MRI Phase Correction via Dynamic FOV Stretch Factor
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Solution Overview
Problem
Magnetic resonance imaging (MRI) using Echo Planar Imaging (EPI) techniques experiences image distortion due to phase errors caused by static magnetic field nonuniformity and vortex magnetic field switching, which are challenging to correct with existing two-dimensional phase correction methods, especially when the Field of View (FOV) stretch factor is fixed, leading to aliasing and incomplete object representation.
Innovation Solution
The MRI apparatus dynamically adjusts the FOV stretch factor based on the object size and shape, as well as the phase encode direction, during the template shot to generate accurate phase correction data, allowing for improved two-dimensional phase correction and reducing aliasing by optimizing the FOV size in the phase encode direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fixed FOV stretch factor is used in template shot, then the imaging process is simple and fast, but the object region may not be fully captured within the FOV leading to aliasing and incomplete phase correction
Solution Approach 1:
The patent applies dynamics by making the FOV stretch factor variable rather than fixed. The system dynamically adjusts the FOV stretch factor based on the actual size of the object region detected in the sensitivity distribution image, allowing the FOV to adapt to different object sizes and ensure complete capture without aliasing while maintaining imaging efficiency
Solution Approach 2:
The patent changes the parameter of FOV stretch factor from a fixed value to a dynamically determined value based on object size. By calculating the appropriate FOV stretch factor according to the detected object region dimensions, the system optimizes both the completeness of object capture and the accuracy of phase correction
2Manufacturing precision
If the FOV is expanded to capture the entire object region, then aliasing is reduced and phase correction is more accurate, but the imaging time and processing complexity increase
Solution Approach 1:
The patent applies preliminary action by performing a sensitivity distribution measurement scan before the actual EPI imaging to detect the object region size. This preliminary detection allows the system to pre-calculate the appropriate FOV stretch factor, ensuring that the subsequent template shot and phase correction process are optimized without requiring excessive FOV expansion or additional imaging time
Solution Approach 2:
The system dynamically determines the FOV stretch factor based on actual object size rather than using a conservative fixed expansion. This dynamic adjustment ensures that the FOV is expanded only as much as necessary to capture the complete object region, minimizing unnecessary imaging time and processing complexity while achieving accurate phase correction
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 enhances the accuracy of phase correction, reduces image distortion, and improves the quality of MRI images by ensuring the entire object region is captured within the Field of View, even in cases where the object size and shape vary significantly.
Implementation Method 1
nuclear spins inside an object placed in a static magnetic field are magnetically excited
Implementation Method 2
nuclear spins inside an object placed in a static magnetic field are magnetically excited by RF signals having the Larmor frequency
Implementation Method 3
nuclear spins inside an object placed in a static magnetic field are magnetically excited by RF signals having the Larmor frequency, and an image is reconstructed from MR signals generated upon the excitation
Implementation Method 4
EPI is designed to perform imaging while reversing a gradient magnetic field at high speed
Implementation Method 5
One of the high-speed imaging methods in the field of magnetic resonance imaging is BPI (Echo Planar Imaging)
Data Source
AI summary
According to one embodiment, a magnetic resonance imaging apparatus includes processing circuitry. The processing circuitry sets imaging parameters for each scan. The processing circuitry specifies the size of the object region in the phase encode direction from a first image. The first image acquired by using a pulse sequence different from EPI. The processing circuitry sets parameters in a field of view in the phase encode direction in a phase correction scan based on the specified size and the size of the field of view in the phase encode direction in a second scan. The phase correction scan is executed for acquiring phase correction information for the first image. The second scan is executed for acquiring a second image by using EPI.