3D MRI Encoding Matrices for Concomitant Field Characterization
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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 high BMI and claustrophobia, and preventing wider access to liver patients with non-alcoholic fatty liver disease (NAFLD).
Innovation Solution
A method and system that utilize an invertible encoding matrix to determine phase accruals from concomitant fields, employing a 5x5 or 6x6 matrix to resolve self-squared and cross terms, allowing phase measurements to mitigate PNR issues, enabling 3D MRE on low field MR systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If low field MR systems are used for 3D MRE, then accessibility and cost are improved, but phase-to-noise ratio deteriorates
Solution Approach 1:
The patent replaces conventional motion encoding gradient methods with a magnetic field perturbation method that applies small, controlled perturbations to the main magnetic field. This substitution allows phase measurements to be made during free decay without requiring complex gradient encoding schemes, thereby improving phase-to-noise ratio while maintaining accessibility of low field systems.
Solution Approach 2:
The patent changes the fundamental measurement parameter from gradient-encoded phase to naturally occurring phase during free decay. By measuring phase accrual during the free decay period after RF excitation rather than during gradient encoding, the method exploits the inherent phase information present in low field systems, converting a limitation into an advantage.
2Measurement precision
If Hadamard motion encoding is applied to increase sensitivity, then motion sensitivity is improved, but concomitant field effects worsen
Solution Approach 1:
The patent extracts and eliminates the problematic concomitant field effects by removing the Hadamard motion encoding gradients entirely. Instead of trying to manage or correct these effects, the method measures phase during free decay when no additional gradients are applied, thereby taking out the source of concomitant field artifacts and achieving clean phase measurements.
Solution Approach 2:
The patent inverts the conventional approach by measuring phase during the absence of gradients (free decay) rather than during gradient application. This inversion transforms the problem from one where concomitant fields create artifacts during encoding to one where the natural free decay provides the measurement window, eliminating the harmful effects entirely.
3Ease of manufacture
If conventional 3D MRE is performed on low field systems, then system cost is reduced, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent employs a self-service measurement approach where the system uses its own inherent magnetic field properties and natural free decay to generate measurable phase information. No additional expensive hardware or complex pulse sequences are required - the method extracts useful information from the natural behavior of spins during free decay, allowing low field systems to achieve adequate signal-to-noise ratio without additional cost.
Solution Approach 2:
The patent utilizes the continuous phase accrual that occurs naturally during the free decay period. Rather than relying on discrete gradient encoding steps that interrupt the signal, the method continuously measures phase information throughout the entire free decay window, maximizing the useful signal extraction from each RF excitation and improving signal-to-noise ratio without requiring higher field strength.
Data Source
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AI summary
The present invention relates to a method of performing 3D Magnetic Resonance Imaging including the step of 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.