Nested Saddle Coil Configuration for MRI Shimming

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Solution Overview

Problem

MRI systems face challenges in achieving high-order spherical harmonic compensation due to spatial constraints and the complexity of resistive shims, leading to reduced shim strength, increased wiring complexity, and sensitivity to positional tolerances, which affects image quality and gradient coil performance.

Innovation Solution

The implementation of nested saddle coils of different orders and degrees inside each other, where the first set of saddle-shape coils is nested within the second set, occupying a reduced radial space and minimizing unwanted harmonics, and utilizing these coils as 'shield' coils to nullify leakage fields, thereby enhancing shim purity and reducing eddy current effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If traditional resistive shims are used for high-order spherical harmonic compensation, then shim strength can be achieved, but radial space is excessively consumed and wiring complexity increases

Engineering Contradiction:

Improveshimming capabilityVSAvoidradial space

Core Design Contradiction:

Adaptability or versatilityVSVolume of moving object

Solution Approach 1:

The patent implements nested saddle coils where lower-order shimming coils are positioned inside higher-order shimming coils. This nesting arrangement allows multiple shimming functions to be integrated within a compact radial footprint, enabling high-order spherical harmonic compensation without proportionally increasing the radial space required. The nested configuration maintains shim strength while dramatically reducing the overall volume occupied by the active shim system.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Adaptability or versatility

If more active shims are added to compensate for higher-order spherical harmonics, then shimming capability is improved, but device complexity and wiring requirements increase significantly

Engineering Contradiction:

Improveshimming capabilityVSAvoidwiring complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The nested saddle coil configuration enables each coil assembly to serve multiple shimming functions simultaneously. By carefully designing the nesting arrangement and current distribution, the system can generate multiple spherical harmonic components (different orders and degrees) using a reduced number of independent coil assemblies. This multi-functionality reduces the total number of separate shims and their associated wiring, thereby decreasing device complexity while maintaining comprehensive shimming capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Volume of moving object

If resistive shims are positioned closer to gradient coils to save space, then radial space is reduced, but eddy current effects and leakage fields increase

Engineering Contradiction:

Improveradial spaceVSAvoideddy current effects

Core Design Contradiction:

Volume of moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent strategically positions the nested resistive shims within the gradient coil assembly structure, converting the potential harm of close proximity into a benefit. The nested configuration allows precise control of current distribution and magnetic field generation, enabling the shims to compensate for gradient non-linearities and eddy current effects rather than merely adding to them. The nested arrangement optimizes the spatial distribution of currents to minimize harmful leakage fields while maintaining effective shimming, thereby converting the close proximity arrangement from a source of harm into a means of correction.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 improves shimming capability, reduces the volume required for active shim coils, enhances image quality by minimizing eddy current effects, and allows for better engineering tools and design specifications, resulting in improved gradient coil performance and reduced sensitivity to positional tolerances.

Implementation Method 1

a nested shim coil assembly for shimming the magnetic field of a magnetic resonance system by generating spherical harmonics

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

Resistive shims are used for compensation of relatively small field disturbances introduced by the investigated subject

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Data Source

PatentUS9638776B2Nested coil configuration of active shims in MRI systems

Publication Date: 2017.05.02 GE PRECISION HEALTHCARE LLC

AI summary

Embodiments of the invention are utilized to improve shimming capability while reducing radial space and the volume required to contain active shim coils by nesting the coils of different degrees and orders inside each other and limiting the azimuthal span of the individual saddle coils. This allows two or more radial shim sets to be combined together in the same layer resulting in a significant radial savings that increases the useable portion of an MRI system.