Two-Dimensional Phase Correction for MRI Ghost Artifacts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional phase/magnitude correction techniques in MRI are one-dimensional, failing to address two-dimensional phase/magnitude differences in EPI scans, leading to ghost artifacts in single shot and multi-shot echo planar imaging.
Innovation Solution
A method and system for two-dimensional phase/magnitude correction in MRI, involving a pre-scan with reduced phase encoding gradient to calculate one-dimensional and two-dimensional phase corrections, applied during image reconstruction to correct k-space lines acquired under different polarity gradients, effectively reducing ghost artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one-dimensional phase correction is applied, then the correction process is simple, but it cannot remove ghost artifacts caused by two-dimensional phase/magnitude differences
Solution Approach 1:
The patent transitions from one-dimensional phase correction (along readout direction only) to two-dimensional phase correction (along both readout and phase encoding directions). This is achieved by acquiring reference data with reduced phase encoding gradient and calculating 2D phase correction values that account for phase/magnitude differences in both x and y directions, thereby eliminating ghost artifacts that 1D correction cannot remove.
Solution Approach 2:
The patent performs a pre-scan with reduced phase encoding gradient before the actual EPI scan to acquire reference data. This preliminary action allows calculation of 2D phase correction values in advance, which are then applied during image reconstruction to correct phase/magnitude inconsistencies without requiring additional scanning time during the main acquisition.
2Ease of operation
If conventional pre-scan with zero phase-encoding gradient is applied, then the scan setup is simple, but it cannot correct artifacts from inconsistent k-space lines
Solution Approach 1:
The patent changes the phase encoding gradient parameter from zero (conventional pre-scan) to a reduced value (no more than half of the phase encoding gradient used in the main scan). This parameter change allows the reference scan to capture phase/magnitude information in both readout and phase encoding directions, enabling 2D phase correction while maintaining relatively simple scan setup.
3Reliability
If two-dimensional phase correction is applied, then ghost artifacts are significantly reduced, but the correction calculation complexity increases
Solution Approach 1:
The patent performs phase correction calculations during a preliminary reference scan with reduced phase encoding gradient, obtaining 2D phase correction values before the main EPI acquisition. This preliminary calculation approach allows complex 2D correction to be performed once, and the correction values are then applied efficiently during reconstruction of the actual scan data, reducing real-time computational burden.
Solution Approach 2:
The patent introduces reference data acquired with reduced phase encoding gradient as an intermediary element. This reference data serves as a mediator that captures the phase/magnitude characteristics of the system, allowing 2D phase correction values to be calculated and then applied to correct the main EPI data without requiring direct complex processing of the main scan data itself.
Data Source
AI summary
Phase and magnitude correction is performed in two dimensions to reduce ghosting in single shot and multi-shot EPI scans. First, a phase/magnitude correction in the readout direction is carried out to reduce echo shifts and gradient waveform distortions. Then, a two dimensional phase/magnitude correction is performed to remove the remaining xy phase/magnitude errors.