Passive Gradient Shield for MRI Eddy Current Reduction
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Solution Overview
Problem
Existing MRI systems face challenges with active shielding of gradient coils, which increases costs, reduces efficiency, and generates noise due to the need for additional structure and increased power requirements to prevent eddy currents.
Innovation Solution
Implementing a passive gradient shield made of high permeability, low electrical conductivity material, such as silicon steel, between the main magnet and gradient coil assembly to reduce eddy currents without the need for active shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If active shielding is used to prevent eddy currents in gradient coils, then image quality is improved, but system cost and complexity increase
Solution Approach 1:
A passive shield made of high permeability material is introduced as an intermediary component between the gradient coil and the main magnet bore. This shield mediates the interaction by providing a preferred magnetic flux path, thereby preventing eddy currents without requiring active control systems or additional gradient coils.
Solution Approach 2:
The patent replaces the active electromagnetic shielding system (requiring additional coils and control electronics) with a passive magnetic shielding system using high permeability material. This substitution eliminates the need for active control while maintaining shielding effectiveness.
2Object-affected harmful factors
If active shielding coils are added to gradient coil assembly, then eddy current interference is reduced, but power consumption and heat generation increase
Solution Approach 1:
The patent employs a passive, non-active shielding approach that does not consume electrical power. The high permeability shield material passively redirects magnetic flux without requiring energy input, eliminating the power consumption and heat generation associated with active shielding coils.
Solution Approach 2:
The passive shield automatically performs the shielding function through its inherent magnetic properties. The high permeability material self-organizes the magnetic flux paths without requiring external control or energy input, making the system self-regulating and energy-independent.
3Reliability
If shield gradient coil is added around primary gradient coil, then flux linkage is decoupled, but gradient coil resistance increases
Solution Approach 1:
The passive high permeability shield acts as an intermediary that provides a low-reluctance path for magnetic flux. This decouples the flux linkage between the gradient coil and main magnet by shunting flux through the shield, without adding series resistance that would increase energy loss.
4Object-affected harmful factors
If additional shield coil structure is implemented, then eddy current prevention is achieved, but acoustic noise increases
Solution Approach 1:
The patent replaces the active coil-based shielding mechanism with a passive magnetic shielding structure. This substitution eliminates the electromagnetic interactions and force interactions between active coils that generate acoustic noise, while maintaining eddy current prevention through flux shunting.
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 solution enhances the efficiency of MRI systems by reducing the electrical current required for gradient field generation, allowing for a thinner coil design, lower costs, and decreased acoustic noise while maintaining image quality.
Implementation Method 1
a passive gradient shield disposed between the main magnet and gradient magnetic coil assembly, where the passive gradient shield is a continuous cylindrical layer of high permeability, low electrical conductivity material
Implementation Method 2
to prevent the generation of eddy currents, the gradient coil and magnet structure (the magnet bore cylinder, magnet windings, or other metal) can be decoupled or isolated
Data Source
AI summary
An MRI system including a main magnet defining a volume, an imaging region disposed within the volume. The main magnet is configured to produce a uniform main magnetic field within the volume, wherein the uniform magnetic field is oriented along a patient axis. The system includes a gradient magnetic coil assembly disposed within the volume and configured to generate a spatially varying magnetic field across the imaging region. The gradient magnetic coil assembly includes a first coil configured to generate a magnetic field in a first axis, a second coil configured to generate a magnetic field in a second axis, and a third coil configured to generate a magnetic field in the patient axis. The system also includes a passive gradient shield disposed between the main magnet and primary gradient magnetic coil assembly, the passive gradient shield can include a continuous cylindrical layer of high permeability, low electrical conductivity material.