Gradient Coil Assembly Stray Field Reduction
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Solution Overview
Problem
Conventional gradient coil assemblies in MRI devices generate stray fields that induce eddy currents and heat in superconducting main field coil assemblies, leading to image quality disturbances and increased energy consumption due to the need for active shielding, which complicates device construction and efficiency.
Innovation Solution
Designing gradient coil assemblies without active shielding by limiting the longitudinal extension of gradient coil conductors to avoid stray fields on superconducting coils, using high-density return conductor segments, and omitting force compensation conductors to reduce inductance and heat generation, thereby minimizing stray fields and thermal losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If active shielding coils are added radially outside the gradient coils, then stray fields affecting superconducting coils are reduced, but device complexity and room requirements increase significantly
Solution Approach 1:
The patent extracts and removes the active shielding layer from the gradient coil assembly, designing gradient coils that inherently minimize stray fields without requiring additional shielding coils. This eliminates the complex radial shielding structure while maintaining protection of superconducting coils through optimized gradient coil conductor positioning and geometry.
Solution Approach 2:
The patent changes the geometric parameters and conductor distribution of the gradient coils themselves to minimize stray field generation at the location of superconducting coils. By optimizing the spatial arrangement and dimensions of gradient coil conductors, the system achieves reduced stray fields without adding shielding components.
2Object-affected harmful factors
If actively shielded gradient coil assemblies are used, then stray fields are reduced, but energy consumption increases due to additional current and voltage supplied to shielding conductors
Solution Approach 1:
The patent removes the active shielding layer entirely, eliminating the additional energy consumption associated with powering shielding conductors. The gradient coils are redesigned to inherently minimize stray fields through optimized conductor positioning, removing the need for separate energy-consuming shielding systems.
3Manufacturing precision
If gradient coil conductors are extended longitudinally to improve gradient performance, then gradient field quality improves, but stray fields on superconducting coils increase
Solution Approach 1:
The patent applies different conductor densities and configurations to different regions of the gradient coils. By optimizing the local conductor distribution in specific longitudinal and radial zones, the system achieves high gradient field quality in the imaging region while minimizing stray field generation in regions affecting superconducting coils.
Solution Approach 2:
The patent optimizes the spatial distribution of gradient coil conductors across multiple dimensions (longitudinal, radial, and azimuthal directions). By carefully controlling conductor positioning in three-dimensional space, the system achieves superior gradient performance while minimizing stray fields through sophisticated geometric optimization rather than simple longitudinal extension.
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
Significantly reduces stray fields and heat deposition on superconducting coils, eliminates the need for active shielding, and provides design freedom by reducing inductance and energy consumption, while maintaining image quality and allowing for more compact and efficient gradient coil assemblies.
Implementation Method 1
the gradient coils adapted to generate a linear magnetic field gradient in a corresponding, in particular cartesian, direction
Implementation Method 2
the main field (also main magnetic field BO) is generated by a superconducting main field coil assembly. To maintain the superconducting state
Implementation Method 3
the stray fields induce eddy currents in conductive material. Such eddy currents (and hence the stray fields) have two main effects
Implementation Method 4
the stray fields induce eddy currents in conductive material
Implementation Method 5
eddy currents produce ohmic heat
Data Source
AI summary
A magnetic resonance imaging (MRI) device may include a superconducting main field coil assembly inside a vacuum vessel of a cryogenic assembly and a cylindrical gradient coil assembly. The vacuum vessel may define a cylindric patient bore in which a homogeneity volume of a main field created by the superconducting main field coil assembly is located. The superconducting main field coil assembly includes multiple superconducting coils including at least two main superconducting coils located in opposing longitudinal end regions of the cryogenic assembly. The cylindrical gradient coil assembly may have at least one transversal gradient coil and may be located inside the cylindric patient bore. The transversal gradient coil may generate a gradient field perpendicular to a longitudinal direction of the patient bore. Conductors of the transversal gradient coil may only extend in a longitudinal conductor region between the two longitudinal end regions.