Dynamic k-space expansion for MR spectroscopic imaging
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Solution Overview
Problem
Spectral line broadening due to magnetic field inhomogeneity in MR spectroscopic imaging (MRSI) limits detection sensitivity and spectral quantification, particularly in brain regions like the orbital frontal cortex and temporal lobe, making it difficult to measure singlet concentrations and multiple resonances, and introduces spatial aliasing and baseline artifacts.
Innovation Solution
A dynamic shimming method that interleaves alternating positive and negative gradient blips between Proton Echo Planar Spectroscopic Imaging (PEPSI) readout gradients to counteract local gradients, expanding k-space with increasing spectral encoding time and readout gradients, thereby compensating for dephasing and reducing spectral line broadening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the voxel size is reduced to reduce the effect of B0 inhomogeneity and spectral line broadening, then spectral line broadening is reduced, but the signal-to-noise ratio per unit time decreases linearly with voxel volume
Solution Approach 1:
The patent applies dynamic k-space expansion where the k-space boundaries are dynamically adjusted based on the local gradient magnitude and spectral encoding time. The effective k-space boundaries are defined as kmax(t) = kmax(0) - γGlt, allowing the acquisition window to adapt to the dephasing caused by local gradients. This dynamic adjustment compensates for the signal loss without requiring smaller voxels, thus maintaining SNR while reducing spectral line broadening.
2Manufacturing precision
If higher order shim coils or better control over existing coils are used to improve B0 shimming capability, then magnetic field inhomogeneity correction is improved, but device complexity and hardware requirements increase
Solution Approach 1:
The patent changes the parameters of the acquisition process rather than modifying the hardware. By dynamically adjusting the k-space boundaries based on local gradient measurements and spectral encoding time, the method achieves B0 shimming capability without adding higher order shim coils or complex control systems. The effective field of view in k-space is modulated to compensate for inhomogeneity effects.
3Measurement precision
If spectral encoding time is increased to improve spectral resolution, then spectral quantification capability is improved, but signal dephasing due to local gradients increases causing spectral line broadening
Solution Approach 1:
The patent implements dynamic k-space expansion where the effective k-space boundaries are continuously adjusted during spectral encoding based on the local gradient magnitude and elapsed time. The boundaries are defined as kmax(t) = kmax(0) - γGlt, which dynamically compensates for the signal dephasing that accumulates with longer spectral encoding times. This allows extended spectral encoding for better resolution without suffering from gradient-induced line broadening.
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 effectively compensates for local gradients in multiple brain regions, resulting in spectral line narrowing and improved signal acquisition without increasing spatial encoding time, maintaining high signal-to-noise ratio (SNR) efficiency.
Implementation Method 1
A dynamic shimming method that interleaves alternating positive and negative gradient blips between Proton Echo Planar Spectroscopic Imaging (PEPSI) readout gradients to counteract local gradients
Implementation Method 2
expanding k-space with increasing spectral encoding time and readout gradients, thereby compensating for dephasing and reducing spectral line broadening
Data Source
AI summary
A method for the compensation of magnetic field inhomogeneity in magnetic resonance spectroscopic imaging comprising the steps of using dynamic k-space expansion in combination with parallel imaging.