Quantifying human gray matter microstructure using neurite exchange imaging (NEXI) and 300 mT/m gradients

Imaging Neuroscience, Journal Year: 2024, Volume and Issue: 2, P. 1 - 19

Published: Feb. 20, 2024

Abstract Biophysical models of diffusion tailored to quantify gray matter microstructure are gathering increasing interest. The two-compartment Neurite EXchange Imaging (NEXI) model has been proposed recently account for neurites, extra-cellular space, and exchange across the cell membrane. NEXI parameter estimation requires multi-shell multi-diffusion time data so far only implemented experimentally on animal collected a preclinical magnetic resonance imaging (MRI) set-up. In this work, translation human cortex in vivo was achieved using 3 T Connectom MRI system with 300 mT/m gradients, that enables acquisition broad range b-values (0 – 7.5 ms/µm²) window covering short intermediate times (20 49 ms) suitable characteristic (10 50 ms). Microstructure estimates four variants: NEXI, NEXIdot (its extension addition dot compartment), their respective versions correct Rician noise floor (NEXIRM NEXIdot,RM) particularly impacts high b-value signal, were compared. reliability each variant evaluated synthetic data. latter, intra-subject (scan-rescan) versus between-subjects variability compared cortex. better performance NEXIRM highlights importance correcting bias obtain accurate parameters cortex, sensitivity framework individual differences cortical microstructure. This application humans represents significant step, unlocking new avenues studying neurodevelopment, aging, various neurodegenerative disorders.

Language: Английский

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Investigating exchange, structural disorder, and restriction in gray matter via water and metabolites diffusivity and kurtosis time-dependence

Imaging Neuroscience, Journal Year: 2024, Volume and Issue: 2, P. 1 - 14

Published: March 18, 2024

Abstract Water diffusion-weighted MRI is a very powerful tool for probing tissue microstructure, but disentangling the contribution of compartment-specific structural disorder from cellular restriction and inter-compartment exchange remains an open challenge. In this work, we use MR spectroscopy (dMRS) water metabolite as function diffusion time in vivo mouse gray matter to shed light on: i) which these concomitant mechanisms (structural disorder, restriction, exchange) dominates measurements ii) with specific signature. We report time-dependence excellent SNR conditions provided by dMRS, up long (500 ms). kurtosis decreases increasing time, showing influence both exchange. However, despite experimental conditions, were not able clearly identify nature (i.e., 1D versus 2D/3D short-range disorder). Measurements purely intracellular metabolites (up 500 ms) show opposite behavior water, time. that signature restricted space, microstructural features such soma’s cell projections’ size can be estimated. Finally, comparing time-dependencies, attempt disentangle effect intra/extracellular extracellular space (both impacting only). Our results suggest relatively short (~1-50 (still unclear if or 2D/3D) most likely coming compartment. This work provides novel insights help interpret diffusion-time dependent terms underlying microstructure suggests may offer new way quantify restrictions matter.

Language: Английский

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The Diffusion Exchange Ratio (DEXR): A minimal sampling of diffusion exchange spectroscopy to probe exchange, restriction, and time-dependence

Journal of Magnetic Resonance, Journal Year: 2024, Volume and Issue: 366, P. 107745 - 107745

Published: Aug. 6, 2024

Language: Английский

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Low-field, high-gradient NMR shows diffusion contrast consistent with localization or motional averaging of water near surfaces

Magnetic Resonance Letters, Journal Year: 2023, Volume and Issue: 3(2), P. 90 - 107

Published: April 9, 2023

Nuclear magnetic resonance (NMR) measurements of water diffusion have been extensively used to probe microstructure in porous materials, such as biological tissue, however primarily using pulsed gradient spin echo (PGSE) methods. Low-field single-sided NMR systems built-in static gradients (SG) much stronger than typical PGSE maximum strengths, which allows for the signal attenuation at extremely high b-values be explored. Here, we perform SG (SGSE) and stimulated (SGSTE) on cells, tissues, gels. Measurements fixed live neonatal mouse spinal cord, lobster ventral nerve starved yeast cells all show multiexponential a scale b with significant fractions observed × D0 ≫ 1 400 ms/μm2. These persistent trend surface-to-volume ratios these systems, expected from media theory. An exception found case vs. cords was attributed faster exchange or permeability millisecond timescale. Data suggests existence multiple processes neural may relevant modeling time-dependent gray matter. The multi-exponential is protons not macromolecules because it remains proportional normalized when specimen washed D2O. that persists also drastically reduced after delipidation, indicating originates lipid membranes restrict diffusion. stretched exponential character appears mono-exponential viewed (b×D0)1/3, suggesting originate localization motional averaging near sub-micron length scales. To try disambiguate two contributions, curves were compared varying temperatures. While align normalizing them scale, they separate scale. This supports source non-Gaussian displacements, but this interpretation still provisional due possible confounds heterogeneity, exchange, relaxation. types gel phantoms designed mimic extracellular matrix, one charged functional groups synthesized polyacrylic acid (PAC) another uncharged polyacrylamide (PAM), both exhibit 1, potentially interacting macromolecules. preliminary finding motivate future research into contrast mechanisms tissue low-field, high-gradient NMR.

Language: Английский

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Linear rotationally invariant kurtosis measures from double diffusion encoding MRI

Magnetic Resonance Imaging, Journal Year: 2025, Volume and Issue: unknown, P. 110399 - 110399

Published: April 1, 2025

To characterize the complete set of linear rotationally invariant kurtosis measures provided by double diffusion encoding (DDE) MRI, show their utility in distinguishing different types multiple Gaussian compartment (MGC) models, and demonstrate simplified acquisition analysis schemes for estimation. The lowest order novel information obtainable with DDE MRI can be encapsulated a six-dimensional tensor. most basic are rotational invariants that this tensor while depending on no other physical quantities. We identify four such any others must combinations these. applied to classify MGC models according whether they include microscopic anisotropy or intercompartmental water exchange. In addition, used investigate effect exchange estimates fractional (μFA). Simplified proposed demonstrated human brain data obtained at 3 T. For considered regions, found largely consistent having anisotropy. They also indicate gray matter may affect μFA. have exchange, estimated simple schemes. Measurements support validity importance modeling matter.

Language: Английский

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Measuring the velocity autocorrelation function using diffusion NMR

The Journal of Chemical Physics, Journal Year: 2025, Volume and Issue: 162(17)

Published: May 2, 2025

Molecular self-diffusion in the presence of barriers results time-dependent displacements that are controlled by barrier characteristics, such as thickness, arrangement, and permeability, which manifests itself form ensemble-average velocity autocorrelation function (VAF). We describe a direct method to measure VAF based on combination diffusion-weighted nuclear magnetic resonance (NMR) measurements two time-shifted diffusion encodings separated longitudinal storage period. The estimated from simulated data is shown agree with known expression for impermeable parallel planes. Simulations periodically spaced, permeable planes connected, box-shaped pores also presented. find scaling faster than t−1/2 indicative permeation or exchange between domains this can be captured proposed method. As an experimental proof-of-concept, we present ex vivo neonatal mouse spinal cord studied using permanent magnet NMR MOUSE system. report transition t−3/2 at t ≈ 10 ms, consistent perhaps transmembrane water exchange. Compared other NMR-based approaches, potentially access several orders magnitude time (ms – s), revealing wealth behaviors one paradigm.

Language: Английский

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Diffusional kurtosis time dependence and the water exchange rate for the multi‐compartment Kärger model

Magnetic Resonance in Medicine, Journal Year: 2023, Volume and Issue: 91(3), P. 1122 - 1135

Published: Nov. 13, 2023

Abstract Purpose To demonstrate an analytic formula giving the time dependence of diffusional kurtosis for Kärger model (KM) with arbitrary number exchanging compartments and its application in estimating mean KM water exchange rate. Theory Methods The general is derived from a power series solution multi‐compartment KM. A lower bound on rate established observation that always logarithmically convex function time. Both are illustrated numerical calculations. also applied to previously published data both brain tumors. Results given by sum which each term associated eigenvector matrix. determined most negative value logarithmic derivative respect In cerebral cortex, found vary 15 76 s −1 , depending experimental details, while tumors considered, it varies 2 4 . Conclusion has simple allows be directly experiment. This may useful tissues complex microstructure difficult explicitly.

Language: Английский

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In vivo mapping of cellular resolution neuropathology in brain ischemia with diffusion MRI

Science Advances, Journal Year: 2024, Volume and Issue: 10(29)

Published: July 17, 2024

Noninvasive mapping of cellular pathology can provide critical diagnostic and prognostic information. Recent advances in diffusion magnetic resonance imaging enabled vivo examination tissue microstructures well beyond the resolution. Here, we proposed to use time–dependent kurtosis ( t DKI) simultaneously assess morphology transmembrane permeability hypoxic-ischemic (HI) brain injury. Through numerical simulations organoid imaging, demonstrated feasibility capturing effective size changes using DKI. In MRI HI-injured mouse brains detected a shift DKI peak longer times, suggesting swelling processes. Furthermore, observed faster decrease tail, reflecting increased associated with up-regulated water exchange or necrosis. Such information, unavailable from single time, predict salvageable tissues. Preliminary applications patients ischemic stroke suggested regions, illustrating DKI’s potential for detecting pathological clinics.

Language: Английский

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Investigating exchange, structural disorder and restriction in Gray Matter via water and metabolites diffusivity and kurtosis time-dependence

Proceedings on CD-ROM - International Society for Magnetic Resonance in Medicine. Scientific Meeting and Exhibition/Proceedings of the International Society for Magnetic Resonance in Medicine, Scientific Meeting and Exhibition, Journal Year: 2023, Volume and Issue: unknown

Published: Aug. 3, 2023

This work reports first-time measurements of the time-dependent diffusivity and kurtosis both water metabolites in vivo mouse gray matter (GM). Our aim is to exploit complementary information provided by diffusion intracellular investigate potentially disentangle role exchange, structural disorder restriction GM. results show evidence that diffusion-time dependence GM mostly driven 1D short-range disorder, alongside exchange. Conversely, metabolites’ exclusively cellular restrictions, paving a new way quantify noninvasively microstructural restrictions

Language: Английский

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Using deep learning to accelerate magnetic resonance measurements of molecular exchange

The Journal of Chemical Physics, Journal Year: 2023, Volume and Issue: 159(5)

Published: Aug. 7, 2023

Real-time monitoring and quantitative measurement of molecular exchange between different microdomains are useful to characterize the local dynamics in porous media biomedical applications magnetic resonance. Diffusion spectroscopy (DEXSY) is a noninvasive technique for such measurements. However, its application largely limited by involved long acquisition time complex parameter estimation. In this study, we introduce physics-guided deep neural network that accelerates DEXSY data-driven manner. The proposed method combines sampling pattern optimization physical estimation into unified framework. Comprehensive simulations experiments based on two-site system conducted demonstrate new terms accuracy, repeatability, efficiency. This general framework can be adapted other resonance

Language: Английский

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