K-Space Trajectory Calibration Using Blank Window MR Signal
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Solution Overview
Problem
Non-uniformity and instability of the background magnetic field in magnetic resonance imaging (MRI) scanners cause deviations in k-space trajectory filling, affecting measurement accuracy.
Innovation Solution
A method involving the use of a blank window after an RF excitation pulse, where no gradient field is applied, to acquire a first magnetic resonance signal reflecting the background field, followed by a second signal with the gradient field applied, allowing for calibration of the k-space trajectory to separate and remove the influence of background field non-uniformity and eddy currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gradient fields are continuously applied during k-space filling, then scanning speed is maintained, but background field non-uniformity and eddy currents cause trajectory deviation and reduce measurement precision
Solution Approach 1:
The method applies preliminary action by inserting a blank window (gradient-free period) before the actual k-space data acquisition. During this blank window, the system measures the background field characteristics and eddy current effects in advance, allowing these influences to be characterized and compensated for before they affect the main measurement, thereby improving trajectory accuracy without significantly extending total scan time
Solution Approach 2:
The k-space filling process is segmented into distinct phases: a blank window phase for background field measurement, and a data acquisition phase for actual imaging. This segmentation allows the system to separately characterize and correct background field effects, improving overall measurement precision while maintaining efficient scanning through structured timing
2Productivity
If gradient fields are applied to accelerate scanning, then productivity increases, but the non-uniformity of the background field causes deviation in k-space trajectory
Solution Approach 1:
The blank window serves as an intermediary measurement phase that captures background field characteristics without the confounding influence of strong gradient fields. This intermediary measurement allows the system to calculate correction factors that are then applied during the main data acquisition, enabling high-speed scanning while maintaining trajectory accuracy through computational compensation
3Measurement precision
If a blank window is inserted to measure background field, then measurement precision improves, but scanning time increases
Solution Approach 1:
The blank window is designed to be just sufficient to capture the essential background field characteristics without being excessively long. By applying partial action (a limited-duration blank window rather than continuous measurement), the system achieves adequate measurement precision for correction purposes while minimizing the time penalty to total scan duration
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
Improves the accuracy and efficiency of k-space trajectory filling by reducing the impact of background field non-uniformity and eddy currents, leading to more precise measurement results.
Implementation Method 1
A radio-frequency (RF) excitation pulse and a slice selection gradient pulse are emitted... A first magnetic resonance signal is acquired in the blank window, which is based on said RF excitation pulse... a second magnetic resonance signal is acquired that is based on the RF excitation pulse and the gradient field
Data Source
AI summary
In a method, apparatus and storage medium for filling a k-space trajectory in magnetic resonance (MR) imaging, a blank window, following an RF excitation pulse, is set in an arbitrary spatial encoding direction, and a first MR signal is acquired in this blank window, to obtain the phase of the first MR signal. A gradient field is activated outside the blank window and a second MR signal is acquired to obtain the phase of the second MR signal. This first and second MR signals are entered into k-space along first k-space and second k-space trajectories that are respectively based on the phase of the first MR signal and the phase of the second MR signal. A calibrated k-space trajectory in the spatial encoding direction is determined based on the first and second k-space trajectories.