Propeller EPI Phase Error Correction in MRI
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Solution Overview
Problem
The EPI-PROPELLER technique in MRI is inefficient in correcting constant, linear, and oblique phase errors, requiring time-consuming blade-by-blade reference scans, which degrades image quality due to motion artifacts and Nyquist ghosts.
Innovation Solution
A method using two or three reference scans to determine constant, linear, and oblique phase errors, allowing for efficient correction of phase errors across multiple blades in MRI systems, thereby improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If blade-by-blade reference scans are used to correct phase errors, then phase error correction accuracy is improved, but scanning time increases and motion artifacts worsen
Solution Approach 1:
The patent segments the phase error correction process into two distinct parts: (1) a single comprehensive reference scan that captures all phase error characteristics, and (2) efficient application of correction parameters across multiple blades. This segmentation eliminates the need for repeated reference scans for each blade while maintaining correction accuracy.
Solution Approach 2:
The patent performs preliminary phase error characterization through a single reference scan before acquiring the actual imaging data. The phase error parameters (constant, linear, and oblique) are determined in advance and then applied to correct all subsequent blades, preventing the need for time-consuming per-blade reference scans.
2Measurement precision
If blade-by-blade reference scans are used to correct phase errors, then phase error correction accuracy is improved, but image quality deteriorates due to motion artifacts
Solution Approach 1:
The patent separates the reference scan from the imaging data acquisition, performing the reference scan once before all imaging blades. This segmentation ensures that the phase error characteristics are captured without being contaminated by motion artifacts that may occur during the imaging process itself.
Solution Approach 2:
By performing the reference scan preliminarily before any imaging data is collected, the patent captures phase error characteristics under stable conditions. The correction parameters derived from this preliminary scan are then applied to all subsequent blades, preventing motion artifacts from degrading the correction accuracy.
3Measurement precision
If multiple reference scans are used to correct all phase errors, then correction comprehensiveness is improved, but device complexity increases
Solution Approach 1:
The patent designs a universal reference scan protocol that can determine all three types of phase errors (constant, linear, and oblique) through a single scan configuration. This universal approach eliminates the need for multiple specialized reference scans, reducing device complexity while maintaining comprehensive correction capability.
Solution Approach 2:
The patent employs parameter change techniques where a single reference scan is performed with varying gradient parameters to extract all necessary phase error characteristics. By systematically varying parameters within one reference scan rather than performing multiple separate scans, the patent achieves comprehensive correction with reduced complexity.
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 significantly reduces motion artifacts and Nyquist ghosts, enhancing the efficiency and quality of MRI images by correcting phase errors across multiple blades with fewer reference scans.
Implementation Method 1
The main magnetic field B0 results in magnetization of the atomic nuclei that are aligned with the main magnetic field B0
Implementation Method 2
The RF pulse can cause the magnetization of the atomic nuclei to nutate away from the direction of the main magnetic field B0
Implementation Method 3
the magnetization of the atomic nuclei precesses about the main magnetic field B0 while returning to an equilibrium state, causing emission of RF radiation at a characteristic frequency
Implementation Method 4
The magnetic field gradients are typically applied along one or more orthogonal axes (x, y, z), the z-axis usually being aligned with the main magnetic field B0, and introduce spatially distributed variations in frequency or phase of the precessing nuclear spins
Data Source
AI summary
In PROPELLER utilizing EPI k-space sampling, phase errors arising primarily from eddy currents can considerably degrade image quality. The phase errors include spatially constant phase errors, spatially linear phase errors, and oblique phase errors. Methods to measure and correct for these phase errors are disclosed. Two or three reference scans are acquired, each reference scan being mutually orthogonal along the orthogonal physical gradient axes in a MRI system. A spatially constant phase error and a spatially linear phase error are determined from each of the reference scans for each relevant physical gradient axis. These phase errors can be used to predict the constant, linear, and oblique phase errors in each blade of an EPI PROPELLER k-space data set. With the known phase errors for each blade, constant, linear, and/or oblique phase correction is applied prior to or during PROPELLER image reconstruction, producing an image with substantially reduced artifacts.