Shim Coil Integrated in Gradient Layer for MR Field Homogeneity
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Solution Overview
Problem
Existing magnetic resonance units face limitations in maintaining magnetic field homogeneity due to first-order magnetic field inhomogeneities, which can lead to image distortions and require additional power for gradient coil compensation, potentially introducing higher-order inhomogeneities and limiting power capacity.
Innovation Solution
Incorporating a shim coil apparatus within the gradient coil layer to compensate for first-order magnetic field inhomogeneities, allowing for simultaneous powering with the gradient coil apparatus without additional space or components, and using a common amplifier for optimized power distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gradient coil apparatus is used to compensate for first-order magnetic field inhomogeneities by feeding offset current, then magnetic field homogeneity is improved, but power capacity is reduced and higher-order inhomogeneities are introduced
Solution Approach 1:
The patent divides the magnetic field compensation function into a separate shim coil apparatus that operates independently from the gradient coil apparatus. The shim coil apparatus is dedicated solely to compensating first-order inhomogeneities, while the gradient coil apparatus maintains its full power capacity for generating magnetic field gradients. This functional segmentation eliminates the power capacity reduction and higher-order inhomogeneity problems associated with using the gradient coil for dual purposes.
Solution Approach 2:
The shim coil apparatus acts as an intermediary component between the magnetic resonance unit and the examination subject, specifically designed to correct first-order magnetic field inhomogeneities. By introducing this intermediate compensation stage, the system achieves better field homogeneity without requiring the gradient coil to operate outside its optimal performance characteristics.
2Manufacturing precision
If separate shim coil apparatus is added outside gradient coil layer, then magnetic field compensation is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent merges the shim coil apparatus with the gradient coil layer, integrating the first-order inhomogeneity compensation function within the existing gradient coil structure. This combining approach allows the shim coil elements to be positioned alongside or within the gradient coil windings, sharing the same spatial envelope and support structures. The result is improved magnetic field homogeneity without adding external components, increasing device complexity, or requiring additional space beyond the gradient coil layer.
Solution Approach 2:
The gradient coil layer is designed to serve multiple functions: generating magnetic field gradients for spatial encoding and providing first-order magnetic field compensation through integrated shim coil elements. This multi-functionality eliminates the need for separate dedicated shim coil structures outside the gradient coil layer, reducing overall device complexity while maintaining compensation effectiveness.
3Manufacturing precision
If gradient coil is powered for compensation, then first-order inhomogeneities are corrected, but higher-order inhomogeneities are generated
Solution Approach 1:
The patent segments the magnetic field generation and compensation functions into distinct apparatuses with different operational characteristics. The shim coil apparatus uses direct current (DC) or low-frequency currents optimized for producing smooth compensating fields without generating significant higher-order inhomogeneities. In contrast, the gradient coil apparatus uses high-frequency switching currents optimized for spatial encoding. This segmentation prevents the generation of harmful higher-order inhomogeneities while maintaining first-order compensation effectiveness.
Solution Approach 2:
The shim coil apparatus creates a compensating magnetic field that copies or mirrors the inhomogeneity pattern but with opposite polarity, effectively canceling out the first-order inhomogeneities. By using a dedicated coil design optimized for this compensation function, the system achieves accurate field correction without introducing the higher-order artifacts that would result from using the gradient coil's complex switching currents for the same purpose.
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 maintains the full power capacity of the gradient coil for magnetic field gradient emission, prevents higher-order inhomogeneities, and simplifies the design by eliminating the need for separate shielding and supporting components, while enabling efficient compensation of magnetic field inhomogeneities.
Implementation Method 1
The shim coil apparatus is configured to compensate for basic magnetic field inhomogeneities of the first order in an examination region of the magnetic resonance unit
Implementation Method 2
Using a gradient coil unit, additional and spatially varying magnetic fields (e.g., magnetic field gradients) may be emitted
Implementation Method 3
The resulting transverse component of the precession of the net magnetization around the direction of the basic magnetic field may lead to induction in the HF antenna unit
Data Source
AI summary
A magnetic resonance unit includes a shim coil apparatus and a gradient coil apparatus. The shim coil apparatus is configured to compensate for basic magnetic field inhomogeneities of the first order in an examination region of the magnetic resonance unit. The shim coil apparatus includes at least one shim coil element. The gradient coil apparatus is arranged in a gradient coil layer. In addition to the gradient coil apparatus, at least one part of the at least one shim coil element is arranged in the gradient coil layer.