Passive Shim Tray With Open Channels For MRI Field Uniformity
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Solution Overview
Problem
Conventional shim trays have limited shim capacity, which restricts the ability to achieve a highly uniform magnetic field, leading to inadequate correction of spatial non-uniformities in magnetic resonance examination systems.
Innovation Solution
The shim tray design features open channels with insertion profiles at both ends, allowing for the secure placement and stacking of ferromagnetic shim elements, which maximizes available volume and enables the use of additional shim elements, including the use of plastic dummy plates to maintain pocket density and secure positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional closed shim pockets are used, then the structure is simple and easy to manufacture, but the shim capacity is limited
Solution Approach 1:
The shim tray is segmented into multiple independent open channels, each capable of holding shim elements. This segmentation allows for increased overall shim capacity while maintaining manageable individual channel structures that are easy to manufacture and assemble.
2Manufacturing precision
If more shim elements are added to increase shim capacity, then the magnetic field uniformity improves, but the risk of displacement due to magnetic forces increases
Solution Approach 1:
Insertion profiles are pre-formed in the channel walls at strategic positions. These profiles are prepared in advance to receive and secure shim elements, ensuring proper positioning and mechanical retention before the shim tray is subjected to strong magnetic forces during operation.
Solution Approach 2:
The insertion profiles act as intermediary mechanical features that mediate between the shim elements and the channel structure. These profiles provide a secure interface that prevents direct displacement of shim elements by magnetic forces while maintaining the intended spatial configuration.
3Volume of stationary object
If the shim tray is designed with open channels instead of closed pockets, then the available volume for shim elements increases, but the mechanical retention of shim elements becomes more challenging
Solution Approach 1:
The channel structure transitions from completely closed pockets to open channels with localized insertion profiles at specific positions. This local modification provides mechanical retention at critical points while maintaining open access and maximum volume throughout the rest of the channel space.
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 design enhances the shim capacity, resulting in a more accurate and uniform magnetic field, allowing for proper shimming of stronger magnetic fields and improved spatial encoding of magnetic resonance signals.
Implementation Method 1
so-called ferromagnetic shim elements (iron or steel) are mounted around the magnet bore
Implementation Method 2
The main magnetic field may have a field strength of 1.5, 3.0, 7.0T or even higher
Implementation Method 3
the end shim elements are held mechanically in position and can withstand the magnetic forces when the shim tray is slid in position
Implementation Method 4
magnetic forces of varying strength and orientations will act on the shim elements of the shim tray while slid longitudinally into position
Implementation Method 5
The shim trays may slide longitudinally (along the direction of the main magnetic field) into their proper position
Data Source
AI summary
A shim tray (10) for a main magnet system of a magnetic resonance examination system comprises a plurality of shim pockets (11), of which an individual shim pocket has side walls (21, 42) forming an open channel (11). Two opposite lateral side walls (21) have insertion profiles (22) to receive an end shim-element (13) at least one open channel's end. Essentially the entire volume of the channel of the shim pocket is available to hold passive shim elements.