MRI Distortion Correction via Reversed Gradient Averaging
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face distortions due to imperfections in static and gradient magnetic fields, particularly in high-speed Echo Planar Imaging (EPI), which limit the accuracy and utility of image detection, especially near air-tissue boundaries.
Innovation Solution
A method involving machine-implemented techniques to estimate voxel displacements by minimizing a cost function expressing the difference between MRI images acquired with opposite gradient fields, using sparse matrix techniques and regularization to reduce distortion, allowing for the construction of a deformation field that corrects image distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed Echo Planar Imaging (EPI) is used for fast imaging, then imaging speed and image definition are improved, but image distortion caused by magnetic field inhomogeneities worsens
Solution Approach 1:
The patent applies the reversed gradient method where a second EPI image is acquired using opposite gradient directions. The distortion correction is achieved by averaging the two images, which cancels out the first-order magnetic field inhomogeneity distortions. This inversion approach allows fast EPI imaging while correcting the inherent distortion problem.
Solution Approach 2:
The patent introduces an intermediary correction field that is calculated from the difference between the two EPI images. This intermediary distortion correction field is then applied to the images to compensate for magnetic field inhomogeneities, enabling both fast imaging and high accuracy.
2Manufacturing precision
If magnetic field gradients are increased to improve image definition, then spatial resolution is improved, but distortion from field inhomogeneities worsens
Solution Approach 1:
The patent uses opposite gradient fields as a counterweight to the distortion caused by magnetic field inhomogeneities. By acquiring images with reversed gradient directions and averaging them, the harmful distortion effects are counteracted, allowing high gradient strengths to be used for improved spatial resolution without suffering from increased distortion.
3Manufacturing precision
If distortion correction methods are applied to EPI images, then image accuracy is improved, but processing time and complexity increase
Solution Approach 1:
The patent performs preliminary action by acquiring two EPI images with opposite gradient directions before the actual distortion correction is needed. This preliminary acquisition of paired images allows the distortion correction to be computed efficiently through simple averaging, reducing the overall processing complexity compared to more complex iterative correction methods.
Data Source
AI summary
Systems and techniques for reducing distortions in magnetic resonance images. In one aspect, machine-implemented method for reducing image distortion in magnetic resonance imaging (MRI) includes receiving a first MRI image and a second MRI image, estimating displacements of voxels between the first MRI image and the second MRI image by minimizing a cost function expressing a cost of the displacements, reducing distortion in an MRI image using the estimated displacements, and making the MRI image having reduced distortion available. The first MRI image and the second MRI image were acquired using different gradient fields.