MRI Diffusion Imaging With Slab-Selective Gradient-Echo Readout
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Solution Overview
Problem
Conventional diffusion-weighted imaging techniques suffer from spatial distortions and specific absorption rate (SAR) limitations, especially at high main field strengths, and lack robust correction for motion-induced magnitude and phase errors.
Innovation Solution
A magnetic resonance imaging method using a slab-selective tip-down radio frequency pulse combined with a reduced field of view (rFOV) approach, incorporating a diffusion preparation module with a gradient echo readout and phase navigator for accurate geometric fidelity and data quality, minimizing SAR and T1 contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional diffusion-weighted imaging uses a diffusion preparation module with diffusion-sensitizing gradients combined with a two-dimensional spin-echo single-shot echo planar imaging (SS-EPI) readout module, then diffusion imaging can be performed, but spatial distortions occur especially for high resolution acquisitions and at higher main field strengths
Solution Approach 1:
The patent changes the readout module type from spin-echo SS-EPI to gradient echo readout, which fundamentally alters the imaging parameters and physics to eliminate the source of spatial distortions while maintaining diffusion weighting capabilities
Solution Approach 2:
The patent uses a phase navigator echo to create a reference copy of the phase information, which is then used to correct phase errors in the actual diffusion-weighted images, thereby achieving accurate geometric fidelity without the spatial distortions of conventional methods
2Manufacturing precision
If a diffusion-preparation module is combined with a turbo spin echo (TSE) or balanced steady-state free precession (bSSFP) readout module for distortion-free diffusion imaging, then spatial distortions are reduced, but specific absorption rate (SAR) limitations occur especially at high main field strength
Solution Approach 1:
The patent changes the readout module from TSE or bSSFP to gradient echo readout, which uses different physical principles and significantly reduces the radiofrequency energy deposition, thereby lowering SAR while maintaining distortion-free imaging capabilities
Solution Approach 2:
The patent replaces the spin-echo based readout mechanism with a gradient echo based readout mechanism, substituting one physical system with another that achieves the same imaging goal but with lower energy consumption and reduced SAR
3Use of energy by moving object
If a diffusion preparation module is combined with low SAR T1 gradient-echo readout modules, then specific absorption rate is reduced, but a relatively long readout duration is required resulting in increased T1 contamination of the acquired magnetic resonance signal
Solution Approach 1:
The patent applies a phase navigator echo before the actual readout to pre-measure and characterize the phase evolution, allowing for predictive correction of phase errors during the readout process, thereby enabling faster readout without increasing T1 contamination
4Loss of time
If the tip-down radio frequency pulse is made slab-selective by applying a first slab selection gradient pulse in a phase-encoding direction, then the field of view is reduced and readout time is shortened, but the complexity of the pulse sequence increases
Solution Approach 1:
The patent applies slab selection only in the phase-encoding direction rather than in all three spatial dimensions, creating a localized reduction in field of view that shortens readout time while avoiding the full complexity of three-dimensional slab selection
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 method achieves high geometric fidelity and data quality with reduced spatial distortions and SAR, while effectively correcting for motion-induced phase errors, enhancing diffusion imaging accuracy.
Implementation Method 1
magnetic resonance diffusion data are acquired in at least one repetition... a magnetic resonance sequence comprising, in each repetition: a diffusion preparation module, comprising at least one tip-down radio frequency pulse
Implementation Method 2
at least one diffusion gradient pulse group between the tip-down pulse and the tip-up pulse... apply symmetric, strong diffusion-sensitizing gradients (often shortly 'diffusion gradients')
Implementation Method 3
at least one tip-up radio frequency pulse... after spins have been excited by a tip-down pulse
Implementation Method 4
a readout module... acquire magnetic resonance diffusion data in k-space
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for operating a magnetic resonance imaging device (16), wherein, for diffusion imaging in an acquisition volume of a patient, a magnetic resonance sequence is used to acquire magnetic resonance diffusion data, wherein the acquisition volume is divided into partitions in a partition direction and the magnetic resonance sequence comprises, in a repetition for each partition: - a diffusion preparation module (1), comprising at least one tip-down radio frequency pulse (4) and at least one diffusion gradient pulse group following the tip-down pulse (4), and - a three-dimensional gradient echo readout module (2), wherein the tip-down radio frequency pulse (4) is slab-selective by applying a slab selection gradient pulse (5) in a phase-encoding direction and the three-dimensional gradient echo module (2) only covers the slab excited by the tip-down radio frequency pulse (4) in the phase-encoding direction.