MRI Phase Shift Correction for EPI Image Distortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face issues with positional shifts in images due to frequency corrections and phase shifts during echo data readout, particularly evident in Single Shot Spin Echo Planar Imaging (SS SE EPI) methods, leading to image distortion and discontinuities when combining multiple images.
Innovation Solution
A magnetic resonance imaging apparatus and method that includes a data acquisition unit, frequency offset acquisition unit, frequency modulation unit, and phase shift correction unit to frequency-modulate the excitation pulse and cancel phase shifts in echo data during readout, thereby reducing positional shifts in images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency correction using frequency offset is applied to the excitation pulse, then image quality is improved by correcting frequency deviations, but positional shift and phase distortion occur in the reconstructed image
Solution Approach 1:
The patent applies preliminary phase correction to the echo data before image reconstruction by calculating the phase shift caused by frequency modulation and compensating for it in advance. This prevents the positional shift from occurring in the final image while maintaining the frequency correction benefit.
Solution Approach 2:
The patent converts the harmful phase shift effect into a calculable parameter by determining the relationship between frequency modulation and phase shift, then using this knowledge to apply corrective phase adjustments that eliminate the distortion while preserving the frequency correction advantage.
2Area of stationary object
If multiple images are combined by compound processing to obtain wide area images, then the field of view is expanded, but step discontinuities appear at image boundaries due to phase shifts
Solution Approach 1:
The patent applies phase correction to each individual image before combining them through compound processing. By correcting the phase shifts in advance, the images can be seamlessly concatenated without step discontinuities at the boundaries, enabling continuous wide area imaging.
3Productivity
If echo data is collected sequentially by inverting gradient magnetic field at high speed using EPI method, then imaging speed is improved, but phase shift accumulates on later echo data causing image distortion
Solution Approach 1:
The patent implements feedback by continuously tracking the phase shift accumulation during sequential echo data collection and applying compensatory phase corrections. This allows high-speed EPI imaging to proceed while maintaining image position accuracy through real-time phase management.
Solution Approach 2:
The patent calculates and applies phase correction factors to echo data in advance of reconstruction, compensating for the cumulative phase shifts that occur during high-speed sequential data collection. This maintains imaging speed while preventing distortion.
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 solution effectively reduces image positional shifts and phase-related distortions, enabling clearer and more accurate image reconstruction without step discontinuities when combining multiple images, improving the quality of MRI scans.
Implementation Method 1
MRI (magnetic resonance imaging) is an imaging method that excites atomic nuclei spins of objects put in a static magnetic field by RF signals having a Larmor frequency and then reconstructs an image from MR signals which occur in response to this excitation
Implementation Method 2
a phase shift correction unit configured to cancel a phase shift occurring on each of the pieces of echo data due to a frequency modulation according to the frequency offset during a readout of the pieces of echo data
Data Source
AI summary
A magnetic resonance imaging apparatus includes a data acquisition unit, a frequency offset acquisition unit, a frequency modulation unit and a phase shift correction unit. The data acquisition unit acquires pieces of echo data due to nuclear magnetic resonance after applying an excitation pulse. The frequency offset acquisition unit acquires a frequency offset. The frequency modulation unit frequency-modulates the excitation pulse according to the frequency offset. The phase shift correction unit cancels a phase shift occurring on each of the pieces of the echo data due to a frequency modulation according to the frequency offset during a readout of the pieces of the echo data.