Gradient Coil Control via Inductive Coupling Feedback
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Solution Overview
Problem
Existing control methods for gradient coils in magnetic resonance systems are suboptimal when current conditions are time-variable, leading to artifacts during image reconstruction, especially when currents differ across coils.
Innovation Solution
Controllers are supplied with reference or actual current signals and their time derivatives from other gradient coils, allowing for the generation of correction signals based on inductive coupling, enabling optimal control of currents across the gradient coil system, even when conditions are time-variable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional control methods are used for gradient coils, then the control is simple and straightforward, but the control becomes suboptimal when current conditions are time-variable, leading to artifacts during image reconstruction
Solution Approach 1:
The control method uses feedback from actual current signals of other gradient coils to adjust the control signal for each gradient coil. The controller receives actual current signals from other gradient coils and uses this feedback information, combined with reference current signals and time derivatives, to generate optimized control signals that compensate for inductive coupling effects and maintain optimal control under time-variable conditions.
Solution Approach 2:
The control method calculates time derivatives of reference current signals in advance and uses these pre-computed values along with actual current signals from other gradient coils to generate correction signals. This preliminary calculation of derivatives and preparation of correction signals before actual control enables the system to respond optimally to time-variable conditions without adding significant real-time complexity.
2Manufacturing precision
If the same current is applied to all coils of a specific gradient axis, then the controller parameters can be easily tuned, but the control becomes inadequate when currents need to be different to account for inductive coupling
Solution Approach 1:
The control method applies different control strategies to different gradient coils based on their specific inductive coupling characteristics. Each gradient coil receives a customized control signal that accounts for its individual coupling with other coils, rather than applying a uniform control approach. This local differentiation enables precise current control for each coil while the overall method remains systematically manageable.
Solution Approach 2:
The control method dynamically adjusts controller parameters based on actual current signals from other gradient coils and time derivatives of reference currents. By changing control parameters in real-time according to the operational state and inductive coupling conditions, the system achieves precise current control for each gradient coil while adapting to varying operational requirements.
3Manufacturing precision
If inductive coupling between gradient coils is not considered, then the control system remains simple, but artifacts occur during image reconstruction when currents differ across coils
Solution Approach 1:
The control method introduces correction signals as intermediaries that mediate between the reference current signals and the actual control signals for each gradient coil. These correction signals are generated based on actual current signals from other gradient coils and time derivatives, serving as a bridge that compensates for inductive coupling effects without requiring direct complex interaction between all coil control circuits.
Solution Approach 2:
The control method replaces physical decoupling of gradient coils with a signal processing approach. Instead of physically isolating the coils to eliminate inductive coupling, the system uses mathematical models and signal processing to calculate and compensate for coupling effects in the control domain, substituting mechanical/physical isolation with computational correction.
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 results in almost fully decoupled operation of gradient coils, achieving virtually optimal control characteristics and reducing artifacts during image reconstruction.
Implementation Method 1
The gradient coils of a gradient coil system of a magnetic resonance system may be inductively coupled to one another. On account of the inductive coupling, a dependence in relation to a specific gradient coil of the voltage required for generating a specific current on the activation state of the other gradient coils results.
Data Source
AI summary
A gradient pulse generator generates reference current signals for a plurality of gradient coils of a gradient coil system of a magnetic resonance system and supplies each of the reference current signals to a controller assigned to one of the gradient coils. Also supplied to the respective controller is an actual current signal that is characteristic of the current flowing in the respective gradient coil. Each of the controllers generates a control signal and accordingly drives a gradient power amplifier assigned to the respective gradient coil. The gradient power amplifiers apply a current to the gradient coils assigned to the gradient power amplifiers in accordance with the generated control signals. Each of the controllers is also supplied with the reference current signal or the actual current signal of at least one other gradient coil or the time derivative of the reference current signal or the actual current signal.