MRI Gradient Coil Timing Misalignment Detection
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Solution Overview
Problem
Current MRI systems face challenges in accurately detecting and correcting timing misalignment between power sources driving magnetic field gradient coils, leading to artifacts and distortion in images, particularly due to variance in power source characteristics and impedance, which is difficult to detect with existing methods that require additional measurement devices.
Innovation Solution
The technique employs a pulse sequence to detect timing misalignment by generating projection images at positive and negative sides of the magnetic field gradient, calculating phase differences, and adjusting drive timing to eliminate phase distortion without needing additional measurement devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple low-output power sources are used in parallel to generate sufficient magnetic field gradient, then the required magnetic field gradient can be achieved, but timing misalignment occurs between the power sources
Solution Approach 1:
The patent employs feedback by measuring the actual current waveforms from each power source and using this information to adjust their timing. The system continuously monitors the output of each power source and makes real-time corrections to synchronize their operation, thereby resolving the timing misalignment issue while maintaining the use of multiple parallel power sources for sufficient magnetic field gradient generation.
Solution Approach 2:
The patent replaces mechanical/electrical timing adjustment mechanisms with a computational approach. Instead of using physical delay circuits or manual synchronization mechanisms, the system uses a computer to calculate the optimal timing offsets based on measured current waveforms and automatically adjusts the power source timing through digital control signals.
2Reliability
If delay circuit is used to adjust timing of power sources, then synchronization can be improved, but additional devices and system complexity are required
Solution Approach 1:
The patent makes the computer serve multiple functions: it not only controls the overall MRI system operation but also specifically performs timing synchronization of the power sources. By integrating the synchronization function into the existing computer control system, the patent avoids adding separate synchronization devices while maintaining reliable timing coordination among multiple power sources.
3Reliability
If traditional timing adjustment method is used, then synchronization can be achieved, but additional measurement devices such as ammeter and magnetic field measuring device are required
Solution Approach 1:
The patent enables the system to perform its own timing measurement and adjustment without external measurement devices. The MRI system uses its existing signal processing capabilities to measure the current waveforms from the power sources and calculate the timing offsets, thereby eliminating the need for separate ammeter or magnetic field measuring devices while achieving accurate timing synchronization.
4Manufacturing precision
If timing misalignment detection is performed with high precision, then artifact and distortion can be eliminated, but detection difficulty increases for misalignment as short as 10 microseconds
Solution Approach 1:
The patent transforms the timing measurement problem from the time domain to the frequency domain by analyzing current waveforms. By converting the timing offset measurement into a frequency-based analysis, the system can achieve high-precision detection of microsecond-level misalignments using standard signal processing techniques, thereby resolving the difficulty of detecting very small timing differences.
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 method allows for high-accuracy detection and correction of timing misalignment, improving image quality by canceling phase rotations caused by sampling timing and static magnetic field uniformity, thereby eliminating artifacts.
Implementation Method 1
The magnetic field gradient generator (102) for generating the magnetic field gradient
Implementation Method 2
apply a high frequency magnetic field and a magnetic field gradient to a subject laid in a static magnetic field, measure the signal generated from the subject through nuclear magnetic resonance
Implementation Method 3
a static magnetic field generator (101) for generating a static magnetic field
Data Source
AI summary
A magnetic resonance imaging device produces a magnetic field gradient with parallel driving of positive-side subcoils and negative-side subcoils with different power sources in the magnetic field gradient direction, to detect a misalignment in drive timing of the positive side and the negative side. Pulse sequences for timing misalignment detection having a slice magnetic field gradient pulse and a read-out magnetic field gradient pulse in the same direction as a magnetic field gradient of interest are executed. A positive-side slice echo and a negative-side slice echo of the magnetic field gradient are acquired. A phase difference between a positive-side projection image and a negative-side projection image is derived by computation with phase error from other factors being removed. From the slope of the phase difference with respect to a location, the drive timing misalignment between the positive-side subcoil and the negative-side subcoil of the magnetic field gradient production is detected.