MRI Phase Correction for Non-Cartesian Field Inhomogeneity
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Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face challenges in correcting imaging errors caused by field inhomogeneities resulting from eddy currents, particularly in non-Cartesian sampling schemes, where linear corrections are insufficient for non-linear field perturbations, leading to significant image disturbances.
Innovation Solution
A method involving the acquisition of magnetic resonance data in both gradient directions to determine phase differences, which are then used to calculate correction information. This correction information is applied to transform and rectify signal curves in the k-space, allowing for improved image reconstruction by compensating for field inhomogeneities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a delay time correction is applied to compensate for field inhomogeneities, then linear field perturbations can be corrected, but non-linear field perturbations cannot be adequately compensated, leading to residual image disturbances
Solution Approach 1:
The patent changes the correction model from a simple delay time parameter to a phase correction model with multiple parameters (phase shift, gradient strength, position dependence). This allows the correction to account for non-linear field perturbations by fitting a phase function that can capture complex spatial variations in the magnetic field inhomogeneities.
Solution Approach 2:
The correction method dynamically adjusts the phase correction based on the specific imaging conditions and measured field inhomogeneities. The phase correction is calculated individually for each k-space line and position, allowing the system to adapt to varying field perturbation patterns rather than using a fixed correction model.
2Productivity
If non-Cartesian sampling schemes are used to improve imaging capabilities, then acquisition efficiency increases, but field inhomogeneities cause strong artifacts in reconstructed image data
Solution Approach 1:
The patent converts the harmful field inhomogeneities into correctable phase differences by measuring them during the acquisition process. The phase differences are extracted from the signal and used to calculate correction information, transforming the artifact-causing field variations into useful correction data that improves image quality.
Solution Approach 2:
The method incorporates feedback by measuring the actual field inhomogeneities during the non-Cartesian acquisition and using this information to calculate phase corrections. The correction information is then applied to the k-space data to compensate for the field perturbations, creating a closed-loop correction system that adapts to the specific imaging conditions.
3Device complexity
If field inhomogeneities are not corrected, then the correction process remains simple, but significant image disturbances such as ghosting and local signal extinctions occur
Solution Approach 1:
The patent performs preliminary measurement of the field inhomogeneities during the acquisition process, extracting phase difference information before the final image reconstruction. This preliminary action allows the correction to be calculated and applied in advance, preventing artifacts from degrading image quality rather than correcting them after they occur.
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
The method effectively corrects for field inhomogeneities, enhancing image quality by accurately accounting for phase errors and field strength variations, even in regions with low signal amplitudes, thereby reducing artifacts and improving the accuracy of image reconstruction.
Implementation Method 1
determining a respective phase difference for a plurality of reference points along a respective position space line in the position space, which line extends in the respective gradient direction, on the basis of a difference between a determined first phase of the magnetic resonance signal at the respective reference point and a determined second phase of the magnetic resonance signal at the respective reference point
Implementation Method 2
correcting imaging errors of a magnetic resonance imaging scan by transforming and rectifying signal curves in a k-space on the basis of the correction information
Data Source
AI summary
In a method for ascertaining correction information for correcting a magnetic resonance imaging scan, respective first and second magnetic resonance data for at least one gradient direction are acquired, where the first magnetic resonance data is acquired while the magnetic field gradient is applied in the respective gradient direction, and the second magnetic resonance data is acquired while the magnetic field gradient is applied counter to the respective gradient direction. The method may further include determining a respective phase difference for reference points along a respective position space line in the position space that extends in the respective gradient direction based on the first and second magnetic resonance data, and providing the phase differences of at least one subgroup of the reference points as correction information or ascertaining the provided correction information based on the phase differences of at least the subgroup of the reference points.