Dixon MR Water-Fat Separation Flow Artifact Suppression
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Solution Overview
Problem
Dixon water/fat MR imaging methods using bipolar acquisition strategies suffer from flow-induced leakage and swapping artifacts, particularly in MR angiography, which can lead to misinterpretation of blood vessels and stenosis severity.
Innovation Solution
The method involves acquiring pairs of echo signals at two different echo times with repeated phase encodings during multiple cardiac phases, reconstructing phase images to account for blood flow velocity variations, and using these images to suppress flow-induced artifacts in the final diagnostic image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bipolar acquisition strategy is used for Dixon water/fat MR imaging, then scan efficiency is improved, but flow-induced leakage and swapping artifacts increase
Solution Approach 1:
The method performs preliminary identification of flow-induced artifacts by comparing phase images from different cardiac phases before final water/fat separation. Phase errors are detected and corrected in advance, preventing leakage and swapping artifacts in the final diagnostic images while maintaining bipolar acquisition efficiency
Solution Approach 2:
The method uses feedback by comparing phase information from multiple cardiac phases to identify flow-induced phase errors. This feedback mechanism allows the system to detect and correct artifacts that occur during bipolar acquisition, resolving the contradiction between scan efficiency and artifact suppression
2Measurement precision
If multiple cardiac phases are acquired to suppress flow artifacts, then image quality is improved, but scan time increases
Solution Approach 1:
The method applies partial action by acquiring multiple cardiac phases only in regions where flow-induced artifacts are likely to occur, rather than uniformly across the entire imaging volume. This selective approach improves image quality in critical areas while minimizing the increase in scan time
Solution Approach 2:
The method changes parameters by utilizing phase information from multiple cardiac phases to identify and correct flow-induced phase errors. By dynamically adjusting the correction based on detected phase variations, the system improves image quality without requiring excessive additional scan time
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 significantly reduces flow-induced leakage and swapping artifacts, resulting in high-quality water/fat-separated images with accurate representation of blood flow and reduced misallocation of signals.
Implementation Method 1
The magnetic field B0 produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field) of defined frequency (so-called Larmor frequency, or MR frequency)
Implementation Method 2
The magnetic field B0 produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field) of defined frequency (so-called Larmor frequency, or MR frequency). From a macroscopic point of view the distribution of the individual nuclear spins produces an overall magnetization which can be deflected out of the state of equilibrium by application of an electromagnetic pulse of appropriate frequency (RF pulse) perpendicular to the z-axis, so that the magnetization performs a precessional motion about the z-axis
Implementation Method 3
After termination of the RF pulse, the magnetization relaxes back to the original state of equilibrium, in which the magnetization in the z direction is built up again with a first time constant T1 (spin-lattice or longitudinal relaxation time), and the magnetization in the direction perpendicular to the z direction relaxes with a second time constant T2 (spin-spin or transverse relaxation time)
Implementation Method 4
In order to realize spatial resolution in the body, constant magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field B0, leading to a linear spatial dependency of the spin resonance frequency
Implementation Method 5
These contributions can be calculated if information from two or more corresponding echoes, acquired at different echo times, is combined. This may be considered as chemical shift encoding, in which an additional dimension, the chemical shift dimension, is defined and encoded by acquiring two or more MR images at slightly different echo times
Data Source
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AI summary
The invention relates to a method of Dixon-type MR imaging. It is an object of the invention to provide a method that enables efficient and reliable Dixon water/fat separation, in particular using a bipolar acquisition strategy, while avoiding flow-induced leakage and swapping artifacts. According to the invention, an imaging sequence is executed which comprises at least one excitation RF pulse and switched magnetic field gradients, wherein pairs of echo signals are generated at two different echo times (TE1, TE2) and during two or more different cardiac phases (AW1, AW2). The echo signals are acquired and phase images are reconstructed therefrom. A final diagnostic image is reconstructed from the echo signal data using water/fat separation, wherein regions of flow and/or estimates of flow- induced phase errors are derived from the phase images to suppress or compensate for flow- induced leakage and/or swapping artifacts in the final diagnostic image. Therein, flow- induced phase offsets are determined by voxel-wise comparison of the phase images associated with the different cardiac phases. Moreover, the invention relates to a MR device (1) and to a computer program to be run on a MR device (1).