MRI Gradient Coil Layout for Force and Torque Balancing
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Solution Overview
Problem
Manufacturing electromagnets for MRI systems is challenging due to the need to generate magnetic fields with specific shapes while minimizing net force and torque, especially when subjected to non-uniform external magnetic fields.
Innovation Solution
A method for constructing electromagnet coils, such as gradient coils, using a stream function approach to optimize current density patterns, balancing force and torque, and accounting for non-uniform external magnetic fields, while ensuring efficient performance metrics like gradient strength and slew rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional force and torque balancing methods are used for gradient coils, then the design assumes a uniform external magnetic field, but in reality the external field is non-uniform causing significant net forces and torque on the coils
Solution Approach 1:
The patent modifies the design parameters by incorporating the actual non-uniform external magnetic field characteristics into the optimization process. The stream function is adjusted to account for radial and axial non-uniformities, transforming the design from uniform-field assumptions to realistic non-uniform field conditions, thereby resolving the contradiction between balancing accuracy and field adaptability
Solution Approach 2:
The patent performs preliminary characterization of the non-uniform external magnetic field before coil design. By measuring or calculating the actual field non-uniformities in advance, the design process can pre-compensate for these effects, enabling accurate force and torque balancing specifically tailored to the actual operating conditions
2Shape
If gradient coils are designed to produce linear magnetic fields with constant tangent, then the magnetic field shape requirement is met, but the coils experience significant net force and torque in non-uniform external fields
Solution Approach 1:
The patent applies different current density characteristics to different regions of the coil windings. By making the current density spatially variable rather than uniform, the coil can produce the required linear magnetic field shape in the imaging region while simultaneously compensating for forces and torques caused by non-uniform external fields in different spatial zones
Solution Approach 2:
The patent extends the design approach from two-dimensional coil geometries to three-dimensional windings with axial variation. By introducing axial dimensionality to the current density distribution, the design can independently optimize both the magnetic field linearity in the imaging plane and the force/torque balance along the axial direction
3Stability of the object's composition
If electromagnets are designed to operate with minimal net force and torque, then mechanical stability is improved, but the ability to generate precise magnetic field shapes may be compromised
Solution Approach 1:
The patent simultaneously optimizes multiple parameters including current density distribution, winding geometry, and turn density to achieve a Pareto-optimal solution that satisfies both mechanical stability requirements and magnetic field shape precision, rather than treating them as conflicting single-parameter optimizations
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
The method enables the production of electromagnets that maintain desired magnetic field shapes with reduced net force and torque, improving efficiency and image quality in MRI systems.
Implementation Method 1
Various electromagnets are integral parts of an MRI system. For example, they allow spatial encoding of the detected signals for the formation of spatial images
Implementation Method 2
When subjected to a strong magnetic field, the vector sum of the nuclear magnetic moments of a large number of atoms possessing a nuclear spin angular momentum, such as hydrogen, which is abundant in water and fat, will produce a net magnetic moment in alignment with the externally applied field. The resultant net magnetic moment can furthermore precess with a well-defined frequency that is proportional to the applied magnetic field
Data Source
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AI summary
A method of manufacturing electromagnet coils for use in a magnetic resonance imaging (MRI) system is provided. The electromagnet coils are located in a non-homogeneous external magnetic field. The method comprises forming a coil representation of a coil surface for the electromagnet coils; setting limits for performance metrics for the electromagnet coils including a magnetic field-shape metric and at least one of an external torque metric and an external force metric, the external torque metric and the external force metric based, respectively, at least in part on a torque and a force exerted on the electromagnet coil by the non-homogeneous external magnetic field; forming a performance functional, based on the coil representation and the performance metrics, for generating a current density pattern over the coil surface; optimizing the performance functional and generating a current density pattern based on the optimized performance functional; and obtaining coil windings.