Gradient Coil Correction Windings for Eddy Current Suppression
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Solution Overview
Problem
Eddy currents induced by gradient coils in magnetic resonance devices cause signal distortions and long recovery times, limiting the efficiency of NMR experiments, especially for complex pulse sequences and diffusion coefficient measurements.
Innovation Solution
An actively shielded gradient coil system with a correction coil is designed, where the correction coil is electrically connected in series with the main and shielding coils, reducing the duration and amplitude of eddy currents by optimizing the residual field to minimize long-lasting eddy currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gradient coils are used to generate gradient fields in magnetic resonance devices, then the efficiency of NMR experiments is improved, but eddy currents are induced causing signal distortions and long recovery times
Solution Approach 1:
A correction coil is introduced as an intermediary element between the gradient coil system and the measuring volume. This correction coil generates a compensating magnetic field that counteracts the harmful eddy currents induced by the gradient coils, thereby reducing signal distortions and recovery times while maintaining the efficiency benefits of gradient field usage
2Measurement precision
If waiting time is extended after gradient pulses for field homogeneity recovery, then signal quality is improved, but experiment duration increases
Solution Approach 1:
The correction coil converts the harmful effect of eddy currents into a beneficial compensating field. By actively generating an opposing magnetic field, the system accelerates field homogeneity recovery, thereby improving signal quality without requiring extended waiting times, thus maintaining short experiment durations
3Duration of action of moving object
If correction coil is added to reduce eddy currents, then eddy current decay time is shortened, but device complexity increases
Solution Approach 1:
The correction coil is designed with multi-functionality to minimize its impact on system complexity. It serves multiple purposes: compensating eddy currents, maintaining field homogeneity, and working in conjunction with existing gradient coils. The correction coil can be integrated into the existing coil structure and controlled through the same control system, thereby reducing the overall complexity increase
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 configuration reduces the waiting time required after gradient pulses for field homogeneity and minimizes signal distortions, enhancing the quality and efficiency of NMR experiments by shortening eddy current decay times.
Implementation Method 1
when a current flows, the gradient coil system generates a gradient field in a measuring volume
Implementation Method 2
During switching on and off, eddy currents are excited in the nearby conducting structures. These, for their part, form a time-dependent magnetic field in the measuring volume
Data Source
AI summary
In a coil arrangement for nuclear magnetic resonance comprising a main coil (13), a shielding coil (14), and at least one correction coil (41), the function of which consists in forming a magnetic field gradient with eddy current properties which are as good as possible, the main coil (13) and the shielding coil (14) are electrically connected in series with the correction coil (41). The deviations of the residual field from the desired design generated by production tolerances are thereby modified by the correction coil in such a fashion that the long-lasting eddy currents are suppressed. This either reduces the waiting time that must lapse after a gradient pulse before a predetermined field homogeneity is achieved or e.g. the deviations from the desired field are minimized in imaging applications.