NMR Pulse Sequence Overlapping Diffusion Times
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Solution Overview
Problem
Existing NMR diffusion measurement techniques face challenges in differentiating between intrinsic bulk diffusivity and restricted diffusivity in porous media, especially when dealing with complex samples containing multiple fluids and small pore sizes, leading to ambiguous results.
Innovation Solution
The method involves applying a nuclear magnetic resonance (NMR) pulse sequence with overlapping diffusion times, using decoupled gradient waveforms to measure diffusion coefficients for both intrinsic and restricted diffusion, allowing for the differentiation between bulk and restricted diffusivity by analyzing NMR signal data over overlapping diffusion times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional NMR diffusion measurement techniques are used, then measurement simplicity is maintained, but the ability to differentiate between bulk and restricted diffusion is insufficient leading to ambiguous results
Solution Approach 1:
The measurement process is segmented into multiple independent diffusion measurements with different diffusion times (Δ1 and Δ2). Each diffusion time encodes different aspects of nuclear motion - shorter times capture bulk diffusion while longer times reveal restricted diffusion effects. This segmentation allows separate characterization of different diffusion regimes without requiring a single complex measurement
Solution Approach 2:
The pulse sequence employs periodic oscillating gradient waveforms applied at different frequencies and phases. These periodic gradient actions enable selective encoding of diffusion information at different time scales. By varying the periodicity and phase of gradient applications, the method can independently probe bulk and restricted diffusion mechanisms
2Measurement precision
If multiple diffusion times are measured separately, then diffusion coefficients can be determined, but the measurement time increases significantly
Solution Approach 1:
Multiple diffusion measurements with different diffusion times are merged into a single integrated pulse sequence. The sequence simultaneously applies gradient encodings for both Δ1 and Δ2 diffusion times within one experiment, allowing extraction of multiple diffusion coefficients without sequentially running separate measurements. This merging reduces total measurement time while maintaining precision
Solution Approach 2:
The pulse sequence maintains continuous useful action by overlapping the diffusion encoding periods. The first set of gradients encodes diffusion during Δ1 while the second set encodes diffusion during Δ2, with temporal overlap that maximizes information extraction per unit time. This continuous encoding approach eliminates idle time between measurements
3Measurement precision
If decoupled gradient waveforms are used to measure both diffusion types, then differentiation capability is improved, but the gradient waveform complexity increases
Solution Approach 1:
The gradient waveforms employ asymmetric timing and amplitude profiles for the two diffusion encodings. The first gradient pair uses parameters optimized for Δ1 diffusion time while the second pair uses different parameters for Δ2. This asymmetric design allows each gradient set to be independently optimized for its target diffusion regime, improving differentiation precision
Solution Approach 2:
The gradient waveforms are made dynamic by allowing independent adjustment of amplitude, duration, and timing for each gradient pair. This dynamic configurability enables the system to adapt gradient strengths to match the specific diffusion time scales being probed, enhancing measurement precision without requiring permanently complex hardware
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 precise differentiation between bulk and restricted diffusion, providing clearer insights into fluid composition and pore size distribution within porous media, enhancing the accuracy of NMR measurements in complex samples.
Implementation Method 1
nuclear magnetic resonance (NMR) can be used to determine properties of a substance. An NMR method includes applying a static magnetic field to the substance. The static magnetic field generates an initial magnetization of atomic nuclei within the substance. Then, an oscillating magnetic field is applied at a particular frequency to the substance.
Implementation Method 2
A first set of pulses and a second set of pulses that encode for overlapping diffusion times... one or more of the sets of pulses is or includes a gradient waveform... The NMR signal is detected and can be used to determine properties of the substance.
Implementation Method 3
a measurement of diffusion... measures an additional decay produced by movement of the atomic nuclei... diffusion coefficient of a fluid, which characterizes the distance that nuclei within the fluid will travel as a function of time... Diffusion that is impeded by small pore size is known as restricted diffusion.
Data Source
AI summary
A method and system for determining a property of a substance using nuclear magnetic resonance (NMR) is described herein. The method includes applying a NMR pulse sequence to the substance. The NMR pulse sequence includes a first set of pulses and a second set of pulses. The first set of pulses and the second set of pulses encode for overlapping diffusion times. By overlapping diffusion times, the NMR pulse sequence can be used to measure a diffusion coefficient for a first diffusion time, a diffusion coefficient for a second diffusion time, and a correlation between the two overlapping diffusion times. This information, in turn, can be used to differentiate between intrinsic bulk diffusivity of the substance and the reduced diffusivity of the substance caused by restricted diffusion.