Diffusion Weighted MR Signal Coherence Path Suppression
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Solution Overview
Problem
Diffusion-weighted magnetic resonance imaging techniques face challenges in suppressing unwanted signal coherence paths, leading to image artifacts and geometric distortions, particularly due to residual eddy currents and high gradient system loading, which affect signal-to-noise ratio and echo time.
Innovation Solution
A method that adjusts the gradient moments of diffusion coding gradients based on a threshold to suppress unwanted coherence paths, using a combination of diffusion and dephasing gradients, ensuring that these paths are reduced without extending the echo time, thereby optimizing gradient system utilization and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If bipolar double spin echo schemes are used to compensate eddy current fields, then geometric distortions are reduced, but echo time is extended and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent changes the gradient moment parameters of diffusion coding gradients to suppress unwanted coherence paths. By adjusting these parameters, the method achieves distortion reduction without requiring additional RF pulses that would extend echo time, thus resolving the contradiction between reducing geometric distortions and maintaining short echo times.
Solution Approach 2:
The patent extracts and suppresses unwanted coherence paths (such as stimulated echo signals and free induction decay signals) by applying specific gradient moment conditions. This extraction of harmful signal components allows the main signal to be preserved without additional processing time, avoiding echo time extension.
2Object-generated harmful factors
If additional spoiler gradients are applied to suppress unwanted coherence paths, then image artifacts are reduced, but echo time is extended and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent merges the suppression of unwanted coherence paths with the existing diffusion coding gradients. Instead of adding separate spoiler gradients, the method combines the dephasing effect with the diffusion weighting process, achieving artifact reduction without additional time consumption that would extend echo time.
Solution Approach 2:
The diffusion coding gradients are made multi-functional: they simultaneously provide diffusion weighting, suppress unwanted coherence paths, and maintain echo time efficiency. This universal application of the gradient moments eliminates the need for separate spoiler gradients while preserving signal-to-noise ratio.
3Reliability
If monopolar spin echo acquisition sequence is used for diffusion coding, then diffusion weighting is achieved, but geometric distortions and residual eddy current fields are strong
Solution Approach 1:
The patent introduces asymmetry in the gradient moment configuration to suppress specific coherence paths. By making the gradient moments asymmetric with respect to the diffusion encoding process, unwanted signal paths are selectively suppressed while maintaining the desired diffusion weighting, thus reducing geometric distortions.
Solution Approach 2:
The patent converts the harmful effect of diffusion-related signal dephasing into a beneficial suppression mechanism. The same gradient moments that provide diffusion weighting are configured to simultaneously suppress unwanted coherence paths, turning the potential harm of signal loss into a benefit for artifact reduction.
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 suppresses unwanted coherence paths, improving signal-to-noise ratio and reducing geometric distortions, while maintaining short echo times and efficiently utilizing the gradient system, thus enhancing the quality of diffusion-weighted MR images.
Implementation Method 1
the diffusion of water molecules reduces along the applied field gradients of the magnetic resonance (MR) signal
Implementation Method 2
two strongly symmetrical gradients are positioned on each side of a 180° refocusing pulse in a spin echo sequence
Implementation Method 3
two strongly symmetrical gradients are positioned on each side of a 180° refocusing pulse in a spin echo sequence
Implementation Method 4
Every activation and deactivation of field gradients can cause such eddy currents that decay with different time constants
Data Source
AI summary
In a method for diffusion-weighted acquisition of MR signals with an acquisition sequence that includes a diffusion module with multiple diffusion coding gradients and a readout module with readout gradients to acquire the MR signals, the acquisition sequence is configured to acquire MR signals that correspond to a predetermined signal coherence path. The method includes the acquisition of MR signals with the acquisition sequence, and the diffusion coding gradients are activated with predetermined gradient moments during the acquisition sequence. The gradient moments of the diffusion coding gradients are set such that MR signals that correspond to other coherence paths than the predetermined coherence path are reduced, wherein the adjustment of the gradient moments to achieve a predetermined reduction ensues on the basis of a threshold.