Spherical Shim Coil Array for MRI Magnetic Field Adjustment
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Solution Overview
Problem
Existing magnetic field adjustment technologies face challenges in achieving high accuracy due to interference between high-order and low-order magnetic field components, particularly in high-magnetic-field environments, where precise adjustment is difficult with current methods, and the size of magnetic field adjustment coils is a concern for reducing the size of MRI devices.
Innovation Solution
A magnetic field adjustment device employing a shim coil array with singular value decomposition to determine current command values, allowing for independent control of shim coils and accurate adjustment of magnetic field distributions using eigenmodes, which do not interfere with each other, enabling precise correction of magnetic fields with smaller currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional local coils are arranged on a cylindrical surface to adjust magnetic field, then magnetic field adjustment capability is improved, but the device size increases due to stacked structure of multiple cylindrical surfaces
Solution Approach 1:
The patent transitions from a two-dimensional cylindrical surface arrangement to a three-dimensional spherical surface arrangement. The shim coils are positioned on a spherical surface with radius R from the magnet center, allowing coils to be distributed in both azimuthal and polar directions. This spatial redistribution enables magnetic field adjustment without requiring stacked cylindrical structures, thereby reducing device size while maintaining adjustment capability.
Solution Approach 2:
The patent divides the magnetic field adjustment function into multiple independent shim coils arranged on the spherical surface. Each coil corresponds to specific spherical harmonic function components, allowing independent control and adjustment of different magnetic field error components. This segmentation enables precise adjustment without requiring a thick stacked structure.
2Adaptability or versatility
If spherical surface harmonic function with multiple order terms is used for magnetic field adjustment, then comprehensive magnetic field coverage is improved, but interference between high-order and low-order terms increases
Solution Approach 1:
The patent assigns specific shim coils to specific spherical harmonic function components based on their positions on the spherical surface. Each coil's geometry and position are optimized to predominantly generate magnetic field components corresponding to particular order terms. This local specialization reduces interference between different order terms while maintaining comprehensive coverage of all necessary magnetic field components.
Solution Approach 2:
The patent employs an iterative adjustment process where magnetic field measurements are taken, spherical harmonic decomposition is performed to identify error components, and shim coil currents are adjusted accordingly. This feedback loop allows for progressive refinement of magnetic field uniformity, addressing interference between order terms through systematic correction rather than attempting to eliminate it entirely in the coil design.
3Adaptability or versatility
If larger current is supplied to shim coils for magnetic field adjustment, then magnetic field adjustment range is improved, but heat generation increases
Solution Approach 1:
The patent optimizes multiple parameters of the shim coil system including coil geometry, winding density, position on spherical surface, and electrical characteristics. By carefully selecting and adjusting these parameters, the system achieves efficient magnetic field generation with minimized current requirements, thereby reducing heat generation while maintaining adequate adjustment range.
Solution Approach 2:
The patent implements dynamic current control of shim coils based on real-time magnetic field measurements and required adjustment magnitude. Rather than supplying large constant currents, the system dynamically adjusts coil currents according to actual needs, minimizing energy consumption and heat generation while maintaining the capability to achieve the required magnetic field adjustment range.
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 high-accuracy magnetic field adjustment with reduced current usage, improving the precision and efficiency of magnetic field control in MRI devices by minimizing interference and optimizing coil arrangement for smaller, more effective magnetic field adjustment systems.
Implementation Method 1
a plurality of shim coils 21 for adjusting a static magnetic field in a magnetic field use area 12
Data Source
AI summary
To provide an operator with operability similar to that of conventional devices with an electromagnetic device that accurately maintains a magnetic field distribution by adjusting the magnetic field for each eigenmode obtained by singular value decomposition. The strength of a unique mode is found from a measurement magnetic field, a current for each unique mode of a negative feedback control according to the magnetic field is calculated and the current is added to each mode to obtain a current for each shim coil, and a coil current is controlled so as to reach the obtained current value. In an interface for an operator, a target for a corrected magnetic field and a magnetic field generated by a shim coil are displayed using a spherical surface harmonic function strength. Due to this configuration, a device which enables accurate magnetic field adjustment while offering operability similar to conventional devices can be provided.