Asymmetric MRI Gradient Coil Offset Field Design
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Solution Overview
Problem
Designing high-performance asymmetrical z-gradient coils for MRI systems is challenging due to the high-density winding requirements near one end of the coil, which complicates construction and causes negative consequences when the main magnetic field shifts during spatial encoding and slice selection.
Innovation Solution
An asymmetric gradient coil system is designed with a constant offset component in the gradient field, allowing the position where the gradient field passes through zero to be offset from the imaging isocentre, reducing winding density and improving efficiency by spacing windings further apart, and incorporating an RF compensator to counteract field shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gradient coil is designed to maintain a symmetric gradient field with isocentre at the system isocentre, then the gradient field linearity is improved, but the winding density becomes extremely high near one end of the coil causing construction problems
Solution Approach 1:
The patent applies asymmetry by deliberately designing the gradient coil to produce an asymmetric magnetic field with a non-zero offset at the system isocentre. This asymmetric field configuration allows the imaging region to be positioned closer to one end of the coil while maintaining acceptable gradient linearity, thereby reducing the extreme winding density requirements that would otherwise be needed to force perfect symmetry.
Solution Approach 2:
The patent changes the field offset parameter from zero (traditional symmetric design) to a non-zero constant value. This parameter change fundamentally alters the coil design requirements, allowing for more distributed winding patterns that are easier to construct while still achieving the desired gradient performance in the asymmetrically positioned imaging region.
2Adaptability or versatility
If the gradient coil allows a net offset field at the isocentre to improve asymmetric imaging performance, then the imaging region can be positioned closer to one end of the coil, but the main magnetic field shifts during pulsing causing negative consequences on imaging
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensating mechanism that counteracts the harmful effects of the offset field before they can degrade imaging quality. The system pre-calculates and applies correction factors to the gradient waveforms or uses additional compensation coils to nullify the unwanted field shifts, thereby maintaining imaging reliability despite the asymmetric offset configuration.
Solution Approach 2:
The patent employs feedback mechanisms to monitor and correct for the main magnetic field shifts caused by the offset gradient field. By continuously measuring the actual field conditions and adjusting the gradient parameters or applying real-time corrections, the system maintains imaging quality while benefiting from the flexible asymmetric positioning capability.
3Stability of the object's composition
If high-density winding grouping is used to maintain symmetric gradient field, then the gradient field uniformity is improved, but the construction complexity and difficulty increase significantly
Solution Approach 1:
The patent uses asymmetry to redistribute the winding density more evenly throughout the coil structure. By accepting a controlled offset in the gradient field, the design avoids the need for extreme winding concentration at specific locations, resulting in a more uniform and manageable winding structure that is easier to construct and maintain while still achieving sufficient field uniformity in the imaging region.
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 enhances the performance and efficiency of the gradient coil by maintaining imaging quality and reducing construction complexities, while allowing for improved power usage and linearity in magnetic field generation.
Implementation Method 1
an asymmetric gradient coil configured to generate a gradient field in the asymmetrically positioned imaging region, at least one gradient axis having the gradient field with a constant offset component
Data Source
AI summary
An asymmetric electromagnet system, method, and method of producing an asymmetric electromagnet system, wherein the asymmetric electromagnet system is for generating an imaging magnetic field in an imaging region with an imaging isocentre, the imaging region being asymmetrically positioned within a gradient coil bore inside a magnetic resonance imaging (MRI) system during imaging, the electromagnet assembly comprising: an asymmetric gradient coil configured to generate a gradient field in the asymmetrically positioned imaging region, at least one gradient axis having the gradient field with a constant offset component such that the position at which the gradient field passes through zero is offset with respect to the imaging isocentre of the asymmetrically positioned imaging region.