MRI Shim Tray Cooling Assembly for Magnetic Field Stability
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Solution Overview
Problem
The temperature increase in the outer vacuum chamber bore tube and shim elements of MRI apparatus due to gradient coil heating and induced electrical currents causes magnetic field drift, affecting the homogeneity and stability of the background magnetic field.
Innovation Solution
A shim tray system with thermally conductive materials and a channel system containing cooling fluid is mounted on the outer vacuum chamber bore tube, allowing for efficient heat transfer and temperature stabilization, using water as the preferred cooling fluid, which also acts as a thermal shield and electrical shield from oscillating magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gradient coils generate oscillating magnetic fields for imaging, then imaging function is achieved, but temperature increase in OVC bore tube and shim elements causes magnetic field drift
Solution Approach 1:
The cooling fluid channels are pre-installed within the shim tray and OVC bore tube structure before operation. The cooling system is prepared in advance to remove heat as it is generated, preventing temperature-induced magnetic field drift before it occurs.
Solution Approach 2:
Cooling fluid acts as an intermediary substance that absorbs heat from the gradient coils and shim elements through thermal conduction. The fluid circulates through channels in the shim tray and OVC bore tube, transferring excess thermal energy away from critical components to maintain magnetic field stability.
2Manufacturing precision
If shim elements are placed near imaging region to improve magnetic field homogeneity, then shimming effect is achieved, but shim elements are subjected to high forces and require compact fixation
Solution Approach 1:
The shim tray merges multiple functions into a single integrated component: it provides mechanical support and compact fixation for shim elements, incorporates cooling fluid channels for thermal management, and maintains structural integrity under high magnetic forces. This consolidation eliminates the need for separate fixation mechanisms.
Solution Approach 2:
The shim tray is constructed from composite or multi-material structure that combines materials with high mechanical strength to withstand magnetic forces, high thermal conductivity to efficiently transfer heat to cooling fluid, and precision machining capabilities to achieve required shimming accuracy.
3Reliability
If cooling fluid channels are integrated into shim tray and OVC bore tube, then temperature stabilization is achieved, but device complexity increases
Solution Approach 1:
The shim tray is designed as a multi-functional component that simultaneously provides mechanical support for shim elements, structural support for the OVC bore tube, and thermal management through integrated cooling fluid channels. This universality eliminates the need for separate cooling plates or thermal management components, reducing overall device complexity.
Solution Approach 2:
The cooling fluid channels are nested within the shim tray structure and OVC bore tube walls. The channels are embedded or hollowed out from the existing structural components rather than being added as separate external elements, allowing thermal management to be incorporated without significantly increasing external dimensions or structural complexity.
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 effectively stabilizes the temperature of the shim elements and the outer vacuum chamber bore tube, maintaining the homogeneity and stability of the magnetic field, reducing the need for active cooling control and enhancing the shimming effect.
Implementation Method 1
By making the shim tray and the rails at least partly of thermally-conductive material, the cooling fluid acts to cool the OVC bore tube, the shim tray and the shim elements
Implementation Method 2
The gradient coils themselves heat during operation, and their oscillating magnetic fields induce electrical currents in nearby conducting surfaces such as shims and OVC bore tube, causing warming of those surfaces
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
An arrangement for shimming a background magnetic field of a magnetic resonance imaging apparatus having an outer vacuum chamber (OVC) bore tube (1). Rails (8, 9) are provided on the OVC bore tube and shim trays (4) are mounted between respective rails.