NMR Gradient Shielding with Opposite Inductive Coupling Regions
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Solution Overview
Problem
Conventional nuclear magnetic resonance (NMR) apparatuses face challenges in designing a shielding configuration that effectively shields RF fields while minimizing coupling with the resonator/coil system, especially when dealing with multiple measuring frequencies and eigenresonances, leading to reduced shielding effectiveness and efficiency.
Innovation Solution
The proposed solution involves a shielding configuration with geometrically positioned regions that have opposite inductive couplings to the resonator system, featuring slots that completely or partially intersect the conducting layer, and capacitive elements to ensure minimal coupling, with the lowest eigenresonance below the NMR resonance frequency, allowing for negligible energy transfer from the resonator/coil system to the shielding configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional shielding configurations with slots and capacitive elements are used to block eddy currents, then gradient switching is enabled, but coupling to the resonator system increases and shielding effectiveness decreases
Solution Approach 1:
The shielding configuration is divided into multiple independent conductor elements arranged in a specific geometric pattern. Each element is segmented and positioned to create regions with opposite inductive couplings, which cancel each other out. This segmentation allows the shielding to block eddy currents while minimizing net coupling to the resonator system.
Solution Approach 2:
The conductor elements are arranged in an asymmetric geometric configuration rather than a simple symmetric pattern. This asymmetric arrangement creates regions with opposite inductive couplings that cancel each other, reducing the overall coupling to the resonator system while maintaining effective eddy current shielding.
2Object-affected harmful factors
If the shielding configuration is made impenetrable to RF fields, then RF shielding effectiveness improves, but coupling with the resonator system increases causing additional loss
Solution Approach 1:
Different regions of the shielding configuration have different local properties. The conductor elements are arranged to create regions with opposite inductive couplings in different spatial locations. This local variation in coupling properties allows the shielding to be effective against RF fields while the opposite couplings cancel out to minimize energy loss in the resonator system.
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 achieves minimal coupling between the resonator/coil system and the shielding configuration, even when an eigenresonance is near or at a measuring frequency, allowing for efficient operation with reduced additional loss, and is adaptable for various NMR frequencies.
Implementation Method 1
a shielding configuration which is positioned radially between the at least one coil/resonator system and the gradient system, wherein the shielding configuration comprises at least one electrically conducting layer with at least one continuous slot
Implementation Method 2
This is obtained through bridging the slots with capacitive elements which appear permeable to RF currents but which block the quasi DC currents during switching of the gradients
Implementation Method 3
additional currents only flow along the perpendicular slots. This increases the resistance for the shielding currents, thereby reducing the decay times
Data Source
AI summary
A nuclear magnetic resonance apparatus for generating a homogeneous static magnetic field in the z-direction, comprising a coil/resonator system, a gradient system, and a shielding configuration which is positioned radially between the coil/resonator system and the gradient system, wherein the shielding configuration comprises an electrically conducting layer with a slot, wherein the electrically conducting layer is disposed about the center of the shielding configuration to be axially symmetrical with respect to the z-axis, is characterized in that, in an axial section z1<z<z2 with z2−z1>L, containing at least 90% of the magnetic field energy of the coil/resonator system, the shielding configuration comprises at least one pair of regions which have a cylinder envelope shape, wherein the regions of each pair are each defined by two respectively closed limiting lines circulating about the z-axis, and wherein the two limiting lines of each region have a mutual axial separationa≤z2-z12from each other and are disposed on planes parallel to the xy plane, wherein the regions are geometrically positioned in such a manner that they have opposite inductive couplings for part of the eigenmodes of the shielding configuration. In this manner, coupling of energy from the resonator/coil system into the shielding configuration is prevented or minimized.