Passive Filter Circuit for Dual-Nuclear NMR Quadrature Phase Shift
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Solution Overview
Problem
Current NMR systems face challenges in simultaneously achieving quadrature phase shifts for nuclei with opposite gyromagnetic ratios, requiring distinct circular polarizations for quadrature excitation and detection, which is not efficiently addressed by existing technologies.
Innovation Solution
A passive filter circuit is designed to apply a quadrature phase shift of a first polarity at the Larmor frequency of a first nucleus and a quadrature phase difference of a second polarity, opposite the first polarity, at the Larmor frequency of a second nucleus, using cascaded filter modules that provide relative phase changes to achieve the desired phase offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a standard broadband hybrid is used for dual-frequency operation, then both nuclei can be excited simultaneously, but the phase difference between output ports is the same for both frequencies, preventing proper quadrature detection for nuclei with opposite gyromagnetic ratios
Solution Approach 1:
The patent introduces frequency-selective phase shifters that provide different phase shifts at different Larmor frequencies. Each nucleus type (positive and negative gyromagnetic ratios) receives the appropriate phase shift required for quadrature detection, rather than applying a uniform phase shift to all frequencies. This local differentiation of phase characteristics resolves the contradiction between dual-nuclear operation and phase shift accuracy.
Solution Approach 2:
The patent employs frequency-dependent phase shifting where the phase shift parameter varies with frequency. By designing the phase shifters to provide opposite phase shifts at the Larmor frequencies of nuclei with opposite gyromagnetic ratios, the system achieves proper quadrature detection for both nucleus types simultaneously, resolving the phase accuracy issue while maintaining dual-nuclear capability.
2Measurement precision
If frequency-selective phase shifting is implemented to achieve proper quadrature phase shifts for opposite polarity nuclei, then detection accuracy improves, but device complexity increases due to additional filter modules
Solution Approach 1:
The patent divides the frequency-selective phase shifting function into multiple cascaded filter modules, each contributing a specific phase shift at its resonant frequency. By segmenting the overall phase shifting requirement across several modules with different resonant frequencies, the system achieves the necessary opposite phase shifts for different nuclei while distributing the complexity across modular components rather than requiring a single complex device.
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
The solution enables simultaneous dual-nuclear magnetic resonance quadrature transmit-receive operations for nuclei with opposite gyromagnetic ratios, ensuring efficient quadrature phase shifts and phase differences, thereby improving the system's ability to handle nuclei with different Larmor frequencies and polarities.
Implementation Method 1
a passive filter circuit, for simultaneous dual-nuclear magnetic resonance quadrature transmit-receive that is configured to apply to an input a quadrature phase shift (phase difference) of a first polarity at a Larmor frequency of a first nucleus and a quadrature phase difference of a second polarity, that is opposite the first polarity, at the Larmor frequency of a second nucleus
Implementation Method 2
The B1 field is orthogonal to the B0 field and is generated using radio frequency (RF) coils resonating at the Larmor frequency
Data Source
AI summary
A passive filter circuit, for simultaneous dual-nuclear magnetic resonance quadrature transmit-receive that is configured to apply to an input a quadrature phase shift of a first polarity at a Larmor frequency of a first nucleus and a quadrature phase difference of a second polarity, that is opposite the first polarity, at the Larmor frequency of a second nucleus