Hybrid FID-CPMG NMR Sequence for Fast Relaxing Media
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Solution Overview
Problem
Current NMR technologies face challenges in detecting fast and slow relaxing components in samples, particularly in large samples, due to limitations in minimum echo time (TE) and the need for separate measurements, which results in reduced accuracy and inefficiency.
Innovation Solution
An NMR apparatus and method that combines Free Induction Decay (FID) and Carr-Purcell-Meiboom-Gill (CPMG) processes to record decay and echo responses, allowing for the determination of relaxation times with extended echo times and simultaneous detection of fast and slow relaxing components in a single measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If CPMG NMR apparatus are configured to minimize TE (time to echo) to detect fast relaxation components, then the ability to detect fast relaxing components is improved, but the minimum TE is limited by coil dimensions, Q factor, and damping circuit, typically resulting in TE around 50-100 microseconds
Solution Approach 1:
The patent combines FID and CPMG measurement sequences into a single hybrid sequence. The FID portion captures fast-relaxing components (T2 < TE) by recording signal decay immediately after the initial pulse, while the CPMG portion captures slow-relaxing components (T2 > TE) through multiple refocusing pulses. This merging allows the system to detect both fast and slow relaxation components without requiring separate measurements, resolving the contradiction between detecting fast components and maintaining practical coil design constraints.
Solution Approach 2:
The patent employs dynamic adjustment of measurement parameters within a single sequence. The system dynamically switches between FID-like recording (for fast components) and CPMG-like refocusing (for slow components) based on the relaxation characteristics being measured. This dynamic approach allows the NMR apparatus to adapt to different sample types and relaxation timescales without requiring physical reconfiguration of the coil system.
2Difficulty of detecting and measuring
If separate FID and CPMG tests are performed for very fast and slow relaxing components, then detection capability is improved, but two separate measurements are required leading to loss of accuracy
Solution Approach 1:
The patent merges FID and CPMG measurements into a single continuous experiment. The hybrid sequence begins with an initial pulse followed by FID recording, then transitions into CPMG refocusing pulses. Both measurement types share the same magnetization pool and are fitted simultaneously using a unified mathematical model, ensuring consistency and accuracy. This eliminates the need for separate measurements and their associated accuracy losses.
Solution Approach 2:
The patent maintains continuous measurement throughout the experiment, with the FID portion immediately followed by the CPMG portion without interruption. The signal acquisition is continuous, capturing the full relaxation trajectory from fast to slow components in one uninterrupted sequence. This continuity preserves all available signal information and allows for more accurate determination of relaxation times across the entire timescale range.
3Volume of stationary object
If large samples are tested, then sample size capability is improved, but TE becomes longer by necessity of coil design, hampering investigation of fast relaxing media
Solution Approach 1:
The patent combines the advantages of FID (sensitive to fast relaxation) and CPMG (compatible with larger samples and longer TE) in a single hybrid sequence. The FID portion of the sequence captures fast-relaxing components even when TE is necessarily longer for large samples, while the CPMG portion handles the slow-relaxing components. This combination allows large samples to be tested without sacrificing the ability to detect fast relaxation processes.
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 enables more accurate and efficient characterization of relaxation times across a wider range of components, allowing for better comparison of samples and larger sample sizes, while reducing the need for multiple measurements and improving magnetic field homogeneity.
Implementation Method 1
NMR (Nuclear Magnetic Resonance) to detect fast relaxation components
Implementation Method 2
record the decay response of the sample between the transverse pulse and the first refocusing pulse
Implementation Method 3
generate a series of one or more refocusing pulses to be applied to the sample... record the echo response at least once after at least one refocusing pulse
Data Source
AI summary
An apparatus, method and computer program for characterising samples using NMR. The apparatus includes a pulse sequence generator; and a response detector. The apparatus is configured to generate transverse and refocusing pulses and to record the decay response of a sample following a transverse pulse and echo response at least once after at least one refocusing pulse in order to enable determination of at least one relaxation time of the sample. In this way, sample or sample components with short relaxation times may be characterized.