MRI Gradient Delay Calibration via Iterative K-Space Shift
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Solution Overview
Problem
Magnetic Resonance Imaging (MRI) systems face challenges in reducing ghost artifacts due to gradient delay and eddy currents, which cause k-space trajectory deviations and result in unclear images.
Innovation Solution
A method and system that acquire and process MR signals using a pulse sequence including an imaging pulse and a pre-scan pulse, iteratively determining a candidate k-space shift and gradient delay to update data lines and reconstruct images based on the corrected gradient delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gradient delay and eddy currents are present in the MRI system, then the MRI system can operate and acquire signals, but the k-space trajectory deviates from design causing ghost artifacts and reducing image quality
Solution Approach 1:
The patent performs a pre-scan before the actual imaging scan to measure the system's gradient delay and eddy current effects. This preliminary measurement allows the system to determine correction factors (k-space shifts) that are then applied during the imaging scan to compensate for trajectory deviations, thereby resolving the contradiction between maintaining operational capability and achieving trajectory accuracy.
2Productivity
If no gradient delay calibration is performed, then the imaging process is faster and simpler, but ghost artifacts increase and image clarity decreases
Solution Approach 1:
The patent implements a pre-scan phase that quickly characterizes the system's gradient behavior and eddy current effects before the actual imaging. This preliminary calibration is performed once and can be reused for multiple subsequent scans, thereby maintaining high imaging speed while ensuring image quality through pre-determined correction parameters.
Solution Approach 2:
The system uses the pre-scan data to provide feedback about the actual gradient behavior versus the ideal gradient waveform. This feedback is used to calculate k-space shift corrections that are then applied during image reconstruction, creating a closed-loop system that maintains image quality without requiring slow real-time adjustments during the actual imaging scan.
3Measurement precision
If iterative correction methods are used to determine gradient delay, then gradient delay calibration accuracy improves, but processing time increases
Solution Approach 1:
The patent performs the iterative correction process during a pre-scan phase before the actual imaging. Although the iterative calculation takes time, this time is spent beforehand when no diagnostic images are being acquired. The corrected parameters are then stored and applied during the actual imaging scan, thereby achieving high calibration accuracy without sacrificing imaging time.
Data Source
AI summary
A system and method for magnetic resonance imaging is provided. The method includes acquiring a first set of MR signals and a second set of MR signals by applying a pulse sequence on a subject. The method also includes obtaining a first data line by filling the first set of MR signals into k-space along a first trajectory, and obtaining a second data line by filling the second set of MR signals into k-space along a second trajectory. The method also includes determining a candidate k-space shift based on the first data line and the second data line, and determining a candidate gradient delay based on the candidate k-space shift obtained in each of a plurality of iterations. The method also includes reconstructing an image of the subject based on the candidate gradient delay obtained in the last iteration.