MRI Gradient Field Error Correction via K-Space Pulse Response
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face significant gradient field errors, particularly in non-Cartesian k-space trajectories and echo planar imaging, leading to artifacts and reduced spatial resolution due to the gradient system's complex response to programmed pulses, which existing correction techniques like GIRF methods struggle to fully address.
Innovation Solution
An MRI system that uses calibration data representing the pulse response of the gradient system in k-space to determine an optimized scan sequence for radio-frequency pulses, gradient pulses, and scan times, allowing for precise prediction and correction of gradient field errors by integrating the pulse response into the determination of the k-space trajectory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GIRF techniques are used to predict gradient fields, then prediction accuracy is improved, but the gradient system still functions as a low pass filter causing persistent gradient field errors during RF pulses
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values in a lookup table before the actual imaging sequence. The system determines correction values based on the gradient system's impulse response function and stores them for rapid retrieval during RF pulse execution, avoiding real-time calculation delays and ensuring accurate gradient field correction during critical imaging periods.
Solution Approach 2:
The patent ensures continuity of useful action by implementing continuous gradient field correction throughout the entire imaging sequence, including during RF pulse emission. The correction is applied continuously by retrieving pre-calculated values from the lookup table based on the actual gradient waveform timing, ensuring no gaps in correction coverage and maintaining gradient field accuracy throughout the scan.
2Speed
If scan sequences with rapid gradient changes are used, then imaging speed is improved, but gradient field errors increase significantly
Solution Approach 1:
The patent implements feedback by using the actually played-back gradient waveform as input to the impulse response function for calculating correction values. This closed-loop approach ensures that the correction adapts to the actual gradient behavior including any deviations, eddy currents, or mechanical resonances that occur during rapid gradient changes, thereby maintaining accuracy even at high imaging speeds.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the correction values based on the actual gradient waveform parameters. The system calculates correction values specific to each gradient pulse sequence by convolving the actual gradient waveform with the impulse response function, allowing the correction to adapt to different imaging protocols, gradient strengths, and timing parameters.
3Reliability
If conventional correction techniques are used, then some gradient field errors are reduced, but errors during RF pulse emission are not addressed
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values in a lookup table before the actual imaging sequence. The system determines correction values based on the gradient system's impulse response function and stores them for rapid retrieval during RF pulse execution, avoiding real-time calculation delays and ensuring accurate gradient field correction during critical imaging periods.
Data Source
AI summary
In a magnetic resonance installation and a corresponding method, a scan sequence is determined based on a representation in k-space of a pulse response of a gradient system of the magnetic resonance installation.