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Biophysical Journal Nov 1999A novel method, single-molecule anisotropy imaging, has been employed to simultaneously study lateral and rotational diffusion of fluorescence-labeled lipids on...
A novel method, single-molecule anisotropy imaging, has been employed to simultaneously study lateral and rotational diffusion of fluorescence-labeled lipids on supported phospholipid membranes. In a fluid membrane composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, in which the rotational diffusion time is on the order of the excited-state lifetime of the fluorophore rhodamine, a rotational diffusion constant, D(rot) = 7 x 10(7) rad(2)/s, was determined. The lateral diffusion constant, measured by direct analysis of single-molecule trajectories, was D(lat) = 3.5 x 10(-8) cm(2)/s. As predicted from the free-volume model for diffusion, the results exhibit a significantly enhanced mobility on the nanosecond time scale. For membranes of DPPC lipids in the L(beta) gel phase, the slow rotational mobility permitted the direct observation of the rotation of individual molecules characterized by D(rot) = 1.2 rad(2)/s. The latter data were evaluated by a mean square angular displacement analysis. The technique developed here should prove itself profitable for imaging of conformational motions of individual proteins on the time scale of milliseconds to seconds.
Topics: Anisotropy; Cell Membrane; Diffusion; Fluorescent Dyes; Molecular Imaging; Movement; Phospholipids; Rotation
PubMed: 10545384
DOI: 10.1016/S0006-3495(99)77118-3 -
Osteoarthritis and Cartilage Mar 2020To date, the pathophysiology of the meniscus has not been fully elucidated. Due to the tissue's limited vascularization, nutrients and other molecular signals spread...
OBJECTIVE
To date, the pathophysiology of the meniscus has not been fully elucidated. Due to the tissue's limited vascularization, nutrients and other molecular signals spread through the extracellular matrix via diffusion or convection (interstitial fluid flow). Understanding transport mechanisms is crucial to elucidating meniscal pathophysiology, and to designing treatments for repair and restoration of the tissue. Similar to other fibrocartilaginous structures, meniscal morphology and composition may affect its diffusive properties. The objective of this study was to investigate the role of solute size, and tissue structure and composition on molecular diffusion in meniscus tissue.
DESIGN
Using a custom FRAP technique developed in our lab, we measured the direction-dependent diffusivity in human meniscus of six different molecular probes of size ranging from ∼300Da to 150,000Da. Diffusivity measurements were related to sample water content. SEM images were used to investigate collagen structure in relation to transport mechanisms.
RESULTS
Diffusivity was anisotropic, being significantly faster in the direction parallel to collagen fibers when compared the orthogonal direction. This was likely due to the unique structural organization of the tissue presenting pores aligned with the fibers, as observed in SEM images. Diffusion coefficients decreased as the molecular size increased, following the Ogston model. No significant correlations were found among diffusion coefficients and water content of the tissue.
CONCLUSIONS
This study provides new knowledge on the mechanisms of molecular transport in meniscal tissue. The reported results can be leveraged to further investigate tissue pathophysiology and to design treatments for tissue restoration or replacement.
Topics: Aged; Anisotropy; Biological Transport; Collagen; Dextrans; Diffusion; Extracellular Fluid; Extracellular Matrix; Female; Fluorescein; Fluorescence Recovery After Photobleaching; Humans; Hydrodynamics; Insulin; Male; Menisci, Tibial; Microscopy, Electron, Scanning; Serum Albumin, Bovine
PubMed: 31917232
DOI: 10.1016/j.joca.2019.12.006 -
Pediatric Radiology Jul 2021Diffusion tensor imaging is a widely used imaging method of brain white matter, but it is prone to imaging artifacts. The data corrections can affect the measured values.
BACKGROUND
Diffusion tensor imaging is a widely used imaging method of brain white matter, but it is prone to imaging artifacts. The data corrections can affect the measured values.
OBJECTIVE
To explore the impact of susceptibility correction on diffusion metrics.
MATERIALS AND METHODS
A cohort of 27 healthy adolescents (18 boys, 9 girls, mean age 12.7 years) underwent 3-T MRI, and we collected two diffusion data sets (anterior-posterior). The data were processed both with and without susceptibility artifact correction. We derived fractional anisotropy, mean diffusivity and histogram data of fiber length distribution from both the corrected and uncorrected data, which were collected from the corpus callosum, corticospinal tract and cingulum bilaterally.
RESULTS
Fractional anisotropy and mean diffusivity values significantly differed when comparing the pathways in all measured tracts. The fractional anisotropy values were lower and the mean diffusivity values higher in the susceptibility-corrected data than in the uncorrected data. We found a significant difference in total tract length in the corpus callosum and the corticospinal tract.
CONCLUSION
This study indicates that susceptibility correction has a significant effect on measured fractional anisotropy, and on mean diffusivity values and tract lengths. To receive reliable and comparable results, the correction should be used systematically.
Topics: Adolescent; Anisotropy; Benchmarking; Child; Corpus Callosum; Diffusion Tensor Imaging; Female; Humans; Male; White Matter
PubMed: 33893847
DOI: 10.1007/s00247-021-05000-3 -
Journal of Neuroscience Methods Jan 2021Diffusion encoding along multiple spatial directions per signal acquisition can be described in terms of a b-tensor. The benefit of tensor-valued diffusion encoding is... (Review)
Review
Diffusion encoding along multiple spatial directions per signal acquisition can be described in terms of a b-tensor. The benefit of tensor-valued diffusion encoding is that it unlocks the 'shape of the b-tensor' as a new encoding dimension. By modulating the b-tensor shape, we can control the sensitivity to microscopic diffusion anisotropy which can be used as a contrast mechanism; a feature that is inaccessible by conventional diffusion encoding. Since imaging methods based on tensor-valued diffusion encoding are finding an increasing number of applications we are prompted to highlight the challenge of designing the optimal gradient waveforms for any given application. In this review, we first establish the basic design objectives in creating field gradient waveforms for tensor-valued diffusion MRI. We also survey additional design considerations related to limitations imposed by hardware and physiology, potential confounding effects that cannot be captured by the b-tensor, and artifacts related to the diffusion encoding waveform. Throughout, we discuss the expected compromises and tradeoffs with an aim to establish a more complete understanding of gradient waveform design and its impact on accurate measurements and interpretations of data.
Topics: Anisotropy; Artifacts; Diffusion; Diffusion Magnetic Resonance Imaging; Diffusion Tensor Imaging
PubMed: 33242529
DOI: 10.1016/j.jneumeth.2020.109007 -
Magnetic Resonance in Medicine Dec 2000Biexponential diffusion decay is demonstrated in the human brain in vivo using b factors up to 4000 sec mm(-2). Fitting of the signal decay data yields values for the... (Comparative Study)
Comparative Study
Biexponential diffusion decay is demonstrated in the human brain in vivo using b factors up to 4000 sec mm(-2). Fitting of the signal decay data yields values for the slow and fast diffusion components and volume fractions in agreement with previous studies in rat and human brain. In addition, differences in the fitted parameters are demonstrated in the white and gray matter and diffusion anisotropy is demonstrated in both the slow and fast diffusing components. Apparent anisotropy in the component fractions is discussed in terms of directionally dependent exchange rates between the compartments. The lack of a relationship between the estimated contribution to the signal of the fast and slow components and echo time appears to rule out T(2) differences in the observed water compartments. Values obtained for the fast diffusion coefficient, including differences between white and gray matter and the degree of anisotropy are compatible with the predictions of extracellular diffusion of water based on tortuosity models and the diffusion of tetramethylammonium ions in rat brain.
Topics: Anisotropy; Body Fluid Compartments; Body Water; Brain; Chi-Square Distribution; Diffusion; Humans; Magnetic Resonance Imaging; Reference Values; Time Factors
PubMed: 11108621
DOI: 10.1002/1522-2594(200012)44:6<852::aid-mrm5>3.0.co;2-a -
Harvard Review of Psychiatry 2002Magnetic resonance diffusion tensor imaging (DTI) is a new technique that can be used to visualize and measure the diffusion of water in brain tissue; it is particularly... (Review)
Review
Magnetic resonance diffusion tensor imaging (DTI) is a new technique that can be used to visualize and measure the diffusion of water in brain tissue; it is particularly useful for evaluating white matter abnormalities. In this paper, we review research studies that have applied DTI for the purpose of understanding neuropsychiatric disorders. We begin with a discussion of the principles involved in DTI, followed by a historical overview of magnetic resonance diffusion-weighted imaging and DTI and a brief description of several different methods of image acquisition and quantitative analysis. We then review the application of this technique to clinical populations. We include all studies published in English from January 1996 through March 2002 on this topic, located by searching PubMed and Medline on the key words "diffusion tensor imaging" and "MRI." Finally, we consider potential future uses of DTI, including fiber tracking and surgical planning and follow-up.
Topics: Anisotropy; Brain; Diffusion; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Mental Disorders; Nervous System Diseases
PubMed: 12485979
DOI: 10.1080/10673220216231 -
Philosophical Transactions of the Royal... Oct 2014Volume transmission is a form of intercellular communication that does not require synapses; it is based on the diffusion of neuroactive substances across the brain... (Review)
Review
Volume transmission is a form of intercellular communication that does not require synapses; it is based on the diffusion of neuroactive substances across the brain extracellular space (ECS) and their binding to extrasynaptic high-affinity receptors on neurons or glia. Extracellular diffusion is restricted by the limited volume of the ECS, which is described by the ECS volume fraction α, and the presence of diffusion barriers, reflected by tortuosity λ, that are created, for example, by fine astrocytic processes or extracellular matrix (ECM) molecules. Organized astrocytic processes, ECM scaffolds or myelin sheets channel the extracellular diffusion so that it is facilitated in a certain direction, i.e. anisotropic. The diffusion properties of the ECS are profoundly influenced by various processes such as the swelling and morphological rebuilding of astrocytes during either transient or persisting physiological or pathological states, or the remodelling of the ECM in tumorous or epileptogenic tissue, during Alzheimer's disease, after enzymatic treatment or in transgenic animals. The changing diffusion properties of the ECM influence neuron-glia interaction, learning abilities, the extent of neuronal damage and even cell migration. From a clinical point of view, diffusion parameter changes occurring during pathological states could be important for diagnosis, drug delivery and treatment.
Topics: Animals; Anisotropy; Astrocytes; Cell Communication; Diffusion; Extracellular Matrix; Humans; Synaptic Transmission
PubMed: 25225101
DOI: 10.1098/rstb.2013.0608 -
Neurobiology of Aging May 2021Diffusion tensor imaging (DTI) consistently detects increased mean diffusivity and decreased fractional anisotropy with advancing age in regions of primarily single...
Diffusion tensor imaging (DTI) consistently detects increased mean diffusivity and decreased fractional anisotropy with advancing age in regions of primarily single white matter (WM) fiber populations, but findings have been inconsistent in regions of more complex fiber architecture. Given that DTI remains more common for characterizing aging WM than advanced diffusion MRI models due to DTI's simplicity, robustness, and efficiency, it is critical to strive to maximize the information extracted from DTI across the entire WM. The present study uses an orthogonal diffusion tensor decomposition based on the 3 eigenvalue moments (mean diffusivity, norm of anisotropy, and mode of anisotropy), yielding clear voxelwise degeneration patterns across the WM, including regions of complex fiber architecture. This indicates that the previous challenges of DTI in these regions were due to the choice of tensor decomposition rather than the DTI model itself. This study therefore presents a revised view of DTI of aging WM and indicates how age-related degeneration in complex fiber architecture can manifest in forms other than decreased fractional anisotropy.
Topics: Aged; Aged, 80 and over; Aging; Anisotropy; Diffusion Tensor Imaging; Female; Humans; Male; Middle Aged; Nerve Degeneration; Nerve Fibers; White Matter
PubMed: 33610963
DOI: 10.1016/j.neurobiolaging.2020.12.020 -
Molecular Biology of the Cell May 2022Chromatin organization and dynamics are critical for gene regulation. In this work we present a methodology for fast and parallel three-dimensional (3D) tracking of...
Chromatin organization and dynamics are critical for gene regulation. In this work we present a methodology for fast and parallel three-dimensional (3D) tracking of multiple chromosomal loci of choice over many thousands of frames on various timescales. We achieved this by developing and combining fluorogenic and replenishable nanobody arrays, engineered point spread functions, and light sheet illumination. The result is gentle live-cell 3D tracking with excellent spatiotemporal resolution throughout the mammalian cell nucleus. Correction for both sample drift and nuclear translation facilitated accurate long-term tracking of the chromatin dynamics. We demonstrate tracking both of fast dynamics (50 Hz) and over timescales extending to several hours, and we find both large heterogeneity between cells and apparent anisotropy in the dynamics in the axial direction. We further quantify the effect of inhibiting actin polymerization on the dynamics and find an overall increase in both the apparent diffusion coefficient D* and anomalous diffusion exponent α and a transition to more-isotropic dynamics in 3D after such treatment. We think that in the future our methodology will allow researchers to obtain a better fundamental understanding of chromatin dynamics and how it is altered during disease progression and after perturbations of cellular function.
Topics: Animals; Anisotropy; Chromatin; Chromosomes; Diffusion; Gene Expression Regulation; Mammals
PubMed: 35352962
DOI: 10.1091/mbc.E21-10-0514 -
AJNR. American Journal of Neuroradiology Oct 2019
Review
Topics: Algorithms; Anisotropy; Diffusion Magnetic Resonance Imaging; Diffusion Tensor Imaging; Humans; Neuroimaging
PubMed: 31558496
DOI: 10.3174/ajnr.A6235