MRI Gradient Control Sequence Amplitude and Direction Rate Limiting
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Solution Overview
Problem
Magnetic resonance imaging systems face significant noise generation due to strong mechanical oscillations of the gradient coil system, which is not adequately addressed by existing control sequences, particularly in echo signal-based methods that require fast switching sequences of the gradient magnetic field.
Innovation Solution
A control sequence for magnetic resonance imaging systems is optimized by limiting the momentary amplitude change rate and direction change rate of the gradient magnetic field, thereby reducing eddy current and Lorentz forces that contribute to noise generation, allowing for nearly noise-free operation by controlling the gradient coil system with time-limited force changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fast switching sequences of the gradient magnetic field are used for echo signal-based data acquisition, then data acquisition speed is improved, but noise generation increases due to strong mechanical oscillations
Solution Approach 1:
The patent applies parameter changes by modifying the gradient magnetic field parameters (amplitude change rate and direction change rate) to resolve the contradiction. Specifically, the gradient magnetic field is controlled such that its amplitude change rate and direction change rate are limited to predetermined values during k-space traversal, enabling faster data acquisition while suppressing mechanical oscillations and noise generation
2Speed
If the amplitude change rate of the gradient magnetic field is increased, then gradient switching speed is improved, but mechanical oscillations and noise increase
Solution Approach 1:
The patent directly applies parameter changes by controlling the amplitude change rate of the gradient magnetic field. The gradient magnetic field parameters are adjusted during k-space traversal to maintain a controlled amplitude change rate, enabling fast gradient switching while suppressing the mechanical oscillations that would otherwise be generated by rapid amplitude changes
3Speed
If the direction change rate of the gradient magnetic field is increased, then trajectory switching speed is improved, but eddy current forces and noise increase
Solution Approach 1:
The patent applies parameter changes by controlling the direction change rate of the gradient magnetic field. During k-space traversal, the gradient magnetic field direction is adjusted with a limited direction change rate, enabling fast trajectory switching while reducing eddy current forces and associated noise that would result from rapid directional changes
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
The optimized control sequence effectively minimizes noise generation in magnetic resonance imaging systems, enabling more precise and quieter data acquisition while maintaining high contrast and resolution, particularly in echo signal-based image acquisition methods.
Implementation Method 1
The gradient coil system to generate the gradient magnetic field is typically a rapidly switched, electrically operated coil system with multiple gradient coils that generate magnetic fields
Implementation Method 2
Due to interaction forces (Lorentz forces) of these currents with the basic magnetic field of the tomography system
Implementation Method 3
the interaction of magnetic scatter fields of the gradient coil system (eddy current forces) with conductive regions of the tomography system
Data Source
AI summary
In a method to determine a control sequence for a magnetic resonance imaging system in order to acquire echo signal-based raw magnetic resonance data in k-space along one or more trajectories on the basis of the control sequence, the control sequence is optimized so that, to control a gradient magnetic field for at least a predetermined portion of the control sequence, a change of an attribute of the gradient magnetic field is limited. The limitation takes place so that a momentary amplitude change rate of the gradient magnetic field falls below a predetermined amplitude change rate limit value, and/or so that a momentary direction change rate of the gradient magnetic field falls below a predetermined direction change rate limit value, and/or so that a momentary gradient change rate of the gradient magnetic field that is based on a combination of the momentary amplitude change rate and the momentary direction change rate falls below a predetermined gradient change rate limit value.