Neurite Exchange Imaging (NEXI): A minimal model of diffusion in gray matter with inter-compartment water exchange

NeuroImage, Год журнала: 2022, Номер 256, С. 119277 - 119277

Опубликована: Май 3, 2022

Biophysical models of diffusion in white matter are based on what is now commonly referred to as the "Standard Model" (SM) non-exchanging anisotropic Gaussian compartments. In this work, we focus MRI gray matter, which requires rethinking basic microstructure modeling blocks. particular, at least three contributions beyond SM need be considered: water exchange across cell membrane - between neurites and extracellular space; non-Gaussian along neuronal glial processes resulting from structural disorder; signal contribution soma. For first contribution, propose Neurite Exchange Imaging (NEXI) an extension diffusion, builds K\"arger model two exchanging Using datasets acquired multiple weightings (b) times (t) rat brain vivo, show that for investigated time window (~10-45 ms) there minimal diffusivity time-dependence more pronounced kurtosis decay with well fit by model. Moreover, observe lower longer high b. light these observations, identify mechanism best explains signatures both low-b high-b regime, thereby NEXI mapping. We finally highlight multi-b multi-t acquisitions protocols being suited estimate parameters reliably. approach, inter-compartment 15 60 ms cortex hippocampus same order or shorter than typical acquisitions. This suggests essential component interpreting measurements matter.

Язык: Английский

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Loss of aquaporin-4 results in glymphatic system dysfunction via brain-wide interstitial fluid stagnation

eLife, Год журнала: 2023, Номер 12

Опубликована: Фев. 9, 2023

The glymphatic system is a fluid transport network of cerebrospinal (CSF) entering the brain along arterial perivascular spaces, exchanging with interstitial (ISF), ultimately establishing directional clearance solutes. CSF facilitated by expression aquaporin-4 (AQP4) water channels on endfeet astrocytes. Mice genetic deletion AQP4 (AQP4 KO) exhibit abnormalities in structure and molecular transport. Yet, no studies have systematically examined how these correlate function. Here, we used high-resolution 3D magnetic resonance (MR) non-contrast cisternography, diffusion-weighted MR imaging (MR-DWI) intravoxel-incoherent motion (IVIM) DWI, while evaluating function using standard dynamic contrast-enhanced to better understand disrupted after AQP4. KO mice had larger spaces total volumes resulting higher content reduced space volumes, despite similar production rates vascular density compared wildtype mice. volume likely resulted increased slow but not fast diffusion measures coincided influx. This markedly altered may result from reduction clearance, leading enlargement stagnation space. Overall, useful tool evaluate serve as valuable translational biomarker study glymphatics human disease.

Язык: Английский

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

Imaging Neuroscience, Год журнала: 2024, Номер 2, С. 1 - 19

Опубликована: Фев. 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.

Язык: Английский

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Diffusion magnetic resonance imaging of cerebrospinal fluid dynamics: Current techniques and future advancements

NMR in Biomedicine, Год журнала: 2024, Номер 37(9)

Опубликована: Май 7, 2024

Abstract Cerebrospinal fluid (CSF) plays a critical role in metabolic waste clearance from the brain, requiring its circulation throughout various brain pathways, including ventricular system, subarachnoid spaces, para‐arterial interstitial and para‐venous spaces. The complexity of CSF has posed challenge obtaining noninvasive measurements dynamics. assessment dynamics circulatory pathways is possible using diffusion magnetic resonance imaging (MRI) with optimized sensitivity to incoherent water movement across brain. This review presents an overview both established emerging MRI techniques designed measure their potential clinical applications. discussion offers insights into optimization acquisition parameters enhance specificity metrics on underlying Lastly, we emphasize importance cautious interpretations diffusion‐based imaging, especially when differentiating between tissue‐ fluid‐related changes or elucidating structural versus functional alterations.

Язык: 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, Год журнала: 2024, Номер 2, С. 1 - 14

Опубликована: Март 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.

Язык: Английский

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Comparison of water exchange measurements between filter‐exchange imaging and diffusion time‐dependent kurtosis imaging in the human brain

Magnetic Resonance in Medicine, Год журнала: 2025, Номер unknown

Опубликована: Янв. 29, 2025

Abstract Purpose Filter‐exchange imaging (FEXI) and diffusion time (t)‐dependent kurtosis (DKI(t)) are two diffusion‐based methods that have been proposed for in vivo measurements of water exchange rates. Few studies directly compared these methods. We aimed to investigate whether FEXI DKI(t) yield comparable the human brain vivo. Methods Eight healthy volunteers underwent multiple‐direction acquisitions on a 3T scanner. performed region interest (ROI) analysis determine correlations between FEXI‐derived apparent rate (AXR) DKI(t)‐derived reciprocal (). Results In both white matter (WM) gray (GM), revealed substantial diffusion‐time dependence diffusivity kurtosis. However, at t ≥ 100 ms, showed weak dependence. WM, this may be due myelin “free” with different T 1 values, although other factors, such as remaining restrictive effects from microstructural barriers, cannot excluded. found significant correlation AXR axial direction within WM. No was present GM, values similar ranges. Conclusion These results suggest could sensitive same process only when is sufficiently long, GM effect microstructure non‐negligible, especially short times (<100 ms).

Язык: Английский

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Comprehensive diffusion MRI dataset for in vivo human brain microstructure mapping using 300 mT/m gradients

Scientific Data, Год журнала: 2022, Номер 9(1)

Опубликована: Янв. 18, 2022

Abstract Strong gradient systems can improve the signal-to-noise ratio of diffusion MRI measurements and enable a wider range acquisition parameters that are beneficial for microstructural imaging. We present comprehensive dataset 26 healthy participants acquired on MGH-USC 3 T Connectome scanner equipped with 300 mT/m maximum strength custom-built 64-channel head coil. For each participant, one-hour long systematically sampled accessible measurement space, including two times (19 49 ms), eight strengths linearly spaced between 30 290 time, 32 or 64 uniformly distributed directions. The data were preprocessed to correct nonlinearity, eddy currents, susceptibility induced distortions. In addition, scan/rescan from subset seven individuals also provided. MGH Diffusion Microstructure Dataset (CDMD) may serve as test bed development new analysis methods, such fiber orientation estimation, tractography modelling.

Язык: Английский

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Probing brain tissue microstructure with MRI: principles, challenges, and the role of multidimensional diffusion-relaxation encoding

NeuroImage, Год журнала: 2023, Номер 282, С. 120338 - 120338

Опубликована: Авг. 19, 2023

Diffusion MRI uses the random displacement of water molecules to sensitize signal brain microstructure and properties such as density shape cells. Microstructure modeling techniques aim estimate these from acquired data by separating between virtual tissue 'compartments' intra-neurite extra-cellular space. A key challenge is that diffusion relatively featureless compared with complexity tissue. Another wildly different within gray white matter brain. In this review, we use results multidimensional encoding discuss challenges their tentative solutions. Multidimensional increases information content varying not only b-value direction but also additional experimental parameters b-tensor echo time. Three main insights have emerged encoding. First, contradict common model assumptions on T2 relaxation illustrates how cause erroneous interpretations in both healthy pathology. Second, many can be dispensed if are The necessary easily vivo using protocols optimized minimize Cramér-Rao lower bounds. Third, microscopic anisotropy reflects presence axons dendrites. This insight stands contrast current 'neurite models' tissue, which assume dendrites feature highly similar diffusion. Nevertheless, an axon-based contrast, differentiate when myelin alterations confound conventional contrasts.

Язык: Английский

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Water exchange rates measure active transport and homeostasis in neural tissue

PNAS Nexus, Год журнала: 2023, Номер 2(3)

Опубликована: Фев. 27, 2023

For its size, the brain is most metabolically active organ in body. Most of energy demand used to maintain stable homeostatic physiological conditions. Altered homeostasis and states are hallmarks many diseases disorders. Yet there currently no direct reliable method assess absolute basal activity cells tissue noninvasively without exogenous tracers or contrast agents. We propose a novel low-field, high-gradient diffusion exchange nuclear magnetic resonance (NMR) capable directly measuring cellular metabolic via rate constant for water across cell membranes. Exchange rates 140±16 s -1 under normal conditions viable ex vivo neonatal mouse spinal cords. High repeatability samples suggest that values intrinsic tissue. Using temperature drug (ouabain) perturbations, we find majority coupled transport by sodium-potassium pump. show this sensitive primarily provides distinct functional information. In contrast, apparent coefficient (ADC) measured with submillisecond times microstructure but not activity. Water appears independently regulated from microstructural oxygenation changes reported ADC T1 relaxation measurements an oxygen-glucose deprivation model stroke; remain 30-40 min before dropping levels similar effect ouabain never completely recovering when oxygen glucose restored.

Язык: Английский

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Mapping tissue microstructure across the human brain on a clinical scanner with soma and neurite density image metrics

Human Brain Mapping, Год журнала: 2023, Номер 44(13), С. 4792 - 4811

Опубликована: Июль 17, 2023

Abstract Soma and neurite density image (SANDI) is an advanced diffusion magnetic resonance imaging biophysical signal model devised to probe in vivo microstructural information the gray matter (GM). This requires acquisitions that include b values are at least six times higher than those used clinical practice. Such high required disentangle contribution of water diffusing soma from neurites extracellular space, while keeping time as short possible minimize potential bias due exchange. These requirements have limited use SANDI only preclinical or cutting‐edge human scanners. Here, we investigate impact neglecting exchange present a 10‐min acquisition protocol enables characterize both GM white (WM) on 3 T We implemented analytical simulations (i) evaluate stability fitting parameters when diminishing number shells; (ii) estimate between space such reduced scheme, comparing it with experimental noise. Then, demonstrated feasibility assessed repeatability reproducibility our approach by computing metrics AMICO toolbox other state‐of‐the‐art models five healthy subjects. Finally, applied multiple sclerosis patients. Results suggest practical method WM tissues performant

Язык: Английский

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