Alternating Gradient MRI Encoding for 3D k-Space
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Solution Overview
Problem
Current parallel MRI techniques face limitations in achieving high acceleration factors for three-dimensional image acquisitions without detrimental effects on g-factor performance, leading to reduced image quality due to aliasing and SNR penalties.
Innovation Solution
The method employs alternating magnetic field gradients during readout to provide differential encoding of echo signals, spreading aliasing patterns uniformly throughout k-space, allowing for improved separation of aliased signals and reduced g-factor penalty.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If parallel MRI techniques are used to accelerate three-dimensional image acquisitions, then scan time is reduced, but g-factor performance deteriorates leading to reduced image quality
Solution Approach 1:
The patent segments k-space into multiple segments and acquires data from different segments using different receiver coils. This segmentation allows for more flexible sampling patterns and enables the use of multiple coils to capture different spatial frequencies, thereby accelerating acquisition while maintaining image quality through proper reconstruction algorithms that account for the segmented sampling pattern
Solution Approach 2:
The patent extends parallel imaging from two-dimensional to three-dimensional k-space sampling. By utilizing the third dimension (partition encoding direction) for coil sensitivity variation, the method achieves better g-factor performance because the additional spatial dimension provides more independent information from each coil, improving the conditioning of the reconstruction problem
2Productivity
If high acceleration factors are used in parallel MRI, then productivity increases, but signal-to-noise ratio deteriorates due to g-factor penalty
Solution Approach 1:
The patent applies different sampling densities to different regions of k-space, with higher sampling density in regions where coil sensitivity variations provide less information and lower sampling density where coil sensitivity variations provide more information. This local optimization of sampling strategy maximizes the information content acquired per unit time while maintaining acceptable image quality and SNR
Solution Approach 2:
The patent combines data from multiple receiver coils with different sensitivity profiles to form a composite dataset. By properly weighting and combining the signals from multiple coils during reconstruction, the method achieves higher acceleration factors while maintaining SNR through the diverse spatial information provided by each coil in the composite dataset
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 ability to separate aliased signals with reduced g-factor penalty, improving image quality and enabling higher acceleration factors in three-dimensional MRI acquisitions.
Implementation Method 1
magnetic field gradients (Gx, Gy, and Gz) are employed
Implementation Method 2
MRI uses the nuclear magnetic resonance ('NMR') phenomenon to produce images
Implementation Method 3
the individual magnetic moments of the nuclei in the tissue attempt to align with this magnetic field, but precess about it in random order at their characteristic Larmor frequency, ω
Data Source
AI summary
A method for imaging a subject with a magnetic resonance imaging (MRI) system using controlled aliasing is provided. A radio frequency (RF) excitation field is applied to excite the spins in a volume-of-interest that may include multiple slice locations. Using the MRI system, a readout magnetic field gradient is established following the application of the RF excitation field to form echo signals. These echo signal receive a differential encoding by way of establishing, while the readout gradient is established, alternating magnetic field gradients along two directions, such as the partition-encoding and phase-encoding directions. Image data is acquired from the formed echo signals and images of the subject are reconstructed from the acquired image data.