Gradient Coil Design Suppressing Error Magnetic Fields
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Solution Overview
Problem
Conventional gradient coils in MRI devices generate error magnetic fields due to current flow through connecting and return lines, leading to eddy currents that distort cross-sectional images, compromising image quality.
Innovation Solution
A gradient coil device with a first coil generating a linear magnetic field and a second coil that suppresses magnetic field leakage, featuring a connecting line width that is four to ten times the return line width, and a coil pattern with a bypassed interval to minimize error magnetic fields, along with a method to calculate and correct error magnetic fields using finite element analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional spiral coil pattern with connecting lines and return lines is used, then current can flow through multiple main lines to generate gradient magnetic field, but error magnetic fields are generated causing eddy currents that distort images
Solution Approach 1:
The patent extracts and removes the problematic return lines from the coil configuration. By eliminating the return lines that cause error magnetic fields, the invention maintains the gradient magnetic field generation capability through the main lines while eliminating the source of harmful eddy currents in the static-magnetic-field coil devices.
Solution Approach 2:
The patent segments the coil into distinct functional components: main lines that generate the desired gradient magnetic field and separate connecting lines that minimize interference. This segmentation allows the main lines to perform their primary function while the connecting lines are optimized to reduce error magnetic field generation.
2Productivity
If connecting lines are added to connect adjacent main lines, then current flow path is established for multi-line coils, but error magnetic fields are generated at the intersection with return lines
Solution Approach 1:
The patent applies different characteristics to different parts of the coil: the main lines are designed with specific properties to generate the gradient magnetic field, while the connecting lines are designed with different properties (such as different widths or positions) to minimize error magnetic field generation at their intersections with return lines.
3Manufacturing precision
If coil pattern is optimized to reduce error magnetic fields, then image quality improves, but coil design complexity increases
Solution Approach 1:
The patent optimizes specific parameters of the coil design, such as the width ratio between connecting lines and return lines, or the positioning of connecting lines relative to return lines. By adjusting these parameters within certain ranges, the invention reduces error magnetic fields and improves image quality while maintaining manageable design complexity.
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 solution effectively suppresses error magnetic fields and eddy currents, enhancing the quality of cross-sectional images by optimizing the coil pattern design to reduce magnetic field interference.
Implementation Method 1
a first coil which generates a linear magnetic field distribution at an imaging region
Implementation Method 2
a second coil which suppresses any leakage of a magnetic field from the first coil to a static-magnetic-field coil
Implementation Method 3
a connecting line part of at least either one of the first coil and the second coil which intersects with a return line from a spiral coil pattern meanders
Implementation Method 4
Such an error magnetic field generates an eddy current at the static-magnetic-field coil devices, and such an eddy current may generate a magnetic field which disturbs the cross-sectional image
Data Source
AI summary
There is provided a gradient coil device which can suppress any generation of an error magnetic field and thus an eddy current, and which can improve the image quality of a cross-sectional image. An MRI device includes a first coil generating a linear magnetic field distribution at an imaging region of the MRI device, and a second coil which suppresses any leakage of a magnetic field from the first coil to a static-magnetic-field coil device that generates a uniform magnetic field distribution at the imaging region.