Low-Field 3D MRE Phase Characterization of Concomitant Fields
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Solution Overview
Problem
Low field MR systems in 3D MRE face challenges with reduced signal-to-noise ratio (SNR) and phase-to-noise ratio (PNR), exacerbated by concomitant fields, limiting their application in conditions like non-alcoholic fatty liver disease (NAFLD) and claustrophobic patients, and increasing the financial barrier for wider adoption.
Innovation Solution
A method and system that applies a magnetic gradient field causing concomitant fields with specific phase accruals, using an invertible encoding matrix to determine phase accruals, allowing for unambiguous phase measurements even at low field strengths, and includes a 6×6 encoding matrix to resolve self-squared and cross terms of the concomitant field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If low field MR systems (B0≤1.0 T) are used to accommodate liver patients with high BMI and/or claustrophobia, then accessibility and patient comfort are improved, but signal-to-noise ratio (SNR) and phase-to-noise ratio (PNR) are reduced
Solution Approach 1:
The patent applies parameter changes by modifying the motion encoding gradient scheme from conventional single-axis encoding to multi-axis Hadamard encoding. This changes the encoding parameters to simultaneously encode motion in multiple directions, thereby improving the PNR and enabling reliable 3D MRE measurements even at low field strengths where SNR and PNR are naturally reduced.
Solution Approach 2:
The patent segments the motion encoding process into multiple independent gradient applications along different axes (x, y, z directions). By applying motion encoding gradients sequentially along each axis with Hadamard encoding, the system can separately measure and combine displacement information from all three dimensions, improving measurement precision without requiring high field strength.
2Measurement precision
If Hadamard motion encoding scheme is applied to increase sensitivity to motion and mitigate decrease in PNR, then phase-to-noise ratio is improved, but concomitant fields become higher with decreasing static magnetic field B0
Solution Approach 1:
The patent extracts and separately measures the harmful concomitant field phase effects from the total measured phase. By using the multi-axis Hadamard encoding scheme, the system can identify and isolate the phase contributions from concomitant fields (which follow specific spatial patterns) from the desired motion-induced phase, allowing the concomitant field effects to be removed or corrected in post-processing.
Solution Approach 2:
The patent implements a feedback mechanism where the measured phase data from multiple encoding directions is used to calculate and subtract the concomitant field contributions. The system uses the known spatial dependence of concomitant fields to model their effect and applies this model to the measured data, iteratively removing the harmful effects to recover the true motion signal.
3Device complexity
If conventional motion encoding is used at low field strengths, then system complexity is reduced, but measurement precision and reliability of 3D MRE deteriorate
Solution Approach 1:
The patent applies universality by designing a multi-axis Hadamard encoding scheme that serves multiple functions simultaneously: it encodes motion in all three spatial dimensions, provides inherent correction for concomitant field effects, and maintains compatibility with standard low-field MR systems. This universal approach enables reliable 3D MRE across different field strengths without requiring specialized hardware modifications.
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
Enables high-quality 3D MRE measurements across all field strengths, including low field MR systems, by mitigating the effects of concomitant fields, thus expanding accessibility to conditions like NAFLD and reducing financial barriers.
Implementation Method 1
applying a magnetic gradient field that causes a concomitant field Bc leading to a phase accrual
Implementation Method 2
γ is the gyromagnetic ratio characteristic of the nuclei
Data Source
AI summary
The present disclosure relates to a method of performing 3D Magnetic Resonance Imaging including applying a magnetic gradient field that causes a concomitant field Bc. A further step of the method includes determining phase accruals due to the self-squared terms of the concomitant field Bc and phase accruals φxz, φyz due to the cross terms of the concomitant field Bc based on an encoding matrix that accounts for the different possible sign combinations of the applied magnetic gradients.