Dixon MR Imaging Flow Artifact Compensation
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Solution Overview
Problem
Current MR imaging techniques face challenges in efficiently compensating for flow artifacts, particularly in contrast-enhanced MR angiography combined with Dixon water/fat separation, as flow affects signal intensity and phase, leading to ghosting artifacts and other distortions.
Innovation Solution
A method involving Dixon sequences with RF pulses and switched magnetic field gradients to generate MR echo signals at multiple echo times, followed by image segmentation to isolate blood vessels, detect and compensate for blood flow-induced variations, and separate water and fat signal contributions, thereby reducing flow-related artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Dixon water/fat separation is performed in contrast-enhanced MR angiography, then water and fat signal separation is achieved, but flow artifacts such as ghosting and signal intensity variations occur due to blood flow affecting amplitude and phase
Solution Approach 1:
The patent segments the image into blood vessel regions and non-blood vessel regions using image processing techniques. By identifying blood vessel locations through analysis of signal intensity variations across multiple echo times and phase information, the method applies different artifact compensation strategies to different regions, thereby reducing flow artifacts in blood vessels while maintaining accurate water/fat separation in non-blood vessel tissues
Solution Approach 2:
The patent applies different signal processing techniques to different spatial regions. In blood vessel regions, flow-induced amplitude and phase variations are compensated using models that account for blood flow dynamics. In non-blood vessel regions, standard Dixon water/fat separation is applied. This localized approach allows the system to optimize for water/fat separation accuracy in most tissues while specifically addressing flow artifacts in vascular regions
2Adaptability or versatility
If multiple gradient echoes are acquired at different echo times for Dixon imaging, then chemical shift encoding is achieved, but flow-induced phase variations and amplitude changes complicate the separation process
Solution Approach 1:
The patent performs preliminary segmentation of blood vessel regions before executing the full water/fat separation algorithm. By pre-identifying blood vessel locations and characterizing flow-induced signal variations in these regions, the system prepares compensation parameters in advance that are then applied during the Dixon separation process, simplifying the overall computational complexity
Solution Approach 2:
The patent utilizes the natural parameter variations that occur with multiple echo times in Dixon imaging. By analyzing how signal amplitude and phase change across different echo times, the system can distinguish between flow-induced variations and true water/fat signal differences, thereby managing the complexity of signal processing while maintaining adaptability
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
Significantly reduces flow-induced artifacts such as ghosting, leakage, and swapping artifacts in MR images, improving the accuracy of water and fat separation by compensating for amplitude and phase variations within blood vessels and predicting and eliminating ghosting artifacts outside vessels.
Implementation Method 1
Image-forming MR methods which utilize the interaction between magnetic fields and nuclear spins in order to form two-dimensional or three-dimensional images
Implementation Method 2
the magnetization performs a precessional motion about the z-axis. The precessional motion describes a surface of a cone whose angle of aperture is referred to as flip angle
Implementation Method 3
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 4
This process can be reversed, similar to the formation of RF induced echoes, by appropriate gradient reversal forming a so-called gradient echo
Implementation Method 5
there is a known precessional frequency difference between hydrogens in fat and water. In its simplest form, water and fat can be seen as forming a 2-line spectrum
Data Source
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AI summary
The invention relates to a method of MR imaging of a body (10) of a patient. It is an object of the invention to provide a method that enables efficient compensation of flow artifacts, especially for MR angiography in combination with Dixon water/fat separation. The method of the invention comprises the steps of: a) generating MR echo signals at two or more echo times by subjecting the portion of the body (10) to a MR imaging sequence of RF pulses and switched magnetic field gradients, wherein the MR imaging sequence is a Dixon sequence; b) acquiring the MR echo signals; c) reconstructing one or more single-echo MR images from the MR echo signals; d) segmenting the blood vessels from the MR images; e) detecting and compensating for blood flow-induced variations of the amplitude or phase in the single-echo MR images within the blood vessel lumen, and f) separating signal contributions from water and fat spins to the compensated single-echo MR images. Moreover, the invention relates to a MR device (1) and to a computer program for a MR device (1).