Gradient Coil Current Correction for MRI Eddy Current Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic field distortion due to eddy currents in MRI apparatuses leads to deterioration of image quality, with existing correction methods being costly and inefficient, particularly in addressing temperature-induced changes and perfecting field corrections.
Innovation Solution
A correction device that estimates eddy currents from current and voltage values of the gradient magnetic field coil, using sensors and a control device to adjust the current command value, thereby reducing magnetic field distortion by generating a control command signal and outputting a PWM signal to correct the influence of eddy currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a correction coil is disposed outside the gradient magnetic field coil to correct eddy current influence, then magnetic field distortion is corrected, but device cost and complexity increase
Solution Approach 1:
The invention extracts the correction function from a separate physical correction coil and integrates it into the existing gradient magnetic field coil system through software-based current command correction. The eddy current correction is achieved by calculating correction values based on measured voltage and current signals, eliminating the need for additional correction coils while maintaining correction accuracy
Solution Approach 2:
The invention replaces the mechanical/physical correction coil system with an electronic/software-based correction system. Instead of using physical components (correction coils) to generate counteracting magnetic fields, the system uses electronic signal processing to calculate and apply current command corrections that compensate for eddy current effects
2Ease of manufacture
If a fixed filter with predetermined time constant is used for correction, then correction implementation is simplified, but correction accuracy deteriorates due to inability to adapt to temperature changes
Solution Approach 1:
The invention transforms the static, fixed-time-constant filter approach into a dynamic adaptation system. The system dynamically determines the time constant based on actual voltage and current measurements during operation, allowing the correction parameters to adapt to changing conditions such as temperature variations, while maintaining implementation simplicity through automated calculation
Solution Approach 2:
The invention implements a feedback mechanism where the actual voltage and current signals are continuously measured and used to calculate the eddy current time constant. This feedback loop allows the system to automatically adjust correction parameters based on real-time operating conditions, ensuring accurate correction across varying temperatures without manual recalibration
3Productivity
If high-speed pulsed driving of gradient magnetic field is performed to improve image quality, then imaging speed is enhanced, but eddy current distortion increases leading to image quality deterioration
Solution Approach 1:
The invention applies preliminary anti-action by calculating and applying eddy current correction values to the current command before the gradient magnetic field is actually applied. The system predicts the eddy current effects based on the commanded current waveform and pre-compensates by adjusting the current command, thereby preventing magnetic field distortion before it occurs and maintaining image quality during high-speed imaging
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
Effectively reduces magnetic field distortion, maintaining image quality by accurately correcting current command values and adapting to changes in the time constant of eddy currents without the need for additional hardware or phantoms, thus enhancing MRI image clarity.
Implementation Method 1
a current of several hundred amperes (A) at several hundred Hz is supplied to a coil that generates the gradient magnetic field. Such a high-speed temporal magnetic field change generates eddy currents in a conductor near the coil
Implementation Method 2
Such a high-speed temporal magnetic field change generates eddy currents in a conductor near the coil
Implementation Method 3
a correction device is used for an apparatus including a coil and a conductor in a vicinity of the coil. The correction device corrects an influence of a magnetic field generated by the conductor when a current flows through the coil
Data Source
Figure 1
Figure 2
Figure 3
AI summary
According to one embodiment, a correction device (1) is used for an apparatus including a coil and a conductor in a vicinity of the coil. The correction device (1) corrects an influence of a magnetic field generated by the conductor when a current flows through the coil. The correction device (1) includes a first measuring device (3), a second measuring device (4), and a control device (2). The first measuring device (3) measures a first signal of the coil. The second measuring device (4) measures a second signal of the coil, which is different from the first signal. The control device (2) estimates the influence acting on the coil, based on a difference between the first signal filtered by a first filter and the second signal filtered by a second filter. Furthermore, the control device (2) controls a command signal for flowing the current to the coil, based on an estimation result of the influence.