Gradient Amplifier Control Apparatus for Magnetic Resonance Tomograph
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Solution Overview
Problem
Magnetic resonance tomography devices experience pulse deformations due to magnetic coupling between sub-coils, which affect the gradient amplifier's performance and pulse shape, leading to unwanted distortions in the magnetic field gradients.
Innovation Solution
A control apparatus for gradient amplifiers is introduced, incorporating a differentiation unit and electrical filter units (both low pass and high pass) to process current desired value signals, reducing the impact of magnetic couplings by adjusting the differential control signals through summation and multiplication units, thereby stabilizing the gradient amplifier's response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sub-coils are used in gradient coils to improve magnetic field coverage, then the magnetic field gradient performance is improved, but magnetic coupling between sub-coils causes pulse deformations and destabilizes the gradient amplifier response
Solution Approach 1:
The gradient coil is divided into multiple sub-coils (e.g., Z1, Z2, X1, X2, Y1, Y2) that can be independently controlled by separate gradient amplifiers. This segmentation allows each sub-coil to be optimized for specific spatial regions while maintaining overall system performance through coordinated operation.
Solution Approach 2:
The control apparatus measures the actual current in each sub-coil and feeds this information back to the respective gradient amplifier. This feedback mechanism enables real-time compensation for magnetic coupling effects and ensures that each sub-coil achieves its desired current trajectory despite interference from other sub-coils.
2Adaptability or versatility
If multiple sub-coils are operated simultaneously to enhance gradient performance, then the spatial coverage and imaging capability are improved, but the magnetic coupling between sub-coils creates unwanted pulse deformations
Solution Approach 1:
The control apparatus acts as an intermediary between the gradient amplifiers and the sub-coils, processing control signals and applying appropriate compensation. It calculates correction signals based on measured coupling effects and injects these corrections into the control inputs of each gradient amplifier, thereby eliminating pulse deformations caused by magnetic coupling.
Solution Approach 2:
The control apparatus dynamically adjusts control parameters (such as control signal amplitudes and timing) for each gradient amplifier based on the operating state of the system. By changing these parameters in real-time, the system compensates for varying magnetic coupling effects and maintains accurate pulse shapes across different imaging sequences.
3Device complexity
If the gradient amplifier operates at purely inductive load to simplify control, then the control complexity is reduced, but the low ohmic resistance losses result in insufficient damping of magnetic coupling effects
Solution Approach 1:
The control apparatus implements feedback control by measuring actual sub-coil currents and adjusting control signals accordingly. This feedback mechanism provides the necessary damping to counteract magnetic coupling effects without requiring additional ohmic resistance, thereby maintaining system reliability while preserving the simplicity of the purely inductive load operation.
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 solution significantly reduces the reaction to magnetic couplings in gradient coils, ensuring more stable and accurate magnetic field gradients by compensating for the changes in inductance and flux densities across sub-coils, thus preventing pulse deformations.
Implementation Method 1
a differentiation unit (24) that forms a differential control signal by differential processing from a current desired value signal (I-SOLL)
Implementation Method 2
At least one electrical low pass filter unit (26) is connected in series with the differentiation unit (24)
Implementation Method 3
At least one electrical high pass filter unit (27) is connected in parallel with the differentiation unit (24)
Implementation Method 4
A gradient amplifier (1) with a control apparatus (20)... for generating linear magnetic field gradients
Implementation Method 5
Each of the sub-coils (11, 12) generates a magnetic flux density (B1, B2) that couples with the adjacent sub-coil
Data Source
AI summary
A control apparatus for a gradient amplifier includes a differentiation unit. The differentiation unit forms a differentiation signal by differential processing from a current desired value signal of the gradient amplifier. At least one electrical low pass filter unit is connected in series with the differentiation unit, and/or at least one electrical high pass filter unit is connected in parallel with the differentiation unit.