Variable Echo Magnetic Resonance Fingerprinting for B0 and T1 Quantification
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Solution Overview
Problem
Magnetic resonance fingerprinting (MRF) imaging accuracy is affected by system errors such as inhomogeneity of main magnetic field B0 and RF magnetic field B1+, and the presence of fat, which complicates the quantification of tissue parameters like T1, T2*, and B0, especially when using a fixed number of echoes.
Innovation Solution
A magnetic resonance fingerprinting imaging method with a variable number of echoes is designed, where the sequence parameters, including TR duration, flip angle, and echo time, are optimized to encode and decode tissue and system parameters like T1, T2*, B0, and B1+, allowing for simultaneous quantification of these parameters using a spoiled gradient recalled echo sequence with an inversion pulse, and incorporating the Dixon method for water-fat separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed number of echoes is used in MRF imaging, then the imaging sequence is simple and fast, but the quantification accuracy of multiple parameters (B0, B1+, T1, T2*) is insufficient
Solution Approach 1:
The patent applies dynamics by making the number of echoes variable rather than fixed. The imaging sequence dynamically adjusts the number of echoes collected in each TR period based on the current TR duration and flip angle, allowing the sequence to adapt to different parameter encoding requirements while maintaining systematic control over the encoding process
Solution Approach 2:
The patent changes the parameter of echo number from a fixed value to a variable that depends on TR and flip angle. By establishing a correspondence relationship between TR, flip angle, and echo number, the system can encode multiple parameters (B0, B1+, T1, T2*) simultaneously while managing sequence complexity through systematic parameter coordination
2Measurement precision
If the number of echoes is increased to quantify multiple parameters, then the measurement precision improves, but the scanning time increases
Solution Approach 1:
The patent uses dynamic adjustment of echo number within each TR period to efficiently encode multiple parameters. By varying the echo number according to the specific TR and flip angle combinations, the method achieves comprehensive parameter quantification without requiring a uniformly high number of echoes throughout the entire sequence, thus reducing total scanning time
Solution Approach 2:
The patent employs periodic variation of sequence parameters including flip angle and TR duration, with the echo number adjusted periodically according to the current TR period. This periodic action allows systematic encoding of multiple parameters across different time periods while maintaining overall scanning efficiency
3Loss of information
If fat signal is included in MRF imaging, then the tissue information is more complete, but the quantification accuracy of water tissue parameters is affected due to frequency shift and different relaxation times
Solution Approach 1:
The patent applies segmentation by separating water and fat signals through their different relaxation characteristics. By using variable echo number imaging with different TR and flip angle combinations, the method can distinguish and separately quantify water and fat tissue parameters, preventing fat signal from interfering with water tissue parameter accuracy while maintaining complete tissue information
Solution Approach 2:
The patent applies local quality by treating water and fat tissues with different analysis approaches. The variable echo number sequence allows different portions of the signal (corresponding to different TR and echo combinations) to be optimized for different tissue types, enabling accurate water tissue quantification while preserving fat tissue information
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 method enables accurate quantification of B0, B1+, T1, and T2* in a single scan, improving the diagnostic capabilities for brain and fatty tissue diseases by providing multiple information representations, as demonstrated through in vivo experiments and simulations.
Implementation Method 1
Magnetic Resonance Fingerprinting (MRF) is a relatively accurate quantitative acquisition method of magnetic resonance imaging
Implementation Method 2
a dictionary reflecting the temporal variation of echo signal is established based on Bloch equation
Implementation Method 3
a gradient recalled echo signal acquisition module with variable number of echoes
Implementation Method 4
based on a spoiled gradient recalled echo sequence prepared by an inversion pulse
Implementation Method 5
use classical water-fat separation methods, such as Dixon, collecting in-phase and opposed-phase signals of water and fat by collecting multiple echoes
Implementation Method 6
incorporating the Dixon method for water-fat separation
Data Source
AI summary
The present invention discloses a magnetic resonance fingerprinting imaging method with variable number of echoes, in addition to conventional MRF coding such as changing the excitation pulse angle, the method also introduces the change of the number of echoes, so that quantitative maps of B0, B1+, T1 and T2* can be obtained in a single scan. Further, if the echo time corresponding to the in-phase, opposed-phase and in-phase of water and fat is set for three consecutive echoes, the present invention can also image water and fat, and achieve the accurate quantification of B0, B1+, T1w, T1F, [T2*]w and [T2*]F. Through in vivo experiments and simulations, the effectiveness of the present invention has been proved. Therefore, the present invention can provide multiple information representations for common brain diseases (glioma) and fatty diseases (such as lipoma, fatty liver, etc.), which is conducive to clinical diagnosis and treatment.