Composite hindered and restricted model of diffusion (CHARMED) MR imaging of the human brain.

Apparent Fibre Density: a novel measure for the analysis of diffusion-weighted magnetic resonance images.

White matter characterization with diffusional kurtosis imaging.

Translational motion in solution, either diffusion or fluid flow, is at the heart of chemical and biochemical reactivity. Nuclear Magnetic Resonance (NMR) provides a powerful non-invasive technique for studying the phenomena using magnetic field gradient methods. Describing the physical basis of measurement techniques, with particular emphasis on diffusion, balancing theory with experimental observations and assuming little mathematical knowledge, this is a strong, yet accessible, introduction to the field. A detailed discussion of magnetic field gradient methods applied to Magnetic Resonance Imaging (MRI) is included, alongside extensive referencing throughout, providing a timely, definitive book to the subject, ideal for researchers in the fields of physics, chemistry and biology.

/pdf/nmr-studies-of-translational-motion-1y45lcz4az.pdf

NMR Studies of Translational Motion

Multisite exchange models have been applied frequently to quantify measurements of transverse relaxation and diffusion in living tissues. Although the simplicity of such models is attractive, the precise relationship of the model parameters to tissue properties may be difficult to ascertain. Here, we investigate numerically a two-compartment exchange (Karger) model as applied to diffusion in a system of randomly packed identical parallel cylinders with permeable walls, representing cells with permeable membranes, that may serve particularly as a model for axons in the white matter of the brain. By performing Monte Carlo simulations of restricted diffusion, we show that the Karger model may provide a reasonable coarse-grained description of the diffusion-weighted signal in the long time limit, as long as the cell membranes are sufficiently impermeable, i.e. whenever the residence time in a cell is much longer than the time it takes to diffuse across it. For larger permeabilities, the exchange time obtained from fitting to the Karger model overestimates the actual exchange time, leading to an underestimated value of cell membrane permeability.

Monte Carlo study of a two-compartment exchange model of diffusion

This article examines the way in which microscopic tissue parameters affect the signal attenuation of diffusion-weighted MR experiments. The influence of transmembrane water flux on the signal decay is emphasized using the Karger equations, which are modified with respect to the cellular boundary restrictions for intra- and extracellular diffusion. This analytical approach is extensively compared to Monte-Carlo simulations for a tissue model consisting of two compartments. It is shown that diffusion-weighted MR methods provide a unique tool for estimation of the intracellular exchange time. Restrictions of applicability to in vivo data are examined. It is shown that the intracellular exchange time strongly depends on the size of a cell, leading to an apparent diffusion time dependence for in vivo data. Hence, an analytical model of a two-compartment system with an averaged exchange time is inadequate for the interpretation of signal curves measured in vivo over large ranges of b-values. Furthermore, differences of multiexponential signal curves, as obtained by different methods of diffusion weighting, can be explained by the influence of transmembrane water flux.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.10557

Diffusion in compartmental systems. I. A comparison of an analytical model with simulations.

Diffusion-weighted single-voxel 1H spectroscopic measurements were performed on rat brain tissue in vivo and postmortem. Diffusion weighting was achieved by varying the diffusion time from 23 ms to 1.18 sec via the mixing time in a stimulated echo sequence. A series of constant gradient (cg-) experiments of eight effective gradient strengths q2(q2 = γ2δ2g2) from 24.2 × 103 to 490.2 × 103 mm−2 was performed, resulting in a maximum attenuation factor of b = 580,000 s/mm2. A fit of three exponential terms was found to be appropriate to represent the attenuation signal over the whole b-range. The behavior of the slowest decaying component can be fully understood in terms of a long time limit of a modified Karger formalism for a two-compartment system. This allowed estimation of the transmembrane water exchange rate: the intracellular exchange time was determined to be 622 ± 29 ms and 578 ± 20 ms in vivo and postmortem, respectively. Magn Reson Med 50:510–514, 2003. © 2003 Wiley-Liss, Inc.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.10558

Diffusion in compartmental systems. II. Diffusion-weighted measurements of rat brain tissue in vivo and postmortem at very large b-values.

Publisher Summary In order to monitor the dynamics of tissue water non-invasively and to study mechanisms of volume control, one must use a method that is able to: differentiate intracellular from extracellular water; monitor the exchange of water across the cell membrane; register anisotropic motions of water. The method of diffusion weighted nuclear magnetic resonance (NMR) spectroscopy (DW-MRS) meets all these requirements. DW-MRS has evolved from pulsed-field-gradient nuclear magnetic resonance (PFG-NMR), which was a tool to assess the water diffusion. Addition of spatial localization in this tool result into DW-MRS. Diffusion weighted preparation of the water signal in the PFG experiment can be combined with any of the spatial encoding techniques of water detection (magnetic resonance imaging) to obtain an image contrast, which depends upon the diffusion behavior of the observed water within individual volume elements (voxels) of an object. This combination is termed “diffusion weighted imaging” (DWI). Diffusion weighted magnetic resonance spectroscopy and imaging is sensitive methods to monitor non-invasively intracellular and extracellular water diffusion and by this means also cell volumes and volume regulation under normal and pathological conditions.

Cell volume and water exchange in neural cells monitored by diffusion weighted 1H NMR spectroscopy

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Christian Meier

Author Tools

Chat about Author

Papers

Diffusion in compartmental systems. I. A comparison of an analytical model with simulations.

Diffusion in compartmental systems. II. Diffusion-weighted measurements of rat brain tissue in vivo and postmortem at very large b-values.

Cell volume and water exchange in neural cells monitored by diffusion weighted 1H NMR spectroscopy