MRI Electromagnet Coil Optimization for Eddy Field Reduction
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Solution Overview
Problem
Manufacturing electromagnets for MRI systems that generate magnetic fields with desired shapes and minimize eddy fields is challenging, particularly for asymmetric gradient coils, which can disrupt the operation due to net torque and force.
Innovation Solution
A method for manufacturing electromagnet coils involves forming a coil representation, setting performance metric requirements, forming a performance functional, optimizing current density patterns, and obtaining coil windings to minimize eddy fields and achieve desired magnetic field shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If gradient coils are made asymmetric in the longitudinal direction to achieve desired magnetic field shapes, then magnetic field shape requirements are met, but eddy fields and net torque and force are generated which disrupt MRI system operation
Solution Approach 1:
The patent applies asymmetry by intentionally designing gradient coils with asymmetric current density distributions and asymmetric coil windings relative to the imaging region. This allows the coils to generate desired non-linear magnetic field shapes while the asymmetric configuration is optimized to minimize harmful eddy fields and torque through mathematical formulation and numerical optimization.
Solution Approach 2:
The patent changes physical parameters by formulating an objective function that incorporates multiple performance metrics including magnetic field linearity, eddy current minimization, and torque reduction. By adjusting parameters such as current density distribution, coil geometry, and winding patterns through numerical optimization, the system achieves optimal balance between field shape requirements and harmful effect minimization.
2Manufacturing precision
If gradient coils are designed to produce linear magnetic fields, then spatial encoding is achieved, but eddy fields are generated when coils are asymmetric
Solution Approach 1:
The patent formulates an objective function that simultaneously optimizes magnetic field linearity and eddy current minimization by adjusting parameters such as current density distribution and coil geometry. Numerical optimization techniques are used to find parameter sets that achieve both linear field production and reduced eddy fields.
Solution Approach 2:
The patent employs an iterative optimization process where the objective function evaluates both field linearity and eddy current levels, providing feedback for adjusting coil design parameters. This feedback loop continues until optimal parameters are found that satisfy both requirements.
3Ease of manufacture
If conventional coil manufacturing methods are used, then production is straightforward, but coils cannot simultaneously meet multiple performance metric requirements including magnetic field shape and eddy field minimization
Solution Approach 1:
The patent performs preliminary mathematical formulation and numerical optimization during the design phase to determine optimal current density patterns and coil winding configurations. By pre-calculating the optimal design parameters using computer algorithms, the complex performance requirements are translated into specific manufacturing specifications that can be produced using conventional techniques.
Solution Approach 2:
The patent replaces traditional trial-and-error mechanical coil design with computer-based mathematical optimization. An objective function incorporating multiple performance metrics is formulated and solved numerically to determine optimal coil parameters, substituting computational methods for conventional iterative prototyping and testing.
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 approach enables the construction of electromagnets that better meet performance metrics, reducing eddy fields and net torque, thereby improving the operation and image quality of MRI systems.
Implementation Method 1
Various electromagnets are integral parts of an MRI system. They allow the generation of the main magnetic field, the spatial encoding of the detected signals for the formation of spatial images, and correction of any irregularities. Electromagnets perform this function by generating magnetic fields with predetermined shapes.
Implementation Method 2
Gradient coils on the other hand are designed to generate magnetic fields that vary linearly with a constant tangent along the three perpendicular axis of the MRI systems' imaging volume.
Implementation Method 3
When the gradient coils are asymmetric in the longitudinal direction (z), for example, eddy fields and net torque and force can be generated which can disrupt the operation of an MRI system.
Data Source
AI summary
A method of manufacturing electromagnet coils for use in a magnetic resonance imaging (MRI) system is provided. The method comprises forming a coil representation of a coil surface for the electromagnet coils; setting a plurality of performance metric requirements for a plurality of performance metrics for the electromagnet coils, the plurality of performance metrics including a magnetic field-shape metric and an eddy-field metric; forming a performance functional, based on the coil representation and the plurality of performance metrics, for generating a current density pattern over the coil surface; optimizing the performance functional based on the plurality of performance metric requirements; generating a current density pattern over the coil surface based on the minimized performance functional; and obtaining coil windings from the current density pattern.