Single Spin Echo mPFG MRI Without Concomitant Gradient Artifacts
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Solution Overview
Problem
Existing diffusion tensor imaging (DTI) methods struggle to accurately measure and map neural tissue microstructure due to limitations such as reduced signal-to-noise ratio (SNR) and increased scan time, and are hindered by concomitant gradient field artifacts in multiple pulsed field gradient (mPFG) methods, which limit the resolution of microscopic features in neural tissue.
Innovation Solution
A single spin echo MR sequence is used to generate b-matrices of arbitrary shape, size, and orientation without concomitant gradient field artifacts, utilizing trapezoidal diffusion gradient pulses and random selection of diffusion weightings to estimate the full 6D diffusion tensor distribution (DTD) in neural tissue, capturing features of anisotropy and heterogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple pulsed field gradient (mPFG) methods are used to resolve microscopic features, then measurement precision is improved, but concomitant gradient field artifacts are generated that limit the resolution
Solution Approach 1:
The patent extracts and removes the harmful concomitant gradient field artifacts from the mPFG measurement process by using a single spin echo sequence with symmetric gradient pulse placement, separating the diffusion encoding function from the artifact-generating asymmetric gradient structure
Solution Approach 2:
The patent applies asymmetry in reverse by enforcing symmetry in the gradient pulse placement around the 180° RF pulse, which eliminates the concomitant gradient field artifacts that arise from asymmetric gradient configurations in traditional mPFG methods
2Measurement precision
If increased spatial resolution is used to overcome DTI limitations, then measurement precision is improved, but signal-to-noise ratio is reduced and scan time is increased
Solution Approach 1:
The patent changes the diffusion weighting parameters by using multiple pulsed field gradients with varying b-matrices to probe microscopic diffusion anisotropy at the original voxel scale, avoiding the need for increased spatial resolution while maintaining measurement precision through alternative physical parameter optimization
3Measurement precision
If traditional block design mPFG experiments are used, then diffusion weighting is achieved, but echo time is increased and coherence artifacts are created
Solution Approach 1:
The patent merges multiple diffusion encoding gradient pulses into a single spin echo sequence, combining the diffusion weighting functionality with the refocusing pulse to achieve multiple b-matrix measurements without extending the echo time or creating coherence artifacts
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 efficiently measures and maps neural tissue microstructure, reducing echo time and coherence artifacts, enabling accurate estimation of the DTD and providing detailed insights into tissue heterogeneity and anisotropy, suitable for assessing diseases and developmental processes in the brain and other soft tissues.
Implementation Method 1
applying to a sample a plurality of sets of diffusion-sensitizing gradient pulse pairs separated by a diffusion time
Implementation Method 2
diffusion-sensitizing gradient pulses are symmetric about a 180° pulse
Implementation Method 3
A single spin echo MR sequence is used to generate b-matrices of arbitrary shape, size, and orientation without concomitant gradient field artifacts
Implementation Method 4
applying first multi-directional diffusion sensitizing gradient pulses to a specimen and then applying a 180° pulse during a diffusion time
Data Source
AI summary
Diffusion sensitizing gradient pulse pairs are prescribed in a manner to mitigate effects of concomitant gradient artifacts. Measured MR signals generated by applying a plurality of diffusion sensitizing gradient matrices are obtained and processed to determine a second order mean diffusion tensor and a fourth order covariance tensor. Quantities derived from these tensors are measured and mapped within an imaging volume which describe features of diffusion anisotropy and heterogeneity within each imaging voxel.