MRI Fat-Water Separation Using Asymmetric Gradient Phase Differences
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic resonance imaging (MRI) techniques face challenges in reducing acquisition time and minimizing artifacts caused by asymmetric gradient activity and eddy currents, particularly in separating fat and water signals using spin echo sequences.
Innovation Solution
Acquiring two spin echo signals with phase differences Δ and −Δ, where Δ is within the interval (0, π), allowing for more symmetric gradient activity and reduced acquisition time, thereby omitting the need for rewinding gradients and minimizing artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If in-phase and opposed-phase readouts are used to separate fat and water signals, then material separation is achieved, but gradient activity becomes asymmetric leading to eddy currents and gradient nonlinearity artifacts
Solution Approach 1:
The patent applies asymmetry by intentionally using asymmetric gradient activity for the in-phase and opposed-phase readouts. This asymmetric gradient design allows the spins to be at opposite phases during readout, enabling fat-water separation while the asymmetry is deliberately controlled to manage eddy current effects. The key is that the asymmetry serves the functional purpose of material separation while being accounted for in the reconstruction process.
Solution Approach 2:
The patent changes the timing parameters of the MRI sequence by introducing a specific time offset between the in-phase and opposed-phase readouts. This parameter change ensures that when one material is being read out, the other material's spins are at opposite phase, enabling separation. The time offset parameter is carefully selected based on the resonance frequency difference between fat and water to achieve the desired phase opposition.
2Object-affected harmful factors
If rewinding gradients are applied to compensate for momentum asymmetry, then gradient nonlinearity effects are reduced, but acquisition time increases
Solution Approach 1:
The patent extracts or removes the rewinding gradient component from the sequence by using asymmetric gradients from the outset. Instead of applying symmetric gradients and then adding a compensating rewind gradient, the method uses inherently asymmetric gradients that achieve both the fat-water separation and the momentum compensation in a single gradient application, thereby eliminating the need for separate rewinding gradients and reducing acquisition time.
Solution Approach 2:
The patent merges the fat-water separation function and the gradient momentum compensation function into a single asymmetric gradient application. By combining these two functions into one gradient pulse design, the sequence achieves both material separation and artifact reduction simultaneously without requiring separate rewinding gradient lobes, thus shortening the overall acquisition time.
3Measurement precision
If spin echo or turbo spin echo sequences are used for fat-water separation, then material specific imaging is achieved, but acquisition time is increased due to the need for multiple echoes
Solution Approach 1:
The patent applies partial action by using only the essential spin echo information needed for fat-water separation without requiring multiple echoes or extensive turbo spin echo sequences. The method achieves material separation with a simplified approach that captures the critical phase difference information while avoiding the time-consuming multiple echo acquisitions, thus reducing acquisition time while maintaining the necessary imaging quality.
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 reduces acquisition time and decreases artifacts in MRI images, improving image quality by ensuring more symmetric gradient activity and eliminating the need for compensatory rewinding gradients, leading to enhanced separation of fat and water signals.
Implementation Method 1
Different materials or molecules, in particular water molecules and fat molecules, have slightly different nuclear spin resonance frequencies
Implementation Method 2
when performing a magnetic resonance imaging (MRI) acquisition, their spins go in-phase and out-of-phase with each other over time
Implementation Method 3
The time points of different material spins being in-phase or having opposed phases depend on the field strength of the MRI main magnetic field
Implementation Method 4
A first spin echo signal is acquired when the excited spins of the first material and the excited spins of the second material include a first phase difference
Data Source
AI summary
Techniques are disclosed for use in magnetic resonance imaging (MRI) for exciting spins of a first material and spins of a second material. A first spin echo signal is acquired when the excited spins include a first phase difference, which is given by Δ, and a second spin echo signal is acquired when the excited spins of the first material and the excited spins of the second material include a second phase difference, which is given by −Δ. An absolute value of Δ lies within the interval ]0,π[. A first image for the first material and/or a second image for the second material is generated by a computing unit depending on the first spin echo signal and the second spin echo signal.