Warm Bore Cylinder Segmented Shielding for MRI Vibration Control
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Solution Overview
Problem
Magnetic Resonance Imaging (MRI) systems face challenges with vibrations caused by eddy currents in shielding layers, leading to mechanical failure, heating, and potential quenching of superconducting magnets, especially at higher magnetic fields and frequencies.
Innovation Solution
A warm bore cylinder assembly with an outer and inner conductive cylindrical wall separated by axial braces, which provides increased resistance to vibrations and allows for the placement of shim trays within the openings between the braces, reducing the transmission of pulsed magnetic field energy to the superconducting magnet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thin solid conductive sleeve is used as shielding, then the magnetic field can pass through while shielding against gradient coil pulses, but vibrations increase at higher magnetic fields and frequencies
Solution Approach 1:
The shielding structure is divided into multiple segments separated by axial gaps, with conductive material distributed in discrete segments rather than a continuous solid sleeve. This segmentation reduces the transmission of vibrational energy while maintaining magnetic shielding effectiveness through the distributed conductive elements.
Solution Approach 2:
Conductive material is strategically positioned at specific locations (axial gaps, radial positions) rather than uniformly distributed throughout. The conductive segments are placed at locations where they provide maximum shielding effectiveness while minimizing vibration transmission, creating localized zones of electromagnetic protection.
2Object-affected harmful factors
If eddy currents are increased to dissipate gradient magnetic field, then shielding effectiveness improves, but mechanical vibrations and heating increase
Solution Approach 1:
The continuous conductive path is broken into segmented sections with axial gaps. This segmentation limits the size of eddy current loops while maintaining sufficient electromagnetic shielding. The distributed conductive segments create multiple smaller eddy current paths that generate less heat overall compared to a single large continuous path.
Solution Approach 2:
Axial gaps and non-conductive materials act as intermediaries between conductive segments, interrupting the continuous eddy current path. These gaps serve as thermal and electrical isolators that prevent the propagation of heat and large eddy currents through the entire shielding structure, while still allowing magnetic field penetration.
3Strength
If shielding thickness is increased to reduce vibrations, then mechanical strength improves, but magnetic field transmission increases
Solution Approach 1:
Conductive material is concentrated at specific strategic locations where it provides maximum electromagnetic shielding with minimum overall thickness. The conductive segments are positioned at radial and axial locations optimized for blocking magnetic fields while maintaining structural integrity and minimizing vibration transmission paths.
Solution Approach 2:
The shielding structure combines conductive and non-conductive materials in a composite configuration. Conductive segments provide electromagnetic shielding, while non-conductive gap materials provide vibration isolation and thermal insulation. This composite approach achieves both magnetic field blocking and vibration reduction without requiring excessive thickness.
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 solution enhances imaging quality, reduces the risk of quenching, and improves safety and repair costs by minimizing vibrations and heat generated from gradient coils, while maintaining the strength of magnetic fields.
Implementation Method 1
The pulsing magnetic field of the gradient coil results in eddy currents being created in the shielding, such as the warm bore cylinder. The formation of these eddy currents allows the warm bore cylinder to help dissipate the magnetic field of the gradient coil
Implementation Method 2
the eddy currents interact with the ambient magnetic field and cause the warm bore cylinder (or other shielding) to mechanically vibrate at an increasing magnitude
Data Source
AI summary
A warm bore cylinder assembly having an outer wall, an inner wall, and a plurality of braces is provided. The outer wall is configured to define an inner exterior portion of a cryostat assembly. The outer wall is generally cylindrical, is made of a conductive material, and has an outer wall thickness. The inner wall is disposed radially inwardly of the outer wall. The inner wall is generally cylindrical, is made of a conductive material, and has an inner wall thickness. The braces extend along an axial direction defined by the outer wall and the inner wall. The plurality of braces are interposed between and join the outer wall and inner wall. The plurality of braces define openings disposed between adjacent braces.