Diffusion measurements using the second echo

Fabich, Hilary T.; Nandi, Partha; Thomann, H.; Conradi, Mark S.

doi:10.1002/cmr.a.21462

Cited by 4 publications

(1 citation statement)

References 18 publications

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“…Alternatively, the storage interval can be removed completely by using an SG-double spin echo (SG-SE-SE) sequence. This sequence combines the phase cycles of the classic double spin echo [69] with the standard NMR-MOUSE SG spin echo diffusion sequence [70]. For both sequences, the signal is acquired in a CPMG loop and summed to maximize SNR [71].…”

Section: Methodsmentioning

confidence: 99%

Disentangling the Effects of Restriction and Exchange With Diffusion Exchange Spectroscopy

et al. 2022

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Diffusion exchange spectroscopy (DEXSY) is a multidimensional NMR technique that can reveal how water molecules exchange between compartments within heterogeneous media, such as biological tissue. Data from DEXSY experiments is typically processed using numerical inverse Laplace transforms (ILTs) to produce a diffusion-diffusion spectrum. A tacit assumption of this ILT approach is that the signal behavior is Gaussian—i.e., the spin echo intensity decays exponentially with the degree of diffusion weighting. The assumptions that underlie Gaussian signal behavior may be violated, however, depending on the gradient strength applied and the sample under study. We argue that non-Gaussian signal behavior due to restrictions is to be expected in the study of biological tissue using diffusion NMR. Further, we argue that this signal behavior can produce confounding features in the diffusion-diffusion spectra obtained from numerical ILTs of DEXSY data—entangling the effects of restriction and exchange. Specifically, restricted signal behavior can result in broadening of peaks and in the appearance of illusory exchanging compartments with distributed diffusivities, which pearl into multiple peaks if not highly regularized. We demonstrate these effects on simulated data. That said, we suggest the use of features in the signal acquisition domain that can be used to rapidly probe exchange without employing an ILT. We also propose a means to characterize the non-Gaussian signal behavior due to restrictions within a sample using DEXSY measurements with a near zero mixing time or storage interval. We propose a combined acquisition scheme to independently characterize restriction and exchange with various DEXSY measurements, which we term Restriction and Exchange from Equally-weighted Double and Single Diffusion Encodings (REEDS-DE). We test this method on ex vivo neonatal mouse spinal cord—a sample consisting primarily of gray matter—using a low-field, static gradient NMR system. In sum, we highlight critical shortcomings of prevailing DEXSY analysis methods that conflate the effects of restriction and exchange, and suggest a viable experimental approach to disentangle them.

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Section: Methodsmentioning

confidence: 99%

Disentangling the Effects of Restriction and Exchange With Diffusion Exchange Spectroscopy

et al. 2022

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Dynamic mechanical analysis with portable NMR

Selby

Garland

Mastikhin

2022

Journal of Magnetic Resonance

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Using phase interference to characterize dynamic properties—a review of constant gradient, portable magnetic resonance methods

et al. 2023

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Spatially resolved motion-sensitized magnetic resonance (MR) is a powerful tool for studying the dynamic properties of materials. Traditional methods involve using large, expensive equipment to create images of sample displacement by measuring the spatially resolved MR signal response to time-varying magnetic field gradients. In these systems, both the sample and the stress applicator are typically positioned inside a magnet bore. Portable MR instruments with constant gradients are more accessible, with fewer limitations on sample size, and they can be used in industrial settings to study samples under deformation or flow. We propose a view in which the well-controlled sensitive region of a magnet array acts as an integrator, with the velocity distribution leading to phase interference in the detected signal, which encodes information on the sample’s dynamic properties. For example, in laminar flows of Newtonian and non-Newtonian fluids, the velocity distribution can be determined analytically and used to extract the fluid’s dynamic properties from the MR signal magnitude and/or phase. This review covers general procedures, practical considerations, and examples of applications in dynamic mechanical analysis and fluid rheology (viscoelastic deformation, laminar pipe flows, and Couette flows). Given that these techniques are relatively uncommon in the broader magnetic resonance community, this review is intended for both advanced NMR users and a more general physics/engineering audience interested in rheological applications of NMR.

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Diffusion measurements using the second echo

Cited by 4 publications

References 18 publications

Disentangling the Effects of Restriction and Exchange With Diffusion Exchange Spectroscopy

Disentangling the Effects of Restriction and Exchange With Diffusion Exchange Spectroscopy

Dynamic mechanical analysis with portable NMR

Using phase interference to characterize dynamic properties—a review of constant gradient, portable magnetic resonance methods

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