MRI Gradient Pulse Correction for K-Space Trajectory Artifacts
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Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face challenges in accurately assigning magnetic resonance signals to k-space points due to deviations between the assumed and actual time profiles of measurement gradient pulses, leading to artifacts such as edge overemphasis, ringing, and ghosting, especially in non-linear sampling methods like ramp sampling and spiral imaging.
Innovation Solution
A method involving two correction measurements under controlled conditions to determine a correction function that aligns the actual k-space trajectory with the assumed target profile, using a first measurement with a sampling pattern applied to the measurement gradient pulse and a second measurement with a reference sampling pattern during a plateau of the gradient pulse, allowing for precise correction of signal assignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ramp sampling is used to record magnetic resonance signals during the entire measurement gradient pulse including ramps, then productivity is improved by faster recording, but measurement precision deteriorates due to non-linear k-space sampling causing artifacts
Solution Approach 1:
The patent changes the parameter of gradient pulse shape from ideal trapezoidal to measured actual shape, and adjusts the k-space trajectory calculation based on measured gradient moments. This allows accurate mapping of recording times to k-space positions even during ramp phases, enabling ramp sampling without artifacts.
Solution Approach 2:
The patent introduces a feedback mechanism where the actual gradient pulse shape is measured and used to correct the k-space trajectory assignment. The measured gradient moments feed back into the reconstruction process to accurately map recorded signals to their correct k-space positions, compensating for non-linear sampling effects.
2Device complexity
If an ideal trapezoidal gradient profile is assumed for k-space assignment, then device complexity is reduced by simplifying calculations, but measurement precision deteriorates due to deviations between assumed and actual gradient shapes
Solution Approach 1:
The patent performs preliminary measurement of the actual gradient pulse shape before image reconstruction. This measured gradient profile is stored and used for accurate k-space trajectory calculation during reconstruction, eliminating the need to assume ideal shapes and improving position accuracy without significant additional complexity.
Solution Approach 2:
The patent creates a copy of the actual measured gradient pulse shape and uses this copied profile for k-space assignment calculations. Instead of using the simplified ideal trapezoidal model, the system copies the real gradient behavior and applies it to accurately map recording times to k-space positions.
3Measurement precision
If eddy current compensation is applied to correct gradient shape deviations, then measurement precision is improved, but device complexity increases due to additional compensation mechanisms
Solution Approach 1:
The patent implements a self-service approach where the system measures its own actual gradient pulse shape using built-in capabilities and uses this self-measured information for accurate k-space assignment. This eliminates the need for complex external compensation mechanisms while achieving high precision.
Solution Approach 2:
The patent replaces mechanical/physical eddy current compensation mechanisms with a computational approach. Instead of using additional hardware to physically compensate for gradient distortions, the system measures the actual gradient shape and uses software-based correction in the reconstruction process.
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 approach reduces artifacts by accurately correcting the k-space trajectory, improving image quality and reducing spatially varying electromagnetic field imperfections without the need for additional sensors or complex data integration, serving as a supplement to eddy current compensation.
Implementation Method 1
magnetic resonance imaging (MRI) techniques face challenges in accurately assigning magnetic resonance signals to k-space points
Implementation Method 2
a measurement gradient pulse is used to record magnetic resonance signals for sampling the k-space
Implementation Method 3
by gradient pulses generated by a gradient coil array
Data Source
AI summary
A method for operating a magnetic resonance facility in which a measurement gradient pulse is used to record magnetic resonance signals for sampling k-space along a trajectory section. The recorded magnetic resonance signals are assigned to k-space points using a shape function describing the time profile of the measurement gradient pulse. To correct deviations of the real time profile of the measurement gradient pulse from an assumed target profile, a first correction measurement is performed to ascertain first magnetic resonance signals of the trajectory section. A second correction measurement is then performed using a reference sampling pattern or a reference gradient pulse with fewer deviations from an assigned reference target profile. If a deviation criterion is met, a correction function for the shape function is ascertained by aligning the first and second magnetic resonance signals to one another, providing correction information to be used in an imaging measurement.