach 1:

The patent merges the thermal management function and magnetic shielding function into a single integrated solution. The electrically conductive shield is positioned within the vacuum jacket where it simultaneously serves as part of the thermal management system (allowing the refrigerator to be placed within the vacuum jacket for effective cooling) while providing magnetic field shielding through eddy current generation, thus combining two previously separate functions

Inventive Principle:

Principle #5Merging (Combining)

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

The electrically conductive shield effectively reduces magnetic field distortions caused by moving refrigerator components, enhancing the homogeneity and stability of the magnetic field, thus improving MRI image quality and extending the lifespan of the refrigerator by allowing for removable interfacing.

Implementation Method 1

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Data Source

PatentUS8171741B2Electrically conductive shield for refrigerator

Publication Date: 2012.05.08 SIEMENS HEALTHCARE LTD

AI summary

A cryogenic magnet system, comprising a cryogenic vessel (1) housing a magnet winding, a vacuum jacket (3) enclosing the cryogenic vessel and a refrigerator (4) at least partially housed within the vacuum jacket and thermally linked (6) to the cryogenic vessel. In particular, the system further comprises an electromagnetic shield.