NMR Relaxation Time Determination via Polarization Transfer
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Solution Overview
Problem
Current NMR relaxometry methods require extensive time due to weak magnetic response signals from nuclei with small gyromagnetic ratios, necessitating multiple excitation and measurement sequences, which can take several hours or days to achieve an acceptable signal-to-noise ratio.
Innovation Solution
A method involving the exchange of polarizations between nuclei with different gyromagnetic ratios using a swap sequence of transverse magnetic field pulses, allowing for a stronger magnetization signal and improved signal-to-noise ratio, while also simplifying the experimental setup by reducing the need for gradient pulses and calibration parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple excitation and measurement sequences are performed to improve signal-to-noise ratio for nuclei with small gyromagnetic ratios, then measurement accuracy is improved, but measurement time increases significantly to several hours or days
Solution Approach 1:
The patent introduces a mediator nucleus type (first nuclei with large gyromagnetic ratio) that acts as an intermediary to transfer polarization to the target nuclei (second nuclei with small gyromagnetic ratio). This mediator enables the detection of weak signals from low-gyromagnetic-ratio nuclei by borrowing polarization from high-gyromagnetic-ratio nuclei, thereby achieving acceptable signal-to-noise ratio without requiring excessive numbers of excitation sequences.
Solution Approach 2:
The patent applies preliminary polarization transfer before the actual measurement of the target nuclei. By first polarizing the mediator nuclei and then transferring this polarization to the target nuclei through a swap sequence, the system prepares an enhanced magnetization state in advance, allowing subsequent measurements to proceed with sufficient signal strength without requiring multiple repeated sequences.
2Ease of operation
If standard NMR excitation sequences are used for nuclei with small gyromagnetic ratios, then measurement protocol simplicity is maintained, but signal strength remains weak requiring numerous sequences
Solution Approach 1:
The measurement protocol incorporates a mediator nucleus system that simplifies the overall measurement process by converting a difficult-to-detect signal (from low-gyromagnetic-ratio nuclei) into an easily detectable signal (from high-gyromagnetic-ratio nuclei) through polarization transfer. This intermediary approach maintains protocol simplicity while dramatically enhancing signal strength.
3Power
If polarization transfer between nuclei with different gyromagnetic ratios is implemented, then signal strength and signal-to-noise ratio are improved, but experimental complexity increases due to additional pulse sequences
Solution Approach 1:
The patent utilizes parameter changes in the magnetic field configuration to facilitate polarization transfer. By applying a static longitudinal magnetic field and controlled transverse magnetic field pulses, the system dynamically changes the magnetic field parameters to enable the swap operation between different nucleus types, achieving signal enhancement through physically controlled parameter transitions rather than complex sequence design.
4Measurement precision
If wait time between excitation sequences is extended to allow nuclei to return to equilibrium state, then signal accuracy is improved, but total measurement time increases to several hours or days
Solution Approach 1:
The patent performs preliminary polarization transfer to the target nuclei before measurement, creating an enhanced magnetization state that persists through the measurement process. This preliminary action eliminates the need for extended wait times between sequences, as the transferred polarization provides sustained signal strength without requiring repeated equilibration periods.
Solution Approach 2:
The polarization transfer creates a continuous useful magnetic signal from the target nuclei by maintaining enhanced magnetization throughout the measurement process. This continuous signal presence eliminates the need for intermittent waiting periods, allowing measurements to proceed continuously with sufficient signal accuracy.
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 approach significantly reduces the time required for determining NMR relaxation times and spectra by enhancing the magnetization signal strength and achieving a higher signal-to-noise ratio, allowing for more efficient and accurate measurements in a shorter timeframe.
Implementation Method 1
A first step of polarizing the first nuclei and the second nuclei by applying a longitudinal static magnetic field to the probe
Implementation Method 2
exchanging the polarizations of the first nuclei and the second nuclei by irradiating at least one swap sequence of transverse magnetic field pulses, wherein the temporal length of the at least one swap sequence is substantially identical to the inverse of the longitudinal spin-spin interaction strength between the first nuclei and the second nuclei
Implementation Method 3
A third step of transversely magnetizing the second nuclei by irradiating at least one excitation pulse and measuring the resulting magnetization signal
Data Source
Figure 1~2
Figure 3~4(c)
Figure 5~5(c)
AI summary
The invention relates to a method of determining a nuclear magnetic resonance relaxation time of a probe (P). The method comprises a first step (S1) of polarizing first nuclei (H) and second nuclei (N) by applying a longitudinal static magnetic field (B0) to the probe (P), a second step (S2) of exchanging the polarizations of the first nuclei (H) and the second nuclei (N) by irradiating a swap sequence (SWAP) of transverse magnetic field pulses, a third step (S3) of transversely magnetizing the second nuclei (N) by irradiating at least one excitation pulse (EXC) and measuring the resulting magnetization signal (FID) of the second nuclei (N), and a fourth step (S4) of determining the nuclear magnetic resonance relaxation time of the second nuclei (N) based on the measured magnetization signal (FID) of the second nuclei (N).