Gradient Coil Current Adjustment for MRI Eddy Current Suppression
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Solution Overview
Problem
The challenge in MRI systems is to suppress eddy current magnetic fields generated due to relative deviations between the main and shield coils, which can deteriorate tomographic images and hinder high-speed imaging with high magnetic flux density requirements, while maintaining manufacturing accuracy and economic efficiency.
Innovation Solution
The implementation of current adjusting devices connected in parallel to the shield or main coils allows for independent current adjustments, enhancing the symmetry of the residual magnetic field and minimizing eddy currents, even with positional deviations between the coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the gradient magnetic field intensity is increased to improve imaging quality and speed, then the imaging performance is enhanced, but eddy currents are generated at the metal container part which deteriorate the tomographic image
Solution Approach 1:
The invention introduces a shield coil that generates a residual magnetic field opposite to the main coil's field. The eddy currents generated by the pulsed gradient magnetic field are converted into a beneficial residual magnetic field that cancels out harmful eddy currents at the metal container, transforming the harmful effect into a useful compensation mechanism
Solution Approach 2:
The shield coil acts as an intermediary element between the main coil and the metal container. It mediates the magnetic field interaction by generating a compensating residual magnetic field that prevents direct coupling between the pulsed gradient magnetic field and the metal container, thereby suppressing eddy current generation
2Object-affected harmful factors
If the main coil and shield coil are manufactured with high precision to minimize residual magnetic field, then eddy currents are suppressed, but manufacturing complexity and cost increase
Solution Approach 1:
The invention incorporates current adjusting devices that enable feedback control of the currents flowing through the main coil and shield coil. By measuring the actual residual magnetic field and adjusting the currents accordingly, the system compensates for manufacturing variations, allowing standard manufacturing tolerances to achieve the desired performance
Solution Approach 2:
The invention changes the electrical parameters (current magnitudes and phases) of the main coil and shield coil to optimize the residual magnetic field. By adjusting these parameters rather than relying solely on precise mechanical manufacturing, the system achieves effective eddy current suppression with standard manufacturing capabilities
3Ease of manufacture
If the relative position between main coil and shield coil deviates from design, then eddy current magnetic field increases deteriorating image quality, but manufacturing and assembly become simpler
Solution Approach 1:
The current adjusting devices provide feedback control that compensates for positional deviations between the main coil and shield coil. By adjusting the currents based on measured performance rather than relying on precise positioning, the system maintains effectiveness despite variations in relative coil positions
Solution Approach 2:
The invention introduces dynamic adjustability through the current adjusting devices, allowing the electrical characteristics of the coil system to be modified to compensate for static positional errors. This dynamic parameter adjustment compensates for the lack of precise mechanical positioning
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 effectively suppresses eddy current magnetic fields, ensuring high-quality imaging and meeting the demands for high-speed and high-resolution imaging while maintaining manufacturing efficiency and accuracy.
Implementation Method 1
a main coil (first coil) configured to generate a gradient magnetic field in an imaging region
Implementation Method 2
a shield coil (second coil) arranged on an opposite side of the imaging region across the main coil to suppress the residual magnetic field
Implementation Method 3
eddy currents are generated at a metal container part of the magnet device by the pulsed gradient magnetic field (residual magnetic field)
Data Source
AI summary
In a gradient magnetic field coil device including: a plurality of main coils generating in an imaging region of a magnetic field resonance imaging device a magnetic field distribution in which an intensity linearly inclines; and a plurality of shield coils, arranged on an opposite side of the imaging region across the main coils, suppressing residual magnetic field generated by the main coils on the opposite side. The plurality of main coils and the plurality of shield coils are connected in series. The device further includes a plurality of current adjusting devices, connected to the shield coils in parallel, independently adjusting currents flowing through the shield coils, respectively, to enhance symmetry of the residual magnetic field. The gradient magnetic field coil device is provided which can suppress generation of eddy current magnetic field even if there is a relative position deviation between the main coils and shield coils.