EPI Phase Correction Without Navigators
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Solution Overview
Problem
Echo planar imaging (EPI) techniques in magnetic resonance imaging (MRI) suffer from Nyquist ghost artifacts due to phase errors, particularly in dynamic EPI where navigator-based corrections are inadequate, assuming uniform modulation across echoes which often leads to incomplete correction and ghost drift.
Innovation Solution
A method and apparatus that determine and remove phase errors from EPI data without relying on navigator echo data, using phase correction coefficients to correct for static and temporal phase variations, thereby minimizing Nyquist ghosting and B0 field drift in image reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If navigator-based correction methods are used to correct phase errors in dynamic EPI, then some ghost artifacts are reduced, but the correction is incomplete due to the assumption of uniform modulation across echoes, leading to ghost drift over time
Solution Approach 1:
The patent applies local quality by determining phase errors independently for each echo rather than assuming uniform modulation across all echoes. The phase correction is tailored to each specific echo's characteristics, allowing accurate correction of non-uniform phase variations and preventing ghost drift in dynamic EPI imaging
Solution Approach 2:
The patent changes the parameter approach by calculating phase errors dynamically for each echo based on actual measured data rather than using a static uniform modulation assumption. This allows the correction to adapt to temporal variations in the magnetic field and maintain accuracy throughout the imaging sequence
2Reliability
If traditional phase correction methods are used, then static ghost artifacts are reduced, but dynamic ghost drift cannot be corrected
Solution Approach 1:
The patent implements dynamics by transitioning from static phase correction to dynamic phase correction where phase errors are determined separately for each echo and temporal frame. This allows the system to adapt to changing conditions in real-time, correcting both static ghosts and dynamic ghost drift across multiple temporal frames
Solution Approach 2:
The patent applies preliminary action by determining and storing phase errors for each echo before image reconstruction. This pre-calculation of echo-specific phase errors enables accurate correction to be applied during reconstruction, addressing both static and dynamic artifacts systematically
Data Source
AI summary
An apparatus and method include a computer programmed to implement a scan sequence configured to elicit scan data, wherein the scan sequence comprises an echo planar imaging (EPI) sequence configured to elicit the image data and to acquire the scan data. The computer is also programmed to manipulate the scan data to determine a first plurality of phase errors in the image data responsible for a Nyquist ghost, wherein the manipulated scan data is free of navigator echo data, remove the first plurality of phase errors from the image data, and reconstruct an image based on the image data having the first plurality of phase errors removed therefrom.