Basic Magnet Design for MRI Gradient Coil Vibration Control
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Solution Overview
Problem
Magnetic resonance apparatuses face noise and image artifacts due to oscillations of gradient coil systems caused by rapid switching in strong magnetic fields, leading to compromises in design specifications such as linearity, rise time, and gradient amplitude.
Innovation Solution
A method to design the basic magnet of a magnetic resonance apparatus that accounts for forces acting on the gradient coil system during switching processes, minimizing noise and image artifacts by optimizing the arrangement of winding packages and current density distribution, using finite element methods to determine vibration modes and Lorentz force distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high currents are applied and removed rapidly in gradient coils for spatial coding, then image acquisition speed and resolution are improved, but strong Lorentz forces cause gradient coil oscillations leading to noise and image artifacts
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing force compensation currents that counteract the Lorentz forces before gradient switching occurs. The system determines compensation currents based on predicted gradient coil positions and stored magnetic field data, then applies these compensation currents proactively to prevent oscillations before they occur, rather than reacting to oscillations after they happen.
Solution Approach 2:
The patent implements feedback by continuously monitoring the actual gradient coil position using encoders or other sensing mechanisms, comparing it to the desired position, and adjusting the compensation currents in real-time based on the position error. This closed-loop feedback ensures that compensation remains effective even when gradient coil positions deviate from predicted values, maintaining noise reduction while preserving image acquisition speed.
2Object-generated harmful factors
If gradient coils are designed to minimize net forces in the basic magnetic field, then oscillations and noise are reduced, but compromises must be made in linearity, rise time, gradient amplitude, and scatter field
Solution Approach 1:
The patent applies segmentation by separating the gradient coil system into multiple independently controllable coil sets. This allows different coil sets to be optimized for different functions: some coils can be designed primarily for minimizing forces and reducing noise, while other coils can be optimized for achieving desired linearity, rise time, and gradient amplitude specifications. Each segment can be tuned independently without compromising the overall system performance.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting operating parameters such as current amplitude, switching timing, and gradient coil configuration based on the imaging sequence requirements. This allows the system to optimize the trade-off between force minimization and gradient performance on a per-sequence basis, rather than being constrained by a fixed design compromise. Parameters like gradient strength and duration can be modified to achieve both low oscillations and high image quality.
3Loss of time
If gradient coil switching is performed within the shortest possible time, then image acquisition efficiency is improved, but strong forces act on conductors causing vibrations and eddy current losses
Solution Approach 1:
The patent applies preliminary action by pre-calculating optimal switching trajectories and compensation currents that minimize eddy current losses before gradient switching begins. The system stores pre-computed switching waveforms that account for eddy current effects, allowing rapid switching while maintaining energy efficiency. This proactive approach enables fast image acquisition without incurring excessive eddy current losses.
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 allows for a more optimal design of both the basic magnet and gradient coil system, reducing noise, image artifacts, and eddy current losses, while maintaining desired specifications without compromising on gradient coil performance.
Implementation Method 1
The Lorentz forces that act on electrical charges in electromagnetic fields additively combine to produce large net forces. The forces accordingly acting on the gradient coil generate oscillations of the gradient coil system.
Implementation Method 2
a system of gradient magnetic fields is superimposed on the basic magnetic field for spatial coding of the image information
Implementation Method 3
a system of gradient magnetic fields is superimposed on the basic magnetic field for spatial coding of the image information
Data Source
AI summary
The method for determination of the design of the basic magnet of a magnetic resonance apparatus with at least one gradient coil system, the design of the basic magnet is determined by taking into consideration forces acting on the at least one gradient coil system that may lead to vibrations of the gradient coil system due to switching processes of the gradient coil system in the field of the basic magnet.